Patent Publication Number: US-11661833-B1

Title: Downhole solids separator

Description:
FIELD OF THE INVENTION 
     This disclosure relates to apparatus, and methods and systems using such apparatus, for separation of solids from a fluid. In particular, the apparatus employs centrifugal force to separate sand and other solids from well fluids in a downhole environment. 
     BACKGROUND OF THE INVENTION 
     Petroleum wells can be naturally flowing, injecting, or can be produced by any means of artificial lift. Artificial lift is a process utilized to lift well fluids to surface from a wellbore when the natural drive energy of the reservoir is not strong enough to push the oil to the surface. During the production of these wellbore fluids, solids may be entrained in the fluid that may pose a risk to the downhole production equipment. These downhole production equipment components may comprise of centrifugal pumps, motors, plungers, barrels, valves, and sealing arrangements which are susceptible to erosion and failure due to solids in the production fluid. 
     A particulate separator positioned within a shell of a wellbore of a hydrocarbon production well to separate particulate matter from a fluid mixture and direct the separated particulate matter away from a pump intake of an artificial lift to inhibit the particulate matter from entering the pump intake, which may increase the efficiency and/or the service life of the downhole assembly. 
     A need still exists for solids removal devices and methods having higher reliability and improved efficiency. Ideally, improved solids removal devices and methods could be implemented using economical starting materials, commonly used equipment, and familiar fabrication techniques. 
     SUMMARY OF THE INVENTION 
     The present disclosure provides apparatus, methods, and systems for separating solids from fluids, particularly in a downhole environment. Apparatus, methods, and systems herein are useful for a broad range of fluid flow rates and intermittent or continuous fluid flow. 
     In some embodiments, a separator apparatus for removing solids from an untreated fluid comprises a vortex inducer and a solids collection conduit. The vortex inducer comprises one or more helical apertures and a central aperture. The solids collection conduit is connected to the vortex inducer to form a separation chamber. The one or more helical apertures are positioned to deliver a helical flow of untreated fluid to the separation chamber proximate to an inner surface of the solids collection conduit. The central aperture is positioned to withdraw a treated fluid from the separation chamber proximate to a central axis of the separation chamber. In some embodiments, the vortex inducer comprises a shell element and a core element, and the one or more helical apertures are formed at an interface between a cylindrical inner surface of the shell element and a cylindrical outer surface of the core element. 
     In some embodiments, the cylindrical outer surface of the core element is radially spaced from the central aperture, and the cylindrical inner surface of the shell element comprises one or more helical channels. The core element is slidably joined to the shell element by an overlap of at least a portion of the cylindrical outer surface of the core element and at least a portion of the cylindrical inner surface of the shell element. One or more helical apertures are formed proximate to the overlap by the one or more helical channels and the cylindrical outer surface of the core element. 
     In some embodiments, the cylindrical outer surface of the core element is radially spaced from the central aperture and comprises one or more helical channels. The core element is slidably joined to a shell element by an overlap of at least a portion of the cylindrical outer surface of the core element and at least a portion of the cylindrical inner surface of the shell element. One or more helical apertures are formed proximate to the overlap h the one or more helical channels and the cylindrical outer surface of the core element. 
     In some embodiments, a downhole module comprises a housing, a separator apparatus, an upper housing closure, and a treated fluid discharge conduit. The separator apparatus is mounted within the housing forming an upper space within the housing and above the separator apparatus and a lower space within the housing and below the separator apparatus. The treated fluid discharge conduit is connected to the vortex inducer at its lower end and the upper housing closure at its upper end. The treated fluid discharge conduit fluidly connects the central aperture to an opening in the upper housing closure. The upper housing closure, the treated fluid discharge conduit, and the separator apparatus are connected forming a feed chamber. The feed chamber is fluidly connected to the one or more helical apertures and one or more inlet ports through the housing. 
     In some embodiments, a method for separating solids from an untreated fluid comprises: submerging a downhole module in an untreated fluid having a first solids content; and reducing the pressure inside the treated fluid discharge conduit relative to the pressure outside the downhole module to induce flow of untreated fluid through the one or more inlet ports to the feed chamber, and from the feed chamber through the vortex inducer to the separation chamber. The flow of untreated fluid through the vortex inducer creates a velocity of untreated fluid in the one or more helical apertures, wherein the velocity has a tangential component and an axial component. The tangential component of velocity of untreated fluids exiting the one or more helical apertures creates a vortex in the separation chamber wherein centrifugal force concentrates solids proximate to the inner surface of the solids collection conduit and creating a treated fluid having a second solids content proximate to the central axis of the separation chamber, wherein the second solids content is less than the first solids content. 
     In some embodiments, a method for separating solids from an untreated fluid comprises: adding an untreated fluid comprising a first solids content to a cylindrical space having an outer diameter in the range of from 2 inches (5.1 cm) to 6 inches (15.2 cm); inducing a vortex in the cylindrical space, wherein the vortex has a tangential velocity of at least 100 ft/sec (30 m/sec) near the diameter of the cylindrical space; separating the untreated fluid into a high solids component near the outer diameter of the cylindrical space and a treated fluid having a second solids content; withdrawing the treated fluid from the cylindrical space; and withdrawing the solids component from the cylindrical space. 
     The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter, which form the subject matter of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiments disclosed may be readily utilized as a basis for modifying or designing alternate structures and/or other processes for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. The novel features which are believed to be characteristic of the invention, both as to its structure, method of manufacture, and method of use, together with further objects and advantages will be better understood from the following description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The claimed subject matter may be understood by reference to the following description taken in conjunction with the accompanying drawings, in which like reference numerals identify like elements, and in which: 
         FIG.  1    is a cross-sectional drawing of a first embodiment of a downhole module comprising the separator apparatus described herein; 
         FIG.  2    is a cross-sectional drawing of a second embodiment of a downhole module comprising the separator apparatus described herein; 
         FIG.  3    is a cross-sectional drawing of a third embodiment of a downhole module comprising the separator apparatus described herein; 
         FIG.  4    is a cross-sectional drawing of a fourth embodiment of a downhole module comprising the separator apparatus described herein; 
         FIG.  5    is a cross-sectional drawing of a fifth embodiment of a downhole module comprising the separator apparatus described herein; 
         FIG.  6    is a cross-sectional drawing of a sixth embodiment of a downhole module comprising the separator apparatus described herein; 
         FIGS.  7 A- 7 B  are diagrams describing geometric features common to the embodiment types shown in  FIGS.  1 - 6   ; 
         FIGS.  8 A- 8 C  are drawings from various perspectives showing geometric features of an embodiment of a vortex inducer having a single helical aperture formed from a helical channel on the inner surface of the shell element and the cylindrical outer surface of the core element; 
         FIGS.  9 A- 9 C  are drawings from various perspectives showing geometric features of an embodiment of a vortex inducer having a plurality of helical apertures formed from a plurality of helical channels on the inner surface of the shell element and the cylindrical outer surface of the core element; 
         FIGS.  10 A- 10 C  are drawings from various perspectives showing geometric features of an embodiment of a vortex inducer having a single helical aperture formed from a helical channel on the outer surface of the core element and the cylindrical inner surface of the shell element; 
         FIGS.  11 A and  11 B  are drawings of a downhole module comprising the separator apparatus disclosed herein and a downhole module installed at the termination of downhole piping; and 
         FIG.  12    shows an expanded view of a downhole module. 
     
    
    
     While the disclosed apparatus, process, and system are susceptible to various modifications and alternative forms, the drawings illustrate specific embodiments herein described in detail by way of example. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Illustrative embodiments of the subject matter claimed below will now be disclosed. In the interest of clarity, some features of some actual implementations may not be described in this specification. It will be appreciated that in the development of any such actual embodiments, numerous implementation-specific decisions must be made to achieve the developer&#39;s specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort, even if complex and time-consuming, would be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure. 
     The words and phrases used herein should be understood and interpreted to have a meaning consistent with the understanding of those words and phrases by those skilled in the relevant art. No special definition of a term or phrase, i.e., a definition that is different from the ordinary and customary meaning as understood by those skilled in the art, is intended to be implied by consistent usage of the term or phrase herein. To the extent that a term or phrase is intended to have a special meaning, i.e., a meaning other than the broadest meaning understood by skilled artisans, such a special or clarifying definition will be expressly set forth in the specification in a definitional manner that provides the special or clarifying definition for the term or phrase. 
     For example, the following discussion contains a non-exhaustive list of definitions of several specific terms used in this disclosure (other terms may be defined or clarified in a definitional manner elsewhere herein). These definitions are intended to clarify the meanings of the terms used herein. It is believed that the terms are used in a manner consistent with their ordinary meaning, but the definitions are nonetheless specified here for clarity. 
     Definitions 
     “Core element,” as used herein, means the inner central component of the vortex inducer. 
     “Feed chamber,” as used herein, means a chamber enclosed by the connection of the separator apparatus, the treated fluid discharge conduit, and the housing. 
     “Fluidly connected,” as used herein, means a connection of spaces, chambers, and/or apertures that facilitates the flow of fluid directly from a first space, chamber, and/or aperture to a second space, chamber, and/or aperture, which is directly adjacent to the first space, chamber, and/or aperture. 
     “Helical aperture,” as used herein, means an aperture formed at the interface of a shell element and a corresponding core element by a) a helical channel in the cylindrical inner surface of the shell element and the cylindrical outer surface of a corresponding core element, or b) a helical channel in the cylindrical outer surface of a core element and the cylindrical inner surface of the shell element. 
     “Housing,” as used herein, means a cylindrical body to which the separator apparatus disclosed herein is attached in a downhole module. 
     “Inlet port,” as used herein, mean an opening through the housing wall to permit untreated fluid to flow from outside the housing into the feed chamber. 
     “Separation chamber,” as used herein, means the space defined by the attachment of the vortex inducer to the solids collection conduit. 
     “Shell element,” as used herein, means the outer component of the vortex inducer. 
     “Solids collection conduit,” as used herein, means a substantially cylindrical vertical wall located below the vortex inducer. 
     “Treated fluid discharge conduit,” as used herein, means a pipe or other tubular means fluidly connecting the upper end of the central aperture to an opening in an upper housing closure. 
     “Treated fluid,” as used herein, means a fluid produced after a treated fluid flows through the separator apparatus disclosed herein. 
     “Untreated fluid,” as used herein, means a fluid having a content of suspended solids prior to being fed through the separator apparatus disclosed herein. Such fluid can be water, hydrocarbon, or a mixture thereof. 
     Directional terms such as “above,” below,” “upper,” “lower,” and the like are not limiting and are provided only to aid in describing the orientation and relative position of components of the separator apparatus and the downhole module with respect to one another when the separator apparatus and the downhole module are in the vertical position as shown in  FIGS.  1 - 6   . 
     Separator Apparatus 
     Disclosed herein is a separator apparatus for separating solids from fluids such as, but not limited to, water, liquid hydrocarbon, or a mixture thereof. The separator apparatus is particularly suited for operation in a downhole environment in oil and gas operations but could also be useful for other situations where it is desirable to remove or reduce solids content of fluid flowing into a pump and/or other mechanical equipment. 
     The separator apparatus comprises a vortex inducer and a solids collection conduit. The vortex inducer comprises a central aperture proximate to the central axis of the vortex inducer. The vortex inducer further comprises one or more helical apertures separate from the central aperture and separate from one another. The one or more helical apertures are radially spaced from the central aperture, and the axis of the helix formed by each helical aperture coincides with the central axis of the vortex inducer. In some embodiments, the vortex inducer comprises two or more, three or more, or four or more helical apertures separate from the central aperture and separate from one another. 
     In some embodiments, the solids collection conduit comprises a substantially cylindrical wall that is a vertical wall, a frustoconical wall with decreasing diameter from the upper end to the lower end of such section, a frustoconical wall with increasing diameter from the upper end to the lower end of such section, or a combination thereof. In some embodiments, the solids collection conduit comprises at least one section that is substantially vertical and at least one section that is frustoconical with decreasing diameter from the upper end to the lower end of such section. In some embodiments, the solids collection conduit comprises at least one section that is substantially vertical and at least one section that is frustoconical with increasing diameter from the upper end to the lower end of such section. In some embodiments, the solids collection conduit comprises at least one section that is substantially vertical, at least one section that is frustoconical with decreasing diameter from the upper end to the lower end of such section, and at least one section that is frustoconical with increasing diameter from the upper end to the lower end of such section. In each such embodiment the sections are connected in a manner to form a substantially cylindrical wall, which is a fluid barrier with an opening at the upper end formed by the upper edge of the substantially cylindrical wall and an opening at the lower end formed by the lower edge of the substantially cylindrical wall. 
     The upper end of the solids collection conduit is connected to the lower end of the vortex inducer forming a separation chamber. The upper end of the separation chamber is fluidly connected to a central aperture and one or more helical apertures, and the lower end of the central aperture and the lower end(s) of the one or more helical apertures are the only openings at the upper end of the separation chamber. The only opening at the lower end of the solids separation chamber is defined by the lower edge of the substantially cylindrical wall. 
     In operation, the upper end of the central aperture is separated from the upper end(s) of the one or more helical apertures by the treated fluid discharge conduit. The upper end of the central aperture is operated at a lower pressure than the pressure at the upper end of the one or more helical apertures. In some embodiments, the difference in pressure between the upper end of the central aperture and the pressure at the upper end of the one or more helical apertures is greater than or equal to 10 psig (69 kPa), greater than or equal to 20 psig (138 kPa), greater than or equal to 30 psig (207 kPa), or greater than or equal to 40 psig (276 kPa). Such pressure differential can be constant or intermittent, based on the type of pump used in the relevant operations. Such pump types include, but are not limited to, centrifugal pumps, vertical pumps, and rotary, reciprocating, or pneumatic displacement or positive displacement pumps. 
     In some embodiments, maximum flow rates can range from as low as 100 B/D (16 m 3 /D), 200 B/D (32 m 3 /D), 500 B/D (79 m 3 /D), or 1000 B/D (159 m 3 /D), to as high as 4,000 B/D (636 m 3 /D), 5,000 B/D (795 m 3 /D), 7,000 B/D (1,113 m 3 /D), or 10,000 B/D (1,590 m 3 /D). In some embodiments, a preferred flow rate for a separator apparatus is based on selected range of calculated flow velocity and/or calculated Reynolds number in the one or more helical apertures. In some applications, operating temperatures of the separator apparatus are in the range of from 70° F. (21° C.) to 220° F. (104° C.) or from 100° F. (38° C.) to 200° F. (93° C.). 
     The pressure differential discussed above causes untreated fluid to be drawn into the upper end of the one or more helical apertures, wherein static pressure of untreated fluid prior to entering the one or more helical apertures is converted to dynamic pressure based on the velocity of untreated fluid in the one or more helical apertures. The velocity of the untreated fluid in the one or more helical apertures has a component tangential to the circumference of the helical aperture and a component downwardly in the axial direction. The tangential velocity of the untreated fluid exiting the lower end of the one or more helical apertures creates a vortex in the separation chamber, wherein a centrifugal force concentrates the suspended solids to be concentrated on the cylindrical inner surface or wall of the solids collection conduit. As these concentrated solids are pushed to the wall of the solids collection conduit by the centrifugal force, the concentrated solids are moved downwardly to an opening at the lower end of the solids collection conduit by gravity and/or the axial velocity created by the flow through the one or more helical apertures. In some embodiments, the shape of the solids collection conduit, based on the arrangement of one or more vertical sections and/or one or more frustoconical sections, aids in the downward movement of the solids being collected, while preventing backflow of the collected solids in an upward direction, or a combination thereof. 
     Each of the one or more helical apertures has a uniform cross-sectional area perpendicular to a helical line passing through the centroid of the cross-sectional area. A line tangent to the helical line forms a helix angle θ with the central axis of the vortex inducer based on the rotation of the tangent line and the central axis about a radial line passing through the tangent line and the central axis of the helix and the vortex inducer. If the velocity of the untreated fluid in the helical aperture is u, then the tangential component of the velocity is u(sin θ) and the downward axial component of the velocity is u(cos θ). In some embodiments, the helix angle θ is greater than or equal to 10°, greater than or equal to 20°, greater than or equal to 30°, greater than or equal to 40°, greater than or equal to 50°, or greater than or equal to 60°. In some embodiments, helix angle θ is less than or equal to 80°, less than or equal to 70°, less than or equal to 60°, less than or equal to 50°, less than or equal to 40°, or less than or equal to 30°. In some embodiments, helix angle θ is in the range of from 20° to 80°, from 30° to 70°, from 40° to 65°, or from 45° to 60°. 
     In other embodiments, the helix angle, the cross-sectional area of the one or more helical apertures, or a combination thereof. Improved machining processes, certain casting processes, and 3D printing enable varying the helix angle in a helical aperture to produce a progressively increasing or decreasing helix lead or pitch in the direction of fluid flow in the vortex inducer. Improved machining processes, certain casting processes, and 3D printing enable varying the cross-sectional area of a helical aperture angle in a helical aperture to produce a progressively increasing or decreasing cross-sectional area in a helical aperture in the direction of fluid flow in the vortex inducer. 
     Such concentration of solids on the wall of the solids collection conduit results in treated fluid, having a reduced solids content, proximate to the central axis of the separator apparatus. The lower pressure at the upper end of the central aperture causes the treated fluid to flow upwardly into the central aperture, where it will be routed to the suction of a pump or the like. 
     In some embodiments, each of the one or more helical apertures has a uniform cross-sectional area. Without wishing to be bound by any particular theory, it is believed that the uniform cross-sectional area of the helical apertures in combination with the profile of the wall of the separation chamber provides removal of a higher percentage of solids than is possible from previous separators utilizing helical or cyclonic flows of untreated fluid. The uniform cross-sectional area of the one or more helical apertures produces higher velocities, higher Reynolds numbers, and/or more controlled flow into the solids collection conduit, resulting in less back-mixing of solids into the center of the vortex formed in the solids collection conduit. 
     In some embodiments, the vortex inducer, having a central aperture and one or more helical apertures having a uniform cross-sectional area, is formed by slidable engagement of a shell element and a core element, wherein the inner diameter of the shell element is equal to or substantially equal to the outer diameter of the core element. 
     In some embodiments, at least a portion of the inner surface of the shell element comprises one or more helical channels and at least a portion of the core element has a uniform outer diameter. When slidably engaged, at least a portion of the outer surface of the core element and the inner surface of the shell element having the one or more helical channels overlap forming the one or more helical apertures. 
     In some embodiments, at least a portion of the outer surface of the core element comprises one or more helical channels and at least a portion of the shell element has a uniform inner diameter. When slidably engaged, at least a portion of the inner surface of the shell element and the outer surface of the core element having the one or more helical channels overlap forming the one or more helical apertures. 
     Another aspect of the separator apparatus disclosed herein is that wear surfaces, or surfaces subject to abrasion wear from high velocity solids, are isolated from axial loads produced by downhole piping. Some commercially available separator devices utilize helical flow to separate suspended solids from fluids in downhole environments. However, although the flow of solids is at a lower velocity, such flow of solids impinges on the inner diameter of the housing for such separator devices. Abrasive wear causes thinning of the wall of the housing, and in some cases, thinning to the point of structural failure of the housing, requiring suspension of operations to remove the downhole piping from the well and then retrieval of the failed equipment from the wellbore. The separator apparatus disclosed herein is mounted within the housing but is separate from the housing, such that the housing is shielded from wear from flowing solids. This prevents the aforementioned structural failure of the housing resulting in unplanned loss of production or other shutdown of operations. Isolation of wear to the separator apparatus disclosed herein produces a failure mode of reduced or efficiency of solids removal instead of structural failure. 
     In some embodiments, the shell element, the core element, the solids collection conduit, or a combination thereof, are fabricated from and/or coated with a material that is resistant to wear by abrasion from the flow of solids through the separator apparatus. Since the separator apparatus is a small part of the overall downhole module, use of more costly materials of construction and/or coating can be cost effective, especially where structural failure of the housing might be prevented in harsher environments (corrosive environment and/or higher solids content). Many abrasion-resistant metals are available for fabrication of the shell element, the core element, the solids collection conduit, or a combination thereof. Alloys like carbon, manganese, nickel, chrome, and boron are added in different proportions to increase metal hardness and improve resistance to wear from abrasion form flowing solids, such as, but not limited to sand. Tungsten carbide and various grades of stainless steel are suitable materials of construction for the shell element, the core element, the solids collection conduit, or a combination thereof. Stainless steel can be selected for some applications where corrosion is a concern during operation, such as, but not limited to corrosion resulting from high levels of sulfur and/or carbon-dioxide. Stainless steel can be selected from one or more of austenitic stainless steel, ferritic stainless steel, duplex stainless steel, and martensitic and precipitation hardening stainless steel. SAE Type 630 stainless steel, more commonly known as 17-4 PH, is a grade of martensitic precipitation hardened stainless steel useful for fabrication of components of the separator apparatus subject to abrasion from flowing solids. Also suited for fabrication of components of the separator apparatus subject to abrasion from flowing solids are certain austenitic nickel-chromium-based superalloys (e.g., Inconel™, available from voestalpine Specialty Metals, Houston, Tex.) are oxidation-corrosion-resistant materials well suited for service in extreme environments subjected to pressure and heat and have high-temperature strength derived by solid solution strengthening or precipitation hardening, depending on the alloy. 
     In some embodiments, materials of construction of the shell element, the core element, the solids collection conduit, or a combination thereof, are selected by hardness and/or tensile strength as indirect indicators of abrasion resistance, such as one or more of Rockwell C hardness, Brinell hardness, Vickers hardness, and tensile strength. In some embodiments, a selected metal has a Rockwell C hardness of greater than or equal to 30, greater than or equal to 35, or greater than or equal to 40. In some embodiments, a selected metal has a Brinell hardness of greater than or equal to 285, greater than or equal to 325, or greater than or equal to 375. In some embodiments, a selected metal has a Brinell hardness of greater than or equal to 285, greater than or equal to 325, or greater than or equal to 375. In some embodiments, a selected metal has a Vickers hardness of greater than or equal to 300, greater than or equal to 345, or greater than or equal to 390. In some embodiments, a selected metal has a tensile strength of greater than or equal to 140,000 psi (965 MPa), greater than or equal to 160,000 psi (1,100 MPa), or greater than or equal to 220,000 psi (1500 MPa). 
     In some embodiments, the shell element, the core element, the solids collection conduit, or a combination thereof, are coated with wear resistant materials such as, but not limited to, ceramics, chemical vapor diamond film, or physical vapor deposition of a hydrogen-free diamond like carbon films (e.g., Tetrabond™, available from IonBond US, Duncan, S.C.). 
     In an embodiment, an apparatus for separating solids from fluids, comprises a vortex inducer physically connected to a solids collection conduit, forming a chamber, wherein the vortex inducer comprises a helical aperture and a central aperture, and the chamber is fluidly connected to the helical aperture and the central aperture. In further embodiments, the helical aperture is configured to accept a flow of an untreated fluid into the apparatus, and the central aperture is configured to permit withdrawal of a treated fluid. 
     Certain Embodiments 
     In some embodiments, a separator apparatus for removing solids from an untreated fluid comprises a vortex inducer and a solids collection conduit. The vortex inducer comprises one or more helical apertures and a central aperture. The solids collection conduit is connected to the vortex inducer to form a separation chamber. The one or more helical apertures are positioned for delivering a helical flow of an untreated fluid to the separation chamber proximate to the inner surface of the solids collection conduit. The central aperture is positioned for withdrawing a treated fluid from the separation chamber proximate to a central axis of the separation chamber. In certain embodiments, each helical aperture has a uniform cross-sectional area perpendicular to a helical line passing through the centroid of the cross-sectional area of each helical aperture, which can be characterized by one or more of the following:
         a) a line tangent to the helical line forms a helix angle θ with the central axis of the vortex inducer is: 1) greater than or equal to 10°, greater than or equal to 20°, greater than or equal to 30°, greater than or equal to 40°, greater than or equal to 50°, or greater than or equal to 60°; 2) less than or equal to 80°, less than or equal to 70°, less than or equal to 60°, less than or equal to 50°, less than or equal to 40°, or less than or equal to 30°; or in the range of from 10° to 80°, from 20° to 70°, from 30° to 60°, or from 40° to 50°;   b) the uniform cross-sectional area is sized to produce a velocity in the one or more helical apertures of at least 15 meters/sec, at least 23 meters/sec, at least 31 meters/sec, at least 38 meters/sec, or at least 46 meters/sec at a design flow rate of the separator apparatus; and   c) the uniform cross-sectional area is sized to produce a Reynolds number in the one or more helical apertures of greater than or equal to 100,000, 200,000, 300,000, 400,000, or 500,000 at a design flow rate of the separator apparatus.       

     In some embodiments, in addition to the foregoing, the vortex inducer comprises a shell element and a core element. The one or more helical apertures are at an interface between a cylindrical inner surface of the shell element and a cylindrical outer surface of the core element. In further embodiments, one or more of the core element, the shell element, and the solids collection conduit are further characterized by one or more of:
         a) having a surface with a Rockwell C hardness of greater than or equal to 30, a surface with a Brinell hardness of greater than or equal to 285, a surface with a Vickers hardness of greater than or equal to 300, a tensile strength (yield) of greater than or equal to 965 MPa, or a combination thereof;   b) being fabricated from stainless steel; and   c) having one or more wear surfaces with a ceramic coating.       

     In a first set of embodiments, wherein the vortex inducer comprises a shell element and a core element, the cylindrical outer surface of the core element is radially spaced from the central aperture, and the cylindrical inner surface of the shell element comprises one or more helical channels. The core element is slidably joined to the shell element by an overlap of at least a portion of the cylindrical outer surface of the core element and at least a portion of the cylindrical inner surface of the shell element, and the one or more helical apertures are formed proximate to the overlap by the one or more helical channels and the cylindrical outer surface of the core element. 
     In a second set of embodiments, wherein the vortex inducer comprises a shell element and a core element, the cylindrical outer surface of the core element is radially spaced from the central aperture and comprises one or more helical channels, and the core element is slidably joined to the shell element by an overlap of at least a portion of the cylindrical outer surface of the core element and at least a portion of the cylindrical inner surface of the shell element. The one or more helical apertures are formed proximate to the overlap by the one or more helical channels and the cylindrical inner surface of the shell element. 
     Downhole Module 
     In some embodiments, a downhole module comprises a separator apparatus, a treated fluid discharge conduit, a housing, an upper housing closure, and optionally, a lower housing closure. The housing is a section of pipe, tubing, or other cylindrical body that is suitable for vertical or substantially vertical installation or use proximate to the lower end of piping in a wellbore, wherein such piping will be used to draw liquids from the well to the surface. The following discussion will refer to such vertical or substantially vertical orientation of the downhole module for convenience in order to describe the arrangement of components of the downhole module more clearly with respect to one another. 
     The separator apparatus is mounted within the housing in a manner suitable to divide the space inside the housing into an upper space, which is the space above the separator apparatus within the housing, and a lower space, which is the space below the separator apparatus within the housing. A treated fluid discharge conduit is connected at its lower end such that the space inside the treated fluid discharge conduit is fluidly connected to the central aperture of the separator apparatus. The treated fluid discharge conduit is connected at its upper end to the upper housing closure. The upper housing closure is further connected to the upper end of the housing such that a portion of the above-mentioned upper space is enclosed by the housing, the upper housing closure, the separator apparatus, and the treated fluid discharge conduit forming a feed chamber. The portion of the housing defining the feed chamber comprises one or more inlet ports through the housing, such that the feed chamber is fluidly connected to the space outside the housing by the one or more inlet ports and the one or more helical apertures at the upper end of the separator apparatus. The upper housing closure has at least one opening such that the treated fluid discharge conduit fluidly connects the central aperture of the separator apparatus to the at least one opening in the upper housing closure. The treated fluid discharge conduit further serves to separate the upper end of the one or more helical apertures of the separator apparatus from the upper end of the central aperture of the separator apparatus. The size and number of inlet ports and the size of the feed chamber are selected such that neither will unduly limit flow through the downhole module at the desired flowrate, which can be determined by known methods by one of ordinary skill in the art. 
     The aforementioned lower space below the separator apparatus is for collection and/or storage of solids removed by the separator apparatus when the downhole module is in operation. The optional lower housing closure encloses the lower end of the housing and separates the lower space inside the housing from the environment outside the housing and also provides for containment of removed solids. The length of the housing below the separator apparatus can be sized based on the estimated rate of solids removal and the time for which such removal rate is to be maintained, both of which can be determined by known methods by one of ordinary skill in the art having knowledge of the location of the intended operations. 
     Solids Removal Method 
     In some embodiments, removal of solids from an untreated fluid is accomplished by: accelerating an untreated fluid to a velocity in one or more helical apertures by inducing a pressure drop across the one or more helical apertures, wherein each aperture has an inlet and an outlet; directing the untreated fluid exiting the outlet of each of the one or more helical apertures into a conduit at a downward angle; converting the flow of untreated fluid from an angular flow to a helical flow by containing the flow within the solids collection conduit, wherein centrifugal force induced by the helical flow concentrates a portion of the solids proximate to an inner surface of the conduit; and withdrawing from a central portion of the conduit a treated fluid, wherein the treated fluid has a lower content of solids than the untreated fluid. 
     In some embodiments, a method for separating solids from an untreated fluid comprises submerging a downhole module, comprising a separator apparatus as disclosed herein in an untreated fluid having a first solids content, and reducing the pressure inside the treated fluid discharge conduit relative to the pressure outside the downhole module to induce flow of untreated fluid through the one or more inlet ports to the feed chamber, and from the feed chamber through the vortex inducer to the separation chamber. The induced flow of untreated fluid through the vortex inducer creates a velocity of untreated fluid in the one or more helical apertures having a tangential component and an axial component. The tangential component of velocity of untreated fluids exiting the one or more helical apertures creates a vortex in the separation chamber wherein centrifugal force concentrates solids proximate to the inner surface of the solids collection conduit resulting in creation of a treated fluid having a second solids content proximate to the central axis of the separation chamber, wherein the second solids content is less than the first solids content. In some embodiments, the method further comprises withdrawing the treated fluid through a treated fluid discharge conduit, withdrawing the concentrated solids from the solids collection conduit through gravity and/or the axial component of velocity, or a combination thereof. In some embodiments, the tangential velocity is sufficient to produce a ratio of the second solids content to the first solids content of less than or equal to 0.05, less than or equal to 0.04, less than or equal to 0.03, less than or equal to 0.02, or less than or equal to 0.01. 
     More generally, a method disclosed herein for separating solids from an untreated fluid comprises:
         a) adding an untreated fluid comprising a first solids content to a cylindrical space having an outer diameter in the range of from 2 inches (5.1 cm) to 6 inches (15.2 cm);   b) inducing a vortex in the cylindrical space, wherein the vortex has a tangential velocity of at least 100 ft/sec (30 m/sec) near the diameter of the cylindrical space;   c) separating the untreated fluid into a high solids component near the outer diameter of the cylindrical space and a treated fluid having a second solids content;   d) withdrawing the treated fluid from the cylindrical space; and   e) withdrawing the solids component from the cylindrical space.
 
In some embodiments, the cylindrical space is circumscribed by a cylindrical body comprising one or more sections of pipe, one or more fittings, one or more fabricated components, or a combination thereof. In some instances, fabricated components are machined from solid pieces of metal, thereby facilitating use of nonstandard shapes in constructing the cylindrical body. That is to say, that the cylindrical body can comprise one or more components such that the cylindrical body has one or more section having a uniform inner diameter, one or more sections where such wall is frustoconical with the diameter at the upper end of such sections is greater than the diameter at the lower end of such sections, one or more sections where such wall is frustoconical with the diameter at the lower end of such sections is greater than the diameter at the upper end of such sections, or a combination thereof. In some embodiments, the tangential velocity is sufficient to produce a ratio of the second solids content to the first solids content of less than or equal to 0.05, less than or equal to 0.04, less than or equal to 0.03, less than or equal to 0.02, or less than or equal to 0.01.
 
Certain Embodiments of Separator Apparatus
       

     The downhole modules  100 ,  200 ,  300 ,  400 ,  500 , and  600 , as shown in  FIGS.  1 - 6   , are intended to be sized to facilitate use in typical commercial well casing sizes, such as, but not limited to 5.5 inches (14.0 cm) and 7 inches (17.8 cm). In some embodiments, the downhole module has a nominal pipe diameter of 4 inches (10.2 cm) with an actual outside diameter of 4.5 inches (11.4 cm). The housing can be of any length suitable for a specific application and can be extended with additional lengths of pipe in order to increase storage capacity for removed solids. In some embodiments, the bottom or the housing, or alternatively the bottom-most extension added to the housing is closed. 
     Some embodiments are configured as shown in  FIG.  1   , the downhole module  100  comprises separator apparatus  110  and housing  180 , having central axis  101 . Separator apparatus  110  comprises vortex inducer  120  and solids collection conduit  150 . Vortex inducer  120  comprises shell element  130  and core element  140 . 
     Vortex inducer  120  comprises a central aperture  121  and one or more helical apertures  122 . Each of the one or more helical apertures  122  is characterized by a cross-sectional area A with perimeter P, wherein the cross-sectional area A is perpendicular to a spiral line  123  defined by the centroid of cross-sectional area A at each point along the diameter D 122  of the one or more helical apertures  122 , and hydraulic diameter D h , wherein: 
               D     h   =       ⁢       4   ⁢   A     P           
Spiral line  123  is characterized by a helix lead L 122  and a helix lead angle θ wherein:
 
             θ   =     arctan   ⁡   (       L     1   ⁢   2   ⁢   2         π   ⁢     D     1   ⁢   2   ⁢   2           )           
In some embodiments, the ratio of shell element mating surface length L 131a  and corresponding core element mating surface length L 140a  to helix lead L 122  is less than or equal to 1.0, 0.8, 0.6, 0.4, or 0.2.
 
     Vortex inducer  120  comprises shell element  130  and core element  140 . Shell element  130  comprises an inner cylindrical surface having one or more helical channels  131 , wherein each such channel extends to the upper end of shell element  130 . The outer diameter of shell element  530  is less than the inner diameter of the housing  580 . Shell element  130  starts with a uniform inner diameter D 130 . The inner surface of the shell element  130  is machined by known methods to produce one or more helical channels having a maximum depth C 131  such that each helical channel  131  has a diameter D 131  at the maximum depth of the helical channel  131 . After machining the one or more helical channels  131  into the inner surface of shell element  130 , one or more strips of the original inner surface having a width W 131 , a diameter D 130  and length L 131a  remaining as a first mating surface. Optionally, shell element  130  extends a distance below the lower end of the mating surface for a distance L 131b , wherein such extension has an inner diameter of D 131 . 
     Core element  140  comprises a cylindrical inner surface having a diameter D 140a , which circumscribes the central aperture  121 , a cylindrical outer surface having a diameter D 140b . Length L 140a  is the mating surface of core element  140 , such that the corresponding mating surfaces of the shell element  130  and the core element  140  define the span of the helical apertures  122  when shell element  130  and core element  140  are slidably engaged. Optionally, core element  140  extends for a distance L 140b  below the lower end of the mating surface when core element  140  and shell element  130  are slidably engaged in the intended operating position. 
     In some embodiments, D 140b  is equal or substantially equal to D 130 , where core element  140  and shell element  130  are held in the intended operating position after being slidably engaged by an interference fit between core element  140  and shell element  130 . In some embodiments, D 130  is less than or equal to 5 mil (127 μm), 4 mil (102 μm), 3 mil (76 μm), 2 mil (51 μm), or 1 mil (25 μm) greater than D 140b , where core element  140  and shell element  130  are held in the intended operating position after being slidably engaged by means other than an interference fit, such as, but not limited to one or more set screws or one or more keys. In some embodiments, the core element and shell element are held together by a taper fit, such as, but not limited to, self-holding tapers such as Morse tapers and Jacobs tapers. 
     The vortex inducer  120  is formed by slidably engaging the shell element  130  and the core element  140  such that at least a portion of or all of the mating surface and at least a portion of or all of the cylindrical outer surface of the core element  140  are overlapping. The one or more helical apertures  122  are formed by the inner surface of the one or more helical channels  131  and the outer surface of the core element  140 . 
     Solids collection conduit  150  is attached to the lower end of the vortex inducer  120  to form separation chamber  151 . In some embodiments, solids collection conduit  150  comprises: a) a first section having a length L 150a  and inner diameter D 150a ; b) a second section connected to the lower end of the first section and having a length L 150b  and an inner diameter tapering from D 150a  at its upper end to D 150b  at its lower end; c) a third section connected to the lower end of the second section and having a length L 150c  and inner diameter D 150b ; and d) a fourth section connected to the lower end of the third section and having a length L 150d  and an inner diameter tapering from D 150b  at its upper end to a diameter sufficient to permit attachment of the fourth section to the inner surface of the housing  180 , wherein such attachment separates the opening defined at the lower end of separation chamber  151  by the lower edge of the fourth section from the feed chamber  182 . 
     In some embodiments, solids collection conduit  150  comprises: a) a first section having a first length and a first inner diameter; and b) a second section connected to the lower end of the first section and having a second length and an inner diameter tapering from the first inner diameter at its upper end to a diameter sufficient to permit attachment of the second section to the inner surface of the housing at its lower end. 
     In some embodiments, solids collection conduit  150  comprises a first section having a first length and an inner diameter tapering from the first inner diameter of shell element  130  at its upper end to a diameter sufficient to permit attachment of the first section to the inner surface of the housing at its lower end. 
     In other embodiments, solids collection conduit  150  comprises a substantially cylindrical vertical wall having one or more sections where such wall is vertical, one or more sections where such wall is frustoconical with the diameter at the upper end of such sections is greater than the diameter at the lower end of such sections, one or more sections where such wall is frustoconical with the diameter at the lower end of such sections is greater than the diameter at the upper end of such sections, or a combination thereof. 
     In the foregoing embodiments, separation chamber  151 , formed by attachment of the upper end of solids collection conduit  150  and the lower end of the vortex inducer  120 , is fluidly connected to the one or more helical apertures  122  and the central aperture  121  and to the space below the opening formed by the lower edge of the substantially cylindrical vertical wall comprising the one or more vertical sections and/or one or more frustoconical sections. 
     The connection  160  between the vortex inducer  120  and the solids collection conduit  150  can be by any suitable method sufficient to secure the vortex inducer  120  and the solids collection conduit  150  during operation of the separator apparatus  110 , such as, but not limited to one or more welded connections, one or more threaded connections, or a combination thereof. In some embodiments the connection between the vortex inducer  120  and the solids collection conduit  150  is accomplished by fabrication of a lower portion of the vortex inducer  120  and the upper portion of the solids collection conduit  150  from a common piece of metal. That is to say, that fabrication of the separator apparatus  110 , or its constituent functional parts of the vortex inducer  120  and the solids collection conduit  150 , can comprise fewer or more individual parts and/or fewer or more connection points of such individual parts than are shown in  FIG.  1   , as may be convenient for fabrication of the separator apparatus  110 . The depiction of the vortex inducer  120  and the solids collection conduit  150  and their connection to form separator apparatus  110  in  FIG.  1    are intended to show the functional portions of the separator apparatus  110  and are further intended to include any combination of piping, machined parts, and/or fittings assembled in any suitable manner to perform such functions. 
     The upper end of the separator apparatus  110 , specifically the upper end of the vortex inducer  120 , is physically connected to the lower end of the treated fluid discharge conduit  170 . Although the inner diameter of the central aperture D 140a  and the inner diameter of the fluid discharge conduit  170  appear to be equal in  FIG.  1   , the inner diameter of treated fluid discharge conduit  170  can be either larger are smaller than D 140a . Such differences in diameter and/or the attachment of the vortex inducer  120  to the treated fluid discharge conduit  170  can be accommodated by any combination of piping, machined parts, welded connections, and/or fittings well known in the art. The upper end of the treated fluid discharge conduit  170  is physically connected to the upper end of the housing  180 . The lower end of the separator apparatus  110 , specifically the lower end of the solids collection conduit  150 , is connected to the housing  180  at a location below the one or more inlet ports  181 . Such connection of the separator apparatus  110 , the treated fluid discharge conduit  170 , and the housing  180  forms a feed chamber  182 , which is fluidly connected to the exterior of the housing  180  through inlet ports  181 , fluidly connected to the separation chamber  151  through the one or more helical apertures  122 , and separated from the central aperture  121  by the treated fluid discharge conduit  170 . 
     When in operation, untreated fluid  102  flows into downhole module  100  through one or more inlet ports  181  and then through one or more helical apertures  122 . Upon exiting the one or more helical apertures  122 , a vortex is created in chamber  151  wherein solids  103  are concentrated on the inner service of solids collection conduit  150  by centrifugal force while treated fluid  104  having a lower solids content are withdrawn from the separator apparatus through central aperture  121  and treated fluid discharge conduit  170 . 
     Without wishing to be bound by any particular theory, it is believed that the section of solids collection conduit  150  identified by length L 150c  and D 150b  provides improved efficiency in removal solids since tangential velocity is maintained at a smaller radius, thereby increasing centripetal acceleration. In further embodiments, discontinuities are added to the inner surface of the sections of solids collection conduit  150  identified by length L 150b  and length L 150c , or a combination thereof. Such discontinuities include, but are not limited to, fins, ridges, channels, holes, or other surface discontinuities that serve to reduce tangential velocity of the solids and permit gravity to play a greater role in moving the solids downward and out of the solids collection chamber  150 . 
     Some embodiments are configured as shown in  FIG.  2   , the downhole module  200  comprises separator apparatus  210  and housing  280 , having central axis  201 . Separator apparatus  210  comprises vortex inducer  220  and solids collection conduit  250 . Vortex inducer  220  comprises shell element  230  and core element  240 . 
     Vortex inducer  220  comprises a central aperture  221  and one or more helical apertures  222 . Each of the one or more helical apertures  222  is characterized by a cross-sectional area A with perimeter P, wherein the cross-sectional area A is perpendicular to a spiral line  223  defined by the centroid of cross-sectional area A at each point along the diameter D 222  of the one or more helical apertures  222 , and hydraulic diameter D h , wherein: 
               D     h   =       ⁢       4   ⁢   A     P           
Spiral line  223  is characterized by a helix lead L 222  and a helix lead angle θ wherein:
 
             θ   =     arctan   ⁡   (       L     2   ⁢   2   ⁢   2         π   ⁢     D     2   ⁢   2   ⁢   2           )           
In some embodiments, the ratio of shell element mating surface length L 230a  to and corresponding core element mating surface length L 241a  to helix lead L 222  is less than or equal to 1.0, 0.8, 0.6, 0.4, or 0.2.
 
     Vortex inducer  220  comprises shell element  230  and core element  240 . Core element  240  comprises a cylindrical inner surface having a diameter D 240a , which circumscribes the central aperture  221 , and a cylindrical outer surface having a diameter D 240b . The outer cylindrical surface of core element  240  comprises one or more helical channels  241 , wherein each such channel extends to the upper end of core element  240 . Core element  240  starts with a uniform outer diameter D 240b . The outer surface of the core element  240  is machined by known methods to produce one or more helical channels having a maximum depth C 241  such that each helical channel  241  has a diameter D 241  at the maximum depth of the helical channel  241 . After machining the one or more helical channels  241  into the inner surface of core element  240 , one or more strips of the original inner surface having a width W 241 , a diameter D 240b  and length L 241a  remaining as a first mating surface. Optionally, core element  241  extends a distance below the lower end of the mating surface for a distance L 241b , wherein such extension has an outer diameter of D 241 . 
     Shell element  230  comprises a cylindrical inner surface having a diameter D 230 . Optionally, shell element  230  extends for a distance L 230b  below the lower end of the mating surface when core element  240  and shell element  230  are slidably engaged in the intended operating position. 
     In some embodiments, D 240b  is equal or substantially equal to D 230 , where core element  240  and shell element  230  are held in the intended operating position after being slidably engaged by an interference fit between core element  240  and shell element  230 . In some embodiments, D 230  is less than or equal to 5 mil (127 μm), 4 mil (102 μm), 3 mil (76 μm), 2 mil (51 μm), or 1 mil (25 μm) greater than D 240b , where core element  240  and shell element  230  are held in the intended operating position after being slidably engaged by means other than an interference fit, such as, but not limited to one or more set screws or one or more keys. In some embodiments, the core element and shell element are held together by a taper fit, such as, but not limited to, self-holding tapers such as Morse tapers and Jacobs tapers. 
     The vortex inducer  220  is formed by slidably engaging the shell element  230  and the core element  240  such that at least a portion of or all of the mating surface and at least a portion of or all of the cylindrical inner surface of the shell element  230  are overlapping. The one or more helical apertures  222  are formed by the inner surface of the one or more helical channels  241  and the inner surface of the shell element  230 . 
     Solids collection conduit  250  is attached to the lower end of the vortex inducer  220  to form separation chamber  251 . In some embodiments, solids collection conduit  250  comprises: a) a first section having a length L 250a  and inner diameter D 250a ; b) a second section connected to the lower end of the first section and having a length L 250b  and an inner diameter tapering from D 250a  at its upper end to D 250b  at its lower end; c) a third section connected to the lower end of the second section and having a length L 250c  and inner diameter D 250b ; and d) a fourth section connected to the lower end of the third section and having a length L 250d  and an inner diameter tapering from D 250b  at its upper end to a diameter sufficient to permit attachment of the fourth section to the inner surface of the housing  280 , wherein such attachment separates the opening defined at the lower end of separation chamber  251  by the lower edge of the fourth section from the feed chamber  282 . 
     In some embodiments, solids collection conduit  250  comprises: a) a first section having a first length and a first inner diameter; and b) a second section connected to the lower end of the first section and having a second length and an inner diameter tapering from the first inner diameter at its upper end to a diameter sufficient to permit attachment of the second section to the inner surface of the housing at its lower end. 
     In some embodiments, solids collection conduit  250  comprises a first section having a first length and an inner diameter tapering from the first inner diameter of shell element  230  at its upper end to a diameter sufficient to permit attachment of the first section to the inner surface of the housing at its lower end. 
     In other embodiments, solids collection conduit  250  comprises a substantially cylindrical vertical wall having one or more sections where such wall is vertical, one or more sections where such wall is frustoconical with the diameter at the upper end of such sections is greater than the diameter at the lower end of such sections, one or more sections where such wall is frustoconical with the diameter at the lower end of such sections is greater than the diameter at the upper end of such sections, or a combination thereof. 
     In the foregoing embodiments, separation chamber  251 , formed by attachment of the upper end of solids collection conduit  250  and the lower end of the vortex inducer  220 , is fluidly connected to the one or more helical apertures  222  and the central aperture  221  and to the space below the opening formed by the lower edge of the substantially cylindrical vertical wall comprising the one or more vertical sections and/or one or more frustoconical sections. 
     The connection  260  between the vortex inducer  220  and the solids collection conduit  250  can be by any suitable method sufficient to secure the vortex inducer  220  and the solids collection conduit  250  during operation of the separator apparatus  210 , such as, but not limited to one or more welded connections, one or more threaded connections, or a combination thereof. In some embodiments the connection between the vortex inducer  220  and the solids collection conduit  250  is accomplished by fabrication of a lower portion of the vortex inducer  220  and the upper portion of the solids collection conduit  250  from a common piece of metal. That is to say, that fabrication of the separator apparatus  210 , or its constituent functional parts of the vortex inducer  220  and the solids collection conduit  250 , can comprise fewer or more individual parts and/or fewer or more connection points of such individual parts than are shown in  FIG.  2   , as may be convenient for fabrication of the separator apparatus  210 . The depiction of the vortex inducer  220  and the solids collection conduit  250  and their connection to form separator apparatus  210  in  FIG.  2    are intended to show the functional portions of the separator apparatus  210  and are further intended to include any combination of piping, machined parts, and/or fittings assembled in any suitable manner to perform such functions. 
     The upper end of the separator apparatus  210 , specifically the upper end of the vortex inducer  220 , is physically connected to the lower end of the treated fluid discharge conduit  270 . Although the inner diameter of the central aperture D 240 , and the inner diameter of the fluid discharge conduit  270  appear to be equal in  FIG.  2   , the inner diameter of treated fluid discharge conduit  270  can be either larger are smaller than D 240a . Such differences in diameter and/or the attachment of the vortex inducer  220  to the treated fluid discharge conduit  270  can be accommodated by any combination of piping, machined parts, welded connections, and/or fittings well known in the art. The upper end of the treated fluid discharge conduit  270  is physically connected to the upper end of the housing  280 . The lower end of the separator apparatus  210 , specifically the lower end of the solids collection conduit  250 , is connected to the housing  280  at a location below the one or more inlet ports  281 . Such connection of the separator apparatus  210 , the treated fluid discharge conduit  270 , and the housing  280  forms a feed chamber  282 , which is fluidly connected to the exterior of the housing  280  through inlet ports  281 , fluidly connected to the separation chamber  251  through the one or more helical apertures  222 , and separated from the central aperture  221  by the treated fluid discharge conduit  270 . 
     When in operation, untreated fluid  202  flows into downhole module  200  through one or more inlet ports  281  and then through one or more helical apertures  222 . Upon exiting the one or more helical apertures  222 , a vortex is created in chamber  251  wherein solids  203  are concentrated on the inner service of solids collection conduit  250  by centrifugal force while treated fluid  204  having a lower solids content are withdrawn from the separator apparatus through central aperture  221  and treated fluid discharge conduit  270 . 
     Without wishing to be bound by any particular theory, it is believed that the section of solids collection conduit  250  identified by length L 250c  and D 250b  provides improved efficiency in removal solids since tangential velocity is maintained at a smaller radius, thereby increasing centripetal acceleration. Another advantage of this configuration is that channels  241  on the outer surface of core element  240  provide more improved access to surfaces to be machined. In further embodiments, discontinuities are added to the inner surface of the sections of solids collection conduit  250  identified by length L 250b  and length L 250c , or a combination thereof. Such discontinuities include, but are not limited to, fins, ridges, channels, holes, or other surface discontinuities that serve to reduce tangential velocity of the solids and permit gravity to play a greater role in moving the solids downward and out of the solids collection chamber  250 . 
     Some embodiments are configured as shown in  FIG.  3   , the downhole module  300  comprises separator apparatus  310  and housing  380 , having central axis  301 . Separator apparatus  310  comprises vortex inducer  320  and solids collection conduit  350 . Vortex inducer  320  comprises shell element  330  and core element  340 . 
     Vortex inducer  320  comprises a central aperture  321  and one or more helical apertures  322 . Each of the one or more helical apertures  322  is characterized by a cross-sectional area A with perimeter P, wherein the cross-sectional area A is perpendicular to a spiral line  323  defined by the centroid of cross-sectional area A at each point along the diameter D 322  of the one or more helical apertures  322 , and hydraulic diameter D h , wherein: 
               D     h   =       ⁢       4   ⁢   A     P           
Spiral line  323  is characterized by a helix lead L 322  and a helix lead angle θ wherein:
 
             θ   =     arctan   ⁡   (       L     3   ⁢   2   ⁢   2         π   ⁢     D     3   ⁢   2   ⁢   2           )           
In some embodiments, the ratio of shell element mating surface length L 331a  and corresponding core element mating surface length L 340a  to helix lead L 322  is less than or equal to 1.0, 0.8, 0.6, 0.4, or 0.2.
 
     Vortex inducer  320  comprises shell element  330  and core element  340 . Shell element  330  comprises an inner cylindrical surface having one or more helical channels  331 , each such channel extends to the upper end of shell element  330 . The outer diameter of shell element  330  is less than or equal to the inner diameter of the housing  380 . Shell element  330  starts with a uniform inner diameter D 331 . The inner surface of the shell element is machined by known methods to produce one or more helical channels having a maximum depth C 331  such that each helical channel  331  has a diameter D 331  at the maximum depth of the helical channel  331 . After machining the one or more helical channels  331  into the inner surface of shell element  330 , one or more strips of the original inner surface having a width W 331 , a diameter D 331  and length L 331a  remaining as a first mating surface. Optionally, shell element  330  extends a distance below the lower end of the mating surface for a distance L 331b , wherein such extension has an inner diameter of D 331 . 
     Core element  340  comprises a cylindrical inner surface having a diameter D 340a , which circumscribes the central aperture  321 , and a cylindrical outer surface having a diameter D 340b . Length L 340a  is the mating surface of core element  340 , such that the corresponding mating surfaces of the shell element  330  and the core element  340  define the span of the helical apertures  322  when shell element  330  and core element  340  are slidably engaged. Optionally, core element  340  extends for a distance L 340b  below the lower end of the mating surface when core element  340  and shell element  330  are slidably engaged in the intended operating position. 
     In some embodiments, D 340b  is equal or substantially equal to D 330 , where core element  340  and shell element  330  are held in the intended operating position after being slidably engaged by an interference fit between core element  340  and shell element  330 . In some embodiments, D 331  is less than or equal to 5 mil (127 μm), 4 mil (102 μm), 3 mil (76 μm), 2 mil (51 μm), or 1 mil (25 μm) greater than D 340b , where core element  340  and shell element  330  are held in the intended operating position after being slidably engaged by means other than an interference fit, such as, but not limited to one or more set screws or one or more keys. In some embodiments, the core element and shell element are held together by a taper fit, such as, but not limited to, self-holding tapers such as Morse tapers and Jacobs tapers. 
     The vortex inducer  320  is formed by slidably engaging the shell element  330  and the core element  340  such that at least a portion of or all of the mating surface and at least a portion of or all of the cylindrical outer surface of the core element  340  are overlapping. The one or more helical apertures  322  are formed by the inner surface of the one or more helical channels  331  and the outer surface of the core element  340 . 
     Solids collection conduit  350  is attached to the lower end of the vortex inducer  320  to form separation chamber  351 . In some embodiments, solids collection conduit  350  comprises a substantially cylindrical vertical wall having one or more sections where such wall is vertical, one or more sections where such wall is frustoconical with the diameter at the upper end of such sections is greater than the diameter at the lower end of such sections, one or more sections where such wall is frustoconical with the diameter at the lower end of such sections is greater than the diameter at the upper end of such sections, or a combination thereof. 
     In the foregoing embodiments, separation chamber  351 , formed by attachment of the upper end of solids collection conduit  350  and the lower end of the vortex inducer  320 , is fluidly connected to the one or more helical apertures  322  and the central aperture  321  and to the space below the opening formed by the lower edge of the substantially cylindrical vertical wall comprising the one or more vertical sections and/or one or more frustoconical sections. 
     The connection  360  between the vortex inducer  320  and the solids collection conduit  350  can be by any suitable method sufficient to secure the vortex inducer  320  and the solids collection conduit  350  during operation of the separator apparatus  310 , such as, but not limited to one or more welded connections, one or more threaded connections, or a combination thereof. In some embodiments the connection between the vortex inducer  320  and the solids collection conduit  350  is accomplished by fabrication of a lower portion of the vortex inducer  320  and the upper portion of the solids collection conduit  350  from a common piece of metal. That is to say, that fabrication of the separator apparatus  310 , or its constituent functional parts of the vortex inducer  320  and the solids collection conduit  350 , can comprise fewer or more individual parts and/or fewer or more connection points of such individual parts than are shown in  FIG.  3   , as may be convenient for fabrication of the separator apparatus  310 . The depiction of the vortex inducer  320  and the solids collection conduit  350  and their connection to form separator apparatus  310  in  FIG.  3    are intended to show the functional portions of the separator apparatus  310  and are further intended to include any combination of piping, machined parts, and/or fittings assembled in any suitable manner to perform such functions. 
     The upper end of the separator apparatus  310 , specifically the upper end of the vortex inducer  320 , is physically connected to the lower end of the treated fluid discharge conduit  370 . Although the inner diameter of the central aperture D 340a  and the inner diameter of the fluid discharge conduit  370  appear to be equal in  FIG.  3   , the inner diameter of treated fluid discharge conduit  370  can be either larger are smaller than D 340a . Such differences in diameter and/or the attachment of the vortex inducer  320  to the treated fluid discharge conduit  370  can be accommodated by any combination of piping, machined parts, welded connections, and/or fittings well known in the art. The upper end of the treated fluid discharge conduit  370  is physically connected to the upper end of the housing  380 . The lower end of the separator apparatus  310 , specifically the lower end of the solids collection conduit  350 , is connected to the housing  380  at a location below the one or more inlet ports  381 . Such connection of the separator apparatus  310 , the treated fluid discharge conduit  370 , and the housing  380  forms a feed chamber  382 , which is fluidly connected to the exterior of the housing  380  through inlet ports  381 , fluidly connected to the separation chamber  351  through the one or more helical apertures  322 , and separated from the central aperture  321  by the treated fluid discharge conduit  370 . 
     When in operation, untreated fluid  302  flows into downhole module  300  through one or more inlet ports  381  and then through one or more helical apertures  322 . Upon exiting the one or more helical apertures  322 , a vortex is created in chamber  351  wherein solids  303  are concentrated on the inner service of solids collection conduit  350  by centrifugal force while treated fluid  304  having a lower solids content are withdrawn from the separator apparatus through central aperture  321  and treated fluid discharge conduit  370 . 
     This embodiment provides a more compact feed chamber  382  having a more direct path from the inlet ports  381  to helical apertures  322 , and location of the inlet ports  381  above the separator apparatus  310  permit a larger diameter D 331  of helical aperture. Without wishing to be bound by any particular theory, it is believed that both of these factors contribute to higher flow velocity in the one or more helical apertures D 322 , leading in turn to improved solids removal at a given pressure drop across the vortex inducer  320 . Additionally, this embodiment permits a larger diameter central aperture  321  which results in a lower localized velocity of treated fluid flow  304  at the upper end of separation chamber  351 , thereby reducing the tendency to entrain any solids in treated fluid flow  304  at a given design flow rate through separator apparatus  310 . In further embodiments, discontinuities are added to the inner surface of the sections of solids collection conduit  350 . Such discontinuities include, but are not limited to, fins, ridges, channels, holes, or other surface discontinuities that serve to reduce tangential velocity of the solids and permit gravity to play a greater role in moving the solids downward and out of the solids collection chamber  350 . 
     Some embodiments are configured as shown in  FIG.  4   , the downhole module  400  comprises separator apparatus  410  and housing  480 , having central axis  401 . Separator apparatus  410  comprises vortex inducer  420  and solids collection conduit  450 . Vortex inducer  420  comprises shell element  430  and core element  440 . 
     Vortex inducer  420  comprises a central aperture  421  and one or more helical apertures  422 . Each of the one or more helical apertures  422  is characterized by a cross-sectional area A with perimeter P, wherein the cross-sectional area A is perpendicular to a spiral line  423  defined by the centroid of cross-sectional area A at each point along the diameter D 422  of the one or more helical apertures  422 , and hydraulic diameter D h , wherein: 
               D     h   =       ⁢       4   ⁢   A     P           
Spiral line  423  is characterized by a helix lead L 422  and a helix lead angle θ wherein:
 
             θ   =     arctan   ⁡   (       L     4   ⁢   2   ⁢   2         π   ⁢     D     4   ⁢   2   ⁢   2           )           
In some embodiments, the ratio of shell element mating surface length L 430a  to and corresponding core element mating surface length L 441a  to helix lead L 422  is less than or equal to 1.0, 0.8, 0.6, 0.4, or 0.2.
 
     Vortex inducer  420  comprises shell element  430  and core element  440 . Core element  440  comprises a cylindrical inner surface having a diameter D 440a , which circumscribes the central aperture  421  and a cylindrical outer surface having a diameter D 440b . The outer cylindrical surface of core element  440  comprises one or more helical channels  441 , wherein each such channel extends to the upper end of core element  440 . Shell element  440  starts with a uniform outer diameter D 440b . The outer surface of the core element  440  is machined by known methods to produce one or more helical channels having a maximum depth C 441  such that each helical channel  441  has a diameter D 441  at the maximum depth of the helical channel  441 . After machining the one or more helical channels  441  into the inner surface of core element  440 , one or more strips of the original inner surface having a width W 441 , a diameter D 440b  and length L 441a  remaining as a first mating surface. Optionally, core element  441  extends a distance below the lower end of the mating surface for a distance L 441b , wherein such extension has an outer diameter of D 441 . 
     Shell element  430  comprises a cylindrical inner surface having a diameter D 430 . Optionally, shell element  430  extends for a distance L 430b  below the lower end of the mating surface when core element  440  and shell element  430  are slidably engaged in the intended operating position. 
     In some embodiments, D 440b  is equal or substantially equal to D 430 , where core element  440  and shell element  430  are held in the intended operating position after being slidably engaged by an interference fit between core element  440  and shell element  430 . In some embodiments, D 430  is less than or equal to 5 mil (127 μm), 4 mil (102 μm), 3 mil (76 μm), 2 mil (51 μm), or 1 mil (25 μm) greater than D 440b , where core element  440  and shell element  430  are held in the intended operating position after being slidably engaged by means other than an interference fit, such as, but not limited to one or more set screws or one or more keys. In some embodiments, the core element and shell element are held together by a taper fit, such as, but not limited to, self-holding tapers such as Morse tapers and Jacobs tapers. 
     The vortex inducer  420  is formed by slidably engaging the shell element  430  and the core element  440  such that at least a portion of or all of the mating surface and at least a portion of or all of the cylindrical inner surface of the shell element  430  are overlapping. The one or more helical apertures  422  are formed by the inner surface of the one or more helical channels  441  and the inner surface of the shell element  430 . 
     Solids collection conduit  450  is attached to the lower end of the vortex inducer  420  to form separation chamber  451 . In some embodiments, solids collection conduit  450  comprises a substantially cylindrical vertical wall having one or more sections where such wall is vertical, one or more sections where such wall is frustoconical with the diameter at the upper end of such sections is greater than the diameter at the lower end of such sections, one or more sections where such wall is frustoconical with the diameter at the lower end of such sections is greater than the diameter at the upper end of such sections, or a combination thereof. 
     In the foregoing embodiments, separation chamber  451 , formed by attachment of the upper end of solids collection conduit  450  and the lower end of the vortex inducer  420 , is fluidly connected to the one or more helical apertures  422  and the central aperture  421  and to the space below the opening formed by the lower edge of the substantially cylindrical vertical wall comprising the one or more vertical sections and/or one or more frustoconical sections. 
     The connection  460  between the vortex inducer  420  and the solids collection conduit  450  can be by any suitable method sufficient to secure the vortex inducer  420  and the solids collection conduit  450  during operation of the separator apparatus  410 , such as, but not limited to one or more welded connections, one or more threaded connections, or a combination thereof. In some embodiments the connection between the vortex inducer  420  and the solids collection conduit  450  is accomplished by fabrication of a lower portion of the vortex inducer  420  and the upper portion of the solids collection conduit  450  from a common piece of metal. That is to say, that fabrication of the separator apparatus  410 , or its constituent functional parts of the vortex inducer  420  and the solids collection conduit  450 , can comprise fewer or more individual parts and/or fewer or more connection points of such individual parts than are shown in  FIG.  4   , as may be convenient for fabrication of the separator apparatus  410 . The depiction of the vortex inducer  420  and the solids collection conduit  450  and their connection to form separator apparatus  410  in  FIG.  4    are intended to show the functional portions of the separator apparatus  410  and are further intended to include any combination of piping, machined parts, and/or fittings assembled in any suitable manner to perform such functions. 
     The upper end of the separator apparatus  410 , specifically the upper end of the vortex inducer  420 , is physically connected to the lower end of the treated fluid discharge conduit  470 . Although the inner diameter of the central aperture D 440a  and the inner diameter of the fluid discharge conduit  470  appear to be equal in  FIG.  4   , the inner diameter of treated fluid discharge conduit  470  can be either larger are smaller than D 440a . Such differences in diameter and/or the attachment of the vortex inducer  420  to the treated fluid discharge conduit  470  can be accommodated by any combination of piping, machined parts, welded connections, and/or fittings well known in the art. The upper end of the treated fluid discharge conduit  470  is physically connected to the upper end of the housing  480 . The lower end of the separator apparatus  410 , specifically the lower end of the solids collection conduit  450 , is connected to the housing  480  at a location below the one or more inlet ports  481 . Such connection of the separator apparatus  410 , the treated fluid discharge conduit  470 , and the housing  480  forms a feed chamber  482 , which is fluidly connected to the exterior of the housing  480  through inlet ports  481 , fluidly connected to the separation chamber  451  through the one or more helical apertures  422 , and separated from the central aperture  421  by the treated fluid discharge conduit  470 . 
     When in operation, untreated fluid  402  flows into downhole module  400  through one or more inlet ports  481  and then through one or more helical apertures  422 . Upon exiting the one or more helical apertures  422 , a vortex is created in chamber  451  wherein solids  403  are concentrated on the inner service of solids collection conduit  450  by centrifugal force while treated fluid  404  having a lower solids content are withdrawn from the separator apparatus through central aperture  421  and treated fluid discharge conduit  470 . 
     This embodiment provides a more compact feed chamber  482  having a more direct path from the inlet ports  481  to helical apertures  422 , and location of the inlet ports  481  above the separator apparatus  410  permit a larger diameter D 431  of helical aperture. Without wishing to be bound by any particular theory, it is believed that both of these factors contribute to higher flow velocity in the one or more helical apertures D 422 , leading in turn to improved solids removal at a given pressure drop across the vortex inducer  420 . Additionally, this embodiment permits a larger diameter central aperture  421  which results in a lower localized velocity of treated fluid flow  404  at the upper end of separation chamber  451 , thereby reducing the tendency to entrain any solids in treated fluid flow  404  at a given design flow rate through separator apparatus  410 . Another advantage of this configuration is that channels  441  on the outer surface of core element  440  provide more improved access to surfaces to be machined. In further embodiments, discontinuities are added to the inner surface of the sections of solids collection conduit  450 . Such discontinuities include, but are not limited to, fins, ridges, channels, holes, or other surface discontinuities that serve to reduce tangential velocity of the solids and permit gravity to play a greater role in moving the solids downward and out of the solids collection chamber  450 . 
     Some embodiments are configured as shown in  FIG.  5   , the downhole module  500  comprises separator apparatus  510  and housing  580 , having central axis  501 . Separator apparatus  510  comprises vortex inducer  520  and solids collection conduit  550 . Vortex inducer  520  comprises shell element  530  and core element  540 . 
     Vortex inducer  520  comprises a central aperture  521  and one or more helical apertures  522 . Each of the one or more helical apertures  522  is characterized by a cross-sectional area A with perimeter P, wherein the cross-sectional area A is perpendicular to a spiral line  523  defined by the centroid of cross-sectional area A at each point along the diameter D 522  of the one or more helical apertures  522 , and hydraulic diameter D h , wherein: 
               D     h   =       ⁢       4   ⁢   A     P           
Spiral line  523  is characterized by a helix lead L 522  and a helix lead angle θ wherein:
 
     
       
         
           
             θ 
             = 
             
               arctan 
               ⁡ 
               ( 
               
                 
                   L 
                   
                     5 
                     ⁢ 
                     2 
                     ⁢ 
                     2 
                   
                 
                 
                   π 
                   ⁢ 
                   
                     D 
                     
                       5 
                       ⁢ 
                       2 
                       ⁢ 
                       2 
                     
                   
                 
               
               ) 
             
           
         
       
     
     In some embodiments, the ratio of shell element mating surface length L 531a  and corresponding core element mating surface length L 540a  to helix lead L 522  is less than or equal to 1.0, 0.8, 0.6, 0.4, or 0.2. 
     Vortex inducer  520  comprises shell element  530  and core element  540 . Shell element  530  comprises an inner cylindrical surface having one or more helical channels  531 , each such channel extends to the upper end of shell element  530 . The outer diameter of shell element  530  is less than or equal to the inner diameter of the housing  580 . Shell element  530  starts with a uniform inner diameter D 531a . The inner surface of the shell element is machined by known methods to produce one or more helical channels having a maximum depth C 531  such that each helical channel  531  has a diameter D 531  at the maximum depth of the helical channel  531 . After machining the one or more helical channels  531  into the inner surface of shell element  530 , one or more strips of the original inner surface having a width W 531 , a diameter D 531a  and length L 531a  remaining as a first mating surface. Optionally, shell element  530  extends a distance below the lower end of the mating surface for a distance L 531b , wherein such extension has an inner diameter of D 531 . 
     Core element  540  comprises a cylindrical inner surface having a diameter D 540a , which circumscribes the central aperture  521  and a cylindrical outer surface having a diameter D 540b . Length L 540a  is the mating surface of core element  540 , such that the corresponding mating surfaces of the shell element  530  and the core element  540  define the span of the helical apertures  522  when shell element  530  and core element  540  are slidably engaged. Optionally, core element  540  extends for a distance L 540b  below the lower end of the mating surface when core element  540  and shell element  530  are slidably engaged in the intended operating position. 
     In some embodiments, D 540b  is equal or substantially equal to D 531a , where core element  540  and shell element  530  are held in the intended operating position after being slidably engaged by an interference fit between core element  540  and shell element  530 . In some embodiments, D 540b  is less than or equal to 5 mil (127 μm), 4 mil (102 μm), 3 mil (76 μm), 2 mil (51 μm), or 1 mil (25 μm) greater than D 531a , where core element  540  and shell element  530  are held in the intended operating position after being slidably engaged by means other than an interference fit, such as, but not limited to one or more set screws or one or more keys. In some embodiments, the core element and shell element are held together by a taper fit, such as, but not limited to, self-holding tapers such as Morse tapers and Jacobs tapers. 
     The vortex inducer  520  is formed by slidably engaging the shell element  530  and the core element  540  such that at least a portion of or all of the mating surface and at least a portion of or all of the cylindrical outer surface of the core element  540  are overlapping. The one or more helical apertures  522  are formed by the inner surface of the one or more helical channels  531  and the outer surface of the core element  540 . 
     Solids collection conduit  550  is attached to the lower end of the vortex inducer  520  to form separation chamber  551 . In some embodiments, solids collection conduit  550  comprises: a) a first section having a length L 550a  and inner diameter D 550a ; b) a second section connected to the lower end of the first section and having a length L 550b  and an inner diameter tapering from D 550a  at its upper end to a diameter sufficient to permit attachment of the second section to the inner surface of the housing  580 , wherein such attachment separates the opening defined at the lower end of separation chamber  551  by the lower edge of the second section from the feed chamber  582 . 
     In the foregoing embodiments, separation chamber  551 , formed by attachment of the upper end of solids collection conduit  550  and the lower end of the vortex inducer  520 , is fluidly connected to the one or more helical apertures  522  and the central aperture  521  and to the space below the opening formed by the lower edge of the substantially cylindrical vertical wall comprising the one or more vertical sections and/or one or more frustoconical sections. 
     The connection  560  between the vortex inducer  520  and the solids collection conduit  550  can be by any suitable method sufficient to secure the vortex inducer  520  and the solids collection conduit  550  during operation of the separator apparatus  510 , such as, but not limited to one or more welded connections, one or more threaded connections, or a combination thereof. In some embodiments the connection between the vortex inducer  520  and the solids collection conduit  550  is accomplished by fabrication of a lower portion of the vortex inducer  520  and the upper portion of the solids collection conduit  550  from a common piece of metal. That is to say, that fabrication of the separator apparatus  510 , or its constituent functional parts of the vortex inducer  520  and the solids collection conduit  550 , can comprise fewer or more individual parts and/or fewer or more connection points of such individual parts than are shown in  FIG.  5   , as may be convenient for fabrication of the separator apparatus  510 . The depiction of the vortex inducer  520  and the solids collection conduit  550  and their connection to form separator apparatus  510  in  FIG.  5    are intended to show the functional portions of the separator apparatus  510  and are further intended to include any combination of piping, machined parts, and/or fittings assembled in any suitable manner to perform such functions. 
     The upper end of the separator apparatus  510 , specifically the upper end of the vortex inducer  520 , is physically connected to the lower end of the treated fluid discharge conduit  570 . Although the inner diameter of the central aperture D 540a  and the inner diameter of the fluid discharge conduit  570  appear to be equal in  FIG.  5   , the inner diameter of treated fluid discharge conduit  570  can be either larger are smaller than D 540a . Such differences in diameter and/or the attachment of the vortex inducer  520  to the treated fluid discharge conduit  570  can be accommodated by any combination of piping, machined parts, welded connections, and/or fittings well known in the art. The upper end of the treated fluid discharge conduit  570  is physically connected to the upper end of the housing  580 . The lower end of the separator apparatus  510 , specifically the lower end of the solids collection conduit  550 , is connected to the housing  580  at a location below the one or more inlet ports  581 . Such connection of the separator apparatus  510 , the treated fluid discharge conduit  570 , and the housing  580  forms a feed chamber  582 , which is fluidly connected to the exterior of the housing  580  through inlet ports  581 , fluidly connected to the separation chamber  551  through the one or more helical apertures  522 , and separated from the central aperture  521  by the treated fluid discharge conduit  570 . 
     When in operation, untreated fluid  502  flows into downhole module  500  through one or more inlet ports  581  and then through one or more helical apertures  522 . Upon exiting the one or more helical apertures  522 , a vortex is created in chamber  551  wherein solids  503  are concentrated on the inner service of solids collection conduit  550  by centrifugal force while treated fluid  504  having a lower solids content are withdrawn from the separator apparatus through central aperture  521  and treated fluid discharge conduit  570 . 
     Without wishing to be bound by any particular theory, it is believed that the section of solids collection conduit  550  identified by length L 550b  provides improved efficiency in removal solids since tangential velocity since remaining centrifugal force would have downward component in addition to a radial component due to the frustoconical shape of this section of solids collection conduit  550 . Such component of downward force would promote discharge of solids from the lower end of solids collection conduit  550 . In further embodiments, discontinuities are added to the inner surface of the sections of solids collection conduit  550  identified by length L 550a  and length L 550b , or a combination thereof. Such discontinuities include, but are not limited to, fins, ridges, channels, holes, or other surface discontinuities that serve to reduce tangential velocity of the solids and permit gravity to play a greater role in moving the solids downward and out of the solids collection chamber  550 . 
     Some embodiments are configured as shown in  FIG.  6   , the downhole module  600  comprises separator apparatus  610  and housing  680 , having central axis  601 . Separator apparatus  610  comprises vortex inducer  620  and solids collection conduit  650 . Vortex inducer  620  comprises shell element  630  and core element  640 . 
     Vortex inducer  620  comprises a central aperture  621  and one or more helical apertures  622 . Each of the one or more helical apertures  622  is characterized by a cross-sectional area A with perimeter P, wherein the cross-sectional area A is perpendicular to a spiral line  623  defined by the centroid of cross-sectional area A at each point along the diameter D 622  of the one or more helical apertures  622 , and hydraulic diameter D h , wherein: 
               D     h   =       ⁢       4   ⁢   A     P           
Spiral line  623  is characterized by a helix lead L 622  and a helix lead angle θ wherein:
 
             θ   =     arctan   ⁡   (       L     6   ⁢   2   ⁢   2         π   ⁢     D     6   ⁢   2   ⁢   2           )           
In some embodiments, the ratio of shell element mating surface length L 630a  to and corresponding core element mating surface length L 641a  to helix lead L 622  is less than or equal to 1.0, 0.8, 0.6, 0.4, or 0.2.
 
     Vortex inducer  620  comprises shell element  630  and core element  640 . Core element  640  comprises a cylindrical inner surface having a diameter D 640a , which circumscribes the central aperture  621  and a cylindrical outer surface having a diameter D 640b . The outer cylindrical surface of core element  640  comprises one or more helical channels  641 , wherein each such channel extends to the upper end of core element  640 . Shell element  640  starts with a uniform outer diameter D 640b . The outer surface of the core element  640  is machined by known methods to produce one or more helical channels having a maximum depth C 641  such that each helical channel  641  has a diameter D 641  at the maximum depth of the helical channel  641 . After machining the one or more helical channels  641  into the inner surface of core element  640 , one or more strips of the original inner surface having a width W 641 , a diameter D 640b  and length L 641a  remaining as a first mating surface. Optionally, core element  641  extends a distance below the lower end of the mating surface for a distance L 641b , wherein such extension has an outer diameter of D 641 . 
     Shell element  630  comprises a cylindrical inner surface having a diameter D 630 . Optionally, shell element  630  extends for a distance L 630b  below the lower end of the mating surface when core element  640  and shell element  630  are slidably engaged in the intended operating position. 
     In some embodiments, D 640b  is equal or substantially equal to D 630 , where core element  640  and shell element  630  are held in the intended operating position after being slidably engaged by an interference fit between core element  640  and shell element  630 . In some embodiments, D 630  is less than or equal to 5 mil (127 μm), 4 mil (102 μm), 3 mil (76 μm), 2 mil (51 μm), or 1 mil (25 μm) greater than D 640b , where core element  640  and shell element  630  are held in the intended operating position after being slidably engaged by means other than an interference fit, such as, but not limited to one or more set screws or one or more keys. In some embodiments, the core element and shell element are held together by a taper fit, such as, but not limited to, self-holding tapers such as Morse tapers and Jacobs tapers. 
     The vortex inducer  620  is formed by slidably engaging the shell element  630  and the core element  640  such that at least a portion of or all of the mating surface and at least a portion of or all of the cylindrical inner surface of the shell element  630  are overlapping. The one or more helical apertures  622  are formed by the inner surface of the one or more helical channels  641  and the inner surface of the shell element  630 . 
     Solids collection conduit  650  is attached to the lower end of the vortex inducer  620  to form separation chamber  651 . In some embodiments, solids collection conduit  650  comprises: a) a first section having a length L 650a  and inner diameter D 650a ; b) a second section connected to the lower end of the first section and having a length L 650b  and an inner diameter tapering from D 650a  at its upper end to a diameter sufficient to permit attachment of the second section to the inner surface of the housing  680 , wherein such attachment separates the opening defined at the lower end of separation chamber  651  by the lower edge of the second section from the feed chamber  682 . 
     In the foregoing embodiments, separation chamber  651 , formed by attachment of the upper end of solids collection conduit  650  and the lower end of the vortex inducer  620 , is fluidly connected to the one or more helical apertures  622  and the central aperture  621  and to the space below the opening formed by the lower edge of the substantially cylindrical vertical wall comprising the one or more vertical sections and/or one or more frustoconical sections. 
     The connection  660  between the vortex inducer  620  and the solids collection conduit  650  can be by any suitable method sufficient to secure the vortex inducer  620  and the solids collection conduit  650  during operation of the separator apparatus  610 , such as, but not limited to one or more welded connections, one or more threaded connections, or a combination thereof. In some embodiments the connection between the vortex inducer  620  and the solids collection conduit  650  is accomplished by fabrication of a lower portion of the vortex inducer  620  and the upper portion of the solids collection conduit  650  from a common piece of metal. That is to say, that fabrication of the separator apparatus  610 , or its constituent functional parts of the vortex inducer  620  and the solids collection conduit  650 , can comprise fewer or more individual parts and/or fewer or more connection points of such individual parts than are shown in  FIG.  6   , as may be convenient for fabrication of the separator apparatus  610 . The depiction of the vortex inducer  620  and the solids collection conduit  650  and their connection to form separator apparatus  610  in  FIG.  6    are intended to show the functional portions of the separator apparatus  610  and are further intended to include any combination of piping, machined parts, and/or fittings assembled in any suitable manner to perform such functions. 
     The upper end of the separator apparatus  610 , specifically the upper end of the vortex inducer  620 , is physically connected to the lower end of the treated fluid discharge conduit  670 . Although the inner diameter of the central aperture D 640a  and the inner diameter of the fluid discharge conduit  670  appear to be equal in  FIG.  6   , the inner diameter of treated fluid discharge conduit  670  can be either larger are smaller than D 640a . Such differences in diameter and/or the attachment of the vortex inducer  620  to the treated fluid discharge conduit  670  can be accommodated by any combination of piping, machined parts, welded connections, and/or fittings well known in the art. The upper end of the treated fluid discharge conduit  670  is physically connected to the upper end of the housing  680 . The lower end of the separator apparatus  610 , specifically the lower end of the solids collection conduit  650 , is connected to the housing  680  at a location below the one or more inlet ports  681 . Such connection of the separator apparatus  610 , the treated fluid discharge conduit  670 , and the housing  680  forms a feed chamber  682 , which is fluidly connected to the exterior of the housing  680  through inlet ports  681 , fluidly connected to the separation chamber  651  through the one or more helical apertures  622 , and separated from the central aperture  621  by the treated fluid discharge conduit  670 . 
     When in operation, untreated fluid  602  flows into downhole module  600  through one or more inlet ports  681  and then through one or more helical apertures  622 . Upon exiting the one or more helical apertures  622 , a vortex is created in separation chamber  651  wherein solids  603  are concentrated on the inner service of solids collection conduit  650  by centrifugal force while treated fluid  604  having a lower solids content are withdrawn from the separator apparatus through central aperture  621  and treated fluid discharge conduit  670 . 
     Without wishing to be bound by any particular theory, it is believed that the section of solids collection conduit  650  identified by length L 650b  provides improved efficiency in removal solids since tangential velocity since remaining centrifugal force would have downward component in addition to a radial component due to the frustoconical shape of this section of solids collection conduit  650 . Such component of downward force would promote discharge of solids from the lower end of solids collection conduit  650 . In further embodiments, discontinuities are added to the inner surface of the sections of solids collection conduit  650  identified by length L 650a  and length L 650b , or a combination thereof. Such discontinuities include, but are not limited to, fins, ridges, channels, holes, or other surface discontinuities that serve to reduce tangential velocity of the solids and permit gravity to play a greater role in moving the solids downward and out of the solids collection chamber  650 . Another advantage of this configuration is that channels  641  on the outer surface of core element  640  provide more improved access to surfaces to be machined. 
     More detail of certain geometric features is shown in  FIGS.  7 A and  7 B .  FIG.  7 A  shows a side and top view of a simplified shell element  730  having two helical channels in the cylindrical inner surface. Simplified shell element  730  is functionally equivalent to shell elements  130 ,  330 , and  530  as shown in  FIGS.  1 ,  3 , and  5   , respectively. Central axis  739  is shown in the side view of simplified shell element  730  at the top of  FIG.  7 A . Inner diameter D 732  is the diameter prior to fabricating the helical channel  731 . Area A 734  having centroid  736  is the area of the helical channel  731  when viewed from the top of shell element  730 . Perimeter P 731  is the perimeter of the helical channel  731  when viewed from the top of shell element  730 . For calculation of area A 734  and perimeter P 731 , the “open” side of the helical channel  731  is assumed to be along the perimeter of inner surface of shell element  730  as this is equivalent to the helical aperture area and perimeter formed when the shell element is slidably engaged with the corresponding core element. A helical line is defined by the centroid  736  at every point along helical channel  731 . Line  738  represents a line tangent to the aforementioned helical line, which in combination with the central axis defines the helix angle θ 740 . The helix lead or pitch is the axial distance between the centerline of adjacent coils of the helix or the axial length of a 360° section of the helix. The helix lead (L) is calculated as: 
     
       
         
           
             L 
             = 
             
               
                 π 
                 ⁢ 
                 
                   D 
                   
                     7 
                     ⁢ 
                     3 
                     ⁢ 
                     0 
                   
                 
               
               
                 tan 
                 ⁢ 
                 
                   θ 
                   
                     7 
                     ⁢ 
                     3 
                     ⁢ 
                     1 
                   
                 
               
             
           
         
       
     
     The flow area of each helical channel  731 , as a precursor for each helical aperture, is the cross-sectional area of helical channel  731  perpendicular to the helical line formed by the centroid  736  of area A 731  at every point along helical channel  731 . The flow area (A f ) is calculated as: 
       A   f   =A   731  sin θ 731    
     The velocity in the aperture formed by each helical channel  731 , as a precursor for each helical aperture, is calculated as: 
     
       
         
           
             u 
             = 
             
               F 
               
                 n 
                 × 
                 
                   A 
                   f 
                 
               
             
           
         
       
     
     wherein:
         u is the flow speed of the fluid in meters/sec;   F is the design flow rate of the separator apparatus in meter 3 /sec; and   n is the number of helical apertures.       

     The flow perimeter of each helical channel, as a precursor for each helical aperture, is the perimeter of helical aperture to be formed by helical channel  731  perpendicular to the helical line formed by the centroid  736  of area A 731  at every point along helical channel  731 . The flow perimeter (P f ) is calculated as:
 
 P   f   =P   731  sin θ 731  
 
     The hydraulic diameter (D h ) of each helical aperture to be formed by helical channel  731 , is calculated as: 
     
       
         
           
             
               D 
               h 
             
             = 
             
               
                 
                   4 
                   ⁢ 
                   
                     A 
                     f 
                   
                 
                 
                   P 
                   f 
                 
               
               = 
               
                 
                   4 
                   ⁢ 
                   
                     A 
                     
                       7 
                       ⁢ 
                       3 
                       ⁢ 
                       1 
                     
                   
                 
                 
                   P 
                   
                     7 
                     ⁢ 
                     3 
                     ⁢ 
                     1 
                   
                 
               
             
           
         
       
     
       FIG.  7 B  shows a side and top view of a simplified core element  740  having two helical channels in the cylindrical outer surface. Simplified core element  740  is functionally equivalent to core elements  240 ,  440 , and  640  as shown in  FIGS.  2 ,  4 , and  6   , respectively. Central axis  749  is shown in the side view of simplified core element  740  at the top of  FIG.  7 B . Outer diameter D 740  is the diameter prior to fabricating the helical channel  741 . Area A 741  having centroid  746  is the area of the helical channel  741  when viewed from the top of core element  740 . Perimeter P 741  is the perimeter of the helical channel  741  when viewed from the top of core element  740 . For calculation of area A 741  and perimeter P 741 , the “open” side of the helical channel  741  is assumed to be along the perimeter of inner surface of shell element  740  as this is equivalent to the helical aperture area and perimeter formed when the shell element is slidably engaged with the corresponding core element. A helical line is defined by the centroid  746  at every point along helical channel  741 . Line  748  represents a line tangent to the aforementioned helical line, which in combination with the central axis defines the helix angle θ 740 . The helix lead or pitch is the axial distance between the centerline of adjacent coils of the helix or the axial length of a 360° section of the helix. The helix lead (L) is calculated as: 
     
       
         
           
             L 
             = 
             
               
                 π 
                 ⁢ 
                 
                   D 
                   
                     7 
                     ⁢ 
                     4 
                     ⁢ 
                     0 
                   
                 
               
               
                 tan 
                 ⁢ 
                 
                   θ 
                   
                     7 
                     ⁢ 
                     4 
                     ⁢ 
                     1 
                   
                 
               
             
           
         
       
     
     The flow area of each helical channel  741 , as a precursor for each helical aperture, is the cross-sectional area of helical channel  741  perpendicular to the helical line formed by the centroid  746  of area A 741  at every point along helical channel  741 . The flow area (A f ) is calculated as:
 
 A   r   =A   741  cos θ 741  
 
     The velocity in the aperture formed by each helical channel  741 , as a precursor for each helical aperture, is calculated as: 
     
       
         
           
             u 
             = 
             
               F 
               
                 n 
                 × 
                 
                   A 
                   f 
                 
               
             
           
         
       
     
     wherein:
         u is the flow speed of the fluid in meters/sec;   F is the design flow rate of the separator apparatus in meter 3 /sec; and   n is the number of helical apertures.       

     The flow perimeter of each helical channel, as a precursor for each helical aperture, is the perimeter of helical aperture to be formed by helical channel  741  perpendicular to the helical line formed by the centroid  746  of area A 741  at every point along helical channel  741 . The flow perimeter (P f ) is calculated as:
 
 P   f   =P   741  cos θ 741  
 
     The hydraulic diameter (D h ) of each helical aperture to be formed by helical channel  741 , is calculated as: 
     
       
         
           
             
               D 
               h 
             
             = 
             
               
                 
                   4 
                   ⁢ 
                   
                     A 
                     f 
                   
                 
                 
                   P 
                   f 
                 
               
               = 
               
                 
                   4 
                   ⁢ 
                   
                     A 
                     
                       7 
                       ⁢ 
                       4 
                       ⁢ 
                       1 
                     
                   
                 
                 
                   P 
                   
                     7 
                     ⁢ 
                     4 
                     ⁢ 
                     1 
                   
                 
               
             
           
         
       
     
     In some embodiments, without wishing to be bound by any particular theory, Applicant believes that higher efficiencies are achieved by targeting an average velocity of greater than or equal to 50 feet/sec (15 meters/sec), 75 feet/sec (23 meters/sec), 100 feet/sec (31 meters/sec), 125 feet/sec (38 meters/sec), or 150 feet/sec (46 meters/sec), wherein the velocity is the calculated velocity in each of the one or more helical apertures based on a selected flow rate through the separator apparatus. 
     In some embodiments, without wishing to be bound by any particular theory, Applicant believes that higher efficiencies are achieved by targeting a Reynolds number of greater than or equal to 100,000, 200,000, 300,000, 400,000, or 500,000, wherein Reynolds number is calculated as: 
     
       
         
           
             Re 
             = 
             
               
                 ρ 
                 ⁢ 
                 uL 
               
               μ 
             
           
         
       
     
     wherein:
         Re is the Reynolds number;   ρ is the density of the fluid;   u is the flow speed of the fluid;   L is the characteristic linear dimension;   μ is the dynamic viscosity of the liquid; and   Re is the calculated velocity in each of the one or more helical apertures based on a selected flow rate through the separator apparatus.       

     In some embodiments, for convenience, the fluid is assumed to be water at 77° F. (25° C.), resulting in ρ equal to 62.2 lbm/ft 3  (997 kg/m 3 ) and μ equal to 1.857×10 −5  lbf·s/ft 2  (8.90×10 −4  Pa·s). L is the hydraulic diameter D h  of each helical aperture, resulting in a Reynolds number calculated as: 
     
       
         
           
             Re 
             = 
             
               
                 
                   ( 
                   
                     
                       2 
                       . 
                       8 
                     
                     ⁢ 
                     0 
                     × 
                     1 
                     ⁢ 
                     
                       0 
                       6 
                     
                   
                   ) 
                 
                 × 
                 F 
               
               
                 ( 
                 
                   n 
                   × 
                   
                     P 
                     f 
                   
                 
                 ) 
               
             
           
         
       
     
     wherein:
         n is the number of helical apertures on a vortex inducer;   P f  is the perimeter of each helical aperture in meters; and   F is the design flow rate of the separator apparatus in meters/sec.       

       FIGS.  8 A- 8 C  show different views of an embodiment of a vortex inducer  820  having a central aperture  821  and a single helical aperture  822 , analogous to the vortex inducers  120 ,  320 , and  520 , as shown in  FIGS.  1 ,  3 , and  5   . The helical aperture  822  has a right-handed thread when viewed from the top of the vortex inducer  820 . That is to say, when viewed from the top, clockwise travel through the helical aperture  822  would also include axial travel in the downward direction. The vortex inducer  820  comprises shell element  830  and core element  840 .  FIGS.  8 A and  8 C  additionally show the connection of vortex inducer  820  to solids collection conduit  850  and treated fluids discharge conduit  870 , wherein solids collection conduit  850  and shell element  830  are connected by fabrication from a single piece of metal, and core element  840  and treated fluids discharge conduit  870  are connected by fabrication from a single piece of metal. In other embodiments, one or both of these connections can be a threaded connection, a welded connection, a slidable connection with a set screw, or other connection means that provide a secure connection between the relevant elements of the downhole module during operation. 
       FIGS.  9 A- 9 C  show different views of an embodiment of a vortex inducer  920  having a central aperture  921  and three helical apertures  922 , analogous to the vortex inducers  120 ,  320 , and  520 , as shown in  FIGS.  1 ,  3 , and  5   . Each helical aperture  922  has a right-handed thread when viewed from the top of the vortex inducer  920 . That is to say, when viewed from the top, clockwise travel through each helical aperture  922  would also include axial travel in the downward direction. The vortex inducer  920  comprises shell element  930  and core element  940 .  FIGS.  9 A and  9 C  additionally show the connection of vortex inducer  920  to solids collection conduit  950  and treated fluids discharge conduit  970 , wherein solids collection conduit  950  and shell element  930  are connected by fabrication from a single piece of metal, and core element  940  and treated fluids discharge conduit  970  are connected by fabrication from a single piece of metal. In other embodiments, one or both of these connections can be a threaded connection, a welded connection, a slidable connection with a set screw, or other connection means that provide a secure connection between the relevant elements of the downhole module during operation. 
       FIGS.  10 A- 10 C  show different views of an embodiment of a vortex inducer  1020  having a central aperture  1021  and a single helical aperture  1022 , analogous to the vortex inducers  220 ,  420 , and  620 , as shown in  FIGS.  2 ,  4 , and  6   . The helical aperture  1022  has a right-handed thread when viewed from the top of the vortex inducer  1020 . That is to say, when viewed from the top, clockwise travel through the helical aperture  1022  would also include axial travel in the downward direction. The vortex inducer  1020  comprises shell element  1030  and core element  1040 .  FIGS.  10 A and  10 C  additionally show the connection of vortex inducer  1020  to solids collection conduit  1050  and treated fluids discharge conduit  1070 , wherein solids collection conduit  1050  and shell element  1030  are connected by fabrication from a single piece of metal, and core element  1040  and treated fluids discharge conduit  1070  are connected by fabrication from a single piece of metal. In other embodiments, one or both of these connections can be a threaded connection, a welded connection, a slidable connection with a set screw, or other connection means that provide a secure connection between the relevant elements of the downhole module during operation. 
       FIGS.  11 A and  11 B  show different views of an embodiment of a downhole module  1100  having a separator apparatus  1110  analogous to separator apparatus  110 , as shown in  FIG.  1   . Vortex inducer  1120 , solids collection conduit  1150 , separation chamber  1151 , treated fluids discharge  1170 , housing  1180 , inlet ports  1181 , and feed chamber  1182  are analogous to vortex inducer  120 , solids collection conduit  150 , separation chamber  151 , treated fluids discharge  170 , housing  180 , inlet ports  181 , and feed chamber  182 , respectively, as shown in  FIG.  1   . One or more housing extensions  1183  are optionally added below the housing  1180  to provide more capacity for storage of solids removed from untreated fluid by separator apparatus  1110 . Piping  1184  leads to the suction side of a pump for transporting treated fluids to the surface. A seal between the housing  1180  and a well casing is provided by a standard cup packer fitting  1185 . Optional plug  1186  is shown connected to the lower end of housing extension  1183 . 
       FIG.  12    shows an expanded view of downhole module  1200  and certain components thereof shown in  FIGS.  11 A and  11 B . Separator apparatus  1210  analogous to separator apparatus  1110 , as shown in  FIG.  11   . Separator apparatus  1210 , treated fluid discharge conduit  1270 , housing  1280 , inlet ports  1281 , optional housing extension  1283 , and cup packer fitting  1285  are analogous to separator apparatus  1120 , treated fluid discharge conduit  1170 , housing  1180 , inlet ports  1181 , optional housing extension  1183 , and cup packer fitting  1185 , respectively, as shown in  FIG.  11   . Optional lower housing closure or plug  1286  for containment of collected solids is also shown. It can be seen in  FIG.  12    that many additional fittings and connections can optionally be present in downhole module  1200  in support of the operability of separator apparatus  1210 . 
     Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. For the sake of brevity, only certain ranges are explicitly disclosed herein. However, in addition to recited ranges, any lower limit may be combined with any upper limit to recite a range not explicitly recited, as well as, ranges from any lower limit may be combined with any other lower limit to recite a range not explicitly recited, in the same way, ranges from any upper limit may be combined with any other upper limit to recite a range not explicitly recited. Additionally, within a range includes every point or individual value between its end points even though not explicitly recited. Thus, every point or individual value may serve as its own lower or upper limit combined with any other point or individual value or any other lower or upper limit, to recite a range not explicitly recited. 
     All patents, test procedures, and other documents cited in this application are fully incorporated herein by reference for all jurisdictions in which such incorporation is permitted. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the processes, machines, means, methods, and/or steps described in the specification. As one of the ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, means, methods, and/or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein, may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, means, methods, and/or steps.