Patent Publication Number: US-8529756-B2

Title: Separating sand from fluids produced by a well

Description:
This application is a Continuation of U.S. application Ser. No. 13/194,035, filed on Jul. 27, 2011 now U.S. Pat. No. 8,236,182, which is a Continuation of U.S. application Ser. No. 12/769,273, filed on Apr. 28, 2010 now U.S. Pat. No. 8,025,806, which is a Divisional of U.S. Pat. No. 7,731,037 now U.S. Pat. No. 7,731,037, all of which are incorporated herein by reference in their entirety. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to removing solid particles from fluids produced by wells, and more particularly to removing sand from fluids produced by wells. 
     BACKGROUND OF THE INVENTION 
     Fluids such as water, oil, and gas exist under pressure in the pores of subterranean reservoir rock formations. Wells are drilled into reservoir rocks to allow fluids (e.g., gaseous and/or liquid hydrocarbons) to flow or to be pumped to the surface of the formation for commercial use. Drag forces created by fluid flow through the reservoir rocks frequently causes particles or small pieces of the reservoir rocks to loosen and flow with the fluids into the well. The loosened rock pieces flow into the well in small particulate form generally referred to as “sand.” The sand may vary in size from a few microns to several millimeters in diameter. 
     Sand-laden fluids flow from reservoir rock into and upward through the casing and tubing of a well. Upon reaching the top of the casing and the tubing of a well, the sand-laden fluids pass through a configuration of control valves known as a well-head. Sand may abrade metal components of the wellhead and/or form restrictions and blockages. Costly intervention methods must be employed to repair the damaged components and/or to remove the sand blockages in the wellhead. 
     From the well-head, sand-laden fluids enter a flowline, which directs the flow of sand-laden fluids to a separation or other type of processing facility. The flowline often spans a lengthy distance, from a few hundred meters to several thousands of meters, between the well-head and the nearest processing facility. The sand entrained within the fluids can cause abrasion, leaks, and obstructions throughout the span of the flowline, especially where there are abrupt changes in direction and/or elevation of the flowline, often due to the topography of the area. The restrictions, blockages, and/or abrasive damage often occur in remote sections of the flow line that are not readily accessible to vehicles and equipment needed for corrective intervention. Abrasive damage and blockages can also occur at the processing facility, particularly in separators, storage tanks, and/or pumps. 
     When components of the well are damaged, restricted and/or obstructed by sand, components must be shut-down for repair, which impacts the commercial viability of the well. Because fluids from several wells converge to such facilities, shutting facilities down for repairs requires shutting-in of multiple wells, which adversely impacts the commercial viability of the wells. Separators are used to remove sand and other solid particles from the fluid. However, removing accumulated sand and other solid particles from the separators typically requires manned-entry into such vessels, which poses formidable health and safety hazards, such as possible entrapment, suffocation, drowning, poisoning, and burning. 
     SUMMARY OF THE INVENTION 
     One or more embodiments of the present invention provide a method for intercepting solid particles within a stream of fluids flowing from a wellhead, through an interconnecting wellhead line and to a flowline. The method includes the step of positioning a container in a conduit between and in fluid communication with the interconnecting wellhead line and the flowline. The container has a cross-sectional area greater than the cross-sectional area of the conduit near the inlet to the container and an outer surface including an upper portion above a horizontal axis of a cross-section of the container and a lower portion below the horizontal axis of the container. The container also includes at least one access port located in the upper portion of the container, the at least one access port having a predetermined size that prevents substantial human entry into the access port. The method also includes the step of passing the stream of fluids flowing from the wellhead and interconnecting wellhead line through the conduit and into the container, the container allowing substantially unidirectional and unobstructed fluid flow between the inlet and the outlet. The method further includes the step of reducing the velocity of the fluid when it enters the container, thereby allowing solid particles in the fluid to settle into the lower portion of the container and preventing a portion of the solid particles from entering the flowline. 
     One or more embodiments of the present invention also provides a method for intercepting solid particles within a stream of fluids flowing from a wellhead, through an interconnecting wellhead line and to a flowline. The method includes the step of disposing an elongated container in a conduit between and in fluid communication with the interconnecting wellhead line and the flowline, the elongated container having a cross-sectional area greater than the cross-sectional area of the conduit near the inlet to the elongated container. The elongated container also includes one or more access ports located in an upper half of the container and having a predetermined size that prevents substantial human entry into the one or more access ports. The elongated container further includes an inner surface without any substantial protrusions into an interior cavity of the elongated container. The method also includes the step of passing the stream of fluids flowing from the wellhead and interconnecting wellhead line through the conduit and into the elongated container, wherein the fluid flow through the interior cavity of the elongated container is substantially unidirectional and unobstructed, thereby allowing solid particles in the fluid to settle into the lower portion of the container and preventing a portion of the solid particles from entering the flowline. 
     One or more embodiments of the present invention also provides a settling system for intercepting solid particles within a stream of fluids flowing from a well head line and to a flow line, the system including one or more containers. Each container includes an inlet having a cross sectional area less than a cross sectional area of the container such that a velocity of fluid flowing from the inlet decreases, the decreasing velocity of the fluid allowing solid particles in the fluid to settle to a lower region of the container. Each of the one or more containers also includes an outlet and an inner surface that does not substantially protrude into an inner cavity of the container. At least one access port is located in a top half of each of the one or more containers, the at least one access port adapted to permit mechanical removal of at least a portion of the settled particles from the lower region of the container without substantial human entry into the at least one access port. The one or more containers allow for substantial unidirectional and unobstructed fluid flow between the inlet and the outlet. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a settling system. 
         FIG. 2  illustrates a representation of retention times for one implementation of a settling system. 
         FIG. 3  illustrates a portion of a settling system including an inlet. 
         FIG. 4  illustrates a portion of a settling system including an outlet. 
         FIG. 5  illustrates an example of an access port. 
         FIG. 6  illustrates an example of a vacuum hose in use. 
         FIG. 7  illustrates an example of multiple settling systems connected in parallel. 
         FIG. 8  illustrates an example of multiple settling systems connected in series. 
     
    
    
     Like reference symbols in the various drawings indicate like elements. 
     DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS 
       FIG. 1  illustrates one implementation of a settling system. The settling system will separate, remove, and/or accumulate solid particles (e.g., sand) from fluids (e.g., gaseous and/or liquid hydrocarbons) produced by a well. The settling system may be positioned within a flowline that spans between a wellhead and a separation or processing facility. In the implementation depicted in  FIG. 1 , the settling system  100  is positioned proximate a wellhead apparatus  20 . Fluids  11  containing particles flow from a subterranean formation (not shown) through production conduit  10  to wellhead apparatus  20 . Pressure from the subterranean formation, or mechanical action (e.g., progressive cavity pump or other methods for pumping fluids containing sand), drive fluids  11  from the production conduit  10  to the wellhead apparatus  20 . The wellhead apparatus  20  includes a master-valve  21  and a wing-valve  22  to control the flow of fluids  11 , as desired. A valve  23  coupled to the wellhead apparatus  20  restricts fluid flow to provide access to the production tubing  10  to perform maintenance and repairs. 
     After fluids  11 , containing solid particles, flow through the production tubing  10  and wellhead apparatus  20 , the fluids enter a flowline  101   a  which couples the wellhead apparatus to the settling system. The flowline  101   a  is coupled to an inlet-line  30 . From inlet-line  30 , the fluids  11  flow into the settling system  100 . The settling system illustrated by  FIG. 1  includes a container  40 ; an inlet  44 ; an outlet  48 ; access ports  60 ,  70  and  80 , and bypass line  90 . The fluids  11  exit container  40  and enter an outlet-line  50 . From outlet-line  50  the fluids  11  enter flowline  101   b . Once in flowline  101   b , the fluids  11  may flow to a separation or other type of processing facility (not shown). 
     The settling system  100  may include one or more containers  40  coupled in series or parallel. The containers in a multi-container system may contain different structural characteristics. The container(s) may be formed of metal, plastic, or other durable material, and may include a coating, such as a coating to inhibit corrosion. The container(s) may have a substantially circular, substantially oval, substantially square, substantially oblong, substantially rectangular, and/or irregular cross-sectional shape. The container(s) may include flanged ends. A portion of an end of the container(s) may be planar and/or curved. For example, the container(s) may be a cylindrical container with curved ends. The container(s) may be a vessel, such as a pressure vessel. In one implementation, the settling system includes a container that cannot be pressurized due to government or industry standards, as use of this type of container will facilitate government and/or industry approval of the settling system. 
     The configuration of container  40 , as shown in the implementation of  FIG. 1 , allows all or a portion of sand and/or other particles in fluid  11  to settle in the container. The container  40  is designed such that gravitational forces separate sand in the fluid  11  as the fluid flows through the container. 
     The container  40  of the implementation shown in  FIG. 1  has an internal diameter larger than the internal diameter of inlet line  30 , which causes a substantial reduction in the lateral velocity of fluids  11  entering the container, since flow velocity through a conduit is inversely proportional to a diameter of the conduit squared. As fluid  11  enters container  40 , lateral drag forces, caused by fluid flow on particles in the fluid, decrease to an extent that vertical gravitational forces pull the particles towards a lower region of the container. A substantial reduction of velocity of the inlet particle-laden fluids causes a reduction of the viscous carrying forces of the fluids so that the viscous carrying forces arc no longer sufficient to carry a particle in a horizontal direction. In certain implementations, since the length and the internal diameter of the container are sufficiently sized for suitable retention time to meet criteria of demonstrated scientific conventions such as Stoke&#39;s Law, a substantial amount of particles (often including sand) separate and settle within the container rather than being carried by the fluids and exiting the container into the continuation of the flowline. 
     In some implementations, the settling system will include a container with a cross-sectional area greater than the cross-sectional area of the inlet of the container and/or the conduit coupled to the container (e.g., flowline). The cross-sectional area of the container may, for example, be more than 3 times greater than the cross-sectional area of the inlet conduit. 
     In some implementations, the container will comprise a volume that is large enough to accumulate bulk quantities of settled particles. For example, the container may remove sand from fluids produced from wells on the order of hundreds of liters. Container  40  may have a length (e.g., to contain a volume of internal space large enough) to provide a sufficient retention time for sand to separate, descend, settle, and/or accumulate in piles  102  at the bottom of the container. 
     A container may have a length such that, during use, a predetermined amount of sand settles from the fluid into the container and is retained in the container. Depending upon the structural features of a container, at least about 50%, at least about 75%, or at least about 90% of particles may be separated from a fluid. For example, a container may have a length of about 15 feet to about 25 feet. In a preferred implementation, a container may have a length of about 18 feet to about 20 feet. 
       FIG. 2  depicts a representation of typical retention times for one implementation of a settling system. As can be seen from straight line shown on  FIG. 2 , as the flow rate in barrels per day increases through a container (accumulator) of fixed dimensions, the lateral velocity of the fluid increases. Furthermore, as the flow rate in barrels per day increases through a container (accumulator) of fixed dimensions, the residence time of the fluid in the container decreases. A settling system may require a retention time of less than 1000 seconds to remove at least approximately 75% of particles in fluid. Alternatively, a settling system may require at least 450 seconds to substantially separate sand from fluids flowing through a container. For example, a viscous fluid such as oil flowing through an 18 inch diameter by 13.5 foot length container at approximately 400 barrels per day (BPD) may require at least 450 seconds for a substantial amount of solid particles (which may include sand) to settle to a lower region of the container. 
     In certain implementations, the top of a container will be at a height that makes manned entry difficult or impossible. Since a container may be cleaned mechanically, a container need not be sized for manned entry, thus reducing costs associated with the production and operation of settling systems. Utilizing a container that precludes manned entry will typically facilitate governmental and/or industry approval of the container. In addition, utilizing a container that precludes manned entry should reduce costs of operation of a well, since sand must be mechanically removed without entry into the container (e.g., reduced permit costs, insurance costs, labor costs, etc.). 
     In some implementations, a container allows fluid to flow through the container substantially uninhibited. In such implementations, the container will not include baffles and/or filters, which may clog and/or be damaged by sand flowing through the container. Additionally, the container may have an inner surface that does not substantially protrude into a cavity of the container. For example, inlets, outlets, and/or access ports may be coupled to the container such that the inlet is approximately flush with the inner surface of the container and/or does not create turbulence such as eddies. Typically, the turbulence of the boundary layer of the fluid flow in the container may be reduced by utilizing a container that has an inner surface that does not substantially protrude into a cavity of the container. 
       FIG. 3  illustrates a portion of one embodiment of a settling system. An inlet end  40   a  of container  40  may be a hollow, hemispherical end-cap  42 . End-cap  42  may be coupled to inlet end  40   a  by a weld  41 . One end of a cylindrically-shaped, inlet sleeve  44  may be coupled to an opening in an upper portion of end-cap  42  by a weld  43 . The other end of inlet-sleeve  44  may include internal threads (not shown) that form a connection with external threads (not shown) on an end of inlet-line  30 . 
     Connector  31 , located at an end of flowline  101   a , may allow coupling and decoupling of container  40  and its accompanying inlet-line  30  to and from flowline  101   a . Connector  31  may facilitate repair and/or removal of container  40 . Within the span of flowline  101   a  is valve  32  (e.g., a ball-valve), which may allow hydraulic isolating of container  40  and its accompanying inlet-line  30  from flowline  101   a . Isolation of container  40  may facilitate access (e.g., via access ports, or removal of an end-cap) for sand removal at access ports  60 ,  70 , and  80  shown in  FIG. 1 . Fluid from flowline  101  a may be diverted from the container into bypass line  90 . 
       FIG. 4  illustrates another portion of one implementation of a settling system. An outlet end  40   b  of container  40  may be enclosed by an end-cap  46 . End-cap  46  may be coupled to outlet end  40   b  by a weld  45 . An end of a cylindrically shaped outlet-sleeve  48  may be coupled to an opening proximate an upper portion of end-cap  46  by a weld  47 . The other end of the outlet-sleeve  48  possesses internal threads (not shown) which form a connection with the external threads (not shown) on the terminus of outlet-line  50 . 
     Connector  51 , located proximate the inlet of flowline  101   b , may allow coupling and decoupling of container  40  and its accompanying outlet-line  50  to and from flowline  101   b . Within the span of flowline  101   b  is a valve  52  (e.g., a ball-valve), which may be closed to hydraulically isolate container  40  and its accompanying outlet-line  50  from flowline  101   b  to allow container  40  to be accessed and/or opened for sand removal at entry ports  60 ,  70 , and  80 , shown in  FIG. 1 . 
     As best shown in  FIG. 1 , along a length of an upper surface of container  40  are access ports  60 ,  70 , and  80 . Access ports allow access to an interior of container  40  for sand removal. For example, access ports may be used by an operator during use to remove quantities of sand  102  accumulated in the container  40 . In some implementations, mechanical sand removal systems (e.g., vacuums, hoses, pumps, etc.) may be coupled to access ports and/or may be inserted through access ports to access an interior of the container to remove accumulated sand. Access ports may be manually removed (i.e., removed using bare human hands, with or without use of hand-held tools) to allow instruments such as suction-hoses and spray nozzles to readily probe and remove the accumulated sand from within. In certain implementations, all access ports are located on a top surface. Positioning access ports on the top surface may facilitate access by operators to the access ports. 
     As shown in  FIG. 1 , a plurality of access ports  60 ,  70 , and  80  may be installed along the length of the crest of the container  40 . In some implementations, access ports  60 ,  70 , and  80  may be oriented perpendicular to the horizontal plane. Access ports  60 ,  70 , and  80  may be approximately equally spaced from each other. A set of access ports  60 ,  70 , and  80  maybe centered between container ends  40   a  and  40   b . The orientation and the spacing of access ports  60 ,  70 , and  80  may vary based on the types and the shapes of instruments used to extract accumulated sand  102  from the interior of container  40  and/or the location at which sand  102  is expected to accumulate. 
     Access ports  60 ,  70 , and  80  may be similar in construction, material, and/or size.  FIG. 5  illustrates an exemplary access port  60  and  FIG. 6  illustrates an exemplary access port  60  with an exemplary vacuum hose  110  in use to remove material at the bottom of the settling system. Access port  60  may include a conduit  62 . Conduit  62  may be have any regular or irregular cross-sectional shape The internal diameter and the length of conduit  62  are sized to permit the passage of instruments, such as vacuum hoses and forced-stream nozzles, necessary for the removal of accumulated sand  102  ( FIG. 1 ). The lower end of conduit  62  is coupled to a cut, circular opening in the upper crest of container  40  by a weld  61 . The upper end of the conduit  62  is coupled to a flange  64 , by a weld  63 . A flange-cap  65 , is secured to flange  64  by bolts  66  to form a metal-to-metal, hydraulic seal. Components of an access port may be coupled to each other and access ports may be coupled to container  40  such that they form a hydraulic seal and possess strength capable of withstanding anticipated differences in pressure between the exterior and interior of the settling system  100 . In some implementations, weld  61  and/or conduit  62  may be coupled to container  40  such that they do not substantially protrude into an inner surface of the container. For example, conduit  62  may be welded such that the weld  61  is approximately flush with an inner surface of container  40 . 
     In some implementations, needle valves or pressure-relief valves may be coupled to container  40  at various points to relieve internal pressure in the container prior to opening access ports  60 ,  70 , or  80  for sand removal or prior to decoupling container  40  for repairs and/or for replacement. 
     A bypass line  90  may allow fluids  11  containing particles (e.g., sand) to flow through flowlines  101   a  and  101   b  while accumulated sand is removed from container  40  (e.g., by inserting a vacuum through access ports  60 ,  70 , and  80 ). Bypass line  90  may have an internal diameter approximately equal to the internal diameter of flowlines  101   a  and  101   b , and inlet and outline lines  30  and  50 . Bypass line  90  may have a similar cross-sectional shape to flowlines  101   a  and  101   b  to facilitate coupling between tines. Bypass line  90  may be activated by opening a valve  91  arid closing valves  32  and  52 . A connector  92  may couple bypass line sections together. 
     The type, composition, wall-thicknesses, and coupling methods of the container, valves, lines, conduits, ports, etc. may be based on anticipated internal pressures during operation. For example, coupling may include bonding, gluing, welding, use of threaded or compression connections, bolting, cementing or other types of connecting techniques. In some implementations, containers, lines, conduits, ports, etc. may be include carbon steel because of its strength and ability to withstand pressure differences several multiples above atmospheric pressure. Materials of lesser strength, such as polyvinyl chloride (PVC), with respective threaded and cement bonding methods, can be used when internal pressures are not expected to deviate much above or below atmospheric pressure. Ball-valves are reliable and quickly activated and thus may be selected parts of the settling system. Other valve types, such as the gate-valve, can also be used. 
     The settling system may be located at any position within the span of a flowline where the use of the settling system is deemed advantageous for separating and accumulating sand from sand-laden fluids, and/or where the settling system can be easily accessed by vehicles and equipment needed to remove the sand from the settling system. A typical, but not only, location for the settling system is in close proximity to the wellhead, since the wellhead area is inherently accessible to rigs, vehicles, and equipment, needed for sand removal. An additional advantage to positioning the settling system near the wellhead is that a majority of the flowline may be protected from sand abrasion and blockages. As shown in  FIGS. 7 and 8 , multiple settling systems may be placed in parallel ( FIG. 7 ) or series ( FIG. 8 ) configurations. 
     A number of implementations have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the various implementations. In addition, it is will be understood that the technology used herein is for the purpose of describing particular implementations and is not intended to be limiting. As used in this specification, the singular forms “a”, “an” and “the” include plural referents unless the content clearly indicates otherwise. Thus, for example, reference to “an access port” includes a combination of two or more access ports and reference to “a fluid” includes mixture of fluids. Accordingly, other implementations are within the scope of the following claims.