Abstract:
An apparatus and method is disclosed for conducting a fluid and solids production test in a subterranean well. A testing apparatus may be inserted into a wellbore. The apparatus may employ a tubular housing with entry port(s) through the housing. An inner assembly may be positioned within the tubular housing, the inner assembly being configured for connection to the tubular housing. The inner assembly may include a fluid permeable screen and a distal end forming a reservoir that is scaled, or may be adapted to be scaled, for the collection of solids during a well production testing event. Following a testing event, the apparatus may be removed from the wellbore to enable the collected solids to be measured to determine the amount of solids generated by a subterranean formation at actual field flow conditions.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention is directed to an apparatus and method for capturing produced solids and measuring the sanding propensity of a subterranean formation penetrated by a wellbore. 
       BACKGROUND 
       [0002]    In the oil and gas industry, hydrocarbons are produced from underground formations. In some hydrocarbon-bearing formations, such as sandstone formations, solids may be produced with the hydrocarbons. Production of solids with hydrocarbons is undesirable for many reasons. Fluids containing solids generally are much more erosive, and may damage metallic conduits and pipe in the wellbore and in the surface oil and gas processing equipment. Excess production of solids may plug or block the wellbore, or inhibit flow of fluids through processing equipment. When this occurs, it may require costly wellbore or surface facility cleanout operations before hydrocarbon production may resume. 
         [0003]    It is known that solids production varies considerably in different subterranean formations. Solids generally consist of sand (quartz) particles but may also contain other natural or deposited materials such as clays, silts, salts, feldspars, and the like. When completing a well, it is desirable to determine if the well is likely to produce solids with the hydrocarbons. If solids production is likely, then sand or solids production control measures may need to be implemented. Such solids production inhibition methods may include, for example, fracturing and packing the fractured reservoir with sand, gravel or proppant to inhibit further solids production. It may be desirable to install chemical inhibition, consolidation or mechanical screen assemblies in the wellbore. There are many different techniques and equipment available to inhibit solids production. However, solids production control methods must be designed and appropriate for a given wellbore, and the appropriate method may depend upon the depth, pressure, temperature, and other conditions of hydrocarbon production. The implementation of solids production control techniques and installation of solids control apparatus is generally time consuming and costly, as is the addition of surface solids handling and treatment equipment. Further, the requirement to install such equipment reduces the commercial viability of many projects. 
         [0004]    The pressure differential between the wellbore and the subterranean formation is an important factor in determining how much solids will be produced. It is desirable, for a given wellbore, to understand the downhole conditions at which the onset of solids production will occur and the volume of solids that can be expected to be produced. By understanding solids production characteristics of a wellbore, it is possible to tailor a solids production control strategy that is likely to prove successful for the least amount of effort and cost. 
         [0005]    Solid particles are generally denser than fluids in water and hydrocarbon wellborcs. During well tests and in production mode, wellbore fluids need to travel faster than a specific rate to lift solid particles to the surface. Once fluid production is stopped in a typical well test, the solids in the produced fluid settle in the wellbore. Heavier solid particles will settle faster than lighter particles and therefore require a higher fluid velocity to lift them to the surface. Settling of solids in the wellbore presents operational problems, including for example the risk of a stuck drill pipe in subsequent operations. Solids settling velocities also mean that surface samples are an unreliable measure of the total produced solids. 
         [0006]    This invention is directed to apparatus and methods for determining or measuring solids production characteristics for a subterranean formation penetrated by a wellbore, while avoiding some of the problems inherent in capturing the solids at surface. 
       SUMMARY OF THE INVENTION 
       [0007]    The invention is directed to an apparatus and method for conducting a solids production test in a subterranean well. The apparatus includes a tubular housing with a proximal end and a closed distal end. The housing has one or more entry ports on its exterior surface, the entry ports passing through the thickness of the housing and positioned between the proximal and distal ends of the housing. An attachment mechanism is positioned on the proximal end of the tubular housing and configured to suspend the tubular housing within a wellbore. 
         [0008]    An inner assembly is positioned within the tubular housing. The inner assembly includes a proximal end and a distal end. The inner assembly is configured for connection to the tubular housing. The inner assembly includes a fluid permeable screen designed to facilitate fluid flow but retard passage of solids through the screen. The inner assembly may be sealed at its distal end. An annular space is provided between the inner assembly and the tubular housing. The apparatus is configured for receiving a flow of production fluids and solids through the entry ports into the annular space. 
         [0009]    The distal end of the tubular housing may include a reservoir adapted for receiving and storing solids for subsequent analysis. The reservoir may be comprised of several separate catchment volumes, or catchment compartments. A first catchment compartment includes at least one barrier. The barrier is capable of manipulation from an open position to a closed position to seal off the first catchment compartment. The first catchment compartment is configured to receive and store solids received in the first phase of the solids production test or tests. 
         [0010]    A second catchment compartment is positioned proximally (above as shown in the Figures) of the first catchment compartment. The second catchment compartment is configured for receiving solids through its interior space to the first catchment compartment during a first solids production test phase. The second catchment compartment is adapted for receiving and storing solids produced during a second solids production test phase. 
         [0011]    In one embodiment of the invention, the distal end of the inner assembly comprises an aperture configured to receive a plug. The distal end of the inner assembly may be sealed by the plug, which can be run into the wellbore by wireline. In some instances, a well test for fluid pressure and/or sampling is run without solids capture, and then the plug is set in the distal end of the inner assembly, as further discussed herein. 
         [0012]    Typically, the inner assembly also includes a screen. The fluid may proceed from the annulus through the screen of the inner assembly. Solids produced from the subterranean well may be deposited in the reservoir. In some embodiments of the invention, the distal end of the inner assembly is permanently sealed. In other applications, the distal end of the inner assembly comprises a valve or plug. The proximal end of the tubular housing may be configured for location in or connection to a packer. The inner assembly also may include a fluid pressure gauge with the ability to store fluid pressure in memory for later retrieval, or may be configured for real time readout by the well operator during the testing. Various detectors, including a solids particle detector, also may be provided upon the inner assembly. 
         [0013]    Wiper seals may be positioned on the exterior surface of the tuhular housing. The wiper seals may be provided in intimate contact with the exterior of the tubular housing, and may serve as a barrier to unwanted fluid flow below the level of the test apparatus in the annular space outside of the apparatus. The distal end of the tubular housing also may be configured for connection to a perforating gun. In some instances in cased hole for example, a perforating step may be performed, followed by a test of the perforation using the apparatus of the invention. 
         [0014]    If operating in an uncased open-hole, perforation or stimulation may not be required. Alternatively, perforating in a cased wellbore may be performed as a separate activity or may already be extant if the test is performed in an older well. The testing apparatus may be lowered into the wellbore adjacent a subterranean formation. Then, the surface pressure may be reduced to induce a first flow rate. This causes formation fluids and solids to flow from the subterranean formation through the entry ports and into the annular space of the testing apparatus. Then, formation fluids are passed through the fluid permeable screen into the inner assembly. Solids are prevented from passing through the fluid permeable screen, and are collected in a reservoir below the screen, as further shown in the Figures. Once solids have been collected for a particular test condition or flow pressure, the apparatus may be removed from the wellbore, and the solids may be characterized as to the quantity produced and the particle size distribution. 
         [0015]    The reservoir of the testing apparatus may include a first catchment compartment with a barrier. The barrier may be capable of manipulation from an open position to a closed position to seal off the first catchment compartment, further wherein the first catchment compartment is configured to receive and store solids. Further, a barrier or door may be provided for closure in the upper portion of the first catchment compartment, forming a floor in the second catchment compartment. A second, third, fourth, fifth, or additional compartment may be employed, with corresponding barriers. Numerous such compartments may be used to collect samples corresponding to reservoir tests at different pressures or conditions. 
         [0016]    The reservoir of the testing apparatus also may include a second catchment compartment. In some cases, a second flow test or test phase is conducted by adjusting the pressure in the testing apparatus to increase the flow rate of formation fluids and solids to a higher second flow rate. Then, and prior to the rate increase, the barrier of the first catchment compartment may be closed. Formation fluids may be passed through the fluid permeable screen into the inner assembly. Solids are blocked from passing through the fluid permeable screen, and are collected in the second catchment compartment. Further, a barrier may be provided for closure in the upper portion of the second catchment compartment, forming a seal for the second catchment compartment and a floor for a third catchment compartment, if a third catchment compartment is employed. Additional catchment compartments could be employed as well. 
         [0017]    More than two or three catchment compartments may be included in the apparatus. A practical limit however would be determined by the length and service life of the sand screen employed, the time taken to perform the number of test phases, and the barrier actuation mechanisms and signaling requirements. 
         [0018]    Once solids are collected, the testing apparatus may be removed from the wellbore. Solids in the catchment compartments then may be weighed, measured and analyzed. 
         [0019]    In some embodiments of the invention, the inner assembly also includes various detectors, including (for example) pressure, temperature, dielectric, fluid flow rate and solids detection. In such embodiments, the method may also include an observation of the pressure, water cut and flow rate at which solids first begin to contact the solids detector. It is possible to measure the amount of solids entrained in the fluid flow with respect to rate and time. 
         [0020]    The method may be practiced by employing upon the inner assembly a solids detector and a pressure gauge. Further, it is feasible to measure the pressure at which solids first begin to contact the detector. The method may also include determining whether the solids flow is transient or continuous. It may be possible to measure the total quantity of solids in the flowing formation fluids. Also, it may be possible to measure flow rates, fluid composition, time and pressure. It also may be useful to measure a representative sample of solids directly produced from a flowing perforation or an open-hole interval. In all instances, it will be useful to calibrate or verify the total quantity of solids produced at the end of each known flow rate or test phase. The invention, in one embodiment, makes it possible to calibrate and verify proprietary and industry solids production prediction models us well. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0021]    The various aspects of the invention may be observed by reference to one or more Figures as follows. However, the scope of the invention is not limited to embodiments disclosed in the Figures. 
           [0022]      FIG. 1  shows a well test string apparatus within a cased wellbore in which the apparatus is positioned adjacent perforations in the subterranean well. 
           [0023]      FIG. 2  illustrates the apparatus of  FIG. 1  in which a plug has been run in the well on wirclinc and engaged to the distal end of the inner assembly to seal the inner assembly. 
           [0024]      FIG. 3  shows the apparatus of  FIGS. 1-2  during a sanding test, wherein formation fluid containing solids are produced into the apparatus and collected in a first (lower) catchment compartment of the reservoir. 
           [0025]      FIG. 4  shows a later stage of the sanding test, conducted at a different pressure, at a later point in time, in which solids from this subsequent test is collected in a second catchment compartment. 
           [0026]      FIG. 5  illustrates a second embodiment of the invention in which an apparatus is run into the well on wireline and landed into place below a packer. 
           [0027]      FIG. 6  shows the second embodiment (same apparatus as shown in  FIG. 5 ) during a sanding test in which fluid and solids produced from the formation enter the apparatus and solids are collected in the sealed distal end of the tubular housing. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0028]    The design of well tests in exploratory and appraisal wells sometimes is made more difficult because key factors such as production rate, drawdown and produced solids quantity are largely unknown or uncertain. For example, it is typically not known the quantity of solids that will be produced by the first well drilled in a new region or field. The amount of solids production is very important in determining the design and completion configuration for wells drilled in that field. 
         [0029]    In general, the amount of solids, the properties of the sandstone, the fluid type and viscosity, the fluid production rate, the solids particle size distribution, and other factors may contribute to the determination of the quantity of solids likely to be entrained in the fluid and produced to the surface during well production and testing. Once solids are produced into the wellbore, such solids desirably will be lifted to the surface to prevent downhole tools from becoming lodged in the wellbore. If the production flow is not sufficient, all or part of the solids may not be lifted to the surface. Heavier particles require more flow rate than lighter particles to reach the surface. 
         [0030]    Surface sampling therefore is not preferred, as it can present an unreliable measure of the total produced solids. Additionally, conventional sand samples are obtained from full or side-wall formation coring operations. These samples do not fully represent the actual solids that might be produced from the perforations as the formation starts to produce solids. However, the application of this invention provides a new and improved apparatus and method for making onset and volume estimates of solids production in a well and for capturing a more representative sample of produced solids impacting a future sand control installation. 
         [0031]    Solids are produced when a sandstone (or other solid in the formation) begins to fail or already has failed mechanically due to diminishing reservoir pressure. In that instance, the fluid flow conditions enable the entrainment of the loosely attached solids particles. To test a formation, it may be necessary to cause the structure of the sandstone to fail. Facilitating the physical failure of the rock in reservoirs that have never produced hydrocarbons may require a relatively high drawdown pressure. Facilitating high drawdown pressures may require in turn the use of surface or downhole lift or pumping systems that are not compatible with solids production. For example, excessive solids may clog or damage electrical submersible pumps. 
         [0032]    Testing formations for solids production often is omitted or avoided in many well appraisal programs, which is undesirable. One advantage of the testing apparatus and method of this invention is that many of the uncertainties of sanding test design may be avoided by allowing lift or pump systems to apply high drawdown pressures directly to the subterranean formation, allowing for subsequent collection of a representative sample of the produced solids for analysis. 
         [0033]    In  FIG. 1 , an apparatus  20  is shown suspended from a hanger or packer  21 . A ported tubular housing  23  comprises a proximal end  22  and a distal end  24 . Entry ports  26 ,  28  (as examples) are provided through the housing, which provides an entry point for formation fluid and sand. Several entry ports in addition to entry ports  26 ,  28  may be provided for fluid entry into the apparatus  20 , depending upon the configuration of the apparatus  20 . An attachment mechanism  30  is provided for secure and releasable connection of apparatus  20  to packer  21 . An inner assembly  32  is fixed or located in an nipple (not shown) on the inside of the tubular housing  23 . Inner assembly  32  is provided with a proximal end  34  and a distal end  36  (distal end shown open in  FIG. 1 ). The distal end  36  of the inner assembly includes a nipple cavity  35  which is designed to receive in locking engagement nipple  37  of plug  62  (plug  62  is shown in  FIGS. 2-4 ). The inner assembly  32  may be provided with a sliding sleeve  33  and with a fluid permeable screen  38  that facilitates fluid flow into the apparatus  20 , but retards solids movement into apparatus  20 . The sliding sleeve  33  permits fluid entry later if the screen becomes clogged with solids. The entire inner assembly  32  can be removed separately during the test if the screen becomes clogged or solids are not expected. An annular space  40  is a circular “donut-shaped” cavity that exists outside of the inner assembly  32 , and is bounded by the inner surface of tubular housing  23 . Relief valves  45 ,  46  are provided in each compartment if the compartment barriers  52 ,  54 ,  56  are pressure sealing. The compartment barriers  52 ,  54 ,  56  may be designed to be either only solids tight, i.e. prevent solids from passing, or may be pressure tight to obtain a fluid sample. 
         [0034]    Perforations  42  are shown in the subterranean formation. These perforations facilitate the flow of oil and gas from the formation to the apparatus  20 . Near the distal end  24  of the tubular housing, a reservoir  44  is provided. The reservoir  44  receives sand, as will be further discussed herein. In the first embodiment of the invention, as shown in  FIGS. 1-4 , the reservoir  44  comprises a first catchment compartment  48  and a second catchment compartment  50 . A third potential catchment compartment  51  also is shown, and may be employed. A barrier  52  is provided, which may be engaged or closed to isolate the lower portion of first catchment compartment  48 , just prior to entry of solids into reservoir  44 . This permits access to the firing head and perforating guns below for example and if required. A barrier  54  is capable of movement between an open and a closed position. Barrier  54  may be engaged (closed) to capture collected solids in first catchment compartment  48 , as further discussed herein. Barrier  56  likewise may be engaged/closed to capture solids collected in second catchment compartment  50 . Barrier  56  also forms the floor for third catchment compartment  51 . 
         [0035]    Barriers  52 ,  54 ,  56  may consist of either a plug that may be dropped or installed by wire-line or coil tubing, or applied in another type of sealing arrangement. The seal may be only solids tight or may be pressure sealing. If pressure sealing, a relief mechanism (not shown) likely would be included in the catchment compartment design. The barriers  52 ,  54  and  56  may either be installed by wire-line or coiled tubing or be actuated remotely using control lines, timing, pressure or acoustic pulses or another such system available in the industry. 
         [0036]    A firing head and perforating gun  58  is suspended from the distal end  24  of the tubular housing  23 . In the operation of apparatus  20 , the apparatus may be positioned so that the perforating gun  58  is opposite the portion of the subterranean formation  42  to be perforated. Once perforation is completed, the apparatus may be lowered into a position similar to that shown in  FIGS. 1-4  for sanding tests. 
         [0037]    An aperture  60  is provided in the distal end  36  of the inner assembly  32 . Nipple cavity  35  mates with nipple  37  of plug  62 . Plug  62  may be run into the wellbore on a wireline, as further discussed herein, and seated by interaction of nipple  37  with nipple cavity  35 . 
         [0038]    A detector package incorporating for example a solids particle detector  64  also may be provided in association with the inner assembly  32 . The solids detector  64  (if acoustic in nature) may be partially encased in an elastomer to dampen the particle impacts if required. The drill string may be positioned in the well so that the inner assembly  32  and its solids particle detector  64  is provided opposite perforations of that portion of the formation that is to be tested for solids production. The pressure may be monitored and readings stored in memory, or provided to the surface for real time readout, using techniques known in the industry. The solids may be detected by its physical contact with solids detector  64 , so that the onset and amount of solids production may be monitored by way of data capture or in real time during the testing. 
         [0039]    Wiper seal  66  may be provided circumferentially around the outside of tubular housing  23 . In this manner, fluids entering the wellbore are bounded on top by the packer  21  and on below by wiper seals  66 , such that the fluids will not escape but desirably will be produced through the entry ports  26 ,  28  into the apparatus  20 . 
         [0040]      FIG. 2  shows the apparatus of claim  1 , in which plug  62  has been seated in the distal end  36  of inner assembly  32 . Further, barrier  52  has been closed for the sanding test, as shown in  FIG. 2 . The various methods of actuating these barriers  52 ,  54 ,  56  can be either remotely via hydraulic or electrical control lines, by timing and pressure pulses to powered/battery operated devices, by electromagnetic or acoustic pulses through the work string to battery operated devices, physically using wire-line or coiled tubing plugs, or any such other method as is available in the industry. 
         [0041]    A sanding test is conducted as shown in  FIG. 2 . Production fluid  68  passes through entry ports  26 ,  28  into inner assembly  32 . Solids enter through entry ports  26 ,  28  as well, and impact on the detector  64 . Such detector  64  may be operated by way of fiber optics or other means, and such devices are known and available in the industry. Solids  70  are prevented from traveling to the surface with fluid  68  by the solids screen  38 , and instead settle into first catchment compartment  48  as deposited solids  72 . The first catchment compartment  48  seals when required either actuated remotely or at a predetermined or set time and pressure by way of plug or barrier  54  closing to form a seal. 
         [0042]    Next, a high rate or larger drawdown pressure step may commence, in which the pressure is raised and solids again are allowed to enter and are collected in the second catchment compartment  50 , shown in  FIG. 4 . Deposited solids  74  may be collected second catchment compartment  50 . 
         [0043]    A second embodiment of the invention is illustrated in  FIGS. 5-6 . Apparatus  80  is suspended in a wellbore from packer  21 . A tubular housing  82  comprises proximal end  84  and distal end  86 . Entry ports may be numerous, as may be seen for example as entry ports  88  and  90 . A nipple  91  is provided on the proximal end of tubular housing  82  to facilitate engagement with a corresponding void in attachment mechanism  92 . This attachment mechanism  92  facilitates the remote “locking” of the apparatus  80 , as when it is lowered into the well by way of wireline for installation below a packer  21  for a testing event. 
         [0044]    Inner assembly  94  includes a proximal end  96  and a distal end  98 . The distal end  98  is sealed at cap  102 . Fluids from perforations  106  flow into entry ports  88 ,  90  and through screen  100  into the apparatus  80 . Wiper seal  108  forms a fluid boundary below the perforations  106 , while packer  21  forms an upper boundary. In this manner, it is possible to isolate a section of well for fluid movement which facilitates pressure drawdown. 
         [0045]    The second embodiment of the invention, as shown for example in  FIG. 5 , may facilitate the apparatus  80  to be run into the wellbore with perforating guns and detectors attached, in another alternative configuration (not shown in the Figures). 
         [0046]    An apparatus  80  that is conducting a sanding test is shown in  FIG. 6 , wherein solids  112  enter with fluid  110  to the annular space  116 , with solids  112  falling downward while fluid  110  passes through screen  100  to the interior of the inner assembly  94  for production up the well. Reservoir  104  collects deposited solids  114 , which may subsequently be measured for quantity and/or analyzed for particle size distribution of solid particles. 
         [0047]    In the second embodiment of the invention, as seen in  FIGS. 5-6 , the entire apparatus  80  with tubular housing  82  and inner assembly  94  may be retrieved to the surface by a wireline or coiled tubing string once the sanding test is completed. 
         [0048]    The invention is shown by example in the illustrated embodiments. However, it is recognized that other embodiments of the invention having a different configuration but achieving the same or similar result are within the scope and spirit of the invention.