Abstract:
A method and system for tool orientation and positioning and particulate material protection within a well casing for production of hydrocarbons including methane gas from a gas hydrate including a shroud positioned within a production well casing adjacent a cylindrical production tubing screen to shield and isolate the screen from particulate material entrained within production fluid entering the well casing.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application relates to and claims the benefit under 35 U.S.C. § 119(e) of applicants&#39; U.S. Provisional Application Ser. No. 60/752,118 entitled “Systems and Method for Development of Hydrocarbon Bearing Formations,” filed Dec. 20, 2005. The disclosure of this Provisional Application is hereby incorporated by reference as though set forth at length. 
     
    
     BACKGROUND  
       [0002]     This invention is generally related to a method and system for tool orientation and positioning within a production well casing. Aspects disclosed herein include exclusion of particulate material from a subterranean hydrocarbon production formation. In one aspect this invention relates to a method and system for selectively and accurately landing a perforating tool within a well casing so as to avoid damaging instrumentation and cables mounted on the outside of the well casing and/or run in the well. Once accurately perforated, this invention also relates to a method and system for excluding sand from entering production tubing and protecting the sand exclusion system. This invention finds application to various forms of hydrocarbon production, but in one aspect is useful for producing methane gas from gas hydrate formations  
         [0003]     A gas hydrate is a crystalline solid that is a cage-like lattice of a mechanical intermingling of gas molecules in combination with molecules of water. The name for the parent class of compounds is “clathrates” which comes from the Latin word meaning “to enclose with bars.” The structure is similar to ice but exists at temperatures well above the freezing point of ice. Gas hydrates include carbon dioxide, hydrogen sulfide, and several low carbon number hydrocarbons, including methane. Of primary interest for this invention is the recovery of methane from subterranean methane hydrates.  
         [0004]     Methane hydrates are known to exist in large quantities in two types of geologic formations: (1) in permafrost regions where cold temperatures exist in shallow sediments and (2) beneath the ocean floor at water depths greater than 500 meters where high pressures prevail. Large deposits of methane hydrates have been located in the United States in Alaska, the west coast from California to Washington, the east coast in water depths of 800 meters, and in the Gulf of Mexico (other well known areas include Japan, Canada and Russia).  
         [0005]     A U.S. Geological Survey study estimates that in-place gas resources within gas hydrates consist of about 200,000 trillion cubic feet which dwarfs the previously estimated 1,400 trillion cubic feet of conventional recoverable gas reserves in the United States. Worldwide, estimates of the natural gas potential of gas hydrates approach 400 million trillion cubic feet.  
         [0006]     Natural gas is an important energy source in the United States. It is estimated that by 2025 natural gas consumption in the United States will be nearly 31 trillion cubic feet. Given the importance and demand for natural gas the development of new cost-effective sources can be a significant benefit for American consumers.  
         [0007]     Notwithstanding the obvious advantages and potential of methane hydrates, production of methane from gas hydrates is a challenge for the industry. When trying to extract methane from a gas hydrate the sequestered gas molecules must first be dissociated, in situ, from the hydrate. There are typically three methods known that can be used to create this dissociation.  
         [0008]     One method is to heat the gas hydrate formation to liberate the methane molecules. This method is disclosed in United States Patent Application Publication No. US 2006/0032637 entitled “Method for Exploitation of Gas Hydrates” published on Feb. 16, 2006, and of common assignment with the subject application. The disclosure of this publication is incorporated herein by reference as background information with respect to the subject invention.  
         [0009]     Another method envisioned for producing methane hydrates is to inject chemicals into the hydrate formation to change the phase behavior of the formation.  
         [0010]     A third technique is regarded as a depressurization method. This method involves depressurization of a gas hydrate formation and maintaining a relatively constant depressurization on the hydrate formation to allow dissociation and then withdrawing dissociated gas and water through a well casing.  
         [0011]     When an unconsolidated formation is perforated, formation sand is produced into the casing of the well bore. Depending on the rate and volume of sand produced, an appropriate sand management technique must be employed to minimize damage to the completion string. An objective of the sand control procedure is to create unimpeded fluid flow, yet to prevent sand production.  
         [0012]     This disclosure applies to sand management inside a well casing. The subject disclosure contemplates utilizing an orienting device that is operable to precisely locate a perforating tool in order to avoid casing instrumentation and/or cabling.  
         [0013]     Following precise perforation of a well production casing at a hydrocarbon zone, a screen is placed inside the casing and a known proppant is place between the screen and the casing, usually referred to as a gravel pack. There are a number of techniques to place gravel between the screen and the perforation. However, an alternative method is required for some situations where a pumping operation is limited, or not possible. In this case, there is risk of eroding the screen if it is placed directly across the perforations. The present sand management method and system mitigate this risk.  
       SUMMARY OF THE DISCLOSURE  
       [0014]     In one embodiment of the disclosure an indexing device may be run as an integral component of a production casing string. An orienting tool is run inside the casing string to locate the depth and angular position relative to the indexing device regardless of vertical orientation. A perforating device, i.e., a perforating gun, is run below the orienting tool with a known position relative to the orienting features of the orienting tool.  
         [0015]     The orienting tool is landed in the indexing device to achieve proper location and orientation. The casing is then perforated at a precise location and orientation.  
         [0016]     A screen assembly is placed below the same orienting tool using the same indexing device to precisely locate and orient the screen relative to the perforation pattern.  
         [0017]     The screen carries a protective shroud strategically located radially inward with respect to the well casing perforations on the outer diameter of the screen to protect the screen from sand particles coming into the casing at the perforations. 
     
    
     THE DRAWINGS  
       [0018]     Other features and aspects of the disclosure will become apparent from the following detailed description of some embodiments taken in conjunction with the accompanying drawings wherein:  
         [0019]      FIG. 1  is a pictorial view of one context or geological region of permafrost in Alaska where gas hydrates are know to exist;  
         [0020]      FIG. 2  is a pictorial view of another context or geological region of gas hydrates beneath offshore regions of the United States in water greater than 500 meters;  
         [0021]      FIG. 3  is a schematic representation of one technique for producing a methane hydrate that includes a depressurization production system including maintaining a desired level of pressure within a well including returning water into the well from a surface valve system;  
         [0022]      FIG. 4  is an indexing casing coupling (ICC) which is built into the internal diameter of a well casing;  
         [0023]      FIG. 4A  is a detail of the indexing casing coupling showing multiple locating profiles;  
         [0024]      FIG. 5  is a transverse sectional view of an indexing coupling which discloses more detail of an orientating mechanism of the coupling;  
         [0025]      FIG. 6  is a another transverse sectional view of the indexing coupling of  FIG. 5  that has been rotated 90 degrees to further disclose an azimuth rotating feature of the coupling;  
         [0026]      FIG. 7  is a side view of a construction selective locating tool (CSLT) which is used to land on and be oriented by the ICC illustrated in  FIGS. 4-6 ;  
         [0027]      FIG. 8  is a side view of an oriented perforating gun assembly that is mounted below the CSLT to selectively perforate a well casing;  
         [0028]      FIG. 9  is a side schematic view of a distal end of a production well casing with a concentric production tubing with a cylindrical screen at the distal end of the production tubing to block particulates from entering the production tubing and a protective shroud accurately positioned with respect to production perforations in the well casing; and  
         [0029]      FIG. 10  is a cross sectional view taken along section lines  10 - 10  in  FIG. 9  and discloses radial positioning of the protective shrouds with respect to production perforations. 
     
    
     DETAILED DESCRIPTION  
       [0030]     Turning now to the drawings wherein like numerals indicate like parts,  FIG. 1  discloses a pictorial representation of one operating context of the invention. In this view a band of gas hydrate  10  lies in a rather shallow geologic zone beneath a permafrost layer  12  such as exists in Alaska. Other earth formations  14  and/or aquifer regions  16  can exist beneath the gas hydrate.  
         [0031]     In order to recover sequestered methane gas from within the gas hydrate zone one or more wells  18 ,  20  and/or  22  are drilled through the permafrost  12  and into the gas hydrate zone  10 . Usually a casing is cemented within the well and one or more windows are opened directly into the hydrate zone to depressurize irregular regions of the gas hydrate represented by irregular production zones  24 ,  26 ,  28  and  30  extending away from distal terminals of the wells. Although a single well is shown drilled from a single derrick, illustrated at  18  and  22 , it is envisioned that directional drilling, as illustrated at derrick  20  and zone  30 , will be a more common practice to extend the scope of a drilling operation.  
         [0032]     Once one or more wells are drilled, pressure is relieved from the gas hydrate zone around the well and the methane gas and water molecules will separate and enter the wells. The gas can then be separated from the water and allowed to rise to the surface or is pumped to the surface along with water and separated and fed along a pipeline  32  to a compressor station not shown.  
         [0033]     An alternative operating context of the invention is illustrated in  FIG. 2  where a drillship  40  is shown floating upon the surface  42  of a body of water  44  such the Gulf of Mexico. In this marine environment pressures in water depths approximately greater that 500 meters have been conducive to the formation again of geologic layers of gas hydrates  46 , such as methane hydrates, beneath the seabed  48 .  
         [0034]     Offshore drilling in water depths of 500 meters or more is now technically possible so that drilling into the offshore gas hydrate formations  46  and cementing a casing into a well hole offshore to form a production strata  50  is another source of production of methane from a gas hydrate formation. Again, directional drilling from a subsea template enables fifty or more wells to be drilled from a single drillship location.  
         [0035]     Turning now to  FIG. 3 , there will be seen one method and system in accordance with one embodiment of the invention. In this, a well hole  60  is drilled through an earth formation  62  and into a previously identified geologic layer of methane hydrate  64 . A casing  66  is positioned within the well and cemented around the outer annulus for production. At a selected depth, which may be relatively shallow for drilling through permafrost or deep if offshore, the casing is perforated by one or more windows  68  which establish open communication between the interior of the well casing and a zone of methane hydrate under pressure. This opening of the well casing will relieve pressure on the surrounding methane hydrate and will enable previously sequestered methane gas to dissociate from the lattice structure of water molecules to form a physical mixture of gas and water. The gas and water  70  will then flow into the well casing  66  and rise to a level  72  within the casing consistent with a desired level of pressure within the well casing. In other words, the submersible pump pumps water out of the well creating a lower hydrostatic pressure on the hydrate formation. This depressurization causes the solid hydrate to dissociate. Once the hydrate dissociates, the water and gas will flow into the wellbore raising the water level which lowers the drawdown pressure which then tends to prevent further dissociation. This is a self limiting process thus the submersible pump is used to pump out the water within the well casing to lower the water level and to maintain the drawdown necessary for continuous dissociation. The pump creates the drawdown pressure. An automated feedback loop maintains a constant drawdown pressure by re-circulating some amount of produced water.  
         [0036]     In order to recover methane gas from the mixture, the mixture of gas and water is pumped to the surface by an electro submersible pump (ESP)  74  connected to the distal end of a first conduit  76  extending into the well casing  66 .  
         [0037]     Some downhole pumps require a minimum amount of flow rate to stabilize pump performance, such as an ESP. Some hydrocarbon reservoirs do not have enough production flow, such as in methane hydrate production wells, to efficiently use a full production ESP. Methane hydrate production flow depends on not only formation permeability, but also on the rate or volume of hydrate dissociation. Accordingly production rate may change from time to time which may require the pump size to be changed. The present invention endeavors to provide methods and systems that generate the minimum flow rate of fluids for the pump by a flow back loop that may be used to return pumped out fluid back into the well casing to be recycled. In this, it is possible to handle a wide range of production rates with only one large capacity downhole pump.  
         [0038]     At the surface the gas and water mixture passes through a conventional gas and water separator  78  where methane gas is separated, monitored and delivered to a pipe  80  for collection by a compressor unit. Downstream of the separator/monitor  78  is a valve  82  to control the flow of water out of the system. Prior to reaching valve  82  a branch or second conduit  84  is joined into the first conduit and extends back into the well casing  66 . This enables water from the well that has been separated from the mixture at  78  to be reintroduced back into the well casing to maintain at least a minimum level of water  72  within the well casing for efficient operation of the ESP  74 .  
         [0039]     Control of the volume of water reintroduced into the well casing is provided by a choke valve  86  that is positioned within the second conduit  84  as illustrated in  FIG. 3 . The position of the choke valve can be regulated by a control line running from the intake of the ESP to the choke valve  86 . This enables the system to maintain a constant pressure within the well casing  66  by controlling the volume of water reintroduced into the system.  
         [0040]     Depending upon the pressure within the well casing there may be a tendency for the gas and water mixture to solidify within the well casing  66 , ESP  74  or first conduit  76 . The temperature of water returning to the well casing can be regulated by a temperature control unit  90  connected to the return water or second conduit  84  to minimize this issue.  
         [0041]     In addition to collecting methane gas from the separator  78  methane gas is drawn directly from the top of the well casing by a third conduit  92  that passes through a gas production monitor  94  which also delivers gas to a compressor storage system.  
         [0042]     Depending on the downhole well casing pressure and the pressure within the ESP  74  the gas and water mixture  70  may tend to re-solidify during a pumping operation within the ESP intake (thus upstream of the ESP), within the ESP  74  itself or downstream of the ESP within the first conduit  76 . In order to minimize this tendency, a fourth conduit  96  is extended within the casing  66  and is operable to feed a chemical, such as methanol, upstream of the ESP  74 , directly into the ESP or downstream of the ESP to minimize reformation of methane hydrate within the system.  
         [0043]     In producing methane from a gas hydrate, or other hydrocarbon production such as conventional natural gas or oil reserves, the production hydrocarbon flows from a subterranean formation and into a production well casing to be pumped to the surface for processing.  
         [0044]     In such operations particulate material such as sand entrained within hydrocarbon fluid streams can enter access windows or perforations in the well casing along with the hydrocarbon for production.  
         [0045]     In hydrocarbon production operations, where instrumentation and cables are mounted to the outside of a well casing and/or run in the well, special casing couplings are spaced within the well casing relative to a reservoir and the instrumentation. This coupling is constructed with internal orienting and locating features without internal diameter restrictions.  
         [0046]      FIG. 4  discloses an example of an indexing casing coupling  100 . An orienting profile or channel  102  is fashioned within the indexing casing and cooperates with features of a production tube, not shown, to rotate or orient the production tube.  
         [0047]     The indexing casing coupling also is fashioned with a plurality of locating profiles  104 , note an enlargement at  FIG. 4A  to cooperate with corresponding profiles on the exterior surface of perforating tools and production tubing.  
         [0048]      FIGS. 5 and 6  are additional views of an indexing casing coupling of the instant disclosure that is the subject of European Patent Office patent No. EP 0 872 626 B1 published Jun. 15, 2005 Bulletin 2005/24 on a patent entitled “Method and Apparatus for Locating Indexing Systems in a Casing Well and Conducting Multilateral Branch Operations” of assignment to a sister corporation with the subject application. The disclosure of this EPO patent publication is hereby incorporated by reference as though set forth at length.  
         [0049]      FIG. 5  discloses a representative indexing coupling  106  mounted in a casing string  108  for positioning and azimuth indexing of a tool run into the well casing  108 . The indexing coupling defines a selected internal landing profile  110  having circular lands and grooves of a geometry matching the geometry of a well service tool to be landed and oriented therein.  
         [0050]     The indexing coupling  106  includes an orienting slot  112  which can be of any suitable configuration but is depicted in this embodiment as being rectangular  114 . This slot is operable to cooperate with an orienting key  116  of an oriented well tool  118 . As the well tool  118  descends, the orienting key  116  engages a cam surface  120  of the indexing coupling and is mechanically rotated as it descends into slot  112  until it lands at  122  (note  FIG. 6 ) to provide both depth and azimuth precise orientation.  
         [0051]     The well tool is provided with latching dogs  124  having a profile matching the internal landing profile  110  of the indexing coupling  106  so that when the latching dogs  124  are in registry with the internal landing profile they will become seated. The well tool  118  is then subjected to latching activity for the purpose of securing the well tool  118  in latched relation within the indexing coupling  106 ,  
         [0052]     Turning to  FIG. 7  there is shown a construction selective locating tool (CSLT)  130 . This tool has a number of features but for purposes of this discussion it is sufficient to note that spring loaded locator keys  132  are operable to securely engage with corresponding locating profile surfaces as discussed above. A spring loaded orientating key  134  operably cooperates with orientating profile  102  as disclosed in  FIG. 4 . A perforating gun is located beneath the CSLT and is operable to precisely perforate a well casing as will be discussed below.  
         [0053]      FIG. 8  discloses an exemplary oriented perforating gun assembly  140 . The assembly  140  is connected to a working string  142  and an initial component is the CLST with orienting and locking keys  130 . An alignment clutching coupling connects the CSLT  130  to a firing head  146 . Gun spacers  148  and  150  are connected to alignment adjusters  152  and  154  respectively. Gun assemblies  156  and  158  are connected to the alignment adapters and finally the oriented perforating Gun Assembly is completed by an end adapter  160 .  
         [0054]     Turning now to  FIGS. 9 and 10 , a well production casing  170  is shown cemented within a gas hydrate production formation  172 . Production tubing  174  has been extended into the well casing  170  and terminates with a cylindrical particulate or sand screen  176 . At the radially interior locations of the production perforations  178 ,  180 ,  182 , and  184  are sacrificial guards or shrouds  190  and  192  mounted on the screen  176 .  
         [0055]     The shrouds  190  and  192  may be arcuate in cross-section, note  FIG. 10 , and vertically extend in opposition to perforation windows  178 - 184 . The shrouds are held in position by cantilever connecting or support bars  194  and  196 . In one embodiment the shrouds are solid, however, it is also envisioned that the shrouds may be formed by vertical strips of sacrificial material. In addition, the shroud may be designed to be a relative thick sacrificial member.  
         [0056]     The disclosure herein contemplates applications in oriented perforation of well casings. As discussed above, with the advent of “smart” or “intelligent” wells the installation of sensors behind casings is becoming more common. Therefore, there is a growing need for effective methods and systems for accurately perforating well casings. The disclosure herein provides utilizing the CSLT and ICC as reliable mechanical techniques for implementing oriented perforation. In this, the ICC may be located just above the formation to be perforated. Therefore, the sensors and cables behind the casing will be located just below the ICC depth and will run in a straight line. To avoid timed threads, the positions of the cable lines and instruments with respect to the orienting slot on the ICC is recorded once the ICC is installed. With this relative orientation known, the perforating guns are made up to the CSLT orienting key to avoid perforating the sensors.  
         [0057]     In operation an indexing device may be run integral to the casing string. An orienting tool may be run inside the casing string to locate the depth and angular position relative to the indexing device. A perforating device, i.e., a perforating gun, may be run below the orienting tool with a known position relative to the orienting features of the orienting tool. The orienting tool may be landed in the indexing device to achieve proper location and orientation. The casing may be perforated at a precise location and orientation. A specially designed screen assembly may be placed below the same orienting tool using the same indexing device to precisely locate and orient the screen relative to the perforation pattern.  
         [0058]     In this, the screen may be configured with a protective shroud strategically located on the outer diameter of the screen to protect the screen from sand particles coming into the casing at the perforations.  
         [0059]     A casing string may be run with an orienting feature built into the inner diameter of the casing, e.g., Indexing Casing Coupling. The orienting feature allows a mating orienting tool, e.g., CSLT, to be run inside the casing to find and orient itself relative to the orienting feature. The casing string with the orienting feature may be cemented. Then, the mating orienting tool is run with a perforating tool to create holes in the casing at a know location and orientation. Subsequently, a specially designed screen is run with the same mating orienting tool to place the screen to align with the perforations made in the casing. The screen in this case is specifically designed with a protective shroud on the outer diameter of the screen.  
         [0060]     Typically, when a screen is placed directly across perforations the space between the screen and the casing is filled with known proppant, usually referred to as a gravel pack. The present disclosure also contemplates applications where the gravel packing option is limited, or is not possible. The problem with placing an ordinary screen directly across the casing is the risk of sand particles impinging on the screen and eventually eroding a hole in the screen. To avoid this problem, the screen may be run above the perforations, but such an arrangement gives up performance.  
         [0061]     By precisely positioning a specially protected screen directly across the perforations, as shown in  FIG. 9 , flow impedance is minimized while providing sufficient protection for the screen.  
         [0062]     The specially designed screen in this case has a protective member that is cylindrical with flow holes located out of phase from the casing perforations. The protective member may be thick member, or made appropriately to handle the sand erosion. Alternatively, the protective member may be configured from strips of material or patches of material that are attached to the screen in areas that are inline with the perforations. Since the perforations are made using a precise orienting method described above, and the screens are oriented in the same fashion, the protective member may be custom designed as required.  
         [0063]     In describing the invention, reference has been made to some embodiments and illustrative advantages of the disclosure. Those skilled in the art, however, and familiar with the subject disclosure may recognize additions, deletions, modifications, substitutions and other changes which fall within the purview of the subject claims.