Abstract:
In producing methane a bottom hole assembly the borehole may enlarge due to shifting sands in an unconsolidated formation as the methane is produced. The enlargement of the borehole can be sensed in real time such as by using a fiber optic cable. In response to such information parts of the bottom hole assembly near the washout can be isolated or the bottom hole assembly in the vicinity of the washout can be fortified with inserts from the surface to minimize damage from erosion caused by higher velocities resulting from borehole washouts.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a continuation-in-part of U.S. patent application Ser. No. 14/023,982, for “Wellbore Completion for Methane Hydrate Production”, filed on Sep. 11, 2013, and claims the benefit of priority from the aforementioned application. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The field of this invention is completions and more particularly in unconsolidated formations that produce methane hydrate where there is a need for sand control and flow distribution to protect the screen while stabilizing the borehole. 
       BACKGROUND OF THE INVENTION 
       [0003]    Methane hydrate exists as a solid substance in layers that contain sand and other sediment. Hydrate to methane gas and water must be accomplished in order to produce the methane gas. The production of methane hydrate means dissociating methane hydrate in the layers and collecting the resultant methane gas through wells and production systems. To dissociate methane hydrate that is stable at low temperature and under high pressure, there must be an (1) increase in the temperature, (2) decrease in pressure, (3) or both. The optimum methane hydrate production method is one based on the “depressurization method.” However, since methane hydrate layers are unconsolidated sediments, sand production occurs with the methane gas and water. Because removal of the methane, water, and sand, wellbore stability becomes an issue that cannot be overcome with conventional sand control methodologies. Economical and effective measures for preventing sand production and solving borehole stability issues require a novel approach to completion methodology. 
         [0004]    One proposed method to control sand production and provide better borehole stability comprises providing a shape memory polymer foam filter that does not depend on the borehole for containment for sand management. The shape memory polymer will be utilized such that a flow path would not be directly exposed to the screen that would permit the production of sand from the borehole. One other issue related to the depressurization method of methane hydrate production is the uniform application of a differential pressure across the reservoir interface. The method further comprises a porous media under the shaped memory polymer foam filter that can be varied in number and permeability to balance the differential pressure applied to the reservoir being produced. This improves borehole stability via uniform drawdown and flow from the exposed reservoir. While these techniques could be used in a conventional open hole or cased hole completion, it is desirable to under ream or expand the borehole size to help increase wellbore radius and decrease flow velocities at the sand management/reservoir interface. Another aspect is that fiber optic or some other real time way of sensing the location and extent of hole collapse during production can be employed to close off portions of a producing zone or otherwise fortify a portion of the bottom hole assembly against higher velocities that could otherwise erode filtration components to the point of producing sand or other impurities with the methane. 
         [0005]    Several references that employ memory foam in sand control applications are as follows: 
         [0006]    WO/2011/162895A; 
         [0007]    U.S. Pat. No. 8,353,346 
         [0008]    US20110252781 
         [0009]    WO/2011/133319A2 
         [0010]    US20130062067 
         [0011]    WO/2013/036446A1 
         [0012]    US2013016170 
         [0013]    U.S. Pat. No. 8,048,348 
         [0014]    US20100089565 
         [0015]    US20110162780 
         [0016]    U.S. Pat. No. 796,565 
         [0017]    WO/2010/045077A2 
         [0018]    US20110067872 
         [0019]    WO/2011/037950A2 
         [0020]    U.S. Pat. No. 7,832,490 
         [0021]    US20080296023 
         [0022]    US20080296020 
         [0023]    U.S. Pat. No. 7,743,835 
         [0024]    WO/2008/151311A3 
         [0025]    Flow balancing devices are generally discussed in the following references: 
         [0026]    U.S. Pat. No. 7,954,546 
         [0027]    U.S. Pat. No. 7,578,343 
         [0028]    U.S. Pat. No. 8,225,863 
         [0029]    U.S. Pat. No. 7,413,022 
         [0030]    U.S. Pat. No. 7,921,915 
         [0031]    A need exists for an assembly and method of producing methane from an unconsolidated formation surrounding a borehole having methane hydrate, sand or other sediments. Once positioned and set near the formation, the filtration assembly should be able to manage sand and other sediments without having to rely on the geometric configuration of the borehole for containment, such that should the surrounding borehole subsequently enlarge or the space between the formation and the assembly increase due to changing reservoir conditions the geometric configuration of the assembly will not substantially change. 
         [0032]    Those skilled in the art will better appreciate additional aspects of the invention from a review of the detailed description of the preferred embodiment and the associated drawings while appreciating that the full scope of the invention is to be determined by the appended claims. 
       SUMMARY OF THE INVENTION 
       [0033]    In a completion for producing methane the bottom hole assembly has a base pipe with porous media within it for equalizing flow along the base pipe. A shape memory polymer foam surrounds the base pipe with porous media. The borehole can be reamed to reduce produced methane velocities. The borehole may enlarge due to shifting sands in an unconsolidated formation as the methane is produced. The bottom hole assembly helps in fluid flow equalization and protects the foam and layers below from high fluid velocities during production. The enlargement of the borehole can be sensed in real time such as by using a fiber optic cable. In response to such information parts of the bottom hole assembly near the washout can be isolated or the bottom hole assembly in the vicinity of the washout can be fortified with inserts from the surface to minimize damage from erosion caused by higher velocities resulting from borehole washouts. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0034]      FIG. 1  shows the run in position of the bottom hole assembly with the shape memory polymer foam as yet unexpanded; 
           [0035]      FIG. 2  is the view of  FIG. 1  with the polymer foam expanded; 
           [0036]      FIG. 3  is the view of  FIG. 2  showing the start of methane production; 
           [0037]      FIG. 4  shows a washout forming after methane production starts; 
           [0038]      FIG. 5  is the view of  FIG. 4  with blocking some of the base pipe openings aligned with the washout; 
           [0039]      FIG. 6  shows running the fiber optic to the subterranean location on an inner string 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0040]    In broad terms the preferred embodiment can be described as a filtration assembly and method of producing methane from methane hydrate in an unconsolidated formation containing sand and other sediments. The filtration assembly comprises a bottom hole assembly comprising a sand control assembly and a base pipe. The sand control assembly comprises a shape memory porous material, which is adapted to surround the base pipe and form a first discrete filtration layer. In one embodiment, a second discrete filtration layer is located under the first discrete filtration layer and comprises one or more filtration assurance devices adapted to support the first discrete filtration layer, assist in filtering sediment from the methane, or aid in depressurization of the formation, or any combination thereof, such as wire mesh, beadpack or both. 
         [0041]    In a preferred embodiment, the shape memory porous material is an open-cell shape memory foam, such as the foam described in the list of memory foam patents and patent applications referenced above, and the memory foam marketed by Baker Hughes Incorporated under the trademark GEOFORM™. The memory foam is adapted to help manage sand production by inhibiting the formation of a flow path through the filtration layer in which sand may be produced and by providing borehole stability without having to depend on containment by the surrounding borehole. 
         [0042]    To dissociate methane from methane hydrate, a depressurization method is employed by applying a differential pressure across the reservoir interface between the bottom hole assembly and the formation, using, for example, an electric submersible pump. As the methane dissociates from methane hydrate it passes through the filtration assembly, which filters sand and other sediments from the methane and allows the methane to enter the base pipe. In one embodiment, the base pipe comprises a depressurization device designed to help equalize flow along at least one interval of the base pipe and protect the filtration layers from high fluid velocities during production. As previously mentioned, however, the second discrete filtration layer when located under the first discrete filtration layer may also serve as a means of assisting in the depressurization of the formation. The borehole may also be reamed to reduce methane production velocities. 
         [0043]    Should the borehole subsequently enlarge or the space between the formation and the bottom hole assembly increase due to changing reservoir conditions (e.g., shifting of sands or other sediments in an unconsolidated formation as the methane is produced) the geometric configuration of the bottom hole assembly will not substantially change. 
         [0044]    Referring to  FIG. 1  a work string  1  is run through a wellhead  2 . The bottom hole assembly comprises a base pipe  5  with openings. A production packer  6  isolates the methane hydrate reservoir  4 . In one embodiment, the base pipe  5  has depressurization devices  7 , such as an annularly shaped porous member of different thicknesses and porosities, or a housing having one or more tortuous paths of different resistances to fluid flow, adapted to help equalize flow along at least one interval of the base pipe and help protect the filtration layers from high fluid velocities during production such as a choke valve, bead pack, wired mesh  50 . 
         [0045]    In one embodiment, the base pipe comprises a depressurization device for balancing flow along at least one interval of the base pipe, or a selectively or automatically adjustable inflow control member (e.g., an adjustable valve or tubular housing having one or more inflow passages, preferably with a tortuous pathway). See for example, U.S. Pat. Pub. No. 2013/0180724 and flow control products marketed by Baker Hughes Incorporated (United States of America) under the trademark EQUALIZER™. 
         [0046]    In  FIG. 1  the memory polymer foam  3  is in its run in dimension where it has not yet been warmed above its transition temperature. In  FIG. 2  the transition temperature has been reached and the polymer foam  3  has expanded. In  FIG. 3  expansion to fill the borehole is complete. Finally,  FIG. 4  illustrates the onset of methane production that ensues when the pressure in the formation  4  is allowed to be reduced. With the removal of methane a large void volume  33  can be created. This has the beneficial effect of reduction of fluid velocities for the methane. The enlarging of the borehole as well as the flow balancing devices  7  also helps to control high velocity gas erosion to keep the bottom hole assembly serviceable for a longer time before a workover is needed. 
         [0047]    Alternatives can be alloy memory foam or screens of various designs that do not change dimension with thermal stimulus. The flow balancing feature can be a porous annular shape or insert plugs in the base pipe or screen materials that vary in mesh size at different opening locations. 
         [0048]    In another aspect of the invention as shown in  FIGS. 1-6  a production pipe  1  has at least one fiber optic cable  31  attached to it. The base pipe has perforations  9  covered by a screen  7  and expandable media  6  as described above. The borehole extends into a methane hydrate formation  4 . A pressure and/or temperature and/or strain sensor and transmitter  28  can communicate through cable  31  to convey real time pressure/temperature/strain data to the surface during production. A submersible pump  10  can be used to depressurize the formation  4  in the process of producing methane. As shown in  FIG. 4  after exposure to well fluids or fluids or heat added near the expandable media  6  the fiber optic cable  31  is pushed against the borehole wall to get baseline stress readings to the surface in real time. The media  6  essentially grows to fill the borehole in formation  25 . Arrow  40  illustrates the delivery of fluid into the formation  5  as one way to get the media  6  to expand to fill the borehole. In  FIG. 4  arrows  42  show the onset of production and the borehole enlarging as a result of such production. The media  6  has some capacity to fill in as the borehole enlarges but there is a limit to such expansion capability on the part of the media  6 . Eventually, as production continues a washout  33  opens up and the baseline readings of stress on the fiber optic cable  31  changes in a manner as to give real time data at the surface that parts of the borehole have collapsed and the location of such a collapse.  FIG. 5  shows the use of an inner string  32  with a seal assembly  34  delivered to close off some of the base pipe perforations  9  so that production is relocated to arrow  46  that are offset axially from the washout  33 . Other options for dealing with the information as to the occurrence of a washout and its location from changing stress on the fiber optic cable  31  is to vary the production rate or to insert a filtering device within the production pipe so that if there is erosion of the screen  7  it will be backed up by another inserted screen. Note that there is no need to have the media  6  to further expand to fill the washout  33  although forming the media  6  to make that happen is another alternative. Rather the reduction of stress and its location on the fiber optic  31  gives real time notice to take alternative measures such as described above. 
         [0049]    In yet another embodiment shown in  FIG. 6 , the fiber optic cable  31  can be deployed on an inner string  32  inside the base pipe perforations  9 . Fiber optic pressure and distributed temperature can be used to infer flow profiles and possible washouts across the interval. 
         [0050]    The above description is illustrative of the preferred embodiment and many modifications may be made by those skilled in the art without departing from the invention whose scope is to be determined from the literal and equivalent scope of the claims below: