Multi-layered wellbore completion for methane hydrate production

This application is a divisional of U.S. patent application Ser. No. 14/447,009, filed on Jul. 30, 2014, which is a continuation-in-part of U.S. application Ser. No. 14/023,982, filed on Sep. 11, 2013, now U.S. Pat. No. 9,097,108, for “Wellbore Completion for Methane Hydrate Production”, and claims the benefit of priority from the aforementioned application.

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.

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 the temperature, (2) decrease the 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.

The 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 exposed 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. Additionally, consolidated proppant or sand could be deposited adjacent the shape memory foam as it is not the objective to fully occupy the borehole with the foam after it crosses its critical temperature. Instead, in recognition that the hole can be enlarged with initial reaming to reduce fluid velocities or alternatively additional methane production destabilizes the formation and can enlarge the borehole, the consolidated proppant or sand can be an outer protective layer to the foam. Its ability to self-adhere contains the foam and protects the foam from erosive velocity effects of the produced methane.

Several references that employ memory foam in sand control applications are as follows:

WO/2011/162895A; 8353346 US20110252781 WO/2011/133319A2 US20130062067 WO/2013/036446A1 US20130126170 8048348 US20100089565 US20110162780 7926565 WO/2010/045077A2 US20110067872 WO/2011/037950A2 7832490 US20080296023 US20080296020 7743835 WO/2008/151311A3

Flow balancing devices are generally discussed in the following references:

7954546 7578343 8225863 7413022 7921915

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.

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.

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. Surrounding the shape memory polymer is an exterior layer of consolidated proppant or sand that can self-adhere and/or stick to the polymer foam. The proppant or sand can be circulated or squeezed into position although, circulation is preferred. 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.

FIG. 1 shows the run in position of the bottom hole assembly with the shape memory polymer foam as yet unexpanded;

FIG. 2 is the view of FIG. 1 with the polymer foam expanded;

FIG. 3 is the view of FIG. 2 with the consolidated proppant or gravel in position; and

FIG. 4 is the view of FIG. 3 showing the shifting of the unconsolidated borehole wall during methane production.

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, to assist in filtering sand and other sediments from the methane a second discrete filtration layer is placed over the first discrete filtration layer comprising consolidated proppant, gravel or sand, or any combination thereof, that can adhere either to each other, the first discrete filtration layer, or both, and remain adhered should reservoir conditions change. The second discrete filtration layer may be circulated or squeezed into position after the bottom hole assembly has been positioned near the formation, or run in as part of the bottom hole assembly, although circulation is preferred. In an alternative embodiment, the third 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, prepack screen or beadpack.

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.

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 third 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.

When the borehole subsequently enlarges or the space between the formation and the bottom hole assembly increases 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.

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 . A schematically illustrated crossover tool 11 allows placement of the consolidated proppant or sand (gravel) 9 about the shape memory polymer foam 3 . See FIG. 3 . 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, prepack screen or wire mesh 15 .

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™.

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 to a location still short of the borehole wall 12 to leave an annular gap 14 into which the proppant or sand 9 will be deposited using the crossover 11 as illustrated in FIG. 3 . This is done preferably with circulation with crossover 11 and using a wash pipe that is not shown to direct returns that come through the proppant/sand 9 and the memory foam 3 into the upper annulus 8 above the packer 6 . 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 10 can be created. This has the beneficial effect of reduction of fluid velocities for the methane. Those skilled in the art will appreciate that the initial deposition of the proppant or sand 9 could likely fill the remaining annular space around the memory foam 3 by virtue of the addition of the proppant or sand 9 until some pressure resistance is sensed at the surface indicating that the volume in the annulus has packed in. The delivery of the proppant or sand 9 can begin before, during or after the foam 3 reaches its critical temperature and grows dimensionally. In any of those cases the production of methane can hollow out the reservoir as shown in FIG. 4 so the adherence of the proppant or sand 9 to itself and to the foam helps to keep the components within the foam 3 protected from erosive high gas velocities. 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.

The combination of flow balancing with the self-adhering proppant or sand 9 covering the memory polymer foam 3 and to some extent adhering to the foam allows for a longer service life as the layers of filtration remain serviceable longer in adverse conditions such as borehole collapse and potential for erosion caused at least in part by flow imbalance induced high gas velocities.

The proppant/sand 9 can be a commercially available product such as Sandtrol®. The foam is available as GeoFORM®. Alternatives can be alloy memory foam or screens of various designs that do not change dimension with thermal stimulus. The screens can be constructed so that they can be radially expanded for borehole support or to reduce the volume needed for the proppant/sand 9 . 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.

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: