Continuous Circulating Concentric Casing Managed Equivalent Circulating Density (ECD) Drilling For Methane Gas Recovery from Coal Seams

Abstract

A method of drilling multiple boreholes within a single caisson, for recovery of methane gas from a coal bed, including the steps of drilling first and second vertical boreholes from a single location within a single caisson; drilling at least one or more horizontal wells from the several vertical bore hole, the horizontal wells drilled substantially parallel to a face cleat in the coal bed; drilling at least one or more lateral wells from the one or more horizontal wells, the lateral wells drilled substantially perpendicular to one or more face cleats in the coal bed; continuously circulating water through the drilled vertical, horizontal and lateral wells to recover the water and entrained methane gas from the coal bed; applying friction or choke manifold to the water circulating down the well bores so that the water appears to have a hydrostatic pressure within the well sufficient to maintain an equilibrium with the hydrostatic pressure in the coal bed formation; and drilling at least a third vertical borehole within the single caisson, with one or more horizontal boreholes and one or more lateral boreholes for returning water obtained from the lateral wells into a water zone beneath the surface.

Claims

1-14. (canceled)

15. A method of drilling one or more wells in a coal bed formation within a caisson during a drilling phase, wherein said one or more wells are for recovering gas from the coal bed formation during a production phase, comprising the following steps: (a) drilling a first production well within the caisson, the first production well having a first lateral well that is drilled at least substantially parallel to a face cleat or at an angle of about 45 degrees respective to the face cleat in the coal bed formation, and a second lateral well drilled from the first lateral well that is at least substantially perpendicular to one or more face cleats in the coal bed formation; (b) circulating drilling fluid during the drilling phase through the first production well, said drilling fluid having a hydrostatic pressure that is less than coal bed formation hydrostatic pressure, and having a weight; (c) increasing the hydrostatic pressure of the drilling fluid that is circulating in step (b) to effectively increase the weight of the drilling fluid to an effective weight that prevents collapse of the coal bed formation during the drilling phase; and wherein an actual weight of the drilling fluid is not increased in step (c).

16. The method in claim 15, further comprising drilling a second production well within the caisson during the drilling phase, said second production well having a third lateral well drilled at least substantially parallel to a face cleat and a fourth lateral well drilled at least substantially perpendicular to a face cleat, and wherein said first production well and said second production well are operable to recover gas from produced water in the first production well and the second production well during the production phase of the coal bed formation.

17. The method in claim 15, further comprising drilling at least one injection well within the caisson for returning produced fluid received from the first production well into a waste zone beneath a surface of the coal bed formation.

18. The method in claim 17, wherein the produced fluid recovered from the coal bed formation during the production phase is separated removing solids and filtered before being returned down the injection well into the waste zone, and wherein gas recovered from the produced fluid is stored above the surface.

19. The method in claim 15, wherein the hydrostatic pressure of the drilling fluid is increased using friction or choke methods, or a combination of both friction and choke methods, applied to the drilling fluid that is circulating.

20. The method in claim 19, wherein chemicals or weighting agents are not added to the drilling fluid to increase the weight of the drilling fluid.

21. The method in claim 15, wherein gas from the coal bed is recovered from the second lateral well drilled at least substantially perpendicular to the one or more face cleats in the coal bed.

22. The method in claim 15 wherein the drilling fluid is at least substantially clear water.

23. The method in claim 22, wherein applying friction or choke to the drilling fluid that is circulating, increases the hydrostatic pressure of the drilling fluid and weight effect of the drilling fluid that is circulating from a weight of about 8.6 lbs/gal to at least 12.5 lbs/gal.

24. The method in claim 15 wherein methane gas is recovered during the production phase.

25. A method of drilling multiple boreholes in a coal bed formation within a caisson in a drilling phase, comprising the following steps: (a) drilling a first borehole at a first location within the caisson; (b) drilling a first lateral well from the first borehole, said first lateral well drilled at least substantially parallel to a face cleat or at an angle of about 45 degrees respective to a face cleat in the coal bed formation; (c) drilling a second lateral well from the first lateral well, the second lateral well drilled at least substantially perpendicular to one or more face cleats in the coal bed formation; (d) continuously circulating drilling fluid without weighting agents through the first borehole, and through the first lateral well and the second lateral well during the drilling phase, said drilling fluid having a hydrostatic pressure that is less than a coal bed formation hydrostatic pressure and a weight; and (e) increasing the hydrostatic pressure and a weight effect of the drilling fluid a sufficient amount to maintain an equilibrium with the coal bed formation hydrostatic pressure to prevent the coal bed formation from collapsing.

26. The method in claim 25, wherein during a production phase, further comprising recovering gas from the coal bed formation through produced fluid in the second lateral well that is drilled perpendicular to said one or more face cleats in the coal bed formation.

27. The method in claim 26 wherein methane gas is recovered from the produced fluid.

28. The method in claim 26 wherein the drilling fluid is water that is at least substantially clear.

29. The method in claim 26, wherein the second lateral well is drilled perpendicular to a plurality of face cleats to penetrate the plurality of face cleats and to increase gas production during the production phase.

30. A method of recovering gas from a coal bed formation comprising the following steps: (a) drilling a production well, wherein while drilling the production well, drilling fluid that does not include weighting agents is continuously circulated through the production well and wherein a hydrostatic pressure of the drilling fluid is increased while circulating the drilling fluid; (b) producing a production fluid that includes the drilling fluid mixed with gas in the production well; (c) recovering the gas from the production fluid produced in step “b”; and wherein the production well comprises a first well drilled at least substantially parallel to a face cleat in the coal bed formation, and a second well drilled from the first well and drilled at least substantially perpendicular to one or more face cleats in the coal bed.

31. The method of claim 30 further comprising drilling an injection well in step “a”.

32. The method of claim 31 further comprising returning the fluid after step “c” to the coal bed formation via the injection well.

33. The method of claim 30 wherein methane gas is recovered in step (c).

34. The method of claim 30 wherein the drilling fluid is water that is at least substantially clear.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] For a further understanding of the nature, objects, and advantages of the present invention, reference should be had to the following detailed description, read in conjunction with the following drawings, wherein like reference numerals denote like elements and wherein:

[0023] FIG. 1 illustrates an overall view of multiple wells being drilled out of a single caisson from a single location in the method of the present invention;

[0024] FIG. 2 illustrates a cross-section view of the multiple wells within the caisson as illustrated in FIG. 1 in the method of the present invention;

[0025] FIG. 3A illustrates a water injection well to return waste water into the formation utilizing a vertical well in the method of the present invention;

[0026] FIG. 3B illustrates a water injection well returning waste water into the formation through a use of a horizontal well extending from the vertical well in FIG. 3A in the method of the present invention;

[0027] FIG. 4 illustrates yet another embodiment of the water injection well in FIGS. 3A and 3B, where there are multiple lateral wells extending out from the horizontal well in the method of the present invention;

[0028] FIG. 5 illustrates a depiction of the drilling of the lateral wells perpendicular to the face cleats in the coal seam to recover maximum of methane gas from the coal seam in the method of the present invention;

[0029] FIG. 6 illustrates the single pass continuous circulation drilling utilized in the method of the present invention;

[0030] FIG. 7 illustrates the continuous circulating concentric casing pressure management with friction and choke methods in the method of the present invention;

[0031] FIG. 8 illustrates a wellhead for continuous circulation in the method of the present invention;

[0032] FIG. 9 illustrates a plurality of lateral wells which have been lined with liners as the methane gas is collected from the coal seam in the method of the present invention;

[0033] FIG. 10 illustrates an overall view of the methane gas collection from the coal seam utilizing a plurality of lateral wells and the water injection well returning used water into the underground, all through the same caisson in the method of the present invention;

[0034] FIG. 11 illustrates a depiction of a plurality of horizontal wells having been drilled parallel to the face cleats and a plurality lateral wells having been drilled perpendicular to the face cleats in the coal seam for obtaining maximum collection of methane gas; and

[0035] FIG. 12 illustrates a continuous circulating concentric casing in the method of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0036] FIGS. 1 through 11 illustrate the preferred method of the present invention, which in summary is a plurality of wells being drilled through a single caisson from the rig floor, at least two of the wells drilled for the ultimate collection of methane gas from a coal seam, and a third well drilled to return waste water used in the process to a water collection zone beneath the surface.

[0037] Turning now to the individual Figures, as seen in overall view in FIG. 1, and in cross-section view in FIG. 2, there is illustrated in overall view in FIG. 1, a drilling rig 20 having a single caisson 22 with three wells 24, 26, 28 within the single caisson 22. As seen, each of the wells include a vertical well section 29, which terminates in at least one or more horizontal wells 30, which branch off into a plurality of lateral wells 32, for reasons stated herein. Of the three wells depicted, two of the wells 24, 26 are multilateral wells to produce water and methane gas, while the third well 28 comprises an injection well 28 that can inject waste water back into one of the underground reservoirs.

[0038] The two producing wells 24, 26 would produce the water and methane gas after completion, where the recovery from these wells would be run thru a centrifuge 82 (as seen in FIG. 7) to remove the fine particles during the drilling phase and additionally a centrifuge would be used after completion to remove the coal fines for re-injection, while for the third well 28, water would be re-injected back into the earth in a water bearing zone. The configuration of the three wells 24, 26, 28 within a single conduit or caisson 22 is important and novel since this allows the single site to produce gas through the circulated water in wells 24, and 26, and send waste water down into the water bearing zone via well 28, rather than on site collection ponds, which may be required in some jurisdictional legal guidelines.

[0039] As further illustrated in FIGS. 3A and 3B, water 36 is being injected into a vertical well section 29 (FIG. 3A), or into a horizontal well 30 (FIG. 3B) or into a horizontal with multiple laterals 32, as seen in FIG. 4 for sending the water into water bearing zones in formation 31. FIG. 4 depicts injection down the hole of produced water or produced waste water 37 that has been run thru solids removal equipment.

[0040] In understanding the nature of a coal seam, coal seams contain face cleats and butt cleats. All of the face cleats comprise cracks in the coal seam which are in a certain direction and comprise the pathway for gas movement thru the coal seam, while the butt cleats connect the face cleats. In a coal seam all major fractures, or face cleats, are in the same direction. Therefore, if one drills in parallel to the face cleats, and only connects two of them, this is the most stable direction. But, if one drills perpendicular to the face cleats, and connects all of the fractures, the recovery is very good, which has, in effect, created a new mechanical induced butt cleat, i.e., connecting one or more face cleats. Drilling from parallel to perpendicular requires more hydrostatic pressure, i.e. mud weight, going from stable to unstable. Most drillers want to drill parallel to the face cleats to avoid the instability in the well. For example, the mine shaft in a coal mine may be mined parallel to the face cleats, to avoid collapse of the mine shaft. However, in coal bed drilling for methane gas, the recovery, when one drills perpendicular to the face cleats is 10 to 20 times more productive; therefore, the most productive direction is to drill perpendicular.

[0041] With that in mind, turning now to FIG. 5, it has been determined that if there is a fracture in the coal seam, referenced as face cleat fractures 50, that these face cleat fractures 50 would all be parallel one another in the coal seam. One would drill a vertical well, such as well 24, and drill the horizontal well 30 parallel to the fractures 50 for attaining the most stable well bore, which means the less likely to collapse under downhole pressures. Drilling parallel to the fractures 50 is the most stable direction, but it is the least productive of the drilling. One would want to be able to drill perpendicular to the fractures 50 for maximum production of methane gas through the lateral wells 32. As stated earlier, drilling perpendicular to the fractures is useful because production of methane gas is ten to twenty times greater when the production wells are perpendicular to the fractures 50 rather than parallel to the fractures 50.

[0042] In an embodiment of the present invention, to drill perpendicular to the face cleat fractures 50 in a stable environment, one would provide higher hydrostatic pressure by higher mud weight or, with water alone, having the water exhibit characteristics which renders its weight or ECD from 8.6 to 12.6 lbs/gal, for example. An embodiment of the present invention provides the desired weight or ECD thru creating mechanical friction, since fluid has resistance, which creates back pressure. In another embodiment, using fresh water, the method comprises use of chokes on surface. For example, one would pump in 100 gallons, but only let out 90 gallons, therefore creating back pressure. The back pressure caused by this process would give greater weight effect or ECD to the water, and increase sufficient hydrostatic pressure in the well bore.

[0043] In an embodiment of the present invention, one would use treated water free from any chemicals and bacteria. An object of the present invention is to enable a cleaner formation with no damage by chemicals. However, because the perpendicular drilled wells create instability, in order to minimize that problem, a higher bottom hole pressure is useful, when the coal seam is pressurized down hole. As discussed earlier, in order to minimize a coal seam from being damaged by mud additives added to water in order to create a greater hydrostatic pressure, in a preferred embodiment one would drill with clear water. However, it is difficult to obtain the proper hydrostatic pressure to keep the well from collapsing with just water, without increasing the hydrostatic pressure in some manner. In coal reservoirs which are pressured, there is a need for a process to obtain instantaneous increases of hydrostatic pressure from 8.6 to 12.6 lbs per gallon mud or higher, such as barite or other chemicals added to the water. These chemicals damage the permeability in the formation, actually holding back the pressure, and reduce the opportunity for desorption of methane gas from the formation. Therefore, in a preferred embodiment pure or clear water (containing less than 4 microns of solids drilling fluid, for example) is used, which has a weight of 8.6, but has the effect as the heavier mud, at possibly 12 lbs/gal. In a preferred embodiment of the present invention, to address this problem, one would drill the wells from the parallel or sub-parallel to the perpendicular, without agents, such as chemicals, and with use of friction or back pressure, or a combination of both, as discussed earlier. These means, i.e. the friction or back pressure, can increase the circulating density of the fluid, which is only water in a preferred embodiment.

[0044] Turning therefore to FIGS. 6 through 8, these figures show that on the surface systems may be used to increase friction within the well or through the use of a choke manifold, or a combination of both circulated continuously down the concentric annulus, both of which would cause the water to exhibit a greater hydrostatic pressure, of a suitable magnitude, without the use of chemical or surfactants. By creating the higher equivalent of back pressure, through friction or a choke manifold, one is able to the wells perpendicular, for greater recovery of methane gas. That allows one to drill perpendicular and have a higher effective bottom hole pressure without having the bore collapse. There are no chemical agents, such as surfactants involved, which can cause the clay to swell and choke off the flow of gas out of the formation.

[0045] It should be noted that as seen in FIGS. 6 through 8, the system, in a preferred embodiment, would be a continuous circulating system for reducing the likelihood of the formation collapsing under pressure, wherein the water through either friction or the choke valve maintains a 10 lb. per sq. inch pressure down hole, for example, without the use of chemicals.

[0046] In FIG. 6, water is pumped from pumps 70 and 72 via line 74 to the stand pipe 76 and circulated down the borehole. While circulating, due to the hydrostatic pressure of the water and choking effects, for reasons described earlier, the formation remains stable. The water is then returned from the borehole, and after cleansing through the shale shaker 78, de-silter 80, and decanting centrifuge 82, the water returns to pumps 70 and 72.

[0047] In FIGS. 7-8, the water being pumped from pump 70 via line 74 to stand pipe 76 returning up bore 90. Simultaneously pumping with pump 70 from pump 72 via line 103, then down annulus 104 thru perforations 100, and returns comingled with fluid from pump 70 up the inner annulus 98 of the well, and goes to the rig manifold 94. This creates both friction control of the annulus and choking to increase the hydrostatic ECD control of bottom hole pressure. The water is then cleansed and returns to pumps 70 and 72. FIG. 8 illustrates a view of a well head 102, with the water being pumped down an inner bore 96, and returned up an annulus 98 where the water from pump 70 and pump 72 are comingled creating the friction effect for hydrostatic friction which then returns to the rig floor for additional choking effect and separation. In a preferred embodiment the present invention is a continuous system, if circulation stomps, i.e., turn the pumps off, this can create a loss of friction and choking, so that the formation may collapse. Pump 72 during connections can increase its flow to match the gallons per minute of both pumps 70 and 72 to maintain the friction. effect. After a connection is made and flow is re-established to pump 70, pump 72 can slow to the comingled volume and maintain the friction effect.

[0048] As illustrated in FIG. 9, at some point in time during the process, one may wish to case the laterals 32 off. FIG. 9 illustrates slotted liners 60 which have been inserted into each of the laterals 32. This is useful to help maintain the integrity of the laterals 32 during the method of the invention.

[0049] In FIG. 10, there is again depicted an overall view of a drilling rig 20 with multiple wells from a single caisson 22, where some of the laterals 32 from wells 24, 26 are collecting methane gas by continuously circulating water into the formation, while laterals 32 from a third well 28 are returning waste water to the water bearing zones beneath the surface. In FIG. 11, there is depicted the vertical wells extending from the single caisson 22, where there are a plurality of horizontal wells 30 drilled in the same direction as the face cleat fractures 50, to maintain stability, but where there are a plurality of lateral wells 32 being drilled perpendicular to the horizontal wells 30 through multiple face cleats 50 of the coal seam, to obtain maximum methane gas recovery. In an embodiment of the present invention, cased hole or open hole may be used, wherein the hydrostatic pressure is maintained through the continuous circulation of the water through the system under friction or through a choke at the surface, for maintaining the hydrostatic pressure of the water sufficiently high to prevent collapse of the formation at all times.

[0050] In an embodiment of the present invention, the novel system for recovering methane gas from coal seams involves a continuously circulating concentric pressure drilling program which may be adapted to include a splitter wellhead system for purposes of using a single borehole with three wells, or conduits, in the single borehole, with two of the conduits used for completing coal bed methane wells, and the third used as a water disposal well all within a single well caisson.

[0051] An embodiment of the present invention, involves a process for recovering methane from coal seams through the following steps: drilling and installing a caisson with multiple conduits; drilling a well bore through the conduit into a coal seam; using a continuous circulating process to drill and complete those wells within the coal seam with the lateral wells being perpendicular to the face cleats of the coal seam so that the well extends through multiple face cleats for maximum recovery of methane gas; completing each well either open or cased hole; next, drill the second well, and complete a series of multi-lateral wells into the coal seam perpendicular to the face cleat fractures as described earlier; then, in the third conduit, drill a vertical or horizontal or multilateral well for disposing the water produced from the other two conduits. The water would be returned through a pumping mechanism from conduits 1 and 2, filtered for solids removal, and re-injected into the well bore via the borehole in conduit 3. The present invention overcomes problems in the prior art thru use of multiple wells drilled from a single caisson in a coal bed methane system, using friction and choking methods to maintain the proper hydrostatic pressure of pure water, for coal bed methane recovery in at least two of the wells, and injecting water down hole, all within the same vertical well bore.

[0052] In an embodiment of the method of the present invention for a continuous circulating concentric casing managed equivalent circulating density (ECD) drilling method, the method involves a continuous circulating concentric casing using less than conventional mud density. Using less than conventional mud density, the well will be stable and dynamically dead, but may be statically underbalanced (see FIG. 12). As stated earlier, in an embodiment of the invention and in the well planning, one would drill wells perpendicular to the face cleats of the coal. From the face cleat direction, there would be a single fracture, reorientation and a single t-shaped multiple 105 provided as seen in FIG. 5.

[0053] For purposes of the below paragraph, the following abbreviations will apply:

[0054] Equivalent Circulating Density (ECD)

[0055] Managed Pressure Drilling (MPD)

[0056] Bottom Hole Pressure (BHP)

[0057] Bottom Hole Circulating Pressure (BHCP)

[0058] Mud Weight (MW)

[0059] The MPD advantage as seen is at under conventional drilling MPD=MW+Annulus Friction Pressure. BHP control=only pump speed and MW change, because it is an “Open to Atmosphere” system; whereas in Managed Pressure Drilling (MPD), the MPD=MW+Annulus Friction Pressure+Backpressure. BHP control=pump speed, MW change and application of back pressure, because it is an enclosed, pressured system.

[0060] In the continuous circulating concentric casing pressure management, there is provided an adaptive drilling process used to precisely control the annular pressure profile throughout the wellbore. The objectives are to ascertain the downhole pressure environment limits and to manage the annular hydraulic pressure profile accordingly. It is an objective of the system to manage BHP from a specific gravity of 1 to 1.8 utilizing clean, less than 4 microns of solids, for example, in the drilling fluid. The drilling fluid may he comprised of produced water from other field wells. Any influx incidental to the operation would be safely contained using an appropriate process.

[0061] FIG. 12 illustrates a continuous circulating concentric casing where using less than conventional mud density, the well will be stable and dynamically dead, but may be statically underbalanced.

[0062] The following is a list of parts and materials suitable for use in the present invention:

TABLE-US-00001 PARTS LIST: PART NUMBER DESCRIPTION 20 drilling rig 22 caisson 24, 26, 28 wells 29 vertical well section 30 horizontal wells 31 formation 32 lateral wells 36 water 37 produced waste water 50 face cleat fractures 60 slotted liners 70, 72 pumps 74 line 76 stand pipe 78 shale shaker 80 de-silter 82 centrifuge 90 bore 94 rig manifold 96 inner bore 98 annulus 100 perforations 102 well head 103 line from pump 72 104 inner annulus 105 t-shaped multiple

[0063] All measurements disclosed herein are at standard temperature and pressure, at sea level on Earth, unless indicated otherwise.

[0064] The foregoing embodiments are presented by way of example only; the scope of the present invention is to be limited only by the following claims.