A WELL SYSTEM

Abstract

A well system comprising at least one gas well extending from a ground surface into the ground, a water production well extending from a surface into the ground and a water drainage well fluidly connecting the at least one gas well to the water production well.

Claims

1. A well system comprising: at least one gas well extending from a ground surface into the ground; a water production well extending from a surface into the ground; and a water drainage well fluidly connecting the at least one gas well to the water production well, wherein the water drainage well is not drilled into a coal seam.

2. The well system as claimed in claim 1, wherein the water production well comprises a pump towards a lower end thereof to pump liquid in the water production well to the surface.

3. The well system as claimed in claim 1, wherein each of the at least one gas well intersects a coal seam.

4. The well system as claimed in claim 3, wherein each of the at least one gas well is cased.

5. The well system as claimed in claim 4, wherein each of the at least one gas wells is cased in a steel casing.

6. The well system as claimed in claim 4, wherein each of the casings has perforations where the casing intersects the coal seam to enable gas and water from the coal seam to flow into each respective gas well.

7. The well system as claimed in claim 1, wherein each of the at least one gas well is a vertical gas well.

8. The well system as claimed in claim 1, wherein each of the at least one gas well has a wireline entry guide.

9. The well system as claimed in claim 1, wherein the water production well is a vertical water production well.

10. The well system as claimed in claim 1, wherein the water production well is a deviated water production well.

11. The well system as claimed in claim 1, wherein the water production well is used to convey gas from an annulus between a casing of the water production well and tubing located within the water production well to the surface.

12. The well system as claimed in claim 1, wherein the water drainage well fluidly connects a lower portion of each of the at least one gas well to a lower portion of the water production well.

13. The well system as claimed in claim 1, wherein the water drainage well is inclined to assist the flow of water from the at least one gas well to the water production well.

14. The well system as claimed in claim 1, wherein the water drainage well intersects each of the at least one gas well.

15. The well system as claimed in claim 1, wherein the water drainage well is lined and the liner is perforated in proximity to each of the at least one gas well such that each corresponding gas well is fluidly connected to the water drainage well.

16. The well system as claimed in claim 1, wherein the water drainage well is open to a lower portion of the water production well.

17. A method of forming a well system comprising the steps of: providing at least one gas well extending from a ground surface into the ground; drilling a water production well from a surface into the ground; drilling a water drainage well such that the water drainage well fluidly connects a lower portion of each of the at least one gas well to a lower portion of the water production well; and providing a pump in the lower portion of the water production well, wherein the water drainage well is not drilled into a coal seam.

18. A method as claimed in claim 17, wherein the step of drilling a water drainage well such that the water drainage well fluidly connects a lower portion of each of the at least one gas well to a lower portion of the water production well involves drilling the water drainage well from a lower portion of one of the at least one gas well into a lower portion of the water production well.

19. A method as claimed in claim 17, wherein the step of providing at least one gas well extending from a ground surface into the ground includes the step of removing a pump and associated tubing from each of the at least one gas well.

20. The well system as claimed in claim 1, wherein the well system is a coal bed methane well system.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0033] To assist in understanding the invention and to enable a person skilled in the art to put the invention into practical effect, preferred embodiments of the invention will be described by way of example only with reference to the accompanying drawings, wherein:

[0034] FIG. 1 shows a schematic view of a well system according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0035] With reference to FIG. 1, there is shown a CBM well system 100. The CBM well system 100 has gas wells 110, 112 that extend from a surface 12 into the ground and into coal seams 14. A water production well 114 extends from the surface 12 into the ground.

[0036] A water drainage well 116 fluidly connects the gas wells 110,112 to the water production well such that water (water flow indicated by arrows 18) can flow from the gas wells 110,112 through the water drainage well 116 and into the water production well 114. In the water production well 114, water is pumped by a pump 118 through tubing 120 to the surface 12.

[0037] Gas wells 110,112 are drilled from the surface 12 through coal seam 14. The gas wells each have a casing 122. The casings have perforations 124 adjacent the coal such that the gas (gas flow indicated by arrows 16) and the water in the coal seam can flow into the gas wells 110,112.

[0038] Gas wells 110,112 have wireline entry guides 126 fitting on the ends of tubing strings 128. The wireline entry guides 126 assist with the retrieval of reservoir surveillance tools (not shown) when they are pulled upwards towards the well head 130.

[0039] The water drainage well 116 is drilled from a lower portion of the gas well 110 and into the water production well 114. The water drainage well 116 also intersects the gas well 112. The casing 122 of gas well 112 does not extend to the bottom of gas well 112, instead it stops just above the water drainage well 116. In this manner, the drilling of the water drainage well is not impeded by the casing 122 of gas well 112. The water drainage well 116 has a liner 132 that is attached to the lower portion of the gas well 110. The liner 132 has perforations 134 where the water drainage well 116 intersects the gas well 112 such that water can flow from the gas well 112 into the water drainage well 116.

[0040] The water production well 114 is drilled from the surface 12 into the ground. The water production well 114 has a casing 136. The casing 136 is open to the water drainage well 116 such that water can flow from the water drainage well 116 into a lower portion of the water production well 114 where the pump 118 is located, which pumps the water through the tubing 120 to the well head 138 on the surface 12.

[0041] As can be seen from FIG. 1, because water flows through the water drainage well 116 and into the water production well 114, the gas wells 110,112 do not have water pumps disposed therein. A benefit of this is that reservoir surveillance activities are not obstructed in the gas wells. Additional benefits include a reduction in capital expenditure and operating costs, an improvement in vertical flow performance of the gas wells due to a larger effective cross section for gas flow, improved operational times due to less pumps to maintain and operate, and an improved pressure drawdown on the coal reservoir resulting in higher production rates and lower abandonment pressures.

[0042] Although it is counterintuitive, as the present invention requires more wells to be drilled than the prior art, there are advantages, as mentioned above, in having a water drainage well and a water production well.

[0043] The foregoing embodiments are illustrative only of the principles of the invention, and various modifications and changes will readily occur to those skilled in the art. The invention is capable of being practiced and carried out in various ways and in other embodiments. It is also to be understood that the terminology employed herein is for the purpose of description and should not be regarded as limiting.

[0044] In the present specification and claims (if any), the word “comprising” and its derivatives including “comprises” and “comprise” include each of the stated integers but does not exclude the inclusion of one or more further integers unless the context of use indicates otherwise.