A coalbed methane development method for increasing formation temperature and production by injecting fluid into the formation

Abstract

The present invention relates to a method for developing coalbed methane, belonging to the technical field of coalbed methane extraction, and specifically relates to a method for developing coalbed methane by injecting liquid into the formation to increase temperature and enhance production. The present invention utilizes the theory of coalbed methane cooling adsorption and high-temperature desorption, constructs 1 vertical well and 1 multi-branch horizontal well on the ground, and the two wells are connected in the coalbed methane development coal seam section; by injecting water into the vertical well, the heat of the deep high-temperature formation is transported to the development coal seam section, and the coalbed methane is desorbed at a high temperature higher than the initial condition, and is transported and produced to the ground through the main branch and branch channels of the horizontal well under the pumping action of the horizontal well; after the gas is produced, it is output through the ground collection system and utilized, and the pumped water can be used as injection water for cyclic injection. The method of the present invention establishes a low-cost and zero-pollution technology for enhancing the production of coalbed methane, and can provide an effective means for the efficient development and clean utilization of deep coalbed methane.

Description

Technical Field

[0001] The present invention relates to a method for developing coalbed methane, belonging to the technical field of coalbed methane extraction, and specifically relates to a method for developing coalbed methane by injecting liquid into the formation to increase temperature and enhance production. Background Art

[0002] In recent years, as coal mining and coalbed methane development have gradually shifted to deeper depths, the difficulty of gas control in coal mining and surface coalbed methane development has increased. With the increase in burial depth and in-situ stress, the permeability of coalbed methane reservoirs has further decreased. The current coalbed methane development technologies and gas control technologies are not fully applicable, and it is difficult to achieve the same effects as those in shallow coal seams. Summary of the Invention

[0003] The following presents a brief overview of one or more aspects to provide a basic understanding of these aspects. This overview is not an exhaustive survey of all contemplated aspects, and is neither intended to identify key or decisive elements of all aspects nor to define the scope of any or all aspects. Its sole purpose is to present some concepts of one or more aspects in a simplified form as a prelude to the more detailed description that follows.

[0004] The main objective of the present invention is to solve the above-mentioned technical problems in the prior art, and provides a method for developing coalbed methane by injecting liquid into the formation to increase temperature and enhance production. This method can reduce the high investment cost and large engineering difficulty in deep coalbed methane development. It includes:

[0005] To solve the above problems, the solution of the present invention is:

[0006] A method for developing coalbed methane by injecting liquid into the formation to increase temperature and enhance production, including:

[0007] Construct a vertical well from the ground in the coalbed methane development area. The vertical well penetrates the coal seam to be desorbed and its bottom is located in a high-temperature formation, and the temperature of the high-temperature formation is higher than that of the coal seam to be desorbed.

[0008] Construct a horizontal well in the coalbed methane development area. The horizontal section of the horizontal well communicates with the vertical well in the coal seam to be desorbed.

[0009] Inject water into the vertical well and extract gas from the horizontal well.

[0010] Preferably, the above-mentioned method for developing coalbed methane by injecting liquid into the formation to increase temperature and enhance production includes:

[0011] Create a cavity at the position of the vertical well in the coal seam to be desorbed, and when injecting water into the vertical well, make the water surface reach the cavity.

[0012] Preferably, in the above-mentioned method for developing coalbed methane by injecting liquid into the formation to increase temperature and enhance production, the horizontal section of the horizontal well is located in the coal seam to be desorbed.

[0013] Preferably, in the above-mentioned method for developing coalbed methane by injecting liquid into the formation to increase temperature and production, the temperature of the high-temperature formation is more than 30 degrees higher than the temperature of the coal seam to be desorbed.

[0014] Preferably, in the above-mentioned method for developing coalbed methane by injecting liquid into the formation to increase temperature and production, a fiberglass insulation sleeve is provided in the section of the vertical well from the high-temperature formation to the coal seam to be desorbed.

[0015] Therefore, compared with the prior art, the present invention has the following advantages: it can utilize formation thermal energy to achieve coalbed methane desorption and production in deep coalbed methane development, which on the one hand reduces the cost of reservoir transformation projects such as hydraulic fracturing and reduces pollution problems in coal reservoir transformation, and on the other hand can also efficiently utilize formation thermal energy. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The accompanying drawings, which are incorporated herein and form a part of the specification, illustrate embodiments of the present invention and, together with the description, further serve to explain the principles of the invention and to enable one skilled in the art to make and use the present disclosure.

[0017] Figure 1 Schematic diagram of the vertical wellbore structure.

[0018] Figure 2 This is a schematic diagram of the horizontal well body structure and its connection with the vertical well.

[0019] Figure 3 Schematic diagram of horizontal well pumping water and producing gas.

[0020] Figure 4 Schematic diagram of the ground gas and water collection system.

[0021] Embodiments of the present invention will be described with reference to the accompanying drawings. DETAILED DESCRIPTION

[0022] Example

[0023] Coalbed methane has the characteristics of adsorption when the temperature drops and desorption when the temperature rises. When the ambient temperature is higher than the reservoir temperature, the coalbed methane is desorbed from the coal and produced through cracks and other channels under the action of concentration difference and pressure difference. The reservoir temperature of deep coal seams is high, and the temperature of the formation below the coal seams is even higher than that of the coal seams. Therefore, the desorption capacity of deep coalbed methane is higher than that of shallow coal seams.

[0024] The first step is to obtain the stratum temperature at different burial depths in the development area based on the coalbed methane geological data and development requirements, find the adjacent high geothermal strata below the coal seam for coalbed methane development that are 30°C higher than the coal seam temperature, and determine their burial depth, ground temperature and stability.

[0025] In the second step, one vertical well is constructed from the ground. In the first drilling operation, a Φ311.15 mm bit is used to drill to a depth of 20 m below the bedrock surface and then the drilling is completed. A Φ244.5×8.94 mm surface casing is run and cemented in place. After waiting for 24 h for the cement to set and passing the pressure test, in the second drilling operation, a Φ215.9 mm bit is used for normal drilling until the depth of the adjacent high geothermal formation exceeds 10 m. A Φ177.8×9.19 mm heat-insulating casing is run to the top boundary of the high-temperature layer. Among them, fiberglass heat-insulating casings are run in the high-temperature layer and the developed coal seam section respectively, and cement is injected for cementing, with the cement slurry returning to the ground. After the cementing quality inspection and passing the pressure test, the fiberglass casings in the coal seam section and the high-temperature layer section are reamed to create a cavity with a diameter of not less than 0.50 m.

[0026] In the third step, one horizontal well is constructed from the ground. The horizontal section is drilled in the coal seam, and the length of the horizontal section is designed according to the coalbed methane production capacity requirements and economic needs, generally more than 800 m. The horizontal well adopts a three-opening wellbore structure. In the first drilling operation, a Φ444.5 mm bit is used to drill to a depth of 20 m below the bedrock surface and then the drilling is completed. A Φ339.7×9.65 mm heat-insulating surface casing is run and cemented in place. After waiting for 24 h for the cement to set and passing the pressure test, in the second drilling operation, a Φ311.15 mm bit is used for normal drilling. After drilling to the designed landing point, a Φ244.5×8.94 mm heat-insulating technical casing is run, with the top of the casing flush with the ground, and cement is injected for cementing, with the cement returning to the ground. After the second-opening casing has waited for the cement to set and passed the pressure test, in the third drilling operation, a Φ215.9 mm bit is used to drill the main branch of the horizontal section in the coal seam, and the RMRS (Rotary Magnetic Field Range Surveying Method Near Bit) technology is used to connect and communicate with the vertical well in the coal seam section. After the horizontal well is connected to the vertical well, the drill bit is lifted and then side-drilled to complete each branch. The length of each branch is generally 100 - 200 m, the angle with the main branch is 30 - 60°, the distance between the ends of each branch and the main branch exceeds 50 m, and both the main branch and the branches are completed with open holes.

[0027] In the fourth step, tubing is run in the vertical section and the build section of the horizontal well, and the extraction pump is placed at the build section.

[0028] In the fifth step, water is injected from the ground into the vertical well until the bottom of the well, and the injection is stopped after retaining the water level to the cavity position in the coal seam section.

[0029] In the sixth step, a temperature sensor is sent to the water surface in the vertical wellbore by cable. After the measured temperature has been stable and exceeded the coal seam reservoir temperature by more than 30 °C, the extraction pump of the horizontal well is used to pump water and analyze the water quality components. When the components of the produced water are basically the same as those of the injected water, the pumping speed is reduced.

[0030] In the seventh step, when bubbles are detected in the produced water, the pumping speed is implemented according to the slow, controlled, and stable regime to ensure that the coalbed methane can be fully desorbed and stably produced from the annulus between the casing and the tubing of the horizontal well.

[0031] In the eighth step, the gas extracted from the horizontal well enters the ground collection system; the pumped-out water is stored in the ground storage system and recycled as injection water when the gas production decline is obvious.

[0032] The following will elaborate on the above method in conjunction with the attached Figures 1-4 drawings.

[0033] Step 1: Sort out and analyze the geological and test data of coal and coalbed methane in the study area, with a focus on analyzing the formation classification, geological structure, geothermal gradient A, as well as the thickness t c of the developed coal seam, c burial depth h c reservoir temperature T c reservoir pressure P c gas content G,

[0034] fracture development characteristics, permeability, etc. Calculate the formation temperatures of each stratum below the coal seam based on logging, well testing measurements or geothermal gradient. Determine the position of the shallowest adjacent high-temperature formation more than 30 °C above the coal seam temperature according to formula (1). s h c = h c +(T

[0035] In the formula: h s is the burial depth of the shallowest adjacent high-temperature formation S; h c is the burial depth of the developed coal seam; T c is the reservoir temperature of the developed coal seam; A is the geothermal gradient.

[0036] The formation temperature T s of the adjacent high-temperature formation S is:

[0037] T s = T c + 30

[0038] Step 2: Construct 1 vertical well Well-v from the ground in the coalbed methane development area. Adopt a two-opening wellbore structure. In the first opening, use a Ф311.15 mm bit to drill to a depth of 20 m below the bedrock surface and complete the drilling. Run in a Ф244.5×8.94 mm surface casing and cement it. After waiting for 24 h to end and passing the pressure test, use a Ф215.9 mm bit to drill conventionally in the second opening to a depth more than 10 m beyond the depth of the adjacent high-temperature formation S. Run in a Ф177.8×9.19 mm heat-insulating casing to the top boundary of the S layer. Among them, run in a fiberglass heat-insulating casing in the S layer and the C section of the developed coal seam, inject cement (usually G-grade cement) and cement it. The cement slurry returns to the ground. After the cementing quality inspection and passing the pressure test, ream and create a cavity in the fiberglass casing of the S layer and the coal seam section, creating a cavity with a diameter of not less than 0.50 m (see attached Figure 1 drawings).

[0039] Step 3: At a certain distance (designed according to the actual requirements of coalbed methane development, generally more than 800 m) from the vertical well Well-v, one horizontal well Well-h is constructed on the ground. The horizontal section is drilled in the coal seam C. The length of the horizontal section is designed according to the coalbed methane production capacity requirements and economic demands, generally more than 800 m. Well-h uses a three-opening wellbore structure. In the first opening, a Φ444.5 mm bit is used to drill to 20 m below the bedrock surface and then completed. A Φ339.7×9.65 mm thermal insulation surface casing is run and cemented. After waiting for 24 h for setting and passing the pressure test, a Φ311.15 mm bit is used for the second opening for conventional drilling. After reaching the designed landing point, a Φ244.5×8.94 mm thermal insulation technical casing is run. The top of the casing is flush with the ground, and cement (generally G-grade cement) is injected for cementing, and the cement returns to the ground. After the setting of the second-opening casing and passing the pressure test, a Φ215.9 mm bit is used for the third-opening main branch drilling in the coal seam, and the RMRS (Near Bit Rotary Magnetic Field Ranging Method) technology is used to connect and communicate with Well-v in the coal seam section. After Well-h and Well-v are connected and communicated, the drill is lifted and then side-drilled to complete each branch. The number of branches is set according to the length of the main branch, and they are arranged staggered on both sides of the main branch. The length of each branch is generally 100 - 200 m, and the angle with the main branch is generally 30 - 60°. The distance of each branch from the main branch end should exceed 50 m. Both the main branch and the branches use open-hole completion (refer to the attachment Figure 2 ).

[0040] Step 4: Tubing is run into the vertical section and the build section of Well-h, and the extraction pump is placed at the build section position (refer to the attachment Figure 3 ).

[0041] Step 5: Water (generally active water, or surface water nearby after impurity treatment) is injected from the ground into Well-v until the bottom of the well, and the water injection is stopped after retaining the water surface to the cavitation position in the C coal seam section (refer to the attachment Figure 3 ).

[0042] Step 6: The temperature sensor is transported to the water surface in the Well-v wellbore by cable. After the measured temperature is stable and exceeds the coal seam reservoir temperature by more than 30 °C, the extraction pump in Well-h is used to pump water from the tubing, and the water quality components are analyzed when the color or concentration of the visible water changes. When the produced water components are basically the same as the injected water, the pumping speed is reduced (refer to the attachment Figure 3 ).

[0043] Temperature measurement range of the temperature sensor: 20 °C - 150 °C. In the figure, blue represents water and red represents gas.

[0044] Step 7, when bubbles appear in the produced water of Well-h, implement a slow, controlled, and stable drainage system (generally, the water surface drops by no more than 0.5 m per day) to ensure that the coalbed methane within the drilling range can be fully desorbed and stably produced from the annulus between the casing and tubing of Well-h (refer to the appendix Figure 4 ).

[0045] Step 8, store the produced gas from the annulus between the tubing and casing in the surface storage system, transport and utilize it. The extracted water can be temporarily stored in the surface water storage tank and, when the gas production of Well-h significantly declines, be recycled as the injection water for Well-v (refer to the appendix Figure 4 ).

[0046] The coalbed methane development method of formation liquid injection for temperature increase and production increase proposed in this embodiment can utilize formation thermal energy to achieve the desorption and production of coalbed methane in the development of deep coalbed methane. On the one hand, it reduces the engineering costs of reservoir stimulation projects such as hydraulic fracturing and reduces the pollution problems during the transformation of coal reservoirs. On the other hand, it can also efficiently utilize formation thermal energy. The main manifestations are as follows:

[0047] The temperature of the deep formation is high. For the high-temperature formation that meets the conditions below the coal seam depth, the vertical well drilling difficulty is small and the investment cost is low, which has basically no impact on the development of coalbed methane;

[0048] The technology combining the design of multi-branch horizontal wells with high-temperature enhanced desorption and production avoids the pollution and damage to the coal reservoir caused by processes such as hydraulic fracturing stimulation, and reduces the engineering difficulty and cost;

[0049] The technology combining the design of multi-branch horizontal wells with high-temperature enhanced desorption and production can ensure the stable gas production of coalbed methane wells and achieve the green and clean utilization of coalbed methane resources.

[0050] Note that the references in the specification to "one embodiment", "an embodiment", "an exemplary embodiment", "some embodiments", etc. indicate that the described embodiments may include specific features, structures, or characteristics, but each embodiment may not necessarily include the specific features, structures, or characteristics. Moreover, such phrases do not necessarily refer to the same embodiment. In addition, when a specific feature, structure, or characteristic is described in connection with an embodiment, whether or not explicitly described, implementing such a feature, structure, or characteristic in combination with other embodiments will be within the knowledge of those skilled in the art.

[0051] The foregoing description of the present disclosure is provided to enable any person skilled in the art to make or use the present disclosure. Various modifications to the present disclosure will be apparent to those skilled in the art, and the general principles defined herein can be applied to other variations without departing from the spirit or scope of the present disclosure. Thus, the present disclosure is not intended to be limited to the examples and designs described herein, but should be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for developing coalbed methane by injecting liquid into the formation to increase temperature and production, characterized in that, Comprising: Construct a vertical well from the ground in the coalbed methane development area, the vertical well passing through the coal seam to be analyzed and having its bottom located in a high-temperature formation, the temperature of the high-temperature formation being more than 30 degrees higher than the temperature of the coal seam to be analyzed; Construct a horizontal well in the coalbed methane development area, the horizontal section of the horizontal well communicating with the vertical well within the layer to be analyzed; the horizontal section of the horizontal well being located in the coal seam to be analyzed; Inject water into the vertical well and extract the analyzed gas from the horizontal well, specifically by using an oil pipe to extract the injected water from the horizontal well and extracting the desorbed gas from the annulus between the oil pipe and the casing provided inside the horizontal well.

2. The coalbed methane development method for increasing formation temperature and production by injecting liquid into the formation according to claim 1, characterized in that, Comprising: Create a cavity at the position of the vertical well where it is located in the coal seam to be analyzed, and when injecting water into the vertical well, make the water surface reach the cavity-created position.

3. The coalbed methane development method for increasing formation temperature and production by injecting liquid into the formation according to claim 1, characterized in that, Install a fiberglass insulation sleeve in the section of the vertical well from the high-temperature formation to the coal seam to be analyzed.

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