Coal bed gas superimposed multi-lateral horizontal well row mining method

Abstract

The application discloses a coal bed gas superposition multi-branch horizontal well row mining method, which comprises the following steps: S1, adopting the way of circulating water injection and pressure control drainage to the coal reservoir of the coal bed gas superposition multi-branch horizontal well, and discharging the residual fracturing fluid and coal powder particles in the coal reservoir; S2, performing rapid drainage pressure reduction on the coal reservoir treated by the step S1, so that the gas production of the coal reservoir reaches a peak value; S3, after the gas production of the coal reservoir reaches the peak value, the way of slow drainage pressure control is adopted to maintain the stable and high gas production duration; S4, when the production of the coal bed gas superposition multi-branch horizontal well reaches the middle and later stages and the gas production is reduced, the way of circulating water injection and continuous water injection is adopted to stimulate the coal reservoir, and the coal powder generated by the stimulation is discharged from the wellbore; and S5, the way of pressure control drainage is adopted to restore the production of the coal reservoir treated by the stimulation, so that the gas production of the coal bed gas superposition multi-branch horizontal well can be improved without consuming other water, the service life of the coal bed gas well is prolonged, and the economic benefit is improved.

Description

Technical Field

[0001] This invention relates to the field of coalbed methane production, and in particular to a method for producing coalbed methane using multi-branch horizontal wells. Background Technology

[0002] Due to factors such as high regional geostress, poor coal seam permeability, and weak water-bearing properties of coal strata, the geological conditions for coalbed methane development are complex. Simply adopting the traditional drainage and depressurization development method makes it difficult for the reservoir pressure drop funnel to expand, resulting in rapid gas production decline and short service life of coalbed methane wells. This leads to a high proportion of low-yield and inefficient wells in the current coalbed methane development process. Summary of the Invention

[0003] To address the aforementioned problems, this invention provides a method for draining coalbed methane using multi-branch horizontal wells, which can effectively improve the problems of rapid gas production depletion, poor economic benefits, and high environmental pollution risks associated with traditional drainage and depressurization mining methods, and can effectively increase production.

[0004] The technical solution of this invention is: The coalbed methane production method using multi-branch horizontal wells includes the following steps: S1. For coal reservoirs in multi-branch horizontal wells with coalbed methane stacks, use circulating water injection and pressure-controlled drainage to remove residual fracturing fluid and coal dust particles from the coal reservoir. S2. Rapidly drain and depressurize the coal reservoir after the treatment in step S1 so that the gas production of the coal reservoir reaches the peak gas production. S3. After the gas production of the coal reservoir reaches its peak, a slow drainage and pressure control method is used to maintain a stable high gas production for a longer period of time. S4. When the gas production of a multi-branch horizontal well with superimposed coalbed methane reaches the middle and late stage and the gas production decreases, the coal seam is stimulated by circulating water injection and continuous drainage, and the coal powder generated by the stimulation is discharged from the wellbore. S5. The coal seam that has undergone the excitation treatment in step S4 is restored to its production capacity by pressure-controlled drainage.

[0005] In step S1, the water flow velocity for circulating water injection and pressure-controlled drainage is 34.16 × 10⁻⁶. -3 In step S2, the water flow velocity for rapid drainage and pressure reduction is 50 × 10 m / s. -3 In step S3, the water flow velocity for slow drainage and pressure control is 5 × 10 m / s. -3 In step S4, the water flow rate for circulating water injection is 20 × 10 m / s. -3 m / s and 40×10 -3 The alternating flow rate of water at m / s and the continuous drainage flow velocity is 34.16 × 10⁻⁶ m / s. -3 In step S5, the water flow velocity for pressure-controlled drainage is 50 × 10 m / s.-3 m / s.

[0006] The specific method for step S1 is as follows: 1) A continuous and stable drainage rate is used to transfer water in the coal reservoir to a sedimentation tank; 2) Water from the coal reservoir that has undergone sedimentation treatment in the sedimentation tank is injected into the coal reservoir at a continuous and stable injection rate for a period of 20-30 days.

[0007] Step S2 lasts for 230-250 days.

[0008] The duration of step S3 shall not be less than 500 days.

[0009] Step S4 lasts for 10-15 days.

[0010] Step S5 lasts for 150-180 days.

[0011] In the drainage method, a jet pump is used for drainage and a circulating liquid injection pump is used for water injection.

[0012] The beneficial effects of this invention are: This method can improve the problems of rapid gas production decline, poor economic efficiency, and high environmental pollution risk in multi-branch horizontal wells with coalbed methane under traditional drainage and depressurization mining methods. By re-injecting the produced water from the coal seam into the coal reservoir, the reservoir is stimulated, significantly expanding and extending the gas-liquid seepage channels within the well control area and improving the permeability of the coal reservoir. Furthermore, continuous drainage at a certain rate washes away and carries the coal dust generated during the stimulation process in the wellbore and coal reservoir to the sedimentation tank, which can improve the conductivity of fractures in the target coal seam, promote gas-liquid seepage production, and increase coalbed methane production. Circulating water injection can effectively reduce water waste, lower environmental pollution risks, and reduce engineering implementation costs, resulting in good economic, environmental, and social benefits. Attached Figure Description

[0013] Figure 1 This is a flowchart of the coalbed methane stacked multi-branch horizontal well drainage method according to an embodiment of the present invention; Figure 2 This is a schematic diagram of the coal seam in the coalbed methane stacked multi-branch horizontal well drainage method described in the embodiments of the present invention; Figure 3 This is a system diagram of the coalbed methane stacked multi-branch horizontal well drainage method described in the embodiments of the present invention. Detailed Implementation

[0014] The embodiments of the present invention will be further described below with reference to the accompanying drawings.

[0015] Example: like Figures 1-3As shown, the coalbed methane production method using multi-branch horizontal wells includes the following steps: S1. For coal reservoirs in multi-branch horizontal wells with coalbed methane stacks, use circulating water injection and pressure-controlled drainage to remove residual fracturing fluid and coal dust particles from the coal reservoir. The jet pump is started to lift water from the coal reservoir to the surface settling tank at a continuous and stable drainage rate. Then, the circulating fluid injection pump is started to inject the produced water from the settling tank back into the coal reservoir at a continuous and stable injection rate. During this process, the fracturing fluid and coal dust remaining in the coal reservoir are carried to the settling tank along with the produced water, improving the reservoir's conductivity. The circulating water injection and pressure-controlled drainage phase begins at the start of injection and ends at the stop of injection. First, the jet pump is started at a rate of 34.16 × 10⁻⁶. -3 The wastewater is continuously and stably drained into the sedimentation tank at a drainage rate of m / s. Then, the circulating liquid injection pump is activated to pump the settled effluent from the sedimentation tank at a rate of 34.16 × 10⁻⁶ m / s. -3 The water is continuously and stably injected into the coal reservoir at an injection rate of m / s, and this stage generally lasts for 20-30 days.

[0016] S2. Rapidly drain and depressurize the coal reservoir after the treatment in step S1 so that the gas production of the coal reservoir reaches the peak gas production. The circulating fluid injection pump is shut off to stop further water injection into the coal reservoir. The jet pump increases the drainage rate, the annular fluid level slowly decreases, and the annular pressure gradually rises to its upper limit. The daily gas production of the subsequent coalbed methane stacked multi-branch horizontal well reaches a relatively stable state. The rapid drainage, pressure reduction, and production increase phase begins at the injection cessation point and ends at the stable production point. The circulating fluid injection pump is shut off to stop further water injection into the coal reservoir, and the jet pump increases the drainage rate to 50 × 10⁻⁶. -3 m / s, at which point the fluid level in the casing annulus slowly decreases, and the casing annulus pressure begins to appear, gradually increasing to the upper limit. During this process, coalbed methane is continuously produced. The daily gas production of the multi-branch horizontal well with coalbed methane stacks gradually increases and reaches a relatively stable state. This stage generally lasts for 230-250 days.

[0017] S3. After the gas production of the coal reservoir reaches its peak, a slow drainage and pressure control method is used to maintain a stable high gas production for a longer period of time. Reduce the jet pump drainage rate to control the annular fluid level in the casing and gradually decrease it, avoiding large fluctuations. Control the annular pressure in the casing slightly below its upper limit to prolong the period of stable high daily gas production in the multi-branch horizontal well for coalbed methane. The slow drainage and pressure control stabilization phase begins at the stabilization point and ends at the injection start point. First, reduce the jet pump drainage rate to 5×10 -3m / s, control the annular fluid level of the casing to decrease slowly and steadily, and avoid large fluctuations; control the annular pressure of the casing to be slightly lower than its upper limit, and try to prolong the period of stable high daily gas production of multi-branch horizontal wells with coalbed methane stacked, which is generally not less than 500 days.

[0018] S4. When the gas production of a multi-branch horizontal well with superimposed coalbed methane reaches the middle and late stage and the gas production decreases, the coal seam is stimulated by circulating water injection and continuous drainage, and the coal powder generated by the stimulation is discharged from the wellbore. In the middle and late stages of coalbed methane production from multi-branch horizontal wells, daily gas production gradually decreases to 60% of peak production. The circulating fluid injection pump is activated to reinject produced water from the settling tank into the wellbore at a pulsating injection rate, stimulating the coal reservoir. The jet pump's drainage rate is increased to discharge water from the wellbore into the settling tank. This circulating injection and continuous drainage stimulation phase begins at the start of injection and ends at the stop of injection. As the daily gas production of the multi-branch horizontal well gradually decreases to 60% of peak production, the circulating fluid injection pump is activated to inject produced water from the settling tank at a rate of 40 × 10⁻⁶. -3 The water was re-injected into the coal reservoir at an injection rate of m / s, and after 5 minutes the injection rate was adjusted to 20 × 10 m / s. -3 m / s, and after another 5 minutes, adjust the water injection speed again to 40×10 m / s. -3 m / s, 1800 water injection cycles, the fluid level in the annulus of the casing rises to the wellhead; increase the jet pump drainage velocity to 34.16×10 -3 The pump continuously and stably discharges water from the wellbore to the sedimentation tank at a speed of m / s. Because the injection rate of the circulating fluid injection pump is periodically higher than the drainage rate of the jet pump, the pressure in the wellbore also fluctuates with the injection rate of the circulating fluid injection pump, thus stimulating the coal reservoir. Most of the coal dust generated during this stimulation process is within the range of 34.16 × 10⁻⁶ m / s. -3 Under drainage velocity conditions of m / s, the coal will be lifted to the sedimentation tank, and the seepage capacity of the coal reservoir will be greatly improved. This stage generally lasts for 10-15 days.

[0019] S5. The coal seam that has undergone the excitation treatment in step S4 is restored to its production capacity by pressure-controlled drainage.

[0020] The circulating fluid injection pump is shut down, ceasing further water injection into the coal reservoir. The annular fluid level in the casing is at a high level. Increasing the jet pump drainage rate causes the annular fluid level to drop, and the annular pressure gradually increases. The daily gas production of the subsequent coalbed methane-stabilized multi-branch horizontal well returns to a high and stable state. The controlled-pressure drainage recovery phase begins at the injection cessation point and ends at the high-production recovery point. The circulating fluid injection pump is then shut down; at this point, the annular fluid level in the casing is still high, and the jet pump drainage rate is increased to 50 × 10⁻⁶. -3The flow rate reaches m / s, and continuous and stable drainage begins. The annular fluid level in the casing decreases accordingly, and the annular pressure gradually increases. Subsequently, the daily gas production of the multi-branch horizontal well with coalbed methane stacks returns to a relatively stable state. This stage generally lasts for 150-180 days.

[0021] The embodiments described above are merely illustrative of specific implementations of the present invention, and while the descriptions are detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A method for producing coalbed methane using multi-branch horizontal wells, characterized in that, Includes the following steps: S1. For coal reservoirs in multi-branch horizontal wells with coalbed methane stacks, use circulating water injection and pressure-controlled drainage to remove residual fracturing fluid and coal dust particles from the coal reservoir. S2. Rapidly drain and depressurize the coal reservoir after the treatment in step S1 so that the gas production of the coal reservoir reaches the peak gas production. S3. After the gas production of the coal reservoir reaches its peak, a slow drainage and pressure control method is used to maintain a stable high gas production for a longer period of time. S4. When the gas production of a multi-branch horizontal well with superimposed coalbed methane reaches the middle and late stage and the gas production decreases, the coal seam is stimulated by circulating water injection and continuous drainage to discharge the coal powder generated by the stimulation from the wellbore. S5. The coal seam that has undergone the excitation treatment in step S4 is restored to its production capacity by pressure-controlled drainage.

2. The coalbed methane production method using multi-branch horizontal wells according to claim 1, characterized in that, In step S1, the water flow velocity for circulating water injection and pressure-controlled drainage is 34.16 × 10⁻⁶. -3 In step S2, the water flow velocity for rapid drainage and pressure reduction is 50 × 10 m / s. -3 In step S3, the water flow velocity for slow drainage and pressure control is 5 × 10 m / s. -3 In step S4, the water flow rate for circulating water injection is 20 × 10 m / s. -3 m / s and 40×10 -3 The alternating flow rate of water at m / s and the continuous drainage flow velocity is 34.16 × 10⁻⁶ m / s. - 3 In step S5, the water flow velocity for pressure-controlled drainage is 50 × 10 m / s. -3 m / s.

3. The coalbed methane production method using multi-branch horizontal wells according to claim 1, characterized in that, The specific method for step S1 is as follows: 1) A continuous and stable drainage rate is used to transfer water in the coal reservoir to a sedimentation tank; 2) Water from the coal reservoir that has undergone sedimentation treatment in the sedimentation tank is injected into the coal reservoir at a continuous and stable injection rate for a period of 20-30 days.

4. The coalbed methane production method using multi-branch horizontal wells according to claim 1, characterized in that, Step S2 lasts for 230-250 days.

5. The coalbed methane production method using multi-branch horizontal wells according to claim 1, characterized in that, The duration of step S3 shall not be less than 500 days.

6. The coalbed methane production method using multi-branch horizontal wells according to claim 1, characterized in that, Step S4 lasts for 10-15 days.

7. The coalbed methane production method using multi-branch horizontal wells according to claim 1, characterized in that, Step S5 lasts for 150-180 days.

8. The coalbed methane production method using multi-branch horizontal wells according to any one of claims 1-6, characterized in that, In the drainage method, a jet pump is used for drainage and a circulating liquid injection pump is used for water injection.

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