Foam well washing method for low-liquid-yield coal-bed gas well

Abstract

The invention discloses a foam well washing method for a low-liquid-yield coal-bed gas well. The foam well washing method comprises the following steps that S1, equipment needed for well washing is prepared; s2, a well washing pipe column is tripped into a coal bed gas shaft; s3, checking the sealing performance of the equipment; s4, continuous foam flushing is conducted in the gas well; and S5, degassing with clean water and pulling out the well washing pipe string. According to the method, a certain amount of high-concentration well flushing fluid is used firstly, foam blocking is formed near a shaft, and then low-concentration well flushing fluid is used for well flushing operation. Due to the concentration difference, the well washing fluid cannot enter the stratum to cause leakage, so that circulating and efficient well washing is established. Clear water and a defoaming agent are adopted to circulate a wellbore after foam well washing, the wellbore is cleaned, and the stratum is dredged.

Description

Technical Field

[0001] The invention relates to the technical field of oil well flushing, in particular to a foam well flushing method for a low-liquid-yield coalbed methane well. Background Art

[0002] Foam drilling is an underbalanced drilling technique that uses stable foam as the circulating medium. Foam fluid is a mixed phase fluid composed of a foaming base fluid (surfactant solution) and gas. Its low density and hydrostatic pressure significantly minimize or avoid reservoir damage, while also achieving high rates of penetration and reducing soak time. Foam has a high cuttings-carrying capacity and low axial pressure, significantly preventing repeated fragmentation of cuttings and significantly improving drill bit operating conditions, thereby significantly extending drill bit life. Furthermore, foam drilling offers significant advantages over conventional mud drilling in terms of oil and gas visualization and reducing engineering accidents.

[0003] During oil and gas field production, as oil and gas are continuously produced, sand and scale build up in the well, gradually decreasing formation pressure. When formation pressure falls below the hydrostatic pressure, conventional workover fluids cannot establish wellbore circulation, resulting in low workover efficiency and poor safety. Furthermore, some solid particles carried by the workover fluid can leak into the formation, damaging the oil and gas reservoirs. Using foam as a well-washing fluid can avoid these problems associated with conventional workover fluids.

[0004] For coalbed methane low-yield wells, the formation will be depleted in the later stage of liquid production. When the conventional well washing method is used to establish circulation, the well washing fluid will leak into the formation, which can easily cause the following two difficulties: (1) The well washing fluid leaks out and the surface pump pressure of the formation drops, making it difficult to establish circulation in the wellbore. Some fracturing sand is brought into the formation and cannot be circulated and discharged to the surface, making it impossible to effectively wash the well. Moreover, the fracturing sand that enters the formation near the wellbore will be produced again with the production, greatly reducing the well washing effect; (2) The large amount of well washing fluid leakage will greatly pollute the formation near the wellbore. Since the well washing fluid is doped with chemical reagents and is in a foamy state, and the coal seam rocks are mostly hydrophilic, after a large amount of well washing fluid enters the near-wellbore area, a gas-water two-phase gas-water drive process will occur in the pores of the near-wellbore formation. At this time, under the action of capillary force and the Jamin effect, some gas will be sealed in the pore capillaries and difficult to remove, affecting the later production of the gas well. Summary of the Invention

[0005] In order to solve the above problems, the present invention provides a foam well washing method for low-liquid-yield coalbed methane wells, comprising the following steps: S1. preparing the equipment required for well washing; S2. lowering the well washing pipe string into the coalbed methane wellbore; S3. checking the sealing of the equipment; S4. continuously foam flushing the gas well; S5. degassing with clean water and removing the well washing pipe string.

[0006] Furthermore, the step S1 specifically includes the following sub-steps: S11. Setting up well-washing equipment at the well site and pulling out the original well production string; S12. Calculating the wellbore volume and preparing well-washing fluid; S13. Connecting the well-washing equipment and establishing a well-washing fluid circulation.

[0007] Furthermore, the well washing equipment specifically includes: a pump truck, a foam generator, an oil-casing annulus, a well washing string, a nitrogen-generating vehicle group, a derrick hanging weight meter, a vertical derrick, a liquid storage tank, and a sedimentation tank; wherein the oil-casing annulus is arranged on the periphery of the well washing string.

[0008] Furthermore, the well washing fluid circulation in step S13 is specifically as follows: the well washing fluid in the liquid storage tank and the nitrogen generated by the nitrogen generating vehicle are injected into the foam generator by a pump truck to generate nitrogen foam well washing fluid, which is injected from the oil casing annulus and then returned from the well washing string.

[0009] Furthermore, the preparation of the well washing fluid in step S12 specifically includes: preparing 1.5-2 times the volume of the wellbore well washing fluid, adding required chemical reagents thereto and stirring and dissolving them fully; the chemical reagents specifically include: potassium chloride, a foaming agent, and a foam stabilizer.

[0010] Furthermore, the step S2 specifically includes the following sub-steps: S21. lowering the well-washing string into the coalbed methane wellbore; S22. slowing down the lowering speed when the top of the well-washing string is 20 meters away from the coal seam; S23. checking the hanging weight of the derrick.

[0011] Furthermore, the S23 step specifically includes: when the hanging weight drops, it indicates that a sand surface is encountered, the exact position of the sand surface is repeatedly re-explored, and the well washing pipe string is lifted to 5 meters above the sand surface; when the hanging weight increases sharply, it indicates that the friction resistance of the well washing pipe string increases abnormally, and the lowering of the well washing pipe string is stopped.

[0012] Furthermore, the step S4 specifically includes the following sub-steps: S41. Installing a plug valve on the well-washing string joint to control the outflow of the well-washing fluid; S42. Slowly and uniformly lowering the well-washing string into the gas well and observing the hanging weight of the derrick; S43. Adjusting the density of the well-washing fluid to form a negative pressure to remove blockage and flush the gas well.

[0013] Furthermore, the method also includes a defoaming treatment step: after completing the well washing operation, adding a defoaming agent on the ground for defoaming treatment; if foam continues to return from the gas wellhead, adding a defoaming agent into the gas well for defoaming treatment.

[0014] The present invention provides a foam well washing method for a low-liquid-yield coalbed methane well, which has the following beneficial effects: This method first uses a fixed amount of high-concentration well-washing fluid to form a foam barrier near the wellbore, followed by a low-concentration well-washing fluid for the wash operation. Due to the concentration difference, the well-washing fluid will not enter the formation and cause losses, thus establishing a cyclic and efficient well-washing system. After the foam wash, clean water and defoaming agent are circulated through the wellbore to clean the wellbore and unclog the formation. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying any creative work.

[0016] Figure 1 The present invention provides a flow chart of the method. DETAILED DESCRIPTION

[0017] It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0018] The following describes the implementation method of the present invention in detail with reference to the accompanying drawings. The description only includes some embodiments, not all embodiments. For the purpose of clarity, representations and descriptions that are not related to the present invention are omitted in the drawings and descriptions.

[0019] In order to have a clearer understanding of the technical features, purposes and beneficial effects of the present invention, the technical solutions of the present invention are now described in detail below. Obviously, the implementation cases described are part of the embodiments of the present invention, not all of them, and should not be understood as limiting the scope of the implementation of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0020] like Figure 1 As shown, the present invention provides a foam well washing method for low-liquid-yield coalbed methane wells, comprising the following steps: S1. preparing equipment required for well washing; S2. lowering the well washing string into the coalbed methane wellbore; S3. checking the sealing of the equipment; S4. continuously foam washing the gas well; S5. performing clean water degassing and removing the well washing string.

[0021] Among them, step S1 specifically includes the following sub-steps: S11. Setting up well-washing equipment at the well site and pulling out the original well production string; S12. Calculating the wellbore volume and preparing well-washing fluid; S13. Connecting the well-washing equipment and establishing well-washing fluid circulation.

[0022] The well washing equipment specifically includes: a pump truck, a foam generator, an oil-casing annulus, a well washing string, a nitrogen-generating vehicle group, a derrick hanging weight meter, a vertical derrick, a liquid storage tank, and a sedimentation tank; wherein the oil-casing annulus is arranged on the periphery of the well washing string.

[0023] The well washing fluid circulation in step S13 is specifically as follows: the well washing fluid in the liquid storage tank and the nitrogen generated by the nitrogen generating vehicle are injected into the foam generator by a pump truck to generate nitrogen foam well washing fluid, which is injected from the oil casing annulus and then returned from the well washing string.

[0024] The preparation of the well washing fluid in step S12 specifically includes: preparing 1.5-2 times the volume of the wellbore of well washing fluid (if the formation is depleted, preparing 2-3 times the volume of the wellbore of well washing fluid), adding the required chemical reagents thereto, and stirring and dissolving them thoroughly; the chemical reagents specifically include: potassium chloride, a foaming agent, and a foam stabilizer.

[0025] Step S2 specifically includes the following sub-steps: S21. Lowering the well-washing string into the coalbed methane wellbore; S22. Slowing down the lowering speed when the top of the well-washing string is 20 meters away from the coal seam; S23. Checking the hanging weight of the derrick.

[0026] Among them, step S23 specifically includes: when the hanging weight drops, it indicates that a sand surface is encountered, the exact position of the sand surface is re-explored multiple times, and the well washing pipe string is lifted to 5 meters above the sand surface; when the hanging weight increases sharply, it indicates that the friction resistance of the well washing pipe string increases abnormally, and the lowering of the well washing pipe string is stopped.

[0027] The specific steps in step S3 are: closing the wellhead gate valve, starting the pump truck for pressurization, and checking the pressure-bearing capacity of each component of the ground process to ensure there is no leakage.

[0028] Step S4 specifically includes the following sub-steps: S41. Install a plug valve on the well-washing string joint to control the outflow of the well-washing fluid; S42. Slowly and evenly lower the well-washing string into the gas well and observe the hanging weight of the derrick; S43. Adjust the density of the well-washing fluid to create negative pressure to remove blockage and flush the gas well.

[0029] Step S5 specifically involves: After the foam flush is complete, inject 1.5 times the wellbore volume of clean water to displace the foaming fluid in the wellbore to the surface. If foam continues to return from the wellhead, add an appropriate amount of defoamer and continue flushing until the inlet and outlet water colors are consistent. Shut down the pump truck, remove the well-flushing operation string, and dismantle the surface process.

[0030] In the above steps, first, a 5%-10% foaming agent ratio is used to prepare the well washing fluid, and it is injected about X square meters (the directional well will inject the pre-foam to 10 meters above the uppermost coal seam, and the horizontal well will inject it to 10 meters above the A target reservoir), forming a high-concentration bubble near the gas well to temporarily block the formation and prevent the well washing fluid from leaking. Secondly, a 3‰-5‰ foaming agent ratio is used to prepare the well washing fluid and establish a circulating well washing. After completing the foam well washing operation, add a defoaming agent on the ground for defoaming treatment. If there is continuous foam returning from the wellhead, an appropriate amount of defoaming agent can be added to the wellbore for defoaming treatment to improve the pumping and drainage efficiency of the coalbed methane well machine. (When the well washing fluid is prepared in the above proportion, the proportion of the foaming agent to be added is determined according to the actual geological reservoir physical properties) The foregoing description is merely a preferred embodiment of the present invention. It should be understood that the present invention is not limited to the form disclosed herein and should not be construed as excluding other embodiments. Rather, the present invention can be used in various other combinations, modifications, and environments and can be modified within the scope of the concept described herein through the above teachings or techniques or knowledge in the relevant field. Modifications and variations made by those skilled in the art that do not depart from the spirit and scope of the present invention are intended to be protected by the appended claims.

Claims

1. A foam well washing method for low-liquid-yield coalbed methane wells, characterized in that: The following steps are involved: S1. Prepare the equipment needed for well washing; S2. Lower the well-washing string into the coalbed methane wellbore; S3. Check the sealing of the equipment; S4. Continuously perform foam flushing in the gas well; S5. Degas with clean water and remove the well washing string.

2. The foam well washing method for low-liquid-yield coalbed methane wells according to claim 1, characterized in that: The S1 step specifically includes the following sub-steps: S11. Set up well-washing equipment at the well site and remove the original well production string; S12. Calculate the wellbore volume and prepare the well washing fluid; S13. Connect the well-washing equipment and establish a well-washing fluid circulation system.

3. The foam well washing method for low-liquid-yield coalbed methane wells according to claim 2, characterized in that: The well washing equipment specifically includes: a pump truck, a foam generator, an oil-casing annulus, a well washing string, a nitrogen-generating vehicle group, a derrick hanging weight meter, a vertical derrick, a liquid storage tank, and a sedimentation tank; wherein the oil-casing annulus is arranged on the periphery of the well washing string.

4. The foam well washing method for low-liquid-yield coalbed methane wells according to claim 3, characterized in that: The well washing fluid circulation in step S13 is specifically as follows: the well washing fluid in the liquid storage tank and the nitrogen generated by the nitrogen generating vehicle are injected into the foam generator by a pump truck to generate nitrogen foam well washing fluid, which is injected from the oil casing annulus and then returned from the well washing string.

5. The foam well washing method for low-liquid-yield coalbed methane wells according to claim 2, characterized in that: The preparation of the well washing fluid in step S12 specifically includes: preparing 1.5-2 times the volume of the wellbore well washing fluid, adding required chemical reagents thereto and stirring and dissolving them fully; the chemical reagents specifically include: potassium chloride, a foaming agent, and a foam stabilizer.

6. The foam well washing method for low-liquid-yield coalbed methane wells according to claim 1, characterized in that: The S2 step specifically includes the following sub-steps: S21. Lowering the well-washing string into the coalbed methane wellbore; S22. When the top of the well washing string is 20 meters away from the coal seam, slow down the lowering speed; S23. Check the hanging weight of the derrick.

7. The foam well washing method for low-liquid-yield coalbed methane wells according to claim 6, characterized in that: The step S23 specifically includes: when the hanging weight drops, it indicates that a sand surface is encountered, the accurate position of the sand surface is repeatedly re-explored, and the well washing pipe string is lifted to 5 meters above the sand surface; when the hanging weight increases sharply, it indicates that the friction resistance of the well washing pipe string increases abnormally, and the well washing pipe string is stopped from being lowered.

8. The foam well washing method for low-liquid-yield coalbed methane wells according to claim 1 or 3, characterized in that: The step S4 specifically includes the following sub-steps: S41. Installing a plug valve on the well-washing string joint to control the outflow of the well-washing fluid; S42. Slowly and uniformly lowering the well-washing string into the gas well and observing the hanging weight of the derrick; S43. Adjusting the density of the well-washing fluid to form a negative pressure to remove blockage and flush the gas well.

9. The foam well washing method for low-liquid-yield coalbed methane wells according to claim 1, characterized in that: It also includes a defoaming treatment step: after completing the well washing operation, add a defoaming agent on the ground for defoaming treatment. If foam continues to return from the gas wellhead, add a defoaming agent into the gas well for defoaming treatment.

Images