Cracked coal reservoir transformation method

Abstract

The invention relates to the field of coal seam development, in particular to a fragmented coal reservoir transformation method which comprises the steps that hydraulic sand blasting perforation is conducted from a spray gun (3) to a first target interval; active water prepad fluid is injected into the wellbore at the displacement of 3-4 m < 3 > / min, the displacement is gradually increased to the predicted maximum displacement, meanwhile, fluid supplementation is conducted from an oil pipe at the displacement of 1 m < 3 > / min, and a crack channel with effective supporting is formed in the perforation layer (5); and the perforation layer (5) forms a crack channel with effective support. According to the method, the self-isolation effect of jet flow is utilized, the expansion of crack width is limited, the crack length is increased, and the self-suspension propping agent is added in the sand-carrying fluid stage, so that the quartz sand can suspend in the fracturing fluid, the migration distance of the quartz sand is increased, the purpose of forming a supporting long seam in a coal body structure broken block is achieved, and the coal seam fracturing transformation effect is improved; the problem that coal powder blocks a seepage channel is solved through jet flushing.

Description

Technical Field

[0001] The present invention relates to the field of coal seam development, and particularly to a method for reforming a fractured coal reservoir. Background Art

[0002] In China, the exploitation of coalbed methane is difficult, mainly due to problems such as thin coal seams and low permeability. Industrial gas flow cannot be produced relying on the natural pressure of the coal seam. Therefore, reservoir reform is required. Through hydraulic fracturing, an effective channel for the migration of coalbed methane is provided to achieve a stable coalbed methane gas flow and increase the gas production of coalbed methane wells. Coal seams are longitudinally divided into primary structure, fractured structure, crushed grain structure, and mylonite structure. The coal quality of the primary structure coal is good, and reservoir reform is conducive to forming a support channel and is more likely to obtain a higher gas production. For coal seams with fractured, crushed grain, and mylonite structures, due to the broken coal quality, the filtration loss of the fracturing fluid is large during the fracturing construction, and there are situations of overpressure, sand plugging, and difficulty in adding sand. The fracture propagation and extension are not smooth. Due to the limited reform volume, the gas production per well does not reach the expected value. In the high-rank coal block of the Qinshui Basin, which has the best coalbed methane abundance and resource volume in China, more than 60% of the blocks belong to the areas with broken coal body structure. With the advancement of exploration and development work, the domestic coalbed methane industry gradually explores and develops medium-rank and low-rank coalbed methane fields. As the coal rank decreases, the coal quality is worse and the coal body structure is more broken, and the development difficulty is greater. It can be seen that the reservoir reform technology for the areas with broken coal body structure is a major problem faced by the coalbed methane industry.

[0003] At present, the main process of the coalbed methane reservoir reform method is active water sand fracturing. In addition, there are also guar gum fracturing, nitrogen fracturing, and volume fracturing, etc. These reservoir reform methods are generally applied to coal seams with good coal body structures, and the production increase effect for coal seams with broken coal body structures is not ideal. Due to the relatively broken coal body structure of fractured coal, conventional fracturing methods cannot create relatively effective support fractures, the length of the fractures cannot be guaranteed, and the coal powder generated during the fracturing process will block the already formed gas migration channels, and effective production increase effects cannot be achieved with conventional fracturing methods. Therefore, a reservoir reform method for this type of coalbed methane with broken coal body structure is needed.

[0004] Chinese National Patent Application No. CN106869889 A discloses a fracturing method for fractured coalbed methane, which prevents formation sand plugging and reduces construction risks by perforating at relatively stable positions of the coal body structure, increasing the proportion of the preflush fluid, increasing the use of fine sand, and adding sand in a slugging manner.

[0005] The inventor found problems in the prior art:

[0006] The prior art is an improvement on the current main active water sand fracturing process for coalbed methane wells. The fracturing fluid system is still active water, which may be able to improve the occurrence of sand plugging, overpressure, etc., but it cannot fundamentally solve the problem of the small effective transformation volume of coal seam wells with broken coal structures. Moreover, the coal powder generated during the fracturing process of the prior art will block the already formed gas migration channels, and the stimulation effect cannot be guaranteed. Therefore, there is a need in the art for a reservoir transformation method to overcome the defects of the prior art, develop an effective reservoir transformation method for coal seam wells with broken coal structures, and provide support for the technological progress of coalbed methane exploration and development. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a fractured coal reservoir transformation method, which is applicable to coalbed methane blocks with broken coal structures. This process can form effective support fractures of a certain length, improve the fracturing transformation range, and solve problems such as coal powder plugging, sand plugging, and overpressure pump shutdown during fracturing.

[0008] A fractured coal reservoir transformation method of the present invention includes the following steps

[0009] Step 1: Connect the fracturing string.

[0010] Step 2: Replace the liquid in the wellbore with the base fluid. Lower the fracturing string to the first interval, use active water as the fracturing fluid, and wash the wellbore with the base fluid at a displacement of 1 m 3 / min.

[0011] Step 3: Hydro-jet perforation of the first interval.

[0012] Step 4: After perforation, conduct circulating sand washing from the tubing of the fracturing string to clean the wellbore.

[0013] Step 5: Close the production casing of the fracturing string, carry sand fracturing, and agitate and add sand. Inject the sand-carrying fluid into the wellbore in the positive direction at a displacement of 2 - 2.5 m 3 / min.

[0014] Step 6: Open the production casing of the fracturing string, inject active water fracturing fluid into the wellbore at a displacement of 2 - 2.5 m 3 / min to wash and fracture, and flush out the excess coal powder in the coal seam.

[0015] Step 7: Inject active water preflush fluid into the casing at a displacement of 3 - 4 m 3 / min, gradually increase the displacement to the predicted maximum displacement, and the sand ratios are 5%, 7%, 9%, 11%, and 13% in sequence. At the same time, conduct fluid supplementation from the tubing at a displacement of 1 m 3 / min to form an effective support fracture channel.

[0016] Step 8: At a displacement of 4 m 3Start injecting the sand-carrying fluid into the casing in a stepped manner from / min, gradually increasing the displacement to the predicted maximum displacement, with the sand ratios being 5%, 7%, 9%, 11%, and 13% in sequence. At the same time, supplement the fluid from the tubing at a displacement of 1m 3 / min to form a fracture channel with effective support;

[0017] Step Nine: Inject the active water displacement fluid. When the wellhead pressure drops below the fracture closure pressure point, quickly flow back from the tubing;

[0018] Step Ten: Open the sliding sleeve, set the pressure limit to 20 MPa, throw the ball in the closed well state, and send the ball at a displacement of about 0.5m 3 / min. After the ball arrives, open the sliding sleeve, set the pressure limit to 30 MPa, continue to apply pressure until the packer is set, conduct a pressure test of 25 MPa, and open the production casing of the fracturing string;

[0019] Step Eleven: Conduct fracturing for the next interval, repeating Steps Two to Ten.

[0020] The present invention provides a method for reforming a fragmented coal reservoir. Among them, the active water fracturing fluid is a 0.5% KCL solution.

[0021] The present invention provides a method for reforming a fragmented coal reservoir. Among them, in Step Three, the sand ratio of the sand-blasting fluid is 7%, and the displacement is 2 - 2.5m 3 / min to inject the sand-blasting fluid.

[0022] The present invention provides a method for reforming a fragmented coal reservoir. Among them, in Step Four, the sand washing is to conduct a positive circulation sand washing of the wellbore at a displacement of 2 - 2.5m 3 / min.

[0023] The present invention provides a method for reforming a fragmented coal reservoir. Among them, in Step Five, the sand ratio of the sand-carrying fluid is 3%.

[0024] The present invention provides a method for reforming a fragmented coal reservoir. Among them, in Steps Seven, Eight, and Nine, the total amounts of the preflush fluid, sand-carrying fluid, and displacement fluid are determined according to the coal seam thickness, ranging from 150 - 250m 3 / m. The proportion of the preflush fluid is 15 - 25%, the proportion of the sand-carrying fluid is 72 - 80%, and the displacement fluid is calculated according to the wellbore volume; the displacement is injected according to the pressure-controlled displacement. If the pressure drops during sand addition, gradually increase the displacement to 5m for the tubing 3 / min and 10 - 12m for the casing 3 / min. If the pressure rises during sand addition, reduce the displacement.

[0025] The present invention provides a method for reforming a fragmented coal reservoir. Among them, in Step Eight, the sand amount of the sand-carrying fluid is determined according to the coal seam thickness, ranging from 10 - 15m3 Between / m, the proportion of fine sand and medium sand is 1:1. First, pump in fine sand, and then pump in medium sand; in the sand-carrying fluid, the proppant is injected by mixing self-suspending proppant and quartz sand in a ratio of 1:2; the self-suspending proppant is quartz sand wrapped with polymer on the outside, and has a certain viscosity after being mixed with active water, and there is no need to prepare the liquid in advance.

[0026] The difference between a method for fracturing a fractured coal reservoir in the present invention and the prior art lies in that the method for fracturing a fractured coal reservoir in the present invention can solve the problems of small reservoir transformation range and low gas production in coalbed methane blocks with fractured coal structures. By using the self-sealing effect of jet flow, the expansion of crack width is restricted, the crack length is increased, and self-suspending proppant is added in the sand-carrying fluid stage, so that quartz sand can be suspended in the fracturing fluid, improving the migration distance of quartz sand, achieving the goal of forming a supported long crack in the fractured coal structure block, improving the fracturing transformation effect of the coal seam, and solving the problem of coal powder clogging the seepage channel through jet flushing.

[0027] The following further describes a method for fracturing a fractured coal reservoir of the present invention with reference to the accompanying drawings. Description of the Drawings

[0028] Figure 1 It is the front view of a fracturing string for a method for fracturing a fractured coal reservoir.

[0029] Reference numerals: tubing 1, centralizer 2, spray gun 3, sliding sleeve 4, perforated layer 5, artificial bottom hole 6, production casing 7, total depth of the drilled well 8. Detailed Embodiments

[0030] As Figure 1 shown, a method for fracturing a fractured coal reservoir of the present invention includes the following steps

[0031] Step 1: Connect the fracturing string;

[0032] Among them, as Figure 1 shown, from bottom to top is a ball seat + spray gun + centralizer + D73mm extra-heavy tubing to the wellhead. Figure 1 It includes tubing 1, centralizer 2, spray gun 3, sliding sleeve 4, perforated layer 5, artificial bottom hole 6, production casing 7, total depth of the drilled well 8.

[0033] Step 2: Use active water fracturing fluid to replace the formation water in the wellbore at a displacement of 1 m 3 / min, and lower the fracturing string to the first target interval;

[0034] Among them, the active water fracturing fluid is a KCL solution prepared with pure water at a mass percentage of 0.5%.

[0035] Among them, during fracturing, it is fractured from the bottom upwards, and it is all the first target interval to be fractured. The deeper it is, the first target interval is. The segmentation point is determined according to the formation, and it is all coal seams.

[0036] Among them, Figure 1 The inside of the production casing 7 in it is the wellbore.

[0037] Step 3: Conduct hydraulic sandblasting perforation from the spray gun 3 to the first target interval;

[0038] Among them, the sand ratio of the sandblasting fluid is 7%; the sand fluid can also be called the sand-carrying fluid, and the proppant in the sand fluid is injected by mixing self-suspending proppant and quartz sand in a ratio of 1:2;

[0039] Among them, the displacement is 2 - 2.5 m 3 / min to inject the sandblasting fluid;

[0040] Step 4: Conduct circulating sand washing from the tubing 1 of the fracturing string to clean the wellbore;

[0041] Step 5: Close the production casing 7 of the fracturing string, and inject the active water sand-carrying fluid into the string at a displacement of 2 - 2.5 m 3 / min for sand-carrying fracturing;

[0042] Specifically, the sand ratio of the sand-carrying fluid is 3%;

[0043] Step 5 of the present invention provides a prerequisite for creating larger fractures for later coal seam sand addition.

[0044] Step 6: Open the production casing 7 of the fracturing string, and inject the active water fracturing fluid into the wellbore at a displacement of 2 - 2.5 m 3 / min to wash and fracture by injecting, and flush out the excess pulverized coal in the coal seam;

[0045] Among them, the above process is to inject the active water fracturing fluid into the annulus area between the tubing 1 and the wellbore for washing and fracturing.

[0046] Step 7: Inject the active water preflush fluid into the wellbore at a displacement of 3 - 4 m 3 / min, gradually increase the displacement to the predicted maximum displacement, and at the same time conduct liquid supplementation from the tubing at a displacement of 1 m 3 / min, so as to form an effectively supported fracture channel in the perforated interval 5;

[0047] Among them, the above process is to inject the active water preflush fluid into the annulus area between the tubing 1 and the wellbore. Among them, the predicted maximum displacement can be 10 - 12 m 3 / min, and the speed of gradually increasing the displacement is: one step every 5 minutes, and the displacement increases by 1 m 3 / min.

[0048] Step 8: Inject the active water sand-carrying fluid at the predicted maximum displacement, gradually increasing the sand ratio step by step per unit time, and at the same time, supplement the fluid from the tubing at a displacement of 1 m 3 / min to form a fracture channel with effective support in the perforated layer 5; among them, "gradually increasing the sand ratio step by step per unit time" can be understood as: the unit time can be 10 seconds to 10 hours, preferably 5 minutes. The sand ratios per unit time are 3%, 5%, 7%, 9%, 11%, and 13% in sequence. In other words, a total of 6 unit times of injecting the active water sand-carrying fluid are carried out, and the sand ratio of the sand-carrying fluid per unit time is gradually increased. The sand ratios of the above 6 unit times are: 3%, 5%, 7%, 9%, 11%, 13% in sequence.

[0049] Start injecting the sand-carrying fluid into the casing step by step at 4 m 3 / min, gradually increasing the displacement to the predicted maximum displacement, with the sand ratios being 3%, 5%, 7%, 9%, 11%, and 13% in sequence, and at the same time, supplement the fluid from the tubing at a displacement of 1 m 3 / min to form a fracture channel with effective support;

[0050] Specifically, the sand volume of the sand-carrying fluid is determined according to the coal seam thickness, ranging from 10 - 15 m 3 / m, and the ratio of fine sand to medium sand is 1:1. First, pump in the fine sand, and then pump in the medium sand;

[0051] Specifically, the maximum displacement is determined by calculating the construction limit pressure;

[0052] Specifically, the proppant in the sand-carrying fluid is injected by mixing self-suspending proppant and quartz sand in a ratio of 1:2;

[0053] Specifically, the self-suspending proppant is quartz sand wrapped with polymer on the outside, which has a certain viscosity after being mixed with active water, does not require pre-liquid preparation, and has relatively low damage;

[0054] Step 9: Inject the active water displacement fluid into the casing, and at the same time, continue to inject the active water fracturing fluid from the tubing at a displacement of 1 m 3 / min. When the wellhead pressure drops below the fracture closure pressure point, quickly flow back from the tubing;

[0055] Specifically, the closure pressure point is determined by the G-function analysis method;

[0056] Specifically, the total volume of the preflush fluid, sand-carrying fluid, and displacement fluid is determined according to the coal seam thickness, ranging from 150 - 250 m 3 / m. The proportion of the preflush fluid volume is 15 - 25%, the proportion of the sand-carrying fluid is 72 - 80%, and the displacement fluid is calculated according to the wellbore volume; the displacement is injected according to the pressure control displacement. If the pressure drops during sand addition, gradually increase the displacement to 5 m of the tubing 3 / min and 10 m of the casing3 / min. If the pressure increases when adding sand, reduce the displacement.

[0057] Step Ten: Open the sliding sleeve 4, set the pressure limit to 20 MPa, throw the ball in the closed well state, and send the ball at a displacement of 0.5 m 3 / min. After the ball reaches the position, open the sliding sleeve, set the pressure limit to 30 MPa, continue to apply pressure until the separator of the sliding sleeve 4 is seated, conduct a pressure test at 25 MPa, and open the production casing 7 of the fracturing string.

[0058] Step Eleven: Conduct fracturing for the next interval, and repeat Steps Two to Ten.

[0059] The present invention can solve the problems of small reservoir transformation range and low gas production in coal seam gas blocks with broken coal body structures. By utilizing the self-sealing effect of jet flow, it restricts the expansion of crack width, increases the crack length, adds self-suspending proppants during the proppant-carrying fluid stage, enables quartz sand to be suspended in the fracturing fluid, improves the migration distance of quartz sand, realizes the goal of forming a supported long crack in the coal body structure broken block, improves the fracturing transformation effect of the coal seam, and solves the problem of coal powder plugging the seepage channel through jet flushing.

[0060] Among them, the active water fracturing fluid is a KCL solution with a mass percentage of 0.5%.

[0061] Among them, since the concentration of a solution usually refers to the content of the solute in the solution, which can be expressed by mass percentage or volume percentage. Therefore, the 0.5% KCL solution can be understood as a KCL solution expressed by a mass percentage of 0.5%.

[0062] That is to say, the active water fracturing fluid is a 0.5% KCL solution.

[0063] Among them, since the concentration of a solution usually refers to the content of the solute in the solution, which can be expressed by mass percentage or volume percentage. Therefore, the 0.5% KCL solution can be understood as a KCL solution expressed by a mass percentage of 0.5%.

[0064] Among them, in Step Three, hydraulic sandblasting perforation is carried out using a sandblasting fluid with a displacement of 2 - 2.5 m 3 / min and a sand ratio of 7%.

[0065] Among them, in Step Four, the wellbore is flushed in a positive circulation at a displacement of 2 - 2.5 m 3 / min.

[0066] Among them, the sand ratio of the active water proppant-carrying fluid in Step Five is 3%.

[0067] Among them, the ratio of the total volume of the active water preflush fluid, active water proppant-carrying fluid, and active water displacement fluid in Steps Seven, Eight, and Nine to the coal seam thickness ranges from 150 - 250 m3 Between 15 - 25% of the active water preflush volume ratio, 72 - 80% of the active water sand-carrying fluid ratio, and the rest is the active water displacement fluid.

[0068] Among them, the ratio of the volume of the sand in the active water sand-carrying fluid in Step 8 to the coal seam thickness is between 10 - 15 m 3 / m, and the ratio of fine sand to medium sand in the sand of the active water sand-carrying fluid is 1:1.

[0069] Among them, in Step 8, the sand of the active water sand-carrying fluid is first pumped with fine sand and then with medium sand.

[0070] Among them, the proppant of the active water sand-carrying fluid in Step 8 is injected by mixing self-suspending proppant and quartz sand in a ratio of 1:2.

[0071] Among them, the self-suspending proppant of the active water sand-carrying fluid in Step 8 is quartz sand wrapped with polymer

[0072] Among them, the mixture of quartz sand wrapped with polymer and active water has a certain viscosity and does not require pre-mixing of fluids.

[0073] Example 1

[0074] Taking the completion method of Well 15# in a certain block as an example, the present invention will be further described in detail.

[0075] The total depth of Well 15# is 1312 m. The surface casing diameter is D244.5 mm, and the setting depth is 45.96 m. The production casing diameter is D139.7 mm, and the setting depth is 1318.91 m. Its fracturing points are shown in Table 1 below. The following steps are used for fracturing.

[0076] Step 1: Connect the fracturing string, as Figure 1 shown, to achieve layered fracturing of the coal seam. First, fracture the lower layer and then the upper layer;

[0077] Horizon Layer number Jetting point <![CDATA[P1s]]> 11 1151.5 <![CDATA[C3t]]> 27 1255.5

[0078] Table 1 Jetting Points

[0079] Step 2: Replace the liquid in the wellbore with the base fluid. As Figure 1 shown, lower the tubing string. Use active water as the fracturing fluid, a 0.5% potassium chloride aqueous solution, to wash the wellbore with the base fluid at a displacement of 1 m 3 per minute.

[0080] Step 3: Perform hydraulic sandblasting perforation operation for the first stage of fracturing;

[0081] Specifically, the sand ratio of the sand-carrying fluid is 7%, and the sand-carrying fluid is injected at a displacement of 2.5 m 3 per minute for hydraulic perforation operation;

[0082] Step Four: Circulating sand washing, with a displacement of 2.5 m 3 per minute, conduct positive circulating sand washing on the wellbore;

[0083] Step Five: Sand-carrying fracturing, exciting sand addition, closing the casing, with the sand ratio of the sand-carrying fluid being 3%, and with a displacement of 2.5 m 3 per minute, inject the sand-carrying fluid into the wellbore in the positive direction at a high rate, providing a prerequisite for creating larger fractures for later coal seam sand addition.

[0084] Step Six: Open the casing, with a displacement of 2.5 m 3 per minute, inject a potassium chloride aqueous solution of 0.5% of the active water fracturing fluid into the wellbore to wash and fracture, flushing out the excess coal powder in the coal seam;

[0085] Step Seven: The casing injects the preflush fluid at a displacement of 3 - 4 m 3 per minute, and at the same time, the tubing supplements the fluid at a displacement of 1 m 3 per minute. During the injection of the preflush fluid, inject 1 cubic meter of 40 / 70 mesh sand at a displacement of 3 m 3 per minute and 1.5 cubic meters of 40 / 70 sand with a sand ratio of 5% into the tubing at a displacement of 4 m 3 per minute to form a main fracture in the coal seam;

[0086] Step Eight: The sand addition adopts a stepped injection of the sand-carrying fluid. For 40 / 70 mesh sand: the sand ratio and fluid volume are 5% 90 cubic meters of fluid, 7% 90 cubic meters of fluid, 9% 75 cubic meters of fluid, 11% / 72 cubic meters of fluid in sequence; for 20 / 40 mesh sand: the sand ratio and fluid volume are 9% 135 cubic meters of fluid, 11% / 91 cubic meters of fluid, 13% 60 cubic meters of fluid in sequence, forming a fracture channel with effective support.

[0087] Step Nine: Inject 8 cubic meters of displacement fluid, and quickly flow back with the tubing open.

[0088] Step Ten: Open the second-stage sliding sleeve for fracturing, set the pressure limit at 20 MPa, throw the ball in the closed well state, send the ball at a displacement of about 0.5 m3 / min. After the ball arrives, open the sliding sleeve. Set the pressure limit at 30 MPa, continue to apply pressure until the packer seats. Conduct a pressure test at 25 MPa, open the casing, and conduct the second-stage construction.

[0089] Step Eleven: Conduct fracturing on the next target layer section, repeating Steps Two to Ten.

[0090] The above-described embodiments are only descriptions of the preferred embodiments of the present invention, and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for reforming a fragmented coal reservoir, characterized in that: Including the following steps Step 1, connect the fracturing string; Step 2: Use the active water fracturing fluid to replace the formation water in the wellbore at a displacement of 1 m 3 / min, and lower the fracturing string to the first target interval; Step 3, conduct hydraulic sandblasting perforation from the spray gun (3) to the first target interval; Step 4, conduct circulating sand washing from the tubing (1) of the fracturing string to clean the wellbore; Step 5: Close the production casing (7) of the fracturing string, and inject active water sand-carrying fluid into the string at a displacement of 2 - 2.5 m 3 / min for sand-carrying fracturing; Step 6: Open the production casing (7) of the fracturing string and inject active water fracturing fluid into the wellbore at a displacement of 2 - 2.5 m 3 / min to wash and fracture the wellbore with the active water fracturing fluid, and flush out the excess pulverized coal in the coal seam; Step 7: Inject active water preflush fluid into the wellbore at a displacement of 3 - 4 m 3 / min, gradually increase the displacement to the predicted maximum displacement, and at the same time, supplement fluid from the tubing at a displacement of 1 m 3 / min to form an effectively supported fracture channel in the perforated layer (5); Step 8: Inject the active water sand-carrying fluid at the predicted maximum displacement, gradually increasing the sand ratio step by step per unit time, and at the same time supplement the fluid from the tubing at a displacement of 1 m 3 / min to form an effectively supported fracture channel in the perforated layer (5); Step 9: Inject active water displacement fluid into the casing, and at the same time, continue to inject active water fracturing fluid into the tubing at a displacement of 1 m 3 / min. When the wellhead pressure drops below the fracture closure pressure point, quickly flow back from the tubing; Step Ten: Open the sliding sleeve (4), set the pressure limit to 20 MPa, conduct ball injection in the closed well state, and send the ball at a displacement of 0.5 m 3 / min. After the ball reaches the position, open the sliding sleeve, set the pressure limit to 30 MPa, continue to apply pressure until the packer of the sliding sleeve (4) is seated, conduct a pressure test at 25 MPa, and open the production casing (7) of the fracturing string; Step 11, conduct fracturing of the next target interval, and repeat steps 2 to 10.

2. The method for reforming a fragmented coal reservoir according to claim 1, characterized in that: The active water fracturing fluid is a KCL solution with a mass percentage of 0.5%.

3. The method for reforming a fragmented coal reservoir according to claim 1, characterized in that: In the third step, hydraulic sandblasting perforation is carried out using a sandblasting fluid with a displacement of 2 - 2.5 m 3 / min and a sand ratio of 7%.

4. The method for reforming a fragmented coal reservoir according to claim 1, characterized in that: In the fourth step, the wellbore is flushed in positive circulation at a displacement of 2 - 2.5 m 3 / min to remove sand from the wellbore.

5. The method for reforming a fragmented coal reservoir according to claim 1, characterized in that: The sand ratio of the active water sand-carrying fluid in step 5 is 3%.

6. The method for reforming a fragmented coal reservoir according to claim 1, characterized in that: The ratio of the total volume of the active water preflush fluid, the active water sand-carrying fluid, and the active water displacement fluid in Steps Seven, Eight, and Nine to the coal seam thickness ranges from 150 to 250 m 3 / m. The proportion of the active water preflush fluid is 15-25%, the proportion of the active water sand-carrying fluid is 72-80%, and the rest is the active water displacement fluid.

7. The method for reforming a fragmented coal reservoir according to claim 1, characterized in that: In the eighth step, the ratio of the volume of the sand in the activated water sand-carrying fluid to the coal seam thickness ranges from 10 - 15 m 3 per m, and the ratio of fine sand to medium sand in the sand of the activated water sand-carrying fluid is 1:

1.

8. The method for reforming a fragmented coal reservoir according to claim 1, characterized in that: In step 8, fine sand is first pumped into the sand volume of the active water sand-carrying fluid, and then medium sand is pumped in.

9. The method for reforming a fragmented coal reservoir according to claim 1, characterized in that: The proppant of the active water sand-carrying fluid in step 8 is injected by mixing self-suspending proppant and quartz sand in a ratio of 1:

2.

10. The method for reforming a fragmented coal reservoir according to claim 1, characterized in that: The self-suspending proppant of the active water sand-carrying fluid in step 8 is quartz sand wrapped with polymer on the outside.

Images