Coal seam directional multi-cluster hydraulic fracturing permeability increasing method based on intelligent temporary plugging steering

Abstract

The invention discloses a coal seam directional multi-cluster hydraulic fracturing permeability increasing method based on intelligent temporary plugging steering. The method comprises the following steps: firstly, accurately optimizing the position of a fracturing cluster by establishing a geomechanical model and calculating a compressibility index; secondly, after a main crack is formed in the first round of fracturing, based on real-time monitoring data such as microseism, DAS and pressure, intelligent decision is made, and a multi-mode temporary plugging agent is pumped for plugging; when the well mouth pressure has a clear response of'abrupt rise-abrupt drop ', it is indicated that temporary plugging succeeds, second-round fracturing is started immediately, and liquid is forced to turn to activate a new fracture area; and finally, a nano-permeability-increasing proppant and a liquid-phase CO2 slug are introduced in the fracturing tail-chasing stage, and long-acting permeability increasing and gas displacement are achieved. According to the method, full-process optimization from accurate prediction to intelligent decision making to long-acting permeability increasing is achieved, the industrial problems of inter-cluster non-uniform crack initiation and limited transformation volume in coal seam fracturing are effectively solved, and the yield and recovery efficiency of a coal-bed gas well are remarkably improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of coalbed methane exploitation, and particularly relates to a coal seam directional multi-cluster hydraulic fracturing and permeability improvement method based on intelligent temporary plugging and steering. BACKGROUND

[0002] Coalbed methane, as an important unconventional natural gas resource, its efficient development is of great significance for optimizing energy structure and ensuring coal mine safety production. Hydraulic fracturing is a key technology to liberate coalbed methane production capacity. However, coal seams usually have low permeability, soft and brittle, strong heterogeneity and other characteristics, and traditional fracturing technology faces great challenges.

[0003] The existing multi-cluster fracturing technology often only has part of the fracturing clusters being effectively activated due to the difference in ground stress and cluster interference, forming a single and dominant fracture, while other clusters become "ineffective clusters", resulting in limited reservoir reconstruction volume and unsatisfactory permeability improvement effect. Temporary plugging and steering technology is one of the effective means to solve this problem, which forces the fracturing fluid to steer to the unmodified area by temporarily plugging the high permeable flow channel that has been opened.

[0004] However, the existing temporary plugging and steering technology has the following defects:

[0005] Blindness: The temporary plugging decision relies mainly on the experience of field engineers, lacks scientific basis based on geological models and real-time monitoring data, and the steering success rate fluctuates greatly.

[0006] Extensiveness: Usually a single type of temporary plugging agent (such as temporary plugging balls) is used, which can only achieve the plugging of the perforation barrel and is difficult to achieve more precise branch steering inside the fracture.

[0007] Limitation: It focuses on the fracture forming process itself and pays insufficient attention to how to maintain the fracture conductivity for a long time after fracturing and promote gas desorption and production, resulting in a short effective period of yield increase.

[0008] Non-systematic: It fails to form a closed-loop technology system from "accurate prediction" to "real-time decision-making" to "long-term permeability improvement".

[0009] Therefore, there is an urgent need for a comprehensive fracturing method that can achieve accurate, intelligent and efficient steering and long-term permeability improvement. SUMMARY

[0010] The purpose of the present application is to overcome the shortcomings of the prior art and provide a coal seam directional multi-cluster hydraulic fracturing and permeability improvement method based on intelligent temporary plugging and steering. The method realizes uniform, three-dimensional and efficient reconstruction of coal reservoirs through the organic combination of geological modeling, intelligent decision-making, multi-modal temporary plugging and post-fracturing permeability improvement and displacement, and significantly improves single well production and recovery.

[0011] The technical solution of the present application is:

[0012] A coal seam directional multi-cluster hydraulic fracturing and permeability enhancement method based on intelligent temporary plugging and diversion, comprising the following steps:

[0013] S1, pre-fracturing geological evaluation and digital modeling: obtaining well logging data and seismic data of the target coal seam, and establishing a geomechanics model including the ground stress field and natural fracture distribution; based on the geomechanics model, calculating the fracturability index of each position in the horizontal well section, and optimizing the position of multiple fracturing clusters according to the fracturability index;

[0014] S2, first round of fracturing: performing perforation in a flow-restricted manner, with the perforation phase angle oriented towards the direction of the maximum horizontal principal stress; after perforating and completing the well, pumping fracturing fluid to the fracturing clusters for the first round of hydraulic fracturing to form a main fracture;

[0015] S3, intelligent temporary plugging decision and execution: based on real-time monitoring data of the first round of fracturing, deciding and pumping a temporary plugging agent slug to plug the opened main fracture, with the injection volume of the liquid carbon dioxide slug being 1.5 to 2 times the wellbore volume;

[0016] S4, second round of fracturing: after the wellhead pressure response indicates that the temporary plugging is successful, performing the second round of hydraulic fracturing to force the fracturing fluid to divert and activate new fracture areas;

[0017] S5, post-fracturing permeability enhancement and displacement: mixing nano-permeability enhancement proppants into the sand-carrying fluid in the final fracturing stage, and pumping a liquid carbon dioxide slug in the displacement stage.

[0018] Further, in step S1, the fracturability index is calculated by the following formula:

[0019] Fracturability index = (brittleness index x W1) + (natural fracture density x W2) - (stress difference coefficient x W3) + (gas content x W4),

[0020] wherein W1, W2, W3, and W4 are weight coefficients determined based on regression analysis of the work area data.

[0021] Further, in step S3, the real-time monitoring data includes microseismic monitoring data, distributed acoustic sensing (DAS) data, and wellhead pressure data; the intelligent temporary plugging decision specifically includes determining the geometry and stress shadow area of the opened fracture based on the microseismic monitoring data and DAS data, and deciding the type, dosage, and timing of the next round of temporary plugging agent accordingly.

[0022] Further, in step S3, the temporary plugging agent includes degradable temporary plugging balls and composite temporary plugging agents; when the main perforation channel needs to be plugged, degradable temporary plugging balls are selected; when branch diversion in the fracture is needed, composite temporary plugging agents composed of particles and fibers are selected.

[0023] Further, the ratio of the diameter of the degradable ball to the perforation diameter is 1.2:1 to 1.5:1.

[0024] Further, in step S3, the wellhead pressure response indicating that the plugging is successful specifically refers to that after pumping the plugging agent, the wellhead pressure rises by 5-8 MPa within 3-5 minutes, then an abrupt drop of more than 2 MPa occurs and is stabilized at a new pressure platform.

[0025] Further, in step S5, the nano-infiltration proppant is a ceramsite proppant coated with a super-hydrophobic nano-coating, and the mixing ratio thereof in the sand-carrying fluid is 10%-30%.

[0026] The present application has the advantages of:

[0027] (1) Precise targeting: the fracturing cluster position is quantitatively optimized by the crushability index, thereby improving the reservoir's reworkability from the source.

[0028] (2) Uniform initiation: the limited-flow perforation is combined with the directional perforation to create favorable conditions for the initial uniform initiation.

[0029] (3) Intelligent self-adaptation: the decision is made based on real-time monitoring data (microseismic, DAS, pressure), so that the temporary plugging and turning process is upgraded from "experience-driven" to "data-driven", thereby greatly improving the success rate and efficiency of turning.

[0030] (4) Complete turning: the multi-modal plugging system of "degradable ball + composite plugging agent" can not only plug the main channel, but also realize fine turning in the fracture, thereby significantly improving the complexity of the fracture network.

[0031] (5) Long-term permeability enhancement: the innovative "nano-infiltration proppant + liquid CO2" tailing technology effectively reduces the water lock damage and promotes the desorption of coalbed methane through displacement, realizes the integration of "fracturing" and "production increase", and guarantees long-term stable and high production. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 It is a process flow diagram of the present application;

[0033] Figure 2 It is a pressure response curve of the intelligent temporary plugging and turning process. DETAILED DESCRIPTION

[0034] The specific embodiments of the present application will be further described below in conjunction with the drawings. It should be noted that the description of these embodiments is used to help understand the present application, but does not constitute a limitation on the present application. In addition, the technical features involved in the various embodiments of the present application described below can be combined with each other as long as they do not conflict with each other.

[0035] As Figures 1-2 shown:

[0036] Embodiments:

[0037] A horizontal well in a coalbed methane block in the Qinshui Basin of Shanxi Province is taken as an example to apply the fracturing method of the present application.

[0038] Step one, pre-fracturing geological assessment and digital modeling

[0039] First, collect the well logging data (such as gamma, density, acoustic, resistivity) and three-dimensional seismic data of the well. Using these data, a geomechanical model of the target coal seam is established to accurately obtain the Young's modulus, Poisson's ratio, and the size and direction of the maximum / minimum horizontal principal stress of the coal seam and the roof and floor. The development density and orientation of natural fractures are identified by imaging logging.

[0040] Secondly, based on the geomechanical model, the fracturability index of each position in the horizontal section is calculated. The specific calculation formula is as follows:

[0041] Fracturability index = (brittleness index × W1) + (natural fracture density × W2) - (stress difference coefficient × W3) + (gas content × W4)

[0042] Wherein the brittleness index is calculated from the Young's modulus and Poisson's ratio; the stress difference coefficient is the difference between the maximum and minimum horizontal principal stress.

[0043] Through multiple regression analysis of the historical production data of the work area, the weight coefficients are determined as follows: W1 = 0.3, W2 = 0.4, W3 = 0.2, W4 = 0.1. Finally, 5 positions with high fracturability index are selected in the horizontal section as fracturing clusters, and the cluster spacing is designed to be 25 meters.

[0044] Step two, first round of fracturing

[0045] Limited flow perforation technology is used to perforate the 5 fracturing clusters, 16 holes per cluster, hole diameter 10mm. The perforation phase angle is set to 60° and is directed to the direction of the maximum horizontal principal stress determined by the previous modeling, which is beneficial to the initiation and propagation of the fracture along the predetermined direction.

[0046] The pumping program is as follows:

[0047] First, pump 80m 3 of pre-positioned active water at a displacement of 10m 3 / min to break the formation, then pump 250m 3 of sand-carrying fluid, the proppant used is 40 / 70 mesh ceramic proppant, and the sand ratio is increased from 5% to 12% in steps, which is a "polishing slug".

[0048] Then pump 500m 3The main body of the sand-carrying fluid, the proppant was changed to 30 / 50 mesh ceramic proppant, and the sand ratio was increased from 15% to 25%, and finally replaced by active water.

[0049] This stage of microseismic monitoring showed that two main fractures were formed.

[0050] Step three, intelligent temporary plugging decision and execution

[0051] Based on the real-time monitoring data in step two, the microseismic event cloud map showed that two clusters in the middle formed the main fractures, and there was a clear stress shadow zone around them; the DAS data showed that the liquid entering the two end clusters was weak. Based on this, the intelligent decision system determined that steering was needed to activate the two end clusters.

[0052] The decision result was to execute "coarse plugging", that is, to pump degradable temporary plugging balls. According to the number of perforations of the main cluster (2 clusters x 16 holes = 32 holes), 42 degradable temporary plugging balls with a diameter of 12 mm were added with a safety factor of 1.3 times, and the pump-in speed was 20 m 3 / min, and the active water carried the pump-in.

[0053] After pumping, the displacement of the liquid was continued at 10 m 3 / min. The wellhead pressure rose rapidly by 7 MPa in 4 minutes, then there was an abrupt drop of about 3 MPa, and stabilized at a new pressure platform about 4 MPa higher than before steering. This pressure response clearly indicated that the temporary plugging was successful, and the new fractures were activated.

[0054] Step four, second round fracturing

[0055] The second round fracturing was immediately carried out after the pressure response indicated that the temporary plugging was successful. The pumping program was similar to step two, but the preflush volume was reduced to 40 m 3 , and direct sanding with a high sand ratio (starting at 12%, and up to 28%) was carried out to quickly support the newly opened fractures. Microseismic monitoring confirmed that the fracturing clusters at both ends were successfully activated.

[0056] The following is a table of characteristics of the intelligent temporary plugging steering pressure response stage (the curve is shown in Appendix Figure 2 )

[0057]

[0058] Key criterion parameters:

[0059] Parameter Index Value Technical Significance Pressure rise amplitude (ΔP_rise) ≈36 MPa Reflects the effectiveness of the temporary plugging agent plugging and the degree of system energy accumulation. Pressure rise duration (ΔT_rise) ≈4 minutes Characterizes the speed of the temporary plugging agent bridging and pressure accumulation. Pressure drop amplitude (ΔP_drop) ≈21 MPa Core criterion: much greater than 2 MPa, clearly indicating that a new fracture has initiated. New-old fracture propagation pressure difference (ΔP_platform) ≈15 MPa Reflects the difference in propagation difficulty between the newly opened fracture and the initial main fracture.

[0060] Technical conclusion:

[0061] This pressure response curve is direct evidence of the success of temporary plugging steering. The three characteristics of "rapid pressure rise-peak abrupt drop-stable new platform" are indispensable, and constitute the trigger condition for the intelligent decision system to start the next round of fracturing.

[0062] Step 5: Post-compression permeation enhancement and displacement

[0063] In the final stage of the last round of fracturing, 20% of the conventional ceramsite was replaced with a nano-proppant. This proppant consisted of 30 / 50 mesh ceramsite coated with a superhydrophobic nano-coating (such as a fluorosilane compound).

[0064] During the displacement phase, a liquid-phase carbon dioxide slug is pumped in. The calculated wellbore volume is 35 m³. 3 Therefore, the injection volume is 60m. 3 (Approximately 1.7 times the wellbore volume).

[0065] Explanation of the principle:

[0066] Nanoparticle proppant: Its superhydrophobic coating can significantly reduce the capillary force of the aqueous phase on the coal and rock surface, effectively reduce the "water lock" damage caused by fracturing fluid intrusion, promote the backflow of aqueous phase, and thus provide a better channel for gas flow.

[0067] Liquid CO2: After injection, the liquid CO2 rapidly vaporizes at the coal seam temperature, expanding in volume by approximately 500 times and generating strong excitation pressure, which helps to push the fracturing fluid and desorbed gas deeper into the formation. More importantly, CO2 molecules have a stronger adsorption capacity for the coal matrix, effectively replacing (displacing) CH4 molecules adsorbed on the surface of coal micropores, significantly improving gas desorption efficiency and recovery rate.

[0068] After fracturing, the well is shut in and left to simmer for 7 days to allow for full pressure diffusion and complete degradation of the temporary plugging agent, followed by controlled flowback and production. Wells using this invention exhibit significantly better initial gas production and pressure reduction than neighboring wells using conventional fracturing methods.

[0069] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and these variations still fall within the protection scope of the present invention.

Claims

1. A coal seam directional multi-cluster hydraulic fracturing and permeability improvement method based on intelligent temporary blocking diversion, characterized in that, The method comprises the following steps: S1, pre-pressing geological assessment and digital modeling: obtaining well logging data and seismic data of the target coal seam, and establishing a geomechanics model including the ground stress field and the natural fracture distribution; based on the geomechanics model, calculating the crushability index of each position in the horizontal well section, and determining the positions of multiple fracturing clusters according to the crushability index; S2, first round of fracturing: performing perforation in a limited flow manner, and the perforation phase angle is oriented towards the direction of the maximum horizontal principal stress; after perforating and completing the well, pumping fracturing fluid to the fracturing clusters for the first round of hydraulic fracturing to form a main fracture; S3, intelligent temporary plugging decision and execution: based on real-time monitoring data of the first round of fracturing, deciding and pumping a temporary plugging agent slug to plug the opened main fracture, and the injection amount of the liquid carbon dioxide slug is 1.5 to 2 times the volume of the wellbore; S4, second round of fracturing: after the wellhead pressure response indicates that the temporary plugging is successful, performing the second round of hydraulic fracturing to force the fracturing fluid to divert and activate a new fracture area; S5, post-pressing permeability enhancement displacement: mixing nano-permeability enhancement proppants in the sand-carrying fluid in the final fracturing stage, and pumping a liquid carbon dioxide slug in the displacement stage.

2. The coal seam directional multi-cluster hydraulic fracturing and permeability improvement method based on intelligent temporary plugging and turning of claim 1, characterized in that: In step S1, the crushability index is calculated by the following formula: Crushability index = (brittleness index × W1) + (natural fracture density × W2) - (stress difference coefficient × W3) + (gas content × W4), wherein W1, W2, W3, and W4 are weight coefficients determined based on regression analysis of the work area data.

3. The coal seam directional multi-cluster hydraulic fracturing and permeability improvement method based on intelligent temporary plugging and turning of claim 2, characterized in that: In step S3, the real-time monitoring data includes microseismic monitoring data, distributed acoustic sensing (DAS) data, and wellhead pressure data; the intelligent temporary plugging decision specifically includes: determining the geometry and stress shadow area of the opened fracture according to the microseismic monitoring data and DAS data, and deciding the type, amount, and timing of the next round of temporary plugging agent based thereon.

4. The coal seam directional multi-cluster hydraulic fracturing and permeability improvement method based on intelligent temporary plugging and turning of claim 1, characterized in that: In step S3, the temporary plugging agent includes degradable temporary plugging balls and composite temporary plugging agents; when the main perforation channel needs to be plugged, the degradable temporary plugging balls are selected; when branch diversion in the fracture is needed, the composite temporary plugging agent composed of particles and fibers is selected.

5. The coal seam directional multi-cluster hydraulic fracturing and permeability improvement method based on intelligent temporary plugging and turning of claim 4, characterized in that: The ratio of the diameter of the degradable temporary plugging ball to the perforation diameter is 1.2:1 to 1.5:

1.

6. The intelligent temporary plugging diversion based coal seam directional multi-cluster hydraulic fracturing method according to claim 1, characterized in that: In step S3, the wellhead pressure response indicating that the temporary plugging is successful specifically refers to that after pumping the temporary plugging agent, the wellhead pressure rises by 5-8 MPa within 3-5 minutes, then drops by more than 2 MPa and stabilizes at a new pressure platform.

7. The coal seam directional multi-cluster hydraulic fracturing and permeability improvement method based on intelligent temporary plugging and steering according to claim 4, characterized in that: In step S5, the nano-permeability enhancement proppant is a ceramsite proppant coated with a super-hydrophobic nano coating, and the mixing ratio in the sand-carrying fluid is 10%-30%.

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