Tight reservoir intermittent fracturing process

Abstract

The invention belongs to the technical field of underground fracturing, and discloses a tight reservoir intermittent fracturing process. Comprising the steps of determining a single well fracturing scheme, determining imbibition equilibrium pressure, performing underground micro-seismic construction, monitoring wellhead pressure of an adjacent well, performing fracturing construction, processing data and evaluating data. The fracturing process method is reliable and simple, the transformation size can be further increased on the premise that cost is not increased, and a fracture foundation for yield improvement is laid.

Description

Technical Field

[0001] This invention belongs to the field of downhole fracturing technology, specifically relating to an intermittent fracturing process for tight reservoirs. Background Technology

[0002] With conventional oil resources dwindling, unconventional tight oil and gas resources are increasingly becoming the focus of exploration and development. To maximize reservoir stimulation volume, a common practice is to inject low-viscosity fluid carrying small-particle-size proppant via high-speed circulation pumping. However, real-time hydraulic fracturing microseismic monitoring during operation has shown that traditional slickwater volumetric fracturing with continuous pumping cannot provide sufficient horizontal (lateral) coverage in the designed section. Furthermore, core friction tests indicate that after soaking the core in water for a period (24 hours), the friction strength significantly decreases, suggesting that water intrusion facilitates rock sliding and shearing in tight reservoirs, forming a fracture network.

[0003] Literature review revealed a similar technique to this invention: a field fracturing method for generating complex fracture networks using intermittent fracturing (patent CN108952663A). This method involves pumping a pre-set slickwater fracturing fluid into the formation, then stopping the pump and performing pressurized well shut-in until no significant microseismic signals are received. This process is repeated multiple times until the pumped fluid volume reaches the designed value. However, this method lacks pressure monitoring of adjacent wells during construction, making it impossible to definitively prove whether a complex fracture network has formed. Furthermore, the need for repeated operations to achieve the designed fluid volume increases construction costs. Summary of the Invention

[0004] To overcome the shortcomings of existing technologies, this invention provides an intermittent fracturing process for tight reservoirs. The method is reliable and simple, and can further increase the stimulation volume without increasing costs, thus laying the foundation for increased production.

[0005] The above-mentioned objective of this invention is achieved through the following technical solution: an intermittent fracturing process for tight reservoirs, comprising the following steps:

[0006] 1. Determine the single-well fracturing scheme;

[0007] 2. Determine the osmotic equilibrium pressure;

[0008] 3. Downhole microseismic construction;

[0009] 4. Monitoring the pressure at the wellhead of adjacent wells;

[0010] 5. Fracturing operations;

[0011] 6. Data processing;

[0012] 7. Data evaluation.

[0013] Furthermore, step 1 specifically involves: combining the post-fracturing production data of the fracturing wells in the block, statistically analyzing the fracturing construction parameters, and formulating a single-well fracturing plan based on the test simulation results of FracproPT software, taking into account the reservoir conditions, determining the amount of sand, fluid, discharge, and fracturing materials for well fracturing construction, and compiling the fracturing engineering design.

[0014] Furthermore, the fracturing operation parameters specifically include sand volume, liquid volume, discharge volume, and fracturing material.

[0015] Furthermore, step 2 specifically involves: selecting core samples from the target layer and simulating the fracturing fluid usage, expected pressure, and time required for the fracturing fluid to enter the formation and reach a state of permeation-absorption equilibrium under reservoir conditions.

[0016] Furthermore, step 3 specifically involves: selecting adjacent well 1 as the downhole microseismic monitoring well; designing the number of geophone stages and their placement position in the monitoring well according to the principle of the geophone being closest to the target layer of the fracturing well, with a well inclination angle of less than 2 degrees; lowering the geophone into the well and conducting debugging; locating perforation explosion events using the geophone in the monitoring well; real-time processing and interpretation engineers correcting the initial velocity model established before fracturing operations based on the perforation location file; synchronously acquiring downhole microseismic event data in the monitoring well throughout the entire fracturing process; after completing real-time fracturing monitoring, retrieving the geophone, and performing subsequent velocity model correction and downhole microseismic data post-processing and interpretation on the acquired microseismic data to evaluate the fracturing effect.

[0017] Furthermore, step 4 specifically involves: installing a pressure gauge at the wellhead of adjacent well 2 to monitor the changes in the pressure curve at the wellhead of adjacent well 2 during the fracturing operation.

[0018] Furthermore, step 5 specifically involves: pumping 25-40% of the designed fluid volume as pre-fluid into the formation using the designed displacement rate; continuously shutting in the well for 20-24 hours to loosen the formation; and waiting for the surface pressure to reach the expected pressure, i.e., P. 地面压力 +P 液柱压力 ≈P 闭合压力 Continue with the normal pumping procedure.

[0019] Furthermore, step 6 specifically includes downhole microseismic monitoring and adjacent wellhead pressure monitoring. Specifically, downhole microseismic monitoring involves retrieving the geophone and performing subsequent velocity model correction and post-processing on the acquired microseismic data. Adjacent wellhead pressure monitoring involves retrieving the wellhead pressure gauge and plotting the pressure curve.

[0020] Furthermore, step 7 specifically involves evaluating the fracturing effect using the processed downhole microseismic data and pressure curves collected in step 6.

[0021] The beneficial effects of this invention compared with the prior art are as follows: the application of intermittent fracturing technology and evaluation method for tight reservoirs effectively guides field application; the number of microseismic events in the intermittent fracturing section is significantly higher than in other sections; and during the main construction process of the fracturing section, the wellhead pressure of adjacent wells is much higher than in other sections, and also higher than in the pre-fluidization stage; this verifies that the fracturing technology and method are reliable and simple, and can further increase the stimulation volume without increasing costs, laying the foundation for increased production. Attached Figure Description

[0022] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0023] Figure 1 This is a schematic diagram of the intermittent fracturing process provided by the present invention;

[0024] Figure 2 This is a schematic diagram of the sliding seam forming and shearing mesh forming principle provided by the present invention;

[0025] Figure 3 This invention provides the water-soaked core friction intensity variation curve for the target well.

[0026] Figure 4 This is a diagram of fracturing design parameters for the target well provided by the present invention;

[0027] Figure 5 This is a diagram of the intermittent fracturing and sand conveying procedure for the 9th stage of the target well provided by the present invention;

[0028] Figure 6 This is a comparison chart of microseismic events in the target well;

[0029] Figure 7 This is a graph showing the pressure curves at the wellheads of adjacent wells during the fracturing process of the target well (measured by a pressure gauge). Detailed Implementation

[0030] The present invention is described in detail below through specific embodiments, but this does not limit the scope of protection of the present invention. Unless otherwise specified, the experimental methods used in the present invention are all conventional methods, and the experimental equipment, materials, reagents, etc. used can all be obtained commercially.

[0031] Example 1

[0032] Intermittent fracturing technology and evaluation method for tight reservoirs

[0033] The specific implementation process is as follows:

[0034] (1) Determine the fracturing scheme for the target well: Based on the production data of previous wells in the block, statistically analyze the construction parameters (sand volume, fluid volume, discharge rate and fracturing materials) of other fracturing wells in the block, and formulate the fracturing scheme for the target well by comprehensively considering the reservoir conditions, according to the test simulation results of FracproPT software; determine that the target well is to be fractured in 15 sections and 40 clusters, with a total well discharge rate of 12-6 m³ / h. 3 / min, total construction fluid volume 21835m³ 3 Total sand volume: 644m³ 3 Intermittent fracturing technology was implemented on the 9th section to compare its effects with those of other sections, with a fracturing displacement of 12-6m³. 3 / min, liquid volume 1417m 3 Sand volume 35m 3 ;

[0035] (2) Determine the permeation equilibrium pressure: Select the core of the target well and target layer, and simulate the fracturing fluid usage, pressure and time when the fracturing fluid enters the formation to reach the permeation equilibrium state under reservoir conditions. It is initially determined that the fracturing fluid usage is 30% of the total fluid volume, the expected pressure is 38.1 MPa and the time is 24 hours.

[0036] (3) Downhole microseismic construction plan: Select well 1 near the target well as the downhole microseismic monitoring well; monitoring well 1 requires well cleaning and flushing, and there are no other tubing strings in the casing well. Remove its wellhead device and install the operating table; design a 12-level geophone according to the principle that the geophone is closest to the target layer of the fracturing well. The vertical insertion depth in well 1 is (382.316, 382.271, 382.426, 382.674, 382.968, 383.323, 383.729, 384.222, 384.785, 385.339, 385.905, 386.487m), and the well inclination angle is less than 2 degrees; establish a well site test data transmission system at the well site of well 1 and the target well to provide real-time data processing and interpretation on site. Transmission preparations are completed; when the adjacent well 1 has operating equipment with a working height of 15 meters and a lifting capacity of 20 tons to assist in the operation, the geophone is lowered to the designed depth range. After the geophone is lowered to the designed depth, its support arm is pushed to ensure that the monitoring instrument is tightly attached to the casing wall and connects to the formation to achieve the best monitoring effect; downhole background noise monitoring is performed on the geophone; after confirming that the geophone in the adjacent well 1 has started monitoring successfully, the perforation team is notified to ignite the equipment, and the geophone in the adjacent well 1 is located by recording the deflagration event; the real-time processing and interpretation engineer corrects the initial velocity model established before fracturing construction based on the perforation positioning document; the fracturing construction of sections 5, 6, 7, 8, and 9 of the target well is monitored, and the post-fracturing processing and interpretation are performed to evaluate the fracturing effect;

[0037] (4) Pressure monitoring at the wellhead of adjacent well: A pressure gauge was installed at the wellhead of adjacent well 2 to monitor pressure changes during the construction process of sections 4-15;

[0038] (5) Construction of the target well in sections 1-8: Construction is carried out normally according to the fracturing engineering design (pressure monitoring at the wellhead of the adjacent well begins in section 4, and downhole microseismic monitoring begins in section 5);

[0039] (6) Construction of the 9th section of the target well: First pump 410m 3 Slickwater (30% of total fluid volume) was used as a pre-fluid; the well was shut in continuously for 24 hours to loosen the formation; the pressure was allowed to recover to 38.1 MPa (P 地面压力 +P 液柱压力 ≈P 闭合压力 Continue with the normal infusion procedure;

[0040] (7) Construction of the 10th-15th sections of the target well: Construction shall be carried out normally according to the fracturing engineering design;

[0041] (8) Data processing: After the 9th stage of fracturing is completed, the geophone is retrieved, and the acquired microseismic data is subjected to subsequent velocity model correction and post-processing and interpretation of downhole microseismic data to evaluate the fracturing effect; after the 15th stage of fracturing is completed, the wellhead pressure gauge is retrieved, pressure curves are plotted, and the fracturing effect is evaluated.

[0042] To verify the effectiveness of the process of this invention, a comparative test was conducted. Other sections of this well were constructed according to conventional tight oil volumetric fracturing methods. The results of post-fracturing microseismic monitoring showed that the microseismic events in sections 5-8 were significantly less than those in section 9, indicating that the intermittent fracturing process improved the horizontal coverage and formed a complex fracture network. At the same time, during the main construction process of the intermittent fracturing section (section 9), the wellhead pressure of the adjacent well 2 was much higher than that of other sections and higher than that of the pre-fluidization stage, which also proved that intermittent fracturing can further increase the reservoir stimulation volume.

[0043] As of the end of 2023, the target well had been producing for 1622 days, with a cumulative fluid production of 50738 m³. 3 Compared with the production of other wells in the same block (1622 days of production, and the cumulative production of 48122 m³ of the adjacent well 2), 3 A certain comparative well produced a cumulative fluid of 44,812 m³. 3 The advantages are obvious. The fracturing process of this invention is reliable and simple, and can further increase the volume of the fracturing without increasing costs, laying the foundation for increased production.

[0044] The embodiments described above are merely preferred embodiments of the present invention, and not all feasible embodiments of the present invention. Any obvious modifications made by those skilled in the art without departing from the principles and spirit of the present invention should be considered to be included within the scope of protection of the claims of the present invention.

Claims

1. An intermittent fracturing process for tight reservoirs, characterized in that, The steps are as follows: S1. Determine the single-well fracturing scheme; S2. Determine the osmotic equilibrium pressure; S3. Downhole microseismic construction; S4. Monitoring of pressure at adjacent wellheads; S5. Fracturing operation; S6. Data processing; S7. Data Evaluation.

2. The intermittent fracturing process for tight reservoirs according to claim 1, characterized in that, Step S1 specifically involves: combining the post-fracturing production data of the fracturing wells in the block, statistically analyzing the fracturing construction parameters, and formulating a single-well fracturing plan based on the test simulation results of FracproPT software, taking into account the reservoir conditions, determining the sand volume, fluid volume, discharge volume and fracturing materials for well fracturing construction, and compiling the fracturing engineering design.

3. The intermittent fracturing process for tight reservoirs according to claim 2, characterized in that, The fracturing operation parameters specifically include sand volume, liquid volume, discharge volume, and fracturing materials.

4. The intermittent fracturing process for tight reservoirs according to claim 1, characterized in that, Step S2 specifically involves: selecting core samples from the target layer and simulating the fracturing fluid usage, expected pressure, and time required for the fracturing fluid to enter the formation and reach a state of permeation-absorption equilibrium under reservoir conditions.

5. The intermittent fracturing process for tight reservoirs according to claim 1, characterized in that, Step S3 specifically involves: selecting adjacent well 1 as the downhole microseismic monitoring well; designing the number of geophone stages and their placement position in the monitoring well according to the principle of the geophone being closest to the target layer of the fracturing well, with a well inclination angle of less than 2 degrees; lowering the geophone into the well and conducting debugging; locating perforation explosion events using the geophone in the monitoring well; real-time processing and interpretation engineers correcting the initial velocity model established before fracturing operations based on the perforation location file; synchronously acquiring downhole microseismic event data in the monitoring well throughout the entire fracturing process; after completing real-time fracturing monitoring, retrieving the geophone, performing subsequent velocity model correction and post-processing and interpretation of the acquired microseismic data, and evaluating the fracturing effect.

6. The intermittent fracturing process for tight reservoirs according to claim 1, characterized in that, Step S4 specifically involves: installing a pressure gauge at the wellhead of adjacent well 2 to monitor the changes in the pressure curve at the wellhead of adjacent well 2 during the fracturing operation.

7. The intermittent fracturing process for tight reservoirs according to claim 1, characterized in that, Step S5 specifically involves: using the designed displacement rate to pump 25-40% of the designed fluid volume as pre-flush fluid into the formation; continuously shutting in the well for 20-24 hours to loosen the formation; waiting for the surface pressure to reach the expected pressure, i.e., P. 地面压力 +P 液柱压力 ≈P 闭合压力 Continue with the normal pumping procedure.

8. The intermittent fracturing process for tight reservoirs according to claim 1, characterized in that, The data sources in step S6 specifically include downhole microseismic monitoring and pressure monitoring at the wellhead of adjacent wells.

9. The intermittent fracturing process for tight reservoirs according to claim 8, characterized in that, The downhole microseismic monitoring specifically involves: retrieving the geophone, performing subsequent velocity model correction and post-processing on the acquired microseismic data; the adjacent wellhead pressure monitoring specifically involves: retrieving the wellhead pressure gauge and plotting the pressure curve.

10. The intermittent fracturing process for tight reservoirs according to claim 9, characterized in that, Specifically, step S7 involves evaluating the fracturing effect using the processed downhole microseismic data and pressure curves collected in step S6.

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