Fracturing pump injection method for increasing reconstruction volume of tight oil reservoir

Abstract

The invention belongs to the technical field of downhole operation fracturing in the petroleum industry, and discloses a fracturing pump injection method for increasing the transformation volume of a tight oil reservoir. Comprising the steps of determining the target current single-section sand amount, calculating the change of net pressure in an alternate injection seam, comparing parameter change, and adding gel in the slickwater sand adding period for alternate injection. By changing an original fracturing pump injection program, the transformation range of a reservoir around a well and the reserves in the fractures are expanded, software serves as a relying tool, the sand amount needed by the fractures meeting the tight oil artificial fracture flow conductivity under the determined liquid amount is simulated, the fracture size difference of conventional injection and alternate injection of single-cluster fractures is simulated, and the flow conductivity of the fractures is calculated. The liquid amount is controlled in a slick water continuous sand adding mode, and the flow conductivity of the crack reaches a target value in a high sand ratio gel sand adding mode.

Description

Technical Field

[0001] This invention belongs to the field of downhole fracturing technology in the petroleum industry, specifically relating to a fracturing pump injection method for increasing the volume of tight oil reservoirs. Background Technology

[0002] As tight oil production continues, reservoir continuity deteriorates, effective layer thickness thins, and drilling encounter levels decrease. The designed production capacity cannot be achieved using previous stimulation methods, necessitating the development of a method to increase reservoir stimulation volume for effective reserve utilization. Previous research on fluid flow patterns in the matrix-fracture system revealed an inverse relationship between fracture spacing and conductivity requirements. When fracture spacing is too large, the matrix's fluid supply to the fractures is limited, requiring only a small conductivity level to satisfy fluid flow. Conversely, when fracture spacing decreases, the flow rate in the fractures increases, thus requiring a larger conductivity level. Therefore, tight oil reservoirs adhere to a design principle of "sweet spot + dense fracture," increasing fracture density and shifting from well control to fracture control. Further increasing the stimulation volume requires optimization of the fracturing pumping procedure.

[0003] The previous pumping procedure was a slickwater slug-type sand injection, which required a large volume of liquid and also reduced the seepage distance of the reservoir matrix fluid to the artificial fractures due to the dense cutting of multiple fractures.

[0004] Literature review revealed that the current technology is a fracturing method (CN113309502A) for increasing the volume of deep shale gas reservoir stimulation. This method analyzes the compressibility, mechanical properties, and fracturing quality of shale, optimizes fracture morphology parameters and fracturing operation parameters, and increases the net pressure within the fracture through end-point desanding, thereby generating significant induced stress and promoting substantial extension of horizontal bedding fractures and branch fractures. Combined with the acid injected midway, a complex fracture network is formed through the combined physical and chemical effects. The pumping procedure focuses on using a stepped increase of low, medium, and high concentrations of slickwater and gel, along with four types of proppant particles, to achieve multi-scale fracture saturation filling, ultimately forming a sufficiently large effective stimulation volume. However, this technique is only applicable to single-lithology reservoirs, and the selection of fracturing fluid and pumping procedure are relatively simple, which has limitations. It represents a preliminary stage for achieving effective shale gas reservoir stimulation. Summary of the Invention

[0005] To overcome the shortcomings of existing technologies, this invention provides a fracturing pump injection method for increasing the volume of tight oil reservoirs. This method expands the wellbore's surrounding reservoir stimulation range and intra-fracture reserves by modifying the original fracturing pump injection program. Using software as a tool, it simulates the amount of sand required to achieve the conductivity of artificial fractures in tight oil reservoirs under a given fluid volume. It also simulates the difference in fracture size between conventional and alternating injection of single-cluster fractures. The fluid volume is controlled by continuously adding sand using slickwater, and the conductivity of the fractures is achieved to the target value through a high-sand-ratio gel sand addition method. The effectiveness of this pump injection method is verified by pressure changes in the field construction curve, thus achieving the goal of increasing the stimulation volume in the expanded perimeter zone.

[0006] The above-mentioned objective of this invention is achieved through the following technical solution: a fracturing pump injection method for increasing the volume of tight oil reservoirs, comprising the following steps:

[0007] (1) Determine the current target sand volume per section;

[0008] (2) Calculate the change in net pressure within the alternating injection gap;

[0009] (3) Compare parameter changes;

[0010] (4) During the process of adding sand to the slippery water, add gel alternately.

[0011] Furthermore, step (1) specifically involves: determining the amount of sand per segment at the target current scale by combining software simulation of different cluster sizes under a given liquid volume, based on the required flow capacity of the artificial cracks.

[0012] In a further preferred embodiment of the present invention, the software incorporated in step (1) is StimPlan.

[0013] Furthermore, step (2) specifically involves calculating the change in net pressure within the fracture when injecting gel fracturing fluid, i.e., alternating injection, during the slickwater fracturing process using a formula.

[0014] Furthermore, the formula in step (2) is as follows:

[0015]

[0016] Where: P—net pressure in the fracture, E—elastic modulus of the rock, μ a —Fluid viscosity, Q—Pumping flow rate, L—Crack length, h f — Crack height.

[0017] Furthermore, step (3) specifically involves: using a single cluster of cracks to simulate the crack morphology of conventional injection and alternating injection, and comparing the changes in parameters.

[0018] In a further preferred embodiment of the present invention, step (3) also simulates a multi-cluster crack propagation model and compares the specific parameters of the cracks.

[0019] Furthermore, step (4) specifically involves designing a pumping procedure in the test well as continuous sand addition with slickwater followed by high sand ratio gel injection. During the sand addition with slickwater, gel injection is added alternately.

[0020] The beneficial effects of this invention compared to existing technologies are: when applied to the fracturing pump injection program of tight oil horizontal wells, continuous sand injection with slickwater was implemented in 7 wells in the field, with a continuous sand injection volume of 87m³. 3 Three wells with a high sand ratio were tested using the gel injection method, with the highest sand ratio reaching 43%, and no sudden pressure increase was observed. Alternating injection of gel and slickwater effectively guided field application in 16 wells across 200 sections. A significant increase in pressure was observed before and after alternating injection. Calculations using the following formula show an increase in net pressure, accompanied by a subsequent sudden pressure drop, suggesting the formation of new fractures and an increase in the stirred-up volume. Furthermore, the oil-bearing cycle and production were better than other wells in the same block, verifying that this pumping procedure can effectively increase the stirred-up volume of the reservoir.

[0021] Net pressure = Construction pressure + Net fluid column pressure - Bottom hole closure pressure - Along-the-well friction - Near-well friction 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 invention provides a simulation diagram of cracks with different cluster numbers under the same liquid scale.

[0024] Figure 2 This invention provides a single-section sand volume that meets the flow guiding capacity under different cluster numbers.

[0025] Figure 3 This invention provides extended simulation diagrams of single-cluster fractures under two different modes: alternating injection and slickwater injection.

[0026] Figure 4 This invention provides simulation diagrams of the expansion of four clusters of perforation fractures under different modes of alternating injection and slickwater slug-filled sand addition (clusters 1 and 2).

[0027] Figure 5 The results are simulations of multi-cluster perforation under different fracturing methods in well Qian 246F Ping 5-6 (second section) provided in Embodiment 2 of the present invention.

[0028] Figure 6 This is the procedure provided in Embodiment 2 of the present invention for continuous sand addition, alternating injection, high sand ratio gel sand addition fracturing and sand pumping injection of the Qian 246F Ping 5-6 well (second section) with slickwater.

[0029] Figure 7 This is the construction curve of continuous sand addition, alternating injection, and high sand ratio gel sand addition for the Qian 246F Ping 5-6 well (second section) provided in Embodiment 2 of the present invention.

[0030] Figure 8 The data provided in Embodiment 2 of this invention are the production data of wells Qian 246F Ping 5-6 and adjacent wells (with conventional sand addition) Cha 58-17 and Qian 246-25. Detailed Implementation

[0031] 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.

[0032] Example 1

[0033] A fracturing pump injection method for increasing the volume of tight oil reservoirs

[0034] (1) First, based on the required flow capacity of the artificial cracks, the amount of sand per section under the current scale is determined by combining the software simulation of different cluster crack sizes under the given liquid volume.

[0035] (2) The change in net pressure in the fracture was calculated by the following formula when the gel fracturing fluid was injected alternately during the construction of the slippery water. The results showed that the net pressure when the gel was injected alternately was greater than the net pressure when the slippery water was injected.

[0036]

[0037] Where: P—net pressure in the fracture, E—elastic modulus of the rock, μ a —Fluid viscosity, Q—Pumping flow rate, L—Crack length, h f — Crack height.

[0038] (5) The fracture morphology of conventional injection and alternating injection was simulated by single-cluster fractures. The changes in parameters were compared. The results showed that the fracture length of alternating injection was 71.67m, while the fracture length of conventional injection was 61.92m, an increase of 15.7%. Considering the stress and other influencing factors of multi-cluster perforation in horizontal wells, a multi-cluster fracture propagation model was simulated. The fracture propagation length at different perforation locations showed a non-uniform increase.

[0039] (6) The pumping procedure designed for the test well is continuous sand addition with slickwater + high sand ratio gel in the later stage. During the sand addition with slickwater, gel is added and injected alternately.

[0040] Example 2

[0041] Taking the Qian 246F Ping 5-6 well as an example, this well is a horizontal well in the tight oil Qian 246 block, targeting the first sand group of the fourth section of the Fengquan Formation. The whole well uses continuous sand addition with slickwater, high sand ratio with gel, and alternating injection. Taking the second section as an example, the number of perforation clusters in this section is 4.

[0042] The specific implementation process is as follows:

[0043] The first step is to simulate fractures that meet the conductivity requirements under the current geological conditions of this well to determine the required fracturing scale for this section;

[0044] The second step involves designing two different pumping procedures—alternating injection and conventional construction—based on the scale of the cracks, and comparing the specific parameters of the cracks.

[0045] The third step is to design a combination of continuous sand addition, alternating injection, and high sand ratio gel sand addition in the pumping procedure.

[0046] The fourth step is to carry out construction and determine the rationality of the method based on the construction curve results.

[0047] To verify the effectiveness of the present invention, the production data of well Qian 246F Ping 5-6 and adjacent wells were compared. Well Qian 246F Ping 5-6 had a shorter oil-bearing cycle than adjacent wells, and its daily oil and fluid production was slightly higher than that of adjacent wells. This indicates that the fracture conductivity was improved to a certain extent, and the reserves and volume of the fracture were increased. The pumping method of the present invention is effective and reliable, and can effectively improve the production and efficiency of a single well.

[0048] 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. A fracturing pump injection method for increasing the volume of a tight oil reservoir, characterized in that, The steps are as follows: S1. Determine the current sand volume for a single section; S2. Calculate the change in net pressure within the alternating injection gap; S3. Compare parameter changes; S4. During the sand-addition process, add gel alternately.

2. The fracturing pump injection method for increasing the volume of tight oil reservoirs according to claim 1, characterized in that, Specifically, step S1 involves determining the amount of sand per segment at the target current scale by combining software simulation of different cluster sizes based on the required flow capacity of the artificial cracks and the determined liquid volume.

3. The fracturing pump injection method for increasing the volume of tight oil reservoirs according to claim 2, characterized in that, The software used in step S1 is StimPlan.

4. The fracturing pump injection method for increasing the volume of tight oil reservoirs according to claim 1, characterized in that, Step S2 specifically involves calculating the change in net pressure within the fracture when injecting gel fracturing fluid, i.e., alternating injection, during slickwater fracturing.

5. The fracturing pump injection method for increasing the volume of tight oil reservoirs according to claim 4, characterized in that, The formula in step S2 is as follows: Where: P—net pressure in the fracture, E—elastic modulus of the rock, μ a —Fluid viscosity, Q—Pumping flow rate, L—Crack length, h f — Crack height.

6. The fracturing pump injection method for increasing the volume of tight oil reservoirs according to claim 1, characterized in that, Step S3 specifically involves: using a single cluster of fractures to simulate the fracture morphology of conventional injection and alternating injection, and comparing the changes in parameters.

7. The fracturing pump injection method for increasing the volume of tight oil reservoirs according to claim 6, characterized in that, Step S3 also simulates a multi-cluster crack propagation model and compares the specific crack parameters.

8. The fracturing pump injection method for increasing the volume of tight oil reservoirs according to claim 1, characterized in that, The specific step S4 is as follows: the pumping procedure designed in the test well is continuous sand addition with slickwater + high sand ratio gel in the later stage, and gel is added alternately during the sand addition with slickwater.

Images