A method for fracturing with a pre-pad body fracturing in a shale zone

Abstract

The application relates to a method for fracturing a fractured shale zone by using a pre-bridging body, and relates to the field of shale gas fracturing. The method comprises the following steps: establishing a shale fracture development degree judgment model, judging the natural fracture development degree of a target layer according to the shale fracture development degree judgment model; calculating different discharge wellhead pressure values according to well logging data interpretation and small pressure test data, and establishing a fractured shale zone body reconstruction construction pressure judgment standard; adopting a pre-bridging technology for construction in the early stage of fracturing implementation; and adjusting the discharge, liquid viscosity and in-joint bridging process parameters to realize reservoir reconstruction. The method for fracturing a fractured shale zone by using a pre-bridging body can help field engineers to judge the fracture development degree of a formation and evaluate whether fracturing reconstruction is effective, and on this basis, systematic pre-bridging technology and field construction control means are provided, so that the reconstruction effect of the fractured shale zone is effectively improved.

Description

Technical Field

[0001] This application relates to the field of shale gas fracturing, and more specifically, to a method for pre-plugging the main body of shale in fractured zones for fracturing. Background Technology

[0002] Hydraulic fracturing is a key technology for the large-scale development of unconventional oil and gas resources such as shale oil and gas and tight oil and gas. The effectiveness of large-scale volumetric fracturing determines the level of shale gas production. Therefore, in order to ensure a high single-well production, it is necessary to fully modify the shale reservoir.

[0003] A block within a shale gas field is predominantly at normal pressure, with 60% of the area exhibiting strong tectonic deformation and relatively fractured strata, including some areas containing large-scale natural fractures. Currently, the fracturing techniques used in China for shale gas reservoirs with large-scale fractures primarily involve "multi-cluster close-cutting combined with mid-course temporary plugging to promote fracture diversion," without addressing the specific geological condition of "large-scale fractures." Field adjustments are often based on "experience" and "trial and error," resulting in actual operating pressures far lower than the extension pressures of reservoirs in non-fractured zones, exhibiting a clear large-scale fracture-induced phenomenon. Furthermore, the mid-course temporary plugging technique has extremely limited effectiveness in sealing fractures, and the second-stage extension pressure after plugging does not significantly improve. Based on existing construction and testing data, the completed fractured zone wells, after casing testing, have not achieved the desired production levels.

[0004] In China, the following problems still exist in the fracturing and stimulation of shale gas reservoirs with large-scale fractures in fracture zones: First, for shale gas reservoirs with large-scale fractures, on-site engineers lack a means to quickly assess the degree of formation fracture development during fracturing operations; second, for this type of shale gas reservoir, there is a lack of a method to evaluate whether fracturing and stimulation is effective; third, for shale gas reservoirs with fractures, there is a lack of efficient large-scale fracture sealing and fracturing and stimulation technologies. Summary of the Invention

[0005] The purpose of this application is to provide a method for pre-fracturing of fractured shale, which can help field engineers determine the degree of formation fracture development and assess the effectiveness of fracturing stimulation. Based on this, it provides a systematic pre-fracturing process and on-site construction control methods, thereby effectively improving the stimulation effect of fractured shale.

[0006] This application is implemented as follows:

[0007] This application provides a method for pre-fracturing of shale in fractured zones using temporary plugging, comprising the following steps:

[0008] Establish a model for judging the degree of shale fracture development, and judge the degree of natural fracture development in the target stratum based on the model;

[0009] Based on the interpretation of well logging data and the calculation of low-pressure test data, wellhead pressure values ​​with different discharge rates were obtained, and a standard for judging the construction pressure of shale body stimulation in fractured zones was established.

[0010] In the early stages of fracturing, a pre-plugging technique is used.

[0011] Adjusting displacement, liquid viscosity, and temporary plugging process parameters within the fracture can achieve reservoir stimulation.

[0012] In some optional implementation schemes, when establishing a model for judging the degree of shale fracture development, a liquid efficiency > 30% is judged as a reservoir with relatively well-developed natural fractures, a liquid efficiency of 20%-30% is judged as a reservoir with well-developed natural fractures, a liquid efficiency of 15%-20% is judged as a reservoir with excessively developed natural fractures, and a liquid efficiency < 15% is judged as a reservoir with well-developed large-scale fractures.

[0013] In some alternative implementation schemes, when the wellhead pressure values ​​for different discharge rates are calculated based on the interpretation of well logging data and low-pressure test data, the bottom hole fracture pressure and minimum horizontal principal stress are calculated. The frictional resistance along the flow path, the perforation friction, and the bending friction under different discharge rates are obtained through low-pressure tests, and the total frictional resistance and fluid column pressure are calculated. The bottom hole fracture pressure and minimum horizontal principal stress are then converted into wellhead pressure values ​​for different discharge rates.

[0014] In some optional implementation schemes, when establishing the criteria for judging the construction pressure of shale body stimulation in fractured zones, the rock body is considered to be effectively fractured when the wellhead construction pressure is greater than the fracture pressure converted to the wellhead during the formation fracturing stage; when the wellhead pump pressure is greater than the minimum horizontal principal stress converted to the wellhead during the construction process after formation fracturing, the fracture is considered to be extending in the rock body; when the wellhead pump pressure of effectively fractured rock body and fracture extension in rock body is lower than the calculated value, the wellhead pump pressure is increased.

[0015] In some alternative implementations, when the natural fracture development of the target stratum is a large-scale fractured reservoir, the flow-limited perforation technique is used to open each cluster of holes uniformly, with 6 holes per cluster and no more than 45 holes per segment, and the spacing between clusters and segments is 15-25m.

[0016] In some alternative implementation schemes, the pre-implantation plugging process used in the early stages of fracturing includes the following steps:

[0017] S1. After acid reduction, the displacement will be increased to 7-8m³. 3 After pumping for 1 minute, observe the pressure. If there is a pressure window for adding sand, pump in 40-60 ml of 70 / 140 mesh proppant carrying liquid. 3Establish a passage between the wellbore and the natural fracture;

[0018] S2, Reduce displacement to 2-4m 3 Add 150-250 kg of temporary plugging agent per minute to increase the displacement to 7-8 m³ / min. 3 Continue pumping 40-60m / min 3 After carrying the sand and liquid, reduce the discharge rate to 2-4m³. 3 / min, add temporary plugging agent 150-250Kg for the second time;

[0019] S3, with 6-9m 3 / min displacement of adhesive solution 100-150m 3 ;

[0020] S4. After the pressure rises and stabilizes, increase the displacement to the target displacement.

[0021] S5, Construction fluid volume reaches 800-1000m³ 3 At that time, add temporary plugging knots with 50-60% of the number of holes for secondary temporary plugging;

[0022] S6. Perform the second stage of sand fracturing, and stop the pump when the sand and liquid volume reach the design values.

[0023] In some alternative implementations, the discharge rate is adjusted so that the construction pressure is higher than the minimum horizontal principal stress converted to the wellhead.

[0024] In some alternative implementations, when adjusting the temporary plugging process parameters in the joint, if the pressure rises rapidly and the sand addition pressure window is small during the stage of increasing the discharge rate in step S1 when adding the temporary plugging agent, the discharge rate can be increased to 12-14 m after acid degradation. 3 Processing is done in / min.

[0025] In some alternative implementations, in non-lost well sections, the addition of 150-250 kg of temporary plugging agent in step S2 can be replaced with the addition of 100-150 m... 3 A combination of adhesive and 5-7% (by weight) of 70 / 140 mesh support.

[0026] The beneficial effects of this application are as follows: The method for pre-plugging fracturing of fractured shale formations provided in this application includes the following steps: establishing a shale fracture development degree judgment model; judging the natural fracture development degree of the target formation based on the shale fracture development degree judgment model; calculating wellhead pressure values ​​at different discharge rates based on well logging data interpretation and low-pressure test data; establishing a standard for judging the construction pressure of fractured shale formation stimulation; using pre-plugging technology in the early stage of fracturing implementation; adjusting discharge rate, fluid viscosity, and in-fracture plugging process parameters to achieve reservoir stimulation. The method for pre-plugging fracturing of fractured shale formations provided in this application can help field engineers judge the formation fracture development degree and evaluate the effectiveness of fracturing stimulation, and on this basis, provide a systematic pre-plugging technology and on-site construction control methods, thereby effectively improving the stimulation effect of fractured shale formations. Attached Figure Description

[0027] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 This is a schematic flowchart illustrating a method for pre-plugging fracturing of shale in fractured zones, as provided in an embodiment of this application. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely represents selected embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0030] The features and performance of the method for pre-plugging the main body fracturing of shale in fractured zones according to this application are further described in detail below with reference to embodiments.

[0031] like Figure 1 As shown in the figure, this application provides a method for pre-plugging fracturing of shale in fractured zones, comprising the following steps:

[0032] Step 1: Establish a shale fracture development degree assessment model to determine the degree of natural fracture development in the target stratum. The shale fracture development degree assessment model is as follows: when the fluid efficiency is >30%, it is judged as a reservoir with relatively well-developed natural fractures; when the fluid efficiency is 20%-30%, it is judged as a reservoir with well-developed natural fractures; when the fluid efficiency is 15%-20%, it is judged as a reservoir with excessively developed natural fractures; and when the fluid efficiency is <15%, it is judged as a reservoir with large-scale fracture development.

[0033] Step 2: Based on the interpretation of well logging data and low-pressure test data, calculate the wellhead pressure values ​​for different discharge rates, and establish a standard for judging the construction pressure of shale body stimulation in fractured zones. Specifically, when establishing this standard, during the formation fracturing stage, if the wellhead construction pressure is greater than the fracturing pressure converted to the wellhead, it is considered as effectively fracturing the rock body. In the post-formation fracturing stage, if the wellhead pump pressure during construction is greater than the minimum horizontal principal stress converted to the wellhead, it is considered as fractures extending within the rock body. When the wellhead pump pressure for effectively fracturing the rock body and fractures extending within the rock body is lower than the calculated value, increase the wellhead pump pressure. Simultaneously, when the natural fracture development level of the target formation is a large-scale fractured reservoir, use flow-limited perforation technology to ensure uniform opening of each cluster of perforations, with 6 per cluster, no more than 45 per segment, and a cluster-to-segment spacing of 20m.

[0034] Step 3: In the early stages of fracturing, a pre-plugging process is used, which includes the following steps:

[0035] S1. After acid reduction, the displacement will be increased to 8m. 3 After pumping for 1 minute, observe the pressure. If there is a pressure window for adding sand, pump in 50 ml of 70 / 140 mesh proppant carrying sand solution. 3 Establish a passage between the wellbore and the natural fracture;

[0036] S2, Reduce displacement to 4m 3 / min, add 200Kg of temporary plugging agent, increase displacement to 8m 3 Continue pumping 50m / min 3 After carrying the sand liquid, reduce the discharge rate to 3m³. 3 / min, add 200 kg of temporary plugging agent in the second step;

[0037] S3, with 8m 3 / min displacement to introduce adhesive 150m 3 This reduces filtration loss and promotes the initial extension of cracks.

[0038] S4. After the pressure rises and stabilizes, increase the displacement to the target displacement.

[0039] S5, Construction fluid volume reaches 1000m 3At that time, add temporary plugging knots equal to 50% of the number of holes for secondary temporary plugging;

[0040] S6. Perform the second stage of sand fracturing, and stop the pump when the sand and liquid volume reach the design values.

[0041] Step 4: Adjust the displacement, liquid viscosity, and fracture plugging process parameters to achieve reservoir stimulation. When adjusting the displacement, ensure the construction pressure is higher than the minimum horizontal principal stress converted to the wellhead. When adjusting the liquid viscosity, consider the curve morphology and adopt a dynamic viscosity-changing process to meet the construction needs at different stages, based on fracture creation and proppant carrying requirements. When adjusting the fracture plugging process parameters, if the pressure rises rapidly and the proppant pressure window is small during the displacement-increasing stage of step S1 (pressure rise exceeding the conventional pressure by 20% and the proppant pressure window being less than the conventional proppant pressure window by 20%), the displacement can be increased to 14m³ after acid degradation. 3 The process is carried out at a rate of / min; in non-leakage sections, the addition of 200 kg of temporary plugging agent in step S2 can be replaced with the addition of 150 m 3 A combination of adhesive and 5% (by weight) of 70 / 140 mesh support.

[0042] The method for pre-plugging the main body of shale fracturing in fractured zones provided in this application provides a creative approach to fracturing shale in fractured zones by pre-plugging natural fractures in the early stages of fracturing. This allows field engineers to easily assess the degree of formation fracture development and evaluate the effectiveness of fracturing. Based on this, it provides a systematic pre-plugging process, supporting technologies, and on-site construction control methods. It has the advantages of reliable principle, good operability, and high accuracy, and can effectively improve the fracturing effect of shale in fractured zones.

[0043] The embodiments described above are some, but not all, of the embodiments of this application. The detailed description of the embodiments of this application is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

Claims

1. A method for pre-plugging fracturing of shale in fractured zones, characterized in that, Includes the following steps: A model for judging the degree of shale fracture development was established, and the degree of natural fracture development in the target stratum was judged based on the model. Based on the interpretation of well logging data and the calculation of low-pressure test data, wellhead pressure values ​​with different discharge rates were obtained, and a standard for judging the construction pressure of shale body stimulation in fractured zones was established. In the early stages of fracturing, a pre-plugging process is employed, including the following steps: S1. After acid reduction, the displacement will be increased to 7-8m³. 3 After pumping for 1 minute, observe the pressure. If there is a pressure window for adding sand, pump in 40-60 ml of 70 / 140 mesh proppant carrying liquid. 3 Establish a passage between the wellbore and the natural fracture; S2, Reduce displacement to 2-4m 3 Add 150-250 kg of temporary plugging agent per minute to increase the displacement to 7-8 m³ / min. 3 Continue pumping 40-60m / min 3 After carrying the sand and liquid, reduce the discharge rate to 2-4m³. 3 / min, add temporary plugging agent 150-250Kg for the second time; S3, with 6-9m 3 / min displacement of adhesive solution 100-150m 3 ; S4. After the pressure rises and stabilizes, increase the displacement to the target displacement. S5, Construction fluid volume reaches 800-1000m³ 3 At that time, add temporary plugging knots with 50-60% of the number of holes for secondary temporary plugging; S6. Perform the second stage of sand fracturing, and stop the pump when the sand and liquid volume reach the design values. Adjusting displacement, liquid viscosity, and temporary plugging process parameters within the fracture can achieve reservoir stimulation.

2. The method for pre-plugging fracturing of shale in fractured zones according to claim 1, characterized in that, When the wellhead pressure values ​​for different discharge rates are calculated based on the interpretation of well logging data and the small pressure test data, the bottom hole fracture pressure and the minimum horizontal principal stress are calculated. The frictional resistance along the flow path, the perforation friction, and the bending friction under different discharge rates are obtained through the small pressure test, and the total frictional resistance and the fluid column pressure are calculated. The bottom hole fracture pressure and the minimum horizontal principal stress are converted into wellhead pressure values ​​for different discharge rates.

3. The method for pre-plugging fracturing of shale in fractured zones according to claim 1, characterized in that, When establishing the criteria for judging the construction pressure of shale body stimulation in fractured zones, the rock body is considered to be effectively fractured when the wellhead construction pressure is greater than the fracture pressure converted to the wellhead during the formation fracturing stage; when the wellhead pump pressure is greater than the minimum horizontal principal stress converted to the wellhead during the construction process after formation fracturing, it is considered that the fracture extends in the rock body; when the wellhead pump pressure of the effectively fractured rock body and the fracture extending in the rock body is lower than the calculated value, the wellhead pump pressure is increased.

4. The method for pre-plugging fracturing of shale in fractured zones according to claim 1, characterized in that, When the natural fracture development of the target stratum is a large-scale fracture reservoir, the flow-limited perforation technology is used to open each cluster of holes evenly, with 6 holes per cluster and no more than 45 holes per segment, and the spacing between clusters and segments is 15-25m.

5. The method for pre-plugging fracturing of shale in fractured zones according to claim 1, characterized in that, When adjusting the discharge rate, ensure that the construction pressure is higher than the minimum horizontal principal stress converted to the wellhead.

6. The method for pre-plugging fracturing of shale in fractured zones according to claim 1, characterized in that, When adjusting the temporary plugging process parameters in the joint, if the pressure rises rapidly and the sand addition pressure window is small during the stage of increasing the discharge rate in step S1 when adding the temporary plugging agent, the discharge rate should be increased to 12-14 m after acid degradation. 3 Processing is done in / min.

7. The method for pre-plugging fracturing of shale in fractured zones according to claim 1, characterized in that, In the non-leakage section, the addition of 150-250 kg of temporary plugging agent in step S2 can be replaced with the addition of 100-150 kg. 3 A combination of adhesive and 5-7% (by weight) of 70 / 140 mesh support.

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