A control method for improving the success rate of shale oil fracturing construction

Abstract

The present invention relates to a control method for improving the success rate of shale oil fracturing operations. The method comprises: Measure 1: Optimizing the pre-fluid ratio, based on a numerical model of the pre-fluid ratio, by increasing the pre-fluid ratio to reduce the complexity of near-wellbore fracture morphology; Measure 2: Adopting a preset sand ratio process, using a test sand ratio method during the continuous sand addition process, judging the sensitivity of the formation to the sand ratio based on the changes in the construction pressure, and determining the sand carrying ratio for the next step; Measure 3: Adopting an integrated slickwater fracturing fluid system to achieve linear adjustment of the fracturing fluid viscosity to ensure continuous proppant injection; Measure 4: Rationally controlling the construction displacement, reserving a pressure window, and reducing sand blockage in the fracture caused by poor proppant migration. This control method for improving the success rate of shale oil fracturing operations can significantly improve the success rate of shale oil well fracturing operations and the construction scale compliance rate by rationally applying the above measures.

Description

Technical field:

[0001] The present invention relates to the technical field of petroleum extraction, and in particular to a control method for improving the success rate of shale oil fracturing construction. Background technology:

[0002] Shale reservoirs have unique geological conditions, characterized by predominantly nanoscale pores, highly developed lamellae, low horizontal permeability, and a lack of vertical flow, which present challenges in fracturing to stimulate production. Currently, shale oil reservoir stimulation primarily utilizes a composite stimulation approach, combining high-viscosity primary fractures with low-viscosity open lamellae, to enhance the reservoir's vertical production and fracture complexity.

[0003] There are three main problems with existing reservoir transformation technologies: First, continuous sand addition is impossible, and the maximum sand ratio is relatively low: plug-type sand addition is mostly used. As the net pressure in the fracture fluctuates, the near-well bedding fractures open excessively, resulting in multiple fracture competition, difficulty in extending the artificial main fracture, discontinuous sand concentration, and low fracture conductivity; Second, shale oil reservoirs require high-intensity, large-volume fracturing transformation, but their reservoir anisotropy varies significantly, which easily forms complex fractures, resulting in small fracture openings and high pore friction resistance, resulting in a small ground construction pressure window, high construction risks, and easy sand plugging; Third, due to the high difficulty of shale oil fracturing construction, construction difficulties occur from time to time, making it difficult to successfully meet construction requirements. Statistics from previous construction situations show that the average single well exceeded the designed liquid volume by 12.88%, the average sand addition completion rate was only 92.11%, and the construction success rate was only 78.6%. Summary of the invention:

[0004] The present invention addresses the problems existing in the prior art and provides a control method for improving the success rate of shale oil fracturing operations. This control method optimizes the characteristics of shale oil reservoirs, such as developed horizontal bedding, complex near-wellbore fracture morphology, high sand ratio sensitivity, high risk of continuous proppant injection, and a small operation pressure window, to improve the success rate and ensure the scale of operation.

[0005] The present invention solves the problem by the following technical solution: The control method for improving the success rate of shale oil fracturing construction includes:

[0006] Measure 1: Optimize the pre-pad ratio. Based on the pre-pad ratio numerical model, the complexity of the near-wellbore fracture morphology can be reduced by increasing the pre-pad ratio.

[0007] Measure 2: Use the preset sand ratio process and test the sand ratio during the continuous sand addition process to judge the sensitivity of the formation to the sand ratio based on the changes in construction pressure and determine the sand ratio for the next step;

[0008] Measure 3: Adopt an integrated slickwater fracturing fluid system to achieve linear adjustment of fracturing fluid viscosity and ensure continuous proppant injection;

[0009] Measure 4: Reasonably control the construction displacement, control the opening degree of bedding joints, and reserve a pressure window.

[0010] Furthermore, the numerical model of the pre-fluid ratio in the first measure is:

[0011]

[0012] Formula 1 is transformed into:

[0013]

[0014] in:

[0015]

[0016]

[0017] but

[0018] In formula 1-5: V p is the volume of the pre-fluid, m 3 ; V O is the total volume of injected liquid, m 3 ;t f is the time of injecting sand-carrying fluid, min; t i is the total injection time, min; η is the fracturing fluid efficiency, %; h f C is the crack height, m; e is the comprehensive filtration coefficient, ;X f is the crack length, m; q i is the fracturing fluid loss rate, ml / min; W is the crack width, m; is the pre-fluid ratio.

[0019] Furthermore, the proportion of pre-fluid is increased to 25-30% during the pre-fluid pumping stage to ensure that the length and width of the fractures can be effectively expanded, providing favorable conditions for the proppant to smoothly enter the formation during the subsequent sand-carrying fluid stage.

[0020] Furthermore, the method of using the test sand ratio in the continuous sand adding process in the second measure is: at the beginning of each step of the sand ratio, the sand ratio is briefly increased to the next step sand ratio and then dropped back to the lower level sand ratio. If the pressure trend of the next step of sand entering the formation is normal, this method can be used in sequence to increase the sand ratio until the designed sand adding is completed.

[0021] Furthermore, the test sand ratio method is used in the continuous sand adding process to judge the sensitivity of the formation to the sand ratio according to the change of construction pressure. The specific method for determining the sand ratio for the next step is as follows:

[0022] During the sand-carrying fluid pumping process, when the construction pressure rising slope K is between -1 and 0 MPa / min, the pressure trend is normal, indicating that the cracks are extending normally and effectively; when the construction pressure rising slope K is between 0 and 0.2 MPa / min, the construction pressure fluctuates to a certain extent, indicating that there is a certain resistance to crack extension and further observation is required; when the construction pressure rising slope K is between 0.2 and 0.5 MPa / min, the construction pressure fluctuates significantly, indicating that the crack extension resistance is large and the construction sand ratio needs to be controlled; when the construction pressure rising slope K is between 0.5 and 1 MPa / min, the construction pressure fluctuates violently, indicating that the cracks have basically stopped extending and sand replacement needs to be stopped immediately.

[0023] Furthermore, the third measure adopts an integrated slickwater fracturing fluid system, and adjusts the integrated slickwater ratio according to the actual construction conditions and fracturing construction pressure on site to achieve a method for linearly adjusting the viscosity of the fracturing fluid:

[0024] When communicating with natural cracks to build a complex seam network system in the early stage of construction, integrated slippery water with a ratio of 0.1% or 0.2% can be used;

[0025] When the construction pressure fluctuates significantly during construction and sand screening occurs, integrated slickwater with a ratio of 0.3%, 0.4% or even higher can be used to ensure smooth migration of the proppant in the fracture.

[0026] After the construction pressure stabilizes and the cracks extend normally, the ratio of integrated slick water can be reduced again to 0.1% or 0.2% to continue construction.

[0027] Furthermore, the fourth measure is to reasonably control the construction displacement, control the opening degree of the bedding joints, and reserve the pressure window;

[0028] S1. Use the method of controlling the construction displacement, that is, reducing the construction displacement by a certain amount. After reducing the construction displacement, observe the change in the pressure slope. If the pressure slope decreases, it means that some bedding fractures are closed and the artificial fractures continue to extend along the main fracture.

[0029] If there is no obvious change in the pressure slope of S2, the construction displacement can be reduced again by a certain amount to observe the change in the pressure slope. If the pressure slope decreases, it means that some bedding fractures are closed and the artificial fractures continue to extend along the main fracture.

[0030] Furthermore, the S1 step reduces the construction displacement to 0.3-0.5m 3 / min; the S2 step further reduces the construction displacement to 0.3-0.5m 3 / min.

[0031] Furthermore, the method used to reduce the construction displacement is to reduce the operating gear and engine speed of 2 to 3 fracturing trucks.

[0032] Compared with the above background technology, the present invention has the following beneficial effects:

[0033] 1. During the pre-fluid pumping stage, the pre-fluid ratio is increased from the previous 15-20% to 25-30%. On the one hand, it effectively reduces the complexity of the near-well fracture morphology and increases the fracture sweep volume before sand addition. On the other hand, it reduces the insufficient fracturing fluid efficiency caused by excessive filtration of fracturing fluid due to the low viscosity of integrated slick water.

[0034] 2. During the sand-carrying fluid stage, a combination of measures such as tentative injection of proppant-sand ratio, linear change of integrated slickwater viscosity, and reasonable control of construction displacement are used to achieve continuous injection of proppant, thereby avoiding low construction success rate and substandard compliance rate caused by sand blockage.

[0035] The present invention provides a control method for improving the success rate of shale oil fracturing operations. This method reduces the complexity of near-wellbore fracture morphology by increasing the pre-fluid ratio; pre-setting the sand ratio to determine the formation's sensitivity to the sand ratio and the subsequent sand-carrying ratio; and integrating a slickwater fracturing fluid system to linearly adjust the fracturing fluid viscosity. Furthermore, the method reduces the operation flow rate to control the degree of bedding fracture opening, thereby improving the success rate and ensuring the scale of operation. In 2021, this method was applied in the Qingshankou Formation shale oil reservoir in the Qijiagulong Depression of the Songliao Basin. After implementing these control measures, the sand-fluid ratio decreased from 1:23.2 to 1:10.4, the excess fluid volume decreased from 12.88% to 5.09%, the completed sand addition rate increased from 92.11% to 100.19%, and the operation success rate increased from 78.6% before the measures to 100% after the measures, demonstrating significant results. Description of the drawings:

[0036] Figure 1 This is a flow chart of a control method for improving the success rate of shale oil fracturing construction according to the present invention;

[0037] Figure 2 Schematic diagram of the relationship between construction progress and sand carrying ratio in an embodiment of the present invention. Specific implementation method:

[0038] To make the objectives, technical solutions and advantages of the present invention more clear, the embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0039] like Figure 1 As shown, the present invention provides a control method for improving the success rate of shale oil fracturing operations, including: taking measures to increase the pre-fluid ratio during the pre-fluid stage; and taking measures to preset the sand ratio process, linearly adjust the viscosity, and reasonably control the displacement during the sand-carrying fluid stage. Specifically, it includes:

[0040] Measure 1: Optimize the pre-pad ratio. Based on the pre-pad ratio numerical model, the complexity of the near-wellbore fracture morphology can be reduced by increasing the pre-pad ratio.

[0041] The main function of pre-placed high-viscosity fluid is to create fractures. The amount of pre-placed high-viscosity fluid depends on the efficiency of the fracturing fluid; and the efficiency of the fracturing fluid is closely related to the reservoir conditions and the performance of the fracturing fluid. If the pre-placed fluid is insufficient, the extension of the fracture is limited, which may cause construction failure.

[0042] Therefore, we first calculate the optimization adjustment model of the front high mucus ratio:

[0043]

[0044] The pre-fluid ratio can be converted into:

[0045] in:

[0046]

[0047] but

[0048] In formula 1-5: V p is the volume of the front high mucus, m 3 ; V O is the total volume of injected liquid, m 3 ;t f is the time of injecting sand-carrying fluid, min; t i is the total injection time, min; η is the fracturing fluid efficiency, %; h f C is the crack height, m; e is the comprehensive filtration coefficient, X f is the crack length, m; q i is the fracturing fluid loss rate, ml / min; W is the crack width, m; is the pre-fluid ratio.

[0049] Based on the optimization adjustment model of the pre-fluid ratio, it can be seen from the fracturing fluid efficiency formula 4 that the fracturing fluid loss rate is negatively correlated with the fracturing fluid efficiency. When the fracturing fluid loss rate is too high, the fracturing fluid efficiency decreases. If the fracturing fluid efficiency is too low, it will affect the stimulation parameters such as fracture length, fracture width and fracture height. When the fracturing fluid efficiency remains unchanged, excessive fracturing fluid loss will lead to insufficient fracture space, and the proppant in the subsequent sand-carrying fluid stage will not be able to smoothly enter the formation and migrate efficiently in the artificial fracture.

[0050] Equation 5 shows that the amount of pre-fluid is negatively correlated with the efficiency of the fracturing fluid. The lower the fracturing fluid efficiency, the higher the pre-fluid volume required to achieve the relevant scale fracture size. The viscosity of conventional guar gum fracturing fluid is 300-400 MPa*s, while the viscosity of integrated slickwater at a high viscosity ratio of 0.4% is only 50-60 MPa*s. Therefore, the use of an integrated slickwater fracturing fluid system is very likely to cause inefficiency. It is necessary to increase the amount of pre-fluid to improve the fracture-forming efficiency of the fracturing fluid to avoid construction failure due to limited crack extension.

[0051] Therefore, the proportion of integrated slickwater pre-fluid is increased to 25-30%, which can reduce the insufficient fracture size caused by insufficient fracturing fluid efficiency, ensure that the fracture length and width can be effectively expanded, avoid the complex morphology of near-well fractures, increase the fracture sweep volume before sand addition, and provide favorable conditions for the smooth entry of proppant into the formation in the subsequent sand-carrying fluid stage.

[0052] Measure 2: Use the preset sand ratio process and test the sand ratio during the continuous sand addition process to judge the sensitivity of the formation to the sand ratio based on the changes in construction pressure and determine the sand ratio for the next step;

[0053] In the process of continuous sand addition, the test sand ratio method is adopted, that is, at the beginning of each sand ratio, the sand ratio is briefly increased to the next sand ratio and then reduced back to the lower sand ratio. If the pressure trend of the next sand entering the formation is normal, this method can be used in sequence to increase the sand ratio until the designed sand addition is completed. This method can judge the sensitivity of the formation to the sand ratio according to the changes in construction pressure and determine the sand carrying ratio for the next step.

[0054] Figure 2 The relationship diagram between the sand carrying ratio and the construction pressure is shown in the figure. As shown in the figure, during the continuous sand carrying process: when the construction pressure rising slope K is between -1 and 0 MPa / min, the pressure trend is normal, indicating that the cracks extend normally and effectively; when the construction pressure rising slope K is between 0 and 0.2 MPa / min, the construction pressure fluctuates to a certain extent, indicating that there is a certain resistance to crack extension and further observation is required; when the construction pressure rising slope K is between 0.2 and 0.5 MPa / min, the construction pressure fluctuates significantly, indicating that the crack extension resistance is large and the construction sand ratio needs to be controlled; when the construction pressure rising slope K is between 0.5 and 1 MPa / min, the construction pressure fluctuates violently, indicating that the cracks have basically stopped extending and sand replacement needs to be stopped immediately.

[0055] Measure 3: Adopt an integrated slickwater fracturing fluid system to achieve linear adjustment of fracturing fluid viscosity and ensure continuous proppant injection;

[0056] Increasing the slickwater ratio can increase the viscosity of the fracturing fluid. The integrated slickwater with a ratio of 0.1% and 0.2% has a low viscosity and a large filtration loss. The use of low-ratio integrated slickwater in the early stage can ensure that the artificial fractures and natural fractures are fully and effectively connected at the low sand ratio stage, thereby increasing the overall fracturing transformation volume. However, due to its poor sand-carrying performance, it is easy to cause sand shedding. After sand shedding, the proppant settles in the fracture, causing sand blockage, affecting the overall construction efficiency. Therefore, when the construction pressure fluctuates significantly during construction and fracturing fluid sand shedding occurs, the concentration of the integrated slickwater in the fracturing fluid can be adjusted in advance to 0.3%, 0.4% or even a higher ratio to improve the sand-carrying performance of the fracturing fluid, so that the proppant can be smoothly transported in the artificial and natural fractures, ensuring construction continuity. When the construction pressure is stable and the fracture extension is normal, the integrated slickwater ratio can be reduced again to 0.1% or 0.2% to continue construction.

[0057] Measure 4: Reasonably control the construction displacement, control the opening degree of the bedding joints, and reserve a pressure window;

[0058] There is a linear relationship between construction pressure and construction displacement. The higher the construction displacement, the higher the construction pressure. Shale oil wells have unique reservoir geological conditions, extremely developed lamellae, and the pressure is generally high during fracturing. Excessive construction pressure will increase the net pressure in the fracture, thereby opening the bedding fractures in the shale reservoir. When the extremely developed bedding fractures are excessively opened, it will cause multiple fractures to compete, thereby narrowing the width of the artificial fracture. When the sand-to-liquid ratio and the fluidity of the fracturing fluid do not change, if the construction pressure rises at a stable slope, the method of controlling the construction displacement can be adopted, that is, reducing the construction displacement by 0.3 to 0.5 m 3 / min, and observe the change of pressure slope after reducing it. If the pressure slope decreases, it means that part of the bedding fractures are closed and the artificial fractures continue to extend along the main fracture. If the pressure slope does not change significantly, the construction displacement can be reduced again by 0.3-0.5m 3 / min, repeat the previous steps. However, this method should not be used more than twice per step, as it will be ineffective. The actual formation conditions, fracturing fluid properties, and proppant addition should be analyzed separately. Methods for reducing operation displacement include: reducing the operating gear and engine speed of two or three fracturing trucks.

[0059] The control method for improving the success rate of shale oil fracturing construction of the present invention was field tested in shale oil wells in the Qijiagulong Depression of the Songliao Basin in 2021. The comparison of the scale and completion status of shale oil well fracturing construction before and after the adoption of the method and measures of the present invention is shown in Table 1.

[0060] Table 1 Comparison of shale oil well fracturing construction scale and completion status before and after measures

[0061]

[0062] As can be seen from Table 1, compared with before 2021, after taking control measures, the sand-liquid ratio dropped from 1:23.2 to 1:10.4, basically achieving the goal of controlling liquid and stabilizing sand. The construction success rate increased from 78.6% to 100%, and the average sand addition completion rate also increased from 92.11% to 100.19%. The application effect is significant, achieving the goal of improving the construction success rate and ensuring the construction scale.

Claims

1. A control method for improving the success rate of shale oil fracturing operation, characterized by: include: Measure 1: Optimize the pre-pad ratio. Based on the pre-pad ratio numerical model, the complexity of the near-wellbore fracture morphology can be reduced by increasing the pre-pad ratio. Measure 2: Use the preset sand ratio process, use the test sand ratio method during the continuous sand addition process, judge the sensitivity of the formation to the sand ratio according to the changes in construction pressure, and determine the next sand carrying ratio; the specific method is: During the sand-carrying fluid pumping process, when the construction pressure rising slope K is between -1 and 0 MPa / min, the pressure trend is normal, indicating that the crack is extending normally and effectively; when the construction pressure rising slope K is between 0 and 0.2 MPa / min, the construction pressure fluctuates to a certain extent, indicating that there is a certain resistance to crack extension and further observation is required; when the construction pressure rising slope K is between 0.2 and 0.5 MPa / min, the construction pressure fluctuates significantly, indicating that the crack extension resistance is large and the construction sand ratio needs to be controlled; when the construction pressure rising slope K is between 0.5 and 1 MPa / min, the construction pressure fluctuates violently, indicating that the crack has basically stopped extending and sand replacement needs to be stopped immediately; Measure 3: Use an integrated slickwater fracturing fluid system to achieve linear adjustment of fracturing fluid viscosity and ensure continuous proppant injection; the specific method is: When communicating with natural cracks to build a complex seam network system in the early stage of construction, use integrated slickwater with a ratio of 0.1% or 0.2%; When the construction pressure fluctuates significantly during construction and sand screening occurs, use 0.3% or 0.4% or even higher proportion of integrated slick water to ensure smooth migration of proppant in the fracture; After the construction pressure stabilizes and the cracks extend normally, reduce the proportion of integrated slick water to 0.1% or 0.2% and continue construction; Measure 4: Reasonably control the construction displacement, control the opening degree of the bedding joints, and reserve a pressure window; the specific methods are: S1. Use the method of controlling the construction displacement, that is, reducing the displacement by 0.3 to 0.5m 3 / min construction displacement, after reducing the construction displacement, observe the change of pressure slope. If the pressure slope decreases, it means that some bedding fractures are closed and the artificial fractures continue to extend along the main fracture. S2. If there is no significant change in the pressure slope, reduce the pressure again by 0.3 to 0.5 m 3 / min construction displacement, observe the change of pressure slope. If the pressure slope decreases, it means that some bedding fractures are closed and the artificial fractures continue to extend along the main fracture.

2. The control method for improving the success rate of shale oil fracturing according to claim 1, characterized in that: The numerical model of the pre-fluid ratio in measure 1 is: ……（1）； Formula 1 is transformed into: ……（2）； in: …… （3）； …… （4）； but ……(5); In formula 1-5: is the volume of the pre-fluid, m 3 ; is the total volume of injected liquid, m 3 ; is the time of injecting sand-carrying fluid, min; is the total injection time, min; η is the fracturing fluid efficiency, %; is the crack height, m; is the comprehensive filtration coefficient, m / ; is the crack length, m; is the fracturing fluid loss rate, ml / min; is the crack width, m; 3. The control method for improving the success rate of shale oil fracturing according to claim 1, characterized in that: During the pre-fluid pumping stage, the pre-fluid ratio is increased to 25-30%, ensuring that the length and width of the fractures can be effectively expanded, and providing favorable conditions for the proppant to smoothly enter the formation during the subsequent sand-carrying fluid stage.

4. The control method for improving the success rate of shale oil fracturing according to claim 1, characterized in that: The second measure adopts the method of testing sand ratio in the continuous sand adding process: at the beginning of each sand ratio, the sand ratio is briefly increased to the next sand ratio and then reduced back to the lower sand ratio. If the pressure trend of the next sand entering the formation is normal, the sand ratio is increased in sequence using this method until the designed sand adding is completed.

5. The control method for improving the success rate of shale oil fracturing according to claim 1, characterized in that: The method used to reduce the construction displacement is to reduce the operating gear and engine speed of 2 to 3 fracturing trucks.

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