A fracturing process for controlling fracture height and extending tight oil vertical wells

Abstract

A tight oil vertical well controlled fracture height extension fracturing process mainly solves the problem that the existing target reservoir has weak upper and lower stress shielding and lithologic shielding, resulting in the predicted fracture height being much greater than the reservoir thickness, causing serious ineffective transformation of the reservoir exterior. It includes the following steps: S1, predicting the longitudinal extension fracture height of the target layer segment, and determining the top depth and bottom depth of the predicted fracture height; S2, determining the target reservoir to be fractured; S3, performing controlled fracture height extension fracturing construction on the target layer segment, first performing the first stage main fracturing construction; S4, re-increasing the fracturing construction displacement, starting the second stage main fracturing construction, gradually increasing it to the designed main fracturing construction displacement, switching the fracturing fluid to a high-viscosity liquid, starting sand addition, completing the construction according to the designed sand addition procedure, stopping the machine, and switching to the next layer; after the construction of all designed target layer segments is completed, the fracturing string is removed and pumped down for production. The fracturing process of the present invention can control the fracture height extension and reduce ineffective transformation.

Description

Technical Field

[0001] The present invention relates to the technical field of oil production engineering, and in particular to a fracturing process for controlling crack height extension in a tight oil vertical well. Background Art

[0002] For thin-layer tight oil vertical wells, some areas commonly experience weak stress shielding and lithologic shielding above and below the target reservoir, resulting in predicted fracture heights far exceeding the reservoir thickness. This can lead to serious ineffective external reservoir reconstruction. At the same time, if the target reservoir is located above the predicted fracture height, after the main fracturing operation is completed, the proppant will settle to the bottom of the fracture. At this time, the conductivity of the target reservoir will be greatly reduced, affecting the post-fracturing production effect. Therefore, for this type of tight oil vertical well, it is necessary to control the vertical extension height of the fracture, reduce ineffective reconstruction outside the reservoir, ensure effective support within the reservoir, and at the same reconstruction scale, increase the length of the effective support fracture in the lateral direction of the reservoir. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to overcome the phenomenon in the background technology that the upper and lower stress shielding and lithologic shielding of the target reservoir are both weak, which leads to the predicted fracture height being much greater than the reservoir thickness, resulting in serious ineffective transformation of the reservoir outside, and to provide a new type of tight oil vertical well controlled fracture height extension fracturing process method. The new type of tight oil vertical well controlled fracture height extension fracturing process method can control the fracture height extension, reduce ineffective transformation, increase the effective support fracture length of the reservoir in the horizontal direction, and ultimately improve the single well transformation effect.

[0004] The present invention solves the problem by the following technical solution: The novel tight oil vertical well controlled fracture height extension fracturing process method comprises the following steps:

[0005] S1. Conduct logging interpretation of the target well and determine relevant parameters and shielding types based on the logging interpretation results of the target well. Based on the interpretation results of reservoir and barrier layer stress and GR value, predict the longitudinal extension fracture height of the target layer and determine the top and bottom depths of the predicted fracture height.

[0006] S2. Determine the positional relationship between the target reservoir and the predicted fracture height. Based on the positional relationship between the target reservoir and the predicted fracture height, determine and determine the target reservoir that needs to be fractured, and perform controlled fracture height extension fracturing on the target reservoir.

[0007] S3. For the target layer section that needs to be subjected to controlled fracture height extension fracturing, the target layer section is first perforated and scraped to facilitate drilling. After completing the pre-fracturing preparations, the target layer section controlled fracture height extension fracturing is started, and the first stage main fracturing is performed.

[0008] S4. After the first stage of fracturing is completed, the pump is stopped for a period of time, the fracturing displacement is increased again, and the second stage of main fracturing is started. After the construction is completed, the layer is switched to the next stage;

[0009] S5. After the construction of all the designed target layers is completed, the fracturing string in the well is pulled out and the pump is lowered to start production.

[0010] Furthermore, the step S1 determines the relevant parameters as two parameters based on the target well logging interpretation results: the first parameter is the reservoir-interlayer in-situ stress difference, and the second parameter is the reservoir-interlayer GR difference;

[0011] The shielding types are stress shielding and lithologic shielding. Generally, when the interlayer is more than 3m thick and the stress difference between the interlayer and the reservoir is greater than 3MPa, it is considered to have obvious stress shielding. When the interlayer is more than 3m thick and the GR value difference between the interlayer and the reservoir is more than 60API, it is considered to have obvious lithologic shielding.

[0012] Furthermore, the method for determining the positional relationship between the target reservoir and the predicted fracture height in step S2 is as follows: the target reservoir is located above the predicted fracture height, that is, the top depth H2 of the target layer is greater than or equal to the middle position of the predicted fracture height, H2≧H1+(H1-h1) / 2;

[0013] The target reservoir is located at the lower part of the predicted fracture height, that is, the top depth H2 of the target layer is less than the middle position of the predicted fracture height, when H2﹤H1+(H1-h1) / 2;

[0014] Where: H1: predicted depth of the top of the seam height;

[0015] h1: predicted seam height bottom depth;

[0016] H2: depth of top of target layer;

[0017] h2: depth of the bottom of the target layer;

[0018] H1+(H1-h1) / 2: predicted seam height center position;

[0019] Determine and identify the target reservoir that needs fracturing:

[0020] When the target reservoir is located above the predicted fracture height, it is necessary to perform fracture extension fracturing on the target layer with controlled fracture height.

[0021] When the target reservoir is located below the predicted fracture height, there is no need to perform fracture height control and extension fracturing on the target layer.

[0022] Furthermore, the first stage fracturing construction process of step S3 is as follows:

[0023] During the first stage of fracturing in the target layer, the pre-fluid is first injected, and the operation displacement needs to be controlled at the same time;

[0024] After the formation is opened and the pressure is stabilized, a well-mixed quartz sand plug is added;

[0025] After the quartz sand plug is added, the pump is stopped for 20-30 minutes, and the three types of quartz sand with uniform particle sizes are evenly mixed and settled to the bottom of the crack under the action of gravity.

[0026] Furthermore, the pre-fluid placed in the first stage of fracturing construction in step S3 is a low-viscosity liquid; the low-viscosity liquid is integrated low-viscosity slick water; and the viscosity of the liquid does not exceed 10 mPa.s.

[0027] Furthermore, in the first stage of the fracturing operation in step S3, the construction displacement is controlled at 3-5m 3 / min;

[0028] In the first stage of fracturing construction, 6 to 10 well-mixed quartz sand plugs are added; the quartz sand plug to sand ratio is 3 to 7%.

[0029] Furthermore, in step S3, the quartz sand is quartz sand of three commonly used particle sizes of 70-140 mesh, 40-70 mesh, and 20-40 mesh, which are fully mixed in a certain ratio of 3:3:4.

[0030] Furthermore, the concentration of quartz sand added to the slug in step S3 is 80 kg / m 3 .

[0031] Furthermore, the second stage fracturing construction method in step S4 is:

[0032] Increase the step-by-step flow rate gradually to the designed main fracturing operation flow rate, and take 3-4 steps to increase the flow rate to the designed operation flow rate. At the same time, pay attention to the changes in the ground operation pressure during the operation process. If the operation pressure increases too quickly, the number of steps can be further increased.

[0033] Then, the amount of sand added in a single section can be used to determine whether the conditions for adding multiple quartz sand slugs are met. If the total sand volume of the layer section exceeds the designed sand addition volume, additional slug addition is required. Specifically, multiple 70 / 140 mesh quartz sand slugs and 40 / 70 mesh quartz sand slugs are added in sequence, and the fracturing fluid is switched to a high-viscosity liquid. Construction is completed according to the designed sand addition procedure, the machine is stopped, and then the next section is moved to.

[0034] After adding 5-10 70 / 140 mesh quartz sand plugs and 40 / 70 mesh quartz sand plugs in sequence, the fracturing fluid is switched to a high-viscosity liquid.

[0035] Compared with the above background technology, the present invention has the following beneficial effects:

[0036] The present invention targets tight oil vertical wells with target reservoirs located above the predicted fracture height. By pre-pumping a low-viscosity liquid at a low displacement into a uniformly mixed composite proppant of quartz sand of different particle sizes, combined with staged pumping stops, the fracture bottom is effectively shielded and the fracture height extension is controlled, thereby reducing ineffective vertical transformation and increasing the length of effectively supported fractures in the horizontal direction of the reservoir, ultimately improving the single-well transformation effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is a schematic diagram showing that the target reservoir of the vertical well of the present invention is located above the predicted fracture height;

[0038] Figure 2 This is a schematic diagram showing that the target reservoir of the vertical well of the present invention is located below the predicted fracture height;

[0039] Figure 3 This is a curve diagram of the fracture height extension fracturing operation for vertical well A in Example 1 of the present invention. DETAILED DESCRIPTION

[0040] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0041] The present invention discloses a novel fracturing process for controlling fracture height extension in tight oil vertical wells. Targeting thin-layer tight oil vertical wells, particularly those with target reservoirs located above the predicted fracture height, the pre-fluid stage utilizes a low-viscosity, low-displacement pumping method, carrying a pre-mixed, evenly distributed composite proppant of quartz sand of varying particle sizes. This is combined with a pump stop phase to create an effective barrier at the fracture bottom, thereby controlling fracture height extension, reducing ineffective reconstruction efforts, and increasing the length of effectively supported fractures in the lateral direction of the reservoir, ultimately enhancing the effectiveness of single-well reconstruction. The specific details are as follows:

[0042] S1. Conduct logging interpretation of the target well and determine relevant parameters and shielding types based on the logging interpretation results of the target well. Based on the interpretation results of reservoir and barrier layer stress and GR value, predict the longitudinal extension fracture height of the target layer and determine the top depth H1 and bottom depth h1 of the predicted fracture height.

[0043] Two key parameters are considered: the reservoir-barrier in-situ stress difference and the reservoir-barrier GR difference. Shielding is classified into two types: stress shielding and lithologic shielding. Typically, significant stress shielding is observed when the barrier is at least 3 meters thick and the stress difference between the barrier and reservoir is greater than 3 MPa. Significant lithologic shielding is observed when the barrier is at least 3 meters thick and the GR difference between the barrier and reservoir is greater than 60 API. When these stress shielding or lithologic shielding conditions are met, fractures will be less likely to continue extending vertically.

[0044] S2. Determine the positional relationship between the target reservoir and the predicted fracture height. Based on the positional relationship between the target reservoir and the predicted fracture height, determine and determine the target reservoir that needs to be fractured, and perform controlled fracture height extension fracturing on the target reservoir.

[0045] like Figure 1 As shown, the method for determining the positional relationship between the target reservoir and the predicted fracture height is: the target reservoir is located above the predicted fracture height, that is, the top depth H2 of the target layer is greater than or equal to the middle position of the predicted fracture height, H2≧H1+(H1-h1) / 2.

[0046] like Figure 2 As shown, the target reservoir is located at the lower part of the predicted fracture height, that is, the top depth H2 of the target layer is less than the middle position of the predicted fracture height, when H2﹤H1+(H1-h1) / 2.

[0047] When the target reservoir is located above the predicted fracture height, most of the proppant will accumulate at the bottom of the fracture due to the sedimentation of the proppant under the action of gravity after the main fracturing operation is completed, resulting in a significant reduction in the fracture conductivity of the target reservoir corresponding to the fracture height section, thereby affecting the production effect. Therefore, it is necessary to perform controlled fracture height extension fracturing on the target layer. When the target reservoir is located below the predicted fracture height, although there is an ineffective stimulation area above the reservoir, the fracture conductivity of the target reservoir corresponding to the fracture height section will be guaranteed after the proppant settles. Therefore, it is not necessary to perform controlled fracture height extension fracturing on the target layer.

[0048] S3. For the target layer section that needs to be subjected to controlled fracture height extension fracturing, the target layer section is first perforated and scraped to facilitate drilling. After completing the pre-fracturing preparations, the target layer section controlled fracture height extension fracturing is started, and the first stage main fracturing is performed.

[0049] A perforating gun string is run into a completed new well to perforate the target layer. The perforating gun string is then pulled out and a scraping string is run in to scrape the perforated section and the packer setting position. The scraping string is then pulled out. The target layer is perforated and scraped to clear the well.

[0050] After perforating and scraping the well, make preparations before fracturing: lower the fracturing string, install the fracturing wellhead, connect the fracturing manifold, and test the surface pipeline and gate pressure. The pipeline is qualified if there is no puncture, leakage or seepage.

[0051] Before fracturing construction, it is necessary to fully mix the three commonly used particle sizes of quartz sand, 70-140 mesh, 40-70 mesh, and 20-40 mesh, in a ratio of 3:3:4 according to the design.

[0052] During the first stage of fracturing in the target layer, the pre-fluid is first injected, and the operation displacement needs to be controlled at the same time. The pre-fluid stage is the stage of rapid extension of the fracture, and reducing the operation displacement can prevent the fracture from extending vertically too quickly. After the formation is opened and the pressure stabilizes, 6-10 well-mixed quartz sand plugs are added. After the well-mixed quartz sand plugs of three particle sizes are added, the pump is stopped for 20-30 minutes to ensure that the three particle sizes of quartz sand settle to the bottom of the fracture under the action of gravity.

[0053] The pre-fluid placed in the first stage of fracturing construction is a low-viscosity liquid; the low-viscosity liquid is an integrated low-viscosity slick water or other low-viscosity liquid; the liquid viscosity does not exceed 10mPa.s; the construction displacement in the first stage of fracturing construction is controlled at 3-5m 3 / min; 6-10 well-mixed quartz sand plugs are added in the first stage of fracturing construction; the quartz sand plug sand ratio is 3-7%.

[0054] S4. After the first stage of fracturing is completed, the pump is stopped for a period of time, the fracturing displacement is increased again, and the second stage of main fracturing is started. After the construction is completed, the pump is stopped and the layer is switched to the next stage;

[0055] The second stage fracturing construction method of step S4 is:

[0056] Increase the step-by-step flow rate gradually to the designed main fracturing operation flow rate, and take 3-4 steps to increase the flow rate to the designed operation flow rate. At the same time, pay attention to the changes in the ground operation pressure during the operation process. If the operation pressure increases too quickly, the number of steps can be further increased.

[0057] Then, the amount of sand added in a single section can be used to determine whether the conditions for adding multiple quartz sand plugs are met. If the total sand volume of the layer section exceeds the designed sand addition volume, additional plugging is required. Specifically, 5-10 70 / 140 mesh quartz sand plugs and 40 / 70 mesh quartz sand plugs are added in sequence, and the fracturing fluid is switched to a high-viscosity liquid. Construction is completed according to the designed sand addition procedure, the machine is stopped, and then the next section is moved to.

[0058] S5. After the construction of all the designed target layers is completed, the fracturing string in the well is pulled out and the pump is lowered to start production.

[0059] Example 1

[0060] The following uses the application of the tight oil vertical well A in the periphery of Daqing as an example to specifically illustrate a tight oil vertical well controlled fracture height extension fracturing process of the present invention, which includes the following steps:

[0061] Well A is a new vertical well drilled in the Daqing periphery for tight oil. The well encountered four target reservoirs: FII2, FII1, FI4, and FI2. Since the Fuyu reservoir in this block generally has a single-layer sandstone thickness of 2-5m and a vertical stress shielding of 1-3MPa, it is easy to cause the vertical fracture height to be too large, resulting in serious ineffective transformation.

[0062] Well A applied a new type of tight oil vertical well controlled fracture height extension fracturing process, which includes the following steps:

[0063] Step 1: The sandstone thicknesses encountered in the four target reservoirs FII2, FII1, FI4, and FI2 were 5.3, 2, 4.6, and 2 meters, respectively. Well logging interpretation was conducted on Well A. Based on the reservoir-interlayer in-situ stress interpretation results and the GR size, it was predicted that if fracture height control was not performed, the fracture heights of the four target intervals would reach 10 meters, 10 meters, 14 meters, and 6 meters, respectively. The reservoir thickness would only account for 20-53% of the predicted fracture height, indicating a serious ineffective fracturing. At the same time, the top depths of the four target intervals were all greater than the midpoint of the predicted fracture height. Therefore, controlled fracture height extension fracturing was required for the above four target reservoirs.

[0064] Step 2: Run the perforating tool into the wellbore of Well A, perforate each layer, pull out the perforating string, run the scraping string to scrape the perforated section and the packer setting position, and remove the scraping string;

[0065] Step 3: Run the fracturing string, install the fracturing wellhead, connect the fracturing manifold, and conduct pressure test on the surface pipeline and gate. The pipeline is qualified if there is no puncture, leakage or seepage.

[0066] Step 4: Before fracturing construction, quartz sand of three commonly used particle sizes (70-140 mesh, 40-70 mesh, and 20-40 mesh) is fully mixed in advance in a ratio of 3:3:4;

[0067] Step 5: Use low viscosity liquid slippery water 1 as the pre-fluid, and use 3-4m 3 / min displacement to add 5 5% and 5 7% quartz sand slugs of three kinds of particle sizes mixed evenly;

[0068] Step 6: After adding the evenly mixed quartz sand slugs of three different particle sizes, the pump is stopped for 20 minutes. The three particle sizes of quartz sand settle to the bottom of the fracture under the action of gravity, completing the first stage of main fracturing construction.

[0069] Step 7: Re-increase the displacement and start the second stage of main fracturing operation, using 3-6-9m 3Gradually increase the operation flow rate at 1000 rpm. Add five 70-140 mesh quartz sand plugs with a 7% sand ratio and six 40-70 mesh quartz sand plugs with a 7% sand ratio. Further ensure effective shielding of the fracture bottom through quartz sand settling. Switch the fracturing fluid to a high-viscosity liquid and begin continuous sand addition. Complete the operation according to the designed sand addition procedure, stop the operation, and then move on to the next section.

[0070] Step 8: After all the designed target layers are constructed, the fracturing string is pulled out of the well and the pump is lowered to start production.

[0071] The curve of fracture height extension fracturing operation for vertical well A is shown in Figure 3 .

[0072] It should be noted that the embodiments described above are only used to explain the present invention and do not constitute any limitation of the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory words, rather than restrictive words. The present invention may be modified as specified within the scope of the claims of the present invention, and the present invention may be revised without departing from the scope and spirit of the present invention. Therefore, the content of the present invention is not limited to the examples listed, and any equivalent transformations of the technical solutions of the present invention made by ordinary technicians in this field after reading the specification of the present invention are all covered by the claims of the present invention.

Claims

1. A tight oil vertical well controlled fracture height extension fracturing process, characterized by: The following steps are involved: S1. Conduct logging interpretation of the target well and determine relevant parameters and obstruction types based on the logging interpretation results of the target well; Based on the reservoir-interlayer in-situ stress interpretation results and GR value, the longitudinal extension fracture height of the target layer is predicted, and the top and bottom depths of the predicted fracture height are determined; S2. Determine the positional relationship between the target reservoir and the predicted fracture height. Based on the positional relationship between the target reservoir and the predicted fracture height, determine and determine the target reservoir that needs to be fractured, and perform controlled fracture height extension fracturing on the target reservoir. S3. For the target layer section that needs to be subjected to controlled fracture height extension fracturing, the target layer section is first perforated and scraped to facilitate drilling. After completing the pre-fracturing preparations, the target layer section controlled fracture height extension fracturing is started, and the first stage main fracturing is performed. S4. After the first stage of fracturing is completed, the pump is stopped for a period of time, the fracturing displacement is increased again, and the second stage of main fracturing is started. After the construction is completed, the layer is switched to the next stage; S5. After all the designed target layers are constructed, the fracturing string is pulled out of the well and the pump is put into production; The step S1 determines the relevant parameters as two parameters based on the target well logging interpretation results: the first parameter is the reservoir-interlayer in-situ stress difference, and the second parameter is the reservoir-interlayer GR difference; The shielding types are stress shielding and lithologic shielding. Generally, when the interlayer is more than 3m thick and the stress difference between the interlayer and the reservoir is greater than 3MPa, it is considered to have obvious stress shielding. When the interlayer is more than 3m thick and the GR value difference between the interlayer and the reservoir is more than 60API, it is considered to have obvious lithologic shielding. The method for determining the positional relationship between the target reservoir and the predicted fracture height in step S2 is as follows: the target reservoir is located above the predicted fracture height, that is, the top depth H2 of the target layer is greater than or equal to the middle position of the predicted fracture height, and H2≧H1+(H1-h1) / 2; The target reservoir is located at the lower part of the predicted fracture height, that is, the top depth H2 of the target layer is less than the middle position of the predicted fracture height, when H2﹤H1+(H1-h1) / 2; Where: H1: predicted depth of the top of the seam height; h1: predicted seam height bottom depth; H2: depth of top of target layer; h2: depth of the bottom of the target layer; H1+(H1-h1) / 2: predicted seam height center position; Determine and identify the target reservoir that needs fracturing: When the target reservoir is located above the predicted fracture height, it is necessary to perform fracture extension fracturing on the target layer with controlled fracture height. When the target reservoir is located below the predicted fracture height, there is no need to perform controlled fracture height extension fracturing on the target layer; The first stage main fracturing construction process of step S3 is as follows: During the first stage of main fracturing in the target layer, the pre-fluid is first injected, and the operation displacement needs to be controlled at the same time; After the formation is opened and the pressure is stabilized, a well-mixed quartz sand plug is added; After the quartz sand slug is added, the pump is stopped for 20-30 minutes, and the three types of quartz sand with uniform particle sizes are evenly mixed and settled to the bottom of the crack under the action of gravity; The second stage main fracturing construction method of step S4 is: Increase the displacement step by step to the designed main fracturing operation rate in 3-4 steps. At the same time, pay attention to the changes in ground operation pressure during the operation. If the operation pressure increases too quickly, increase the number of steps. Then, based on the amount of sand added in a single section, determine whether it is possible to add multiple quartz sand slugs again. If the total sand volume in the layer section exceeds the designed sand addition volume, additional slugs are required. Specifically, multiple 70 / 140 mesh quartz sand slugs and 40 / 70 mesh quartz sand slugs are added in sequence, and then the fracturing fluid is switched to a high-viscosity fluid. Complete the construction according to the designed sand adding procedure, stop the machine, and then move to the next section.

2. A tight oil vertical well controlled fracture height extension fracturing process according to claim 1, characterized in that: The pre-fluid placed in the first stage of the main fracturing construction in step S3 is a low-viscosity liquid; the low-viscosity liquid is integrated low-viscosity slick water; and the viscosity of the liquid does not exceed 10 mPa.s.

3. The process for controlling fracture height extension in tight oil vertical wells according to claim 1, characterized in that: In the first stage of the main fracturing operation in step S3, the construction displacement is controlled at 3-5m 3 / min; In the first stage of main fracturing construction, 6-10 well-mixed quartz sand plugs are added; the sand ratio of the quartz sand plugs is 3-7%.

4. The process for controlling fracture height extension in tight oil vertical wells according to claim 1, characterized in that: In step S3, the quartz sand is quartz sand of three commonly used particle sizes, namely 70-140 mesh, 40-70 mesh, and 20-40 mesh, which are fully mixed in advance according to a certain proportion.

5. A tight oil vertical well controlled fracture height extension fracturing process according to claim 4, characterized in that: In step S3, the quartz sand is quartz sand of three commonly used particle sizes: 70-140 mesh, 40-70 mesh, and 20-40 mesh, which are fully mixed in advance in a ratio of 3:3:

4.

6. The process for controlling fracture height extension in a tight oil vertical well according to claim 1, characterized in that: After adding 5-10 70 / 140 mesh quartz sand plugs and 40 / 70 mesh quartz sand plugs in sequence, the fracturing fluid is switched to a high-viscosity liquid.

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