Extension fracturing process for controlling fracture height of tight oil vertical well

Abstract

The invention relates to a tight oil vertical well fracture height control extension fracturing process, which mainly solves the problem that the predicted fracture height is far greater than the thickness of a reservoir and the invalid transformation outside the reservoir is serious due to the weak phenomena of upper and lower stress shielding and lithologic shielding of the existing target reservoir. The method comprises the following steps: S1, predicting the longitudinal extension seam height of a target interval, and determining the top depth and the bottom depth of the predicted seam height; s2, determining a target reservoir needing to be fractured; s3, fracture height control extension fracturing construction is carried out on the target interval, and first-stage main fracturing construction is carried out at first; s4, the fracturing construction displacement is increased again, second-stage main fracturing construction is started, the displacement is gradually increased to the designed main fracturing construction displacement, the fracturing fluid is switched to high-viscosity liquid, sand adding is started, and construction, shutdown and layer transfer to the next stage are completed according to the designed sand adding program; and after construction of all designed target layer sections is completed, the fracturing pipe column is pulled out, and a pump is put into production. The fracturing process can control the height extension of the crack and reduce ineffective transformation.

Description

Technical Field

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

[0002] For thin-layer tight oil vertical wells, in some areas, the stress shielding and lithology shielding above and below the target reservoir are weak, which leads to the predicted fracture height being much greater than the reservoir thickness, which will cause serious ineffective transformation of the reservoir outside. At the same time, if the target reservoir is at the upper part of the predicted fracture height, after the main fracturing construction 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 longitudinal extension height of the fracture, reduce the ineffective transformation outside the reservoir, ensure effective support inside the reservoir, and at the same time, under the same transformation scale conditions, the effective support fracture length in the horizontal direction of the reservoir can also be increased. 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 lithology shielding of the target reservoir are both weak, resulting in the predicted fracture height being much greater than the reservoir thickness, causing serious ineffective transformation of the reservoir exterior, 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 lateral direction, and ultimately improve the single well transformation effect.

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

[0005] S1. Carry out logging interpretation of the target well, determine relevant parameters and shielding types based on the logging interpretation results of the target well; predict the longitudinal extension fracture height of the target layer according to the interpretation results of reservoir and barrier layer in-situ stress and GR value, and determine the top depth and bottom depth of the predicted fracture height;

[0006] S2, determining the positional relationship between the target reservoir and the predicted fracture height, based on the determined positional relationship between the target reservoir and the predicted fracture height; judging and determining the target reservoir that needs to be fractured, and performing controlled fracture height extension fracturing on the target layer;

[0007] S3. For the target layer section that needs to be subjected to controlled fracture height extension fracturing construction, the target layer section is first perforated and scraped to pass the well; after completing the pre-fracturing preparation work, the target layer section is subjected to controlled fracture height extension fracturing construction, and the first stage main fracturing construction is first performed;

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

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

[0010] Further, the step S1 determines the relevant parameters as two parameters based on the logging interpretation result of the target well: 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 3 m thick and the stress difference between the interlayer and the reservoir is greater than 3 MPa, it is considered to have obvious stress shielding; when the interlayer is more than 3 m thick and the GR value difference between the interlayer and the reservoir is more than 60 API, 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: the target reservoir is located at the upper part of 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 seam height top depth;

[0015] h1: predicted seam height bottom depth;

[0016] H2: top depth of target layer;

[0017] h2: bottom depth of 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] In the first stage of fracturing operation for the target layer, the pre-fluid is first placed, 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 evenly mixed particle sizes settle to the bottom of the crack under the action of gravity.

[0026] Furthermore, in the first stage of fracturing construction in step S3, the pre-fluid inserted 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 construction 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 sand ratio of the quartz sand plugs is 3 to 7%.

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

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

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

[0032] The step-by-step increase is gradually made to the designed main fracturing operation displacement, and 3-4 step-by-step increases are adopted to reach the designed operation displacement. At the same time, the changes in the ground construction pressure should be paid attention to at all times during the construction process. If the construction pressure increases too quickly, the number of step-by-step increases 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 plugs are met again. If the total sand volume of the layer section is greater than the designed sand addition volume, plugging is required again; specifically, multiple 70 / 140 mesh quartz sand plugs and 40 / 70 mesh quartz sand plugs are added in sequence, and then the fracturing fluid is switched to a high-viscosity liquid; the construction is completed according to the designed sand addition procedure, the machine is stopped, and then the layer is switched to the next section.

[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 aims at a tight oil vertical well whose target reservoir is 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 sands of different particle sizes, combined with staged pumping stops, the bottom of the fracture is effectively shielded, and the extension of the fracture height is controlled, so as to achieve the purpose of reducing ineffective transformation in the vertical direction and increasing the length of the effective supported fracture in the lateral direction of the reservoir, and ultimately improve the transformation effect of a single well. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

[0039] Figure 3 It is a curve diagram of the fracture height extension fracturing construction of the vertical well A in the embodiment of the present invention. Specific implementation method:

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

[0041] The present invention discloses a novel fracturing process for controlling the height extension of cracks in tight oil vertical wells. For thin-layer tight oil vertical wells, especially for target reservoirs in the upper layer of predicted crack height, a low-viscosity and low-displacement pumping method is used in the pre-fluid stage, carrying a pre-mixed and evenly mixed composite proppant of quartz sand with different particle sizes, combined with a staged pump stop, to form an effective shield at the bottom of the crack, thereby controlling the height extension of the crack, achieving the purpose of reducing ineffective transformation and increasing the effective support crack length in the lateral direction of the reservoir, and ultimately improving the transformation effect of a single well. The specific contents are as follows:

[0042] S1. Carry out logging interpretation of the target well, determine relevant parameters and shielding types based on the logging interpretation results of the target well; predict the longitudinal extension fracture height of the target layer according to the interpretation results of reservoir and barrier layer in-situ stress and GR value, and determine the top depth H1 and bottom depth h1 of the predicted fracture height;

[0043] Two core parameters are mainly used as reference. The first parameter is the reservoir-barrier in-situ stress difference, and the second parameter is the reservoir-barrier GR difference. The shielding types are stress shielding and lithologic shielding. Under normal circumstances, when the barrier is more than 3m thick and the stress difference between the barrier and the reservoir is greater than 3MPa, it is considered to have obvious stress shielding. When the barrier is more than 3m thick and the GR difference between the barrier and the reservoir is more than 60API, it is considered to have obvious lithologic shielding. When the above stress shielding conditions or lithologic shielding conditions are met, the fracture will be difficult to continue to extend vertically.

[0044] S2, determining the positional relationship between the target reservoir and the predicted fracture height, based on the determined positional relationship between the target reservoir and the predicted fracture height; judging and determining the target reservoir that needs to be fractured, and performing controlled fracture height extension fracturing on the target layer;

[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 at the upper part of 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 at the upper part of the predicted fracture height, most of the proppants will accumulate at the bottom of the fracture due to the sedimentation of the proppant under the action of gravity after the main fracturing construction, 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 control the fracture height extension fracturing of the target layer. When the target reservoir is located at the lower part of the predicted fracture height, although there is an invalid transformation area in the upper part of the reservoir, after the proppant settles, the fracture conductivity of the target reservoir corresponding to the fracture height section will be guaranteed. Therefore, it is not necessary to control the fracture height extension fracturing of the target layer.

[0048] S3. For the target layer section that needs to be subjected to controlled fracture height extension fracturing construction, the target layer section is first perforated and scraped to pass the well; after completing the pre-fracturing preparation work, the target layer section is subjected to controlled fracture height extension fracturing construction, and the first stage main fracturing construction is first performed;

[0049] In a completed new well, a perforating gun string is run to perforate the target layer, then the perforating string is pulled out, and a scraping string is run to scrape the perforating section and the packer setting position, and the scraping string is pulled out; perforate and scrape the target layer.

[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] In the first stage of fracturing construction of the target layer, the pre-fluid is first placed, and the construction 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 construction displacement can prevent the fracture from extending too quickly in the longitudinal direction; after the formation is opened and the pressure is stabilized, 6-10 evenly mixed quartz sand plugs are added; after the evenly 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 integrated low-viscosity slick water or other low-viscosity liquid; the liquid viscosity does not exceed 10mPa.s; the construction displacement is controlled at 3-5m in the first stage of fracturing construction 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 construction is completed, the pump is stopped for a period of time, the fracturing construction displacement is increased again, and the second stage of main fracturing construction is started. After the construction is completed, the pump is stopped and the layer is transferred to the next stage;

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

[0056] The step-by-step increase is gradually made to the designed main fracturing operation displacement, and 3-4 step-by-step increases are adopted to reach the designed operation displacement. At the same time, the changes in the ground construction pressure should be paid attention to at all times during the construction process. If the construction pressure increases too quickly, the number of step-by-step increases 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 again. If the total amount of sand in the layer section is greater than the designed sand addition amount, it is necessary to perform plugging again; specifically, add 5-10 70 / 140 mesh quartz sand plugs and 40 / 70 mesh quartz sand plugs in sequence, and then switch the fracturing fluid to a high-viscosity liquid; complete the construction according to the designed sand addition procedure, stop the machine, and then switch to the next section.

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

[0059] Example 1

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

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

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

[0063] Step 1: The sandstone thickness encountered in the four target reservoirs FII2, FII1, FI4, and FI2 is 5.3, 2, 4.6, and 2 meters respectively. The logging interpretation of Well A is carried out. According to the interpretation results of the reservoir-interlayer geostress and the size of GR, it is predicted that if the fracture height is not controlled, the fracture height of the four target layers will reach 10m, 10m, 14m, and 6m respectively. The reservoir thickness only accounts for 20-53% of the predicted fracture height, and the ineffective transformation is serious. At the same time, the top depths of the four target layers are all greater than the middle position of the predicted fracture height, so it is necessary to control the fracture height and extend the fracturing of 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 perforating section and the packer setting position, and pull out the scraping string;

[0065] Step 3: Run 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;

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

[0067] Step 5: The pre-fluid is low-viscosity liquid slippery water 1, using 3-4m 3 / min displacement, add 5 5% and 5 7% quartz sand segments of three different particle sizes mixed evenly;

[0068] Step 6: After adding the evenly mixed quartz sand plugs of three sizes, stop the pump for 20 minutes, and the three sizes of quartz sand settle to the bottom of the crack under the action of gravity; the first stage of main fracturing construction is completed;

[0069] Step 7: Re-increase the displacement and start the second stage of main fracturing operation, using 3-6-9m 3 / min gradually increase the construction displacement, then add 5 7% sand ratio 70-140 mesh quartz sand plugs and 6 7% sand ratio 40-70 mesh quartz sand plugs, and further ensure effective shielding of the bottom of the crack through quartz sand sedimentation. Switch the fracturing fluid to a high-viscosity liquid, start continuous sand addition, complete the construction according to the designed sand addition procedure, stop the machine, and then switch to the next layer;

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

[0071] The vertical well A well controlled fracture height extension fracturing operation curve 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 to 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 changes taken by ordinary technicians in the field of the present invention by reading the specification of the present invention to the technical solution 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. Carry out logging interpretation of the target well and determine relevant parameters and shielding types based on the logging interpretation results of the target well; According to 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 depth and bottom depth of the predicted fracture height are determined; S2, determining the positional relationship between the target reservoir and the predicted fracture height, based on the determined positional relationship between the target reservoir and the predicted fracture height; judging and determining the target reservoir that needs to be fractured, and performing controlled fracture height extension fracturing on the target layer; S3. For the target layer section that needs to be subjected to controlled fracture height extension fracturing construction, the target layer section is first perforated and scraped to pass the well; after completing the pre-fracturing preparation work, the target layer section is subjected to controlled fracture height extension fracturing construction, and the first stage main fracturing construction is first performed; S4. After the first stage of fracturing construction is completed, the pump is stopped for a period of time, the fracturing construction displacement is increased again, and the second stage of main fracturing construction is started. After the construction is completed, the layer is transferred to the next stage; S5. After the construction of all the designed target layers is completed, the fracturing string in the well is removed and the pump is lowered to start production.

2. A tight oil vertical well controlled fracture height extension fracturing process according to claim 1, characterized in that: The step S1 determines the relevant parameters as two parameters based on the logging interpretation result of the target well: 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 3 m thick and the stress difference between the interlayer and the reservoir is greater than 3 MPa, it is considered to have obvious stress shielding; when the interlayer is more than 3 m thick and the GR value difference between the interlayer and the reservoir is more than 60 API, it is considered to have obvious lithologic shielding.

3. A tight oil vertical well controlled fracture height extension fracturing process according to claim 1, characterized in that: The method for determining the positional relationship between the target reservoir and the predicted fracture height in step S2 is: the target reservoir is located at the upper part of 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; 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 seam height top depth; h1: predicted seam height bottom depth; H2: top depth of target layer; h2: bottom depth of 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 fracture height control and extension fracturing on the target layer.

4. A tight oil vertical well controlled fracture height extension fracturing process according to claim 1, characterized in that: The first stage fracturing construction process of step S3 is as follows: In the first stage of fracturing operation for the target layer, the pre-fluid is first placed, 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 plug is added, the pump is stopped for 20-30 minutes, and the three types of quartz sand with evenly mixed particle sizes settle to the bottom of the crack under the action of gravity.

5. A tight oil vertical well controlled fracture height extension fracturing process according to claim 4, characterized in that: 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; the liquid viscosity does not exceed 10mPa.s.

6. A tight oil vertical well controlled fracture height extension fracturing process according to claim 4, characterized in that: In the first stage of fracturing construction in step S3, the construction displacement is controlled at 3-5m 3 / min; In the first stage of fracturing construction, 6 to 10 well-mixed quartz sand plugs are added; the sand ratio of the quartz sand plugs is 3 to 7%.

7. A tight oil vertical well controlled fracture height extension fracturing process according to claim 4, characterized in that: The quartz sand in step S3 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.

8. A tight oil vertical well controlled fracture height extension fracturing process according to claim 7, characterized in that: The quartz sand in step S3 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 advance in a ratio of 3:3:

4.

9. A tight oil vertical well controlled fracture height extension fracturing process according to claim 1, characterized in that: The second stage fracturing construction method of step S4 is: The step-by-step increase is gradually made to the designed main fracturing operation displacement, and 3-4 step-by-step increases are adopted to reach the designed operation displacement. At the same time, the changes in the ground construction pressure should be paid attention to at all times during the construction process. If the construction pressure increases too quickly, the number of step-by-step increases can be further increased. Then, according to the amount of sand added in a single stage, it is judged whether the conditions for adding multiple quartz sand plugs are met again; if the total amount of sand in the layer section is greater than the designed amount of sand added, it is necessary to perform plugging again; specifically, multiple 70 / 140 mesh quartz sand plugs and 40 / 70 mesh quartz sand plugs are added in sequence, and then the fracturing fluid is switched to a high-viscosity liquid; Complete the construction according to the designed sand adding procedure, stop the machine, and then switch to the next section.

10. A tight oil vertical well controlled fracture height extension fracturing process according to claim 9, 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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