A method and apparatus for simulating pore pressure changes during fracturing

Abstract

The application discloses a method and device for simulating pore pressure change in a fracturing process, and the method comprises the following steps: obtaining design parameters and perforation parameters of a fracturing well; establishing a hydraulic fracture propagation model according to the design parameters of the fracturing well; establishing a numerical model of drilling pressure interference in a staged fracturing process according to the hydraulic fracture propagation model and the perforation parameters; establishing a numerical model of drilling pressure interference in a staged fracturing process containing a weak formation interface according to the numerical model of drilling pressure interference in the staged fracturing process; and determining the pore pressure change law of the formation around the fracturing well according to the numerical model of drilling pressure interference in the staged fracturing process containing the weak formation interface. The technical scheme has the beneficial effects that the pore pressure change law of the formation around the fracturing well is determined, so that the pore pressure change law of the formation around the fracturing well in the fracturing process can be obtained, and technical support is provided for revealing the mechanism of drilling interference caused by fracturing, and enriching and perfecting related theories.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of drilling, in particular to a method and device for simulating pore pressure change in a fracturing process. BACKGROUND

[0002] Volume fracturing technology refers to a segmented multi-cluster perforation technology, which realizes the communication of artificial fractures and natural fractures and the generation of horizontal fractures by using high net pressure in the fracture and interference between fractures, so as to form a complex fracture network in three-dimensional directions of length, width and height, so that the seepage distance of oil and gas in the matrix in any direction to the fracture is "shortest", and the overall permeability of the reservoir is greatly improved, and the productivity and ultimate recovery of the oil and gas well in the low-permeability unconventional reservoir is improved (for details, please refer to Chinese Invention Patent No. CN201610897188.3).

[0003] At present, the research on the problem of drilling interference caused by volume fracturing is relatively rare. In view of the problem of drilling interference caused by volume fracturing reconstruction, Tian Linhai et al. discussed the problem of fracturing interference to drilling. Tian Linhai et al. believe that the main effects of volume fracturing on drilling include increased well control risk, increased drilling fluid density, and increased downhole failure rate. The main reason for these complex situations is that under the influence of volume fracturing, a kind of abnormal pressure in a closed state is formed within a certain range centered on the fractured well. Under the condition of complex cluster fractures, this abnormal pressure in a closed state formed by volume fracturing has the characteristics of weak abnormal high pressure, which can be transmitted to a farther place, and the pressure weak point here is usually the wellbore, so the fracturing has interference to the drilling process and brings many complex situations.

[0004] With the popularization of volume fracturing in the existing well area, in order to ensure the safety of horizontal well drilling, it is urgent to find a method to solve the problem of volume fracturing interference to drilling. During the volume fracturing process, the pore pressure in the formation around the fractured well will change, which will interfere with the drilling process of the adjacent well. Therefore, it is of great significance to study the pore pressure change in the formation around the fractured well during the fracturing process to reveal the mechanism of fracturing interference to drilling and enrich and perfect the related theory.

[0005] However, in the prior art, there is a lack of research on the pore pressure change in the formation around the fractured well during the fracturing process. SUMMARY

[0006] Therefore, it is necessary to provide a method and device for simulating pore pressure change in a fracturing process, so as to study the pore pressure change in the formation around the fractured well during the fracturing process, and thus provide technical support for revealing the mechanism of fracturing interference to drilling and enriching and perfecting the related theory.

[0007] In order to achieve the above object, the present application provides a method for simulating pore pressure change in fracturing process, comprising:

[0008] obtaining design parameters and perforation parameters of the fracturing well;

[0009] establishing a hydraulic fracture propagation model according to the design parameters of the fracturing well;

[0010] establishing a numerical model of drilling pressure interference in the staged fracturing process according to the hydraulic fracture propagation model and the perforation parameters;

[0011] establishing a numerical model of drilling pressure interference in the staged fracturing process containing weak formation interface according to the numerical model of drilling pressure interference in the staged fracturing process;

[0012] determining the pore pressure change law of the formation around the fracturing well according to the numerical model of drilling pressure interference in the staged fracturing process containing weak formation interface.

[0013] In some embodiments, the design parameters of the fracturing well include well location distribution data of the fracturing well and wellbore trajectory of each fracturing well.

[0014] In some embodiments, the hydraulic fracture propagation model is established according to the design parameters of the fracturing well, specifically, the hydraulic fracture propagation model is established according to the design parameters of the fracturing well based on a fracture propagation criterion, wherein the fracture propagation criterion is Traction-separation criterion.

[0015] In some embodiments, the numerical model of drilling pressure interference in the staged fracturing process is established according to the hydraulic fracture propagation model and the perforation parameters, specifically including:

[0016] adding a liquid injection point in the hydraulic fracture propagation model according to the perforation parameters;

[0017] setting a staged Cohesive unit at each liquid injection point in the hydraulic fracture propagation model to obtain the numerical model of drilling pressure interference in the staged fracturing process.

[0018] In some embodiments, the staged Cohesive unit is COH3D8P unit type.

[0019] In some embodiments, the numerical model of drilling pressure interference in the staged fracturing process containing weak formation interface is established according to the numerical model of drilling pressure interference in the staged fracturing process, specifically:

[0020] setting a weak formation interface Cohesive unit in the numerical model of drilling pressure interference in the staged fracturing process to obtain the numerical model of drilling pressure interference in the staged fracturing process containing weak formation interface.

[0021] In some embodiments, the pore pressure variation law of the formation around the fractured well is determined according to the numerical model of the drilling pressure interference of the staged fracturing with weak formation interface, and specifically comprises:

[0022] According to the numerical model of the drilling pressure interference of the staged fracturing with weak formation interface, the variation processes of stress, displacement, damage factor and fracture width in the fracture propagation process are obtained.

[0023] According to the variation processes of stress, displacement, damage factor and fracture width in the fracture propagation process, the pore pressure variation law of the formation around the fractured well is determined.

[0024] In some embodiments, the variation processes of stress, displacement, damage factor and fracture width in the fracture propagation process are obtained according to the numerical model of the drilling pressure interference of the staged fracturing with weak formation interface, and specifically comprises:

[0025] The numerical model of the drilling pressure interference of the staged fracturing with weak formation interface is imported into the finite element analysis software to obtain the variation processes of stress, displacement, damage factor and fracture width in the fracture propagation process.

[0026] The application further provides a device for simulating the pore pressure variation in the fracturing process, comprising a processor and a memory, wherein the memory stores a computer program, and the computer program is executed by the processor to realize the method for simulating the pore pressure variation in the fracturing process.

[0027] The application further provides a computer readable storage medium, which stores one or more programs, and the one or more programs can be executed by one or more processors to realize the steps in the method for simulating the pore pressure variation in the fracturing process.

[0028] Compared with the prior art, the technical scheme provided by the application has the beneficial effects that: the hydraulic fracture propagation model is established according to the design parameters of the fractured well, the drilling pressure interference numerical model of the staged fracturing process is established in combination with the perforation parameters, then the numerical model of the drilling pressure interference of the staged fracturing with weak formation interface is established according to the drilling pressure interference numerical model of the staged fracturing process, and the pore pressure variation law of the formation around the fractured well is determined according to the numerical model of the drilling pressure interference of the staged fracturing with weak formation interface, so that the pore pressure variation law of the formation around the fractured well in the fracturing process can be obtained, and technical support is provided for revealing the mechanism of the drilling interference caused by the fracturing, enriching and perfecting the related theory. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 is a flowchart of an embodiment of the method for simulating the pore pressure variation in the fracturing process provided by the application;

[0030] Figure 2is a schematic diagram of a Traction-separation bilinear constitutive model;

[0031] Figure 3 is Figure 1 is a flowchart of step S3 in the method;

[0032] Figure 4 is Figure 1 is a flowchart of step S5 in the method;

[0033] Figure 5 is a numerical model of drilling pressure interference in the process of staged fracturing;

[0034] Figure 6 is a numerical model of drilling pressure interference in the process of staged fracturing with weak formation interface;

[0035] Figure 7 is a stress-strain curve under different pore pressures;

[0036] Figure 8 is the relationship between rock strength and pore pressure. DETAILED DESCRIPTION

[0037] The preferred embodiments of the present application will be described in detail below with reference to the drawings, which form a part of this application, and together with the implementation examples of the present application, illustrate the principles of the present application, but are not intended to limit the scope of the present application.

[0038] Please refer to Figure 1 The present application provides a method for simulating the change of pore pressure in the process of fracturing, comprising:

[0039] S1, obtaining the design parameters and perforation parameters of the fracturing well;

[0040] Specifically, the design parameters of the fracturing well include well site distribution data of the fracturing well and borehole trajectory of each fracturing well.

[0041] S2, establishing a hydraulic fracture propagation model according to the design parameters of the fracturing well;

[0042] Specifically, according to the design parameters of the fracturing well, a hydraulic fracture propagation model is established based on a fracture propagation criterion, wherein the fracture propagation criterion is a Traction-separation criterion. In the method based on Traction-separation description, the most commonly used constitutive model is a bilinear constitutive model (such as Figure 2 ). According to the expansion criterion of hydraulic fractures in pure rock, the maximum tensile stress criterion is generally used. That is, when the tensile stress of the rock mass reaches its own tensile strength, the rock mass breaks, and the hydraulic fracture can expand. To further establish a finite element numerical model.

[0043] S3, establishing a drilling pressure interference numerical model of a staged fracturing process according to the hydraulic pressure joint expansion model and the perforation parameters;

[0044] S4, establishing a staged fracturing drilling pressure interference numerical model containing a weak formation interface according to the drilling pressure interference numerical model of the staged fracturing process, the weak formation interface can affect the change of pore pressure in the fracturing process, therefore, the weak formation interface is added in the model, and the change of pore pressure in the fracturing process can be simulated more accurately;

[0045] S5, determining the change rule of pore pressure of a formation around a fracturing well according to the staged fracturing drilling pressure interference numerical model containing the weak formation interface.

[0046] The technical scheme provided by the application establishes a hydraulic pressure joint expansion model through design parameters of a fracturing well, then establishes a drilling pressure interference numerical model of a staged fracturing process in combination with perforation parameters, then establishes a staged fracturing drilling pressure interference numerical model containing a weak formation interface through the drilling pressure interference numerical model of the staged fracturing process, and determines the change rule of pore pressure of a formation around a fracturing well according to the staged fracturing drilling pressure interference numerical model containing the weak formation interface, so that the change rule of pore pressure of the formation around the fracturing well in the fracturing process can be obtained, and technical support is provided for revealing the mechanism of fracturing interference on drilling and enriching and perfecting related theories.

[0047] Specifically, refer to Figure 3 , and step S3 specifically comprises:

[0048] S31, adding a liquid injection point in the hydraulic pressure joint expansion model according to the perforation parameters;

[0049] S32, setting a staged Cohesive unit at each liquid injection point in the hydraulic pressure joint expansion model to obtain a drilling pressure interference numerical model of a staged fracturing process, wherein the staged Cohesive unit is a COH3D8P unit type.

[0050] Specifically, step S4 specifically comprises:

[0051] setting a weak formation interface Cohesive unit in the drilling pressure interference numerical model of the staged fracturing process to obtain a staged fracturing drilling pressure interference numerical model containing a weak formation interface.

[0052] Specifically, refer to Figure 4 , and step S5 specifically comprises:

[0053] S51, obtaining the change process of stress, displacement, damage factor and crack width in the crack expansion process according to the staged fracturing drilling pressure interference numerical model containing the weak formation interface,

[0054] Specifically, the segmented fracturing drilling pressure interference numerical model containing a weak formation interface is introduced into finite element analysis software to obtain the change process of stress, displacement, damage factor and fracture width during fracture propagation.

[0055] S52, according to the change process of stress, displacement, damage factor and fracture width during fracture propagation, the pore pressure change law of the formation around the fractured well is determined.

[0056] In order to verify the feasibility and technical effect of the technical scheme provided by the application, the actual pore pressure change simulation in the fracturing process of a well area is carried out. The specific process is as follows:

[0057] (1) Obtain the design parameters and perforation parameters of the fractured well;

[0058] Obtain the statistical analysis data of the drilling fracturing interference of the field example well, and perform statistical analysis to comprehensively understand the problems of volume fracturing on drilling interference. In order to ensure the safety of horizontal well drilling, research is carried out. According to the statistical analysis results, the target well site is selected, and the design parameters and perforation parameters of the target well site are obtained.

[0059] (2) According to the design parameters of the fractured well, a hydraulic fracture propagation model is established;

[0060] According to the well trajectory and data, it can be easily seen that all the wells are horizontal wells, and the target point positions are all on the entire horizontal section, and the depth is about 3500m-3800m. In actual fracturing construction, the hydraulic fracture initiation position is on the horizontal section, so the relative position relationship between the wells can be determined according to the target point position coordinates on the horizontal section of each well. And the well target point position coordinate data is sorted out;

[0061] Based on such data, in order to reduce the calculation difficulty, the regional model scale is determined. The basic model scale is provided for further determination of the design parameters of the fractured well. Determining the regional model scale includes:

[0062] In order to reduce the calculation difficulty, the model scale is 1 / 2 of the entire range, and the effect of the entire model size is also considered. Therefore, the final model length and width size is determined.

[0063] Based on the regional model scale, the length and width size of the model is finally determined, the reservoir is reformed by using the perforation bridge plug combined with fracturing technology, the cable pumping bridge plug and perforation combined mode are adopted, the bridge plug is lowered into the casing to realize the segmented isolation of the horizontal section, the cable perforation is realized after the bridge plug is segmented to realize the communication between the wellbore and the formation, and the perforation parameters and fracturing construction process are determined.

[0064] Further according to the obtained fracturing well design parameters, a basic parameter and a process are provided for the hydraulic fracture propagation model. Through the fracturing well design parameters and the fracturing operation process, the hydraulic fracture propagation model based on Cohesive, and the fracture propagation judgment criterion, the hydraulic fracture propagation model is further constructed.

[0065] (3) According to the hydraulic fracture propagation model and the perforation parameters, a numerical model of drilling pressure interference in the staged fracturing process is established;

[0066] According to the perforation parameters, a liquid injection point is added in the hydraulic fracture propagation model; a staged Cohesive unit is arranged at each liquid injection point in the hydraulic fracture propagation model, so as to obtain a numerical model of drilling pressure interference in the staged fracturing process, wherein the staged Cohesive unit is a COH3D8P unit type.

[0067] After multiple trial calculations and analyses in the early stage, it is determined that the global size of the grid is defined as 25 m, and the global grid quantity is 726600. Based on the well distribution map, the length and width dimensions of the model are determined as 6000 m x 300 m x 600 m. Based on the perforation parameters of the MaHW6272 well, 9 liquid injection points are arranged on the left side of the model (as shown in Figure 5 ), and each liquid injection point is on a staged Cohesive unit, so as to simulate multi-stage fracturing.

[0068] The material parameters of the numerical model of drilling pressure interference in the staged fracturing process are shown in Table 1.

[0069] Table 1 Material parameters of the numerical model of drilling pressure interference in the staged fracturing process

[0070] Cohesive Stiffness 20 GPa Cohesive Maximum Critical Stress 2 MPa Cohesive Maximum Energy Release Rate 4000 J / m Cohesive Permeability 1e-13 Viscosity 0.001 Pa*s Horizontal Maximum In-Situ Stress 70 MPa Horizontal Minimum In-Situ Stress 55 MPa Vertical Stress 88 MPa Injection Rate 6m 3 / min]]> Rock Young's Modulus 20 GPa Rock Poisson's Ratio 0.3 Rock Permeability 1e-7 Rock Porosity 0.2

[0071] (4) According to the numerical model of drilling pressure interference in the staged fracturing process, a numerical model of drilling pressure interference in the staged fracturing process containing a weak formation interface is established;

[0072] The length and width dimensions of the model are 3000 m x 50 m x 50 m, one liquid injection point is arranged, and three Cohesive units are inserted in the model, wherein the upper and lower parallel Cohesive units simulate the weak interface at the formation junction, and the vertical Cohesive simulates the vertical fracture propagation path.

[0073] Further, after multiple trial calculations and analyses in the early stage, it is determined that the global size of the grid is defined as 2 m, and the global grid quantity is 937500. The grid of the solid unit adopts a C3D8P unit type, and the Cohesive unit adopts a COH3D8P unit type to simulate the fracture propagation in the hydraulic fracturing process.

[0074] Figure 6The segmented fracturing drilling pressure interference numerical model containing a weak formation interface mainly includes: the model has a length and width size of 3000m*50m*50m, one liquid injection point is arranged, three Cohesive units are inserted in the model, the upper and lower parallel Cohesive units simulate the weak interface at the formation junction, and the vertical Cohesive simulates the vertical fracture propagation path.

[0075] The material parameters of the segmented fracturing drilling pressure interference numerical model containing a weak formation interface are shown in Table 2.

[0076] Table 2 Material parameters of the segmented fracturing drilling pressure interference numerical model containing a weak formation interface

[0077] Interface Cohesive Stiffness 14 GPa Interface Cohesive Maximum Critical Stress 1.2 MPa Interface Cohesive Maximum Energy Release Rate 1000 J / m Interface Cohesive Permeability 1e-13 Rock Cohesive Stiffness 20 GPa Rock Cohesive Maximum Critical Stress 2 MPa Rock Cohesive Maximum Energy Release Rate 4000 J / m Rock Cohesive Elastic Modulus 20 GPa Rock Cohesive Permeability 1e-13 Viscosity 0.001 Pa*s Horizontal Maximum In-Situ Stress 70 MPa Horizontal Minimum In-Situ Stress 55 MPa Pore Pressure 61.72 MPa Vertical Stress 88 eMPa Injection Rate 6m 3 / min]]> Injection Time 3000s Rock Young's Modulus 20 GPa Rock Poisson's Ratio 0.3 Rock Permeability 1e-7 Rock Porosity 0.2

[0078] (5) According to the segmented fracturing drilling pressure interference numerical model containing a weak formation interface, the pore pressure variation law of the formation around the fractured well is determined.

[0079] Figure 7 For the rock strength variation law curve under different pore pressures, combined with Figure 7 It can be seen that for different pore pressures, the peak strength of the rock under compression conditions and the pore pressure present a negative correlation. With the decrease of the pore pressure, the rock peak strength generally presents an increasing trend. The linear relationship function of the data fitting is y=0.9235x+97.723, and the correlation coefficient R2=0.7097. The compressive strength decreases from 87.97MPa to 39.96MPa when the pore pressure increases from 5MPa to 46MPa, and the reduction amplitude is 55.1%.

[0080] Combined with Figure 8 It can be seen that when the formation pore pressure increases, the rock strength of the formation decreases, so when the drilling fracturing interference occurs, the rock strength of the drilling formation decreases; based on the fitting relationship between the formation pore pressure and the rock strength in the previous research, with the progress of the hydraulic fracturing construction, the formation pore pressure gradually increases, and the rock strength presents a linearly decreasing variation law.

[0081] The application further provides a device for simulating pore pressure variation in a fracturing process, comprising a processor and a memory, wherein the memory stores a computer program, and the computer program is executed by the processor to realize the method for simulating pore pressure variation in a fracturing process.

[0082] The application further provides a computer readable storage medium, wherein the computer readable storage medium stores one or more programs, and the one or more programs can be executed by one or more processors to realize the steps in the method for simulating pore pressure variation in a fracturing process.

[0083] The above merely provides the preferred but not limiting embodiments of the present application, and any modification or substitution within the technical scope of the present application should be covered within the protection scope of the present application.

Claims

1. A method for simulating pore pressure changes during fracturing, characterized in that, include: Obtain the design parameters and perforation parameters of the fracturing well; Based on the design parameters of the fractured well, a hydraulic fracture propagation model is established; Based on the hydraulic fracturing propagation model and the perforation parameters, a numerical model of drilling pressure interference in the segmented fracturing process is established. Based on the numerical model of drilling pressure interference in the segmented fracturing process, a numerical model of drilling pressure interference in segmented fracturing with weak formation interfaces is established. Based on the numerical model of drilling pressure interference in segmented fracturing wells with weak formation interfaces, the variation law of pore pressure in the formations surrounding the fracturing well is determined. Based on the numerical model of drilling pressure interference in the segmented fracturing process, a numerical model of drilling pressure interference in segmented fracturing with weak formation interfaces is established, specifically as follows: In the numerical model of drilling pressure interference in the segmented fracturing process, weak formation interface Cohesive elements are set to obtain a numerical model of drilling pressure interference in segmented fracturing containing weak formation interfaces. Based on the numerical model of drilling pressure interference in segmented fracturing with weak formation interfaces, the variation law of pore pressure in the formation surrounding the fracturing well is determined, specifically including: Based on the numerical model of segmented fracturing drilling interference with weak formation interfaces, the changes in stress, displacement, damage factor and fracture width during fracture propagation are obtained. Based on the changes in stress, displacement, damage factor, and fracture width during fracture propagation, the variation law of pore pressure in the formation surrounding the fractured well is determined.

2. The method for simulating pore pressure changes during fracturing according to claim 1, characterized in that, The design parameters for the fractured wells include the well location distribution data and the wellbore trajectory of each fractured well.

3. The method for simulating pore pressure changes during fracturing according to claim 1, characterized in that, Based on the design parameters of the fractured well, a hydraulic fracture propagation model is established. Specifically, based on the design parameters of the fractured well and a fracture propagation judgment criterion, a hydraulic fracture propagation model is established, wherein the fracture propagation judgment criterion is the traction-separation criterion.

4. The method for simulating pore pressure changes during fracturing according to claim 1, characterized in that, Based on the hydraulic fracturing propagation model and the perforation parameters, a numerical model of drilling pressure interference in the segmented fracturing process is established, specifically including: Based on the perforation parameters, injection points are added to the hydraulic pressure crack expansion model; A segmented Cohesive element is set at each injection point in the hydraulic fracturing expansion model to obtain a numerical model of drilling pressure interference in the segmented fracturing process.

5. The method for simulating pore pressure changes during fracturing according to claim 4, characterized in that, The segmented Cohesive unit is of the COH3D8P unit type.

6. The method for simulating pore pressure changes during fracturing according to claim 1, characterized in that, Based on the numerical model of segmented fracturing drilling interference with weak formation interfaces, the changes in stress, displacement, damage factor, and fracture width during fracture propagation are obtained, specifically as follows: The numerical model of the segmented fracturing drilling pressure interference containing weak formation interfaces was imported into the finite element analysis software to obtain the changes in stress, displacement, damage factor and fracture width during fracture propagation.

7. A device for simulating pore pressure changes during fracturing, characterized in that, The device includes a processor and a memory, wherein the memory stores a computer program, and when the computer program is executed by the processor, it implements the method for simulating pore pressure changes during fracturing as described in any one of claims 1-6.

8. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores one or more programs that can be executed by one or more processors to implement the steps in the method for simulating pore pressure changes during fracturing as described in any one of claims 1-6.

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