Method for predicting the risk of casing deformation induced by fracturing based on multi-factor analysis

Abstract

The present invention provides a method for predicting the risk degree of casing deformation induced by fracturing based on multi-factor analysis, comprising the following steps: determining the influencing factors of casing deformation induced by fracturing; analyzing logging data to identify the above-mentioned influencing factors; defining the risk factors of casing deformation induced by fracturing according to the logging data analysis results; judging the risk degree level of casing deformation induced by fracturing by the number of risk factors existing in the casing, wherein when the number of risk factors is 0, the risk degree is none, when the number of risk factors is 1, the risk degree is the first level, when the number of risk factors is 2, the risk degree is the second level, when the number of risk factors is 3, according to whether the thickness of the casing is greater than 11mm, the risk degree is between the second level and the third level, and when the number of risk factors is 4, the risk degree is the third level. The present invention can extract and identify the risk degree of casing deformation before fracturing and during fracturing, so as to timely optimize the fracturing construction parameters and reduce the probability of casing deformation.

Description

Technical Field

[0001] The present invention relates to the technical field of shale gas development, and in particular to a method for predicting the risk degree of casing deformation induced by fracturing based on multi-factor analysis. Background Art

[0002] With the deepening of oil and gas exploration and development, the objects of fracturing transformation are no longer limited to conventional oil and gas reservoirs, but have gradually entered unconventional oil and gas reservoirs. Among them, shale oil and gas are typical representatives of unconventional oil and gas reservoirs. In recent years, the scale of domestic shale oil and gas exploration and development has increased year by year, and the number of fracturing wells and stages has also increased year by year. Domestic shale oil and gas fracturing technology has also made great progress. However, with the improvement of shale oil and gas fracturing technology, there are also some technical difficulties.

[0003] The inventors found that casing deformation during shale fracturing leads to complicated situations downhole, including obstruction of the lower perforating gun, stuckness during lifting, and lost sections, which leads to a reduction in the number of designed fracturing sections and a reduction in the overall degree of transformation of the target layer, ultimately affecting the transformation effect of the shale gas reservoir. At present, many scholars have conducted research on the casing deformation problem and casing deformation failure risk analysis during the hydraulic fracturing of shale gas horizontal wells.

[0004] For example, a paper titled "Quantitative Risk Analysis of Shale Gas Well Casing Deformation Failure Based on Bayesian Network" published on July 10, 2018, and written by Zhang Renren, Yan Yifei, etc., recorded a method of converting the accident tree and event sequence model into a Bayesian network, using conditional probability tables to consider the reasoning relationship between events, and establishing a Bayesian network model for shale gas well casing deformation failure. The author used the Bayesian network model of shale gas well casing deformation failure to obtain the most likely cause combination of casing deformation failure, and obtained the dynamic probability of casing deformation failure and its failure consequences. The analysis results are consistent with the safety status of gas well casing at the engineering site.

[0005] The paper entitled Risk Assessment of Fault Slip and Casing Deformation Induced by Hydraulic Fracturing in Sichuan Shale Gas, published on September 15, 2020, and written by Fan Yu, Huang Rui, etc., records a method of establishing a fault model based on geological data, conducting geomechanical analysis on it, and applying quantitative risk analysis (QRA) to assess the risk of fault slip. The author used the Mohr-Coulomb criterion to analyze the activation state of the fault after hydraulic fracturing construction, and applied quantitative risk analysis (QRA) to evaluate the risk of fault slip and the sensitivity of various factors to fault slip. Based on this risk assessment result, the risk of fault slip under hydraulic fracturing construction was identified, providing a reference for optimizing the wellbore trajectory design to slow down casing deformation. These research contents may provide an effective analysis method for solving the problem of casing deformation, but these methods are very complex, and the analysis results obtained are theoretical. There are great limitations in practical application, and it is impossible to form a timely, effective and economical judgment method for on-site construction.

[0006] For on-site construction, the existing casing change risk prediction method only relies on the predicted fracture distribution map and the relative position of the horizontal wellbore provided in the geological data. If the fracture crosses the wellbore, it is considered that the casing change risk is high at that location, which belongs to the single factor pre-fracturing prediction. On-site usually adopts technical means such as controlling the displacement, scale and sand volume of fracturing construction in the transformation of the natural fracture development section to minimize the probability of casing deformation, but the reliability of predicting the casing change point based solely on the indicator of "natural fracture development" is low.

[0007] Therefore, in order to ensure that the fracturing construction meets the design requirements and fully transform the reservoir, a method based on multi-factor analysis to predict the risk of fracturing-induced casing deformation is needed, so as to optimize the fracturing construction parameters in the casing deformation risk section in advance and minimize the probability of casing deformation. Summary of the invention

[0008] The purpose of the present invention is to solve at least one of the above-mentioned deficiencies in the prior art. For example, one of the purposes of the present invention is to provide a method for predicting the risk of casing deformation induced by fracturing before and during fracturing.

[0009] In order to achieve the above-mentioned purpose, the present invention provides a method for predicting the risk degree of casing deformation induced by fracturing based on multi-factor analysis, comprising the following steps: determining the influencing factors of casing deformation induced by fracturing, wherein the influencing factors include abnormal changes in formation stiffness along the wellbore, poor cementing quality, and construction pressure exceeding the permitted range; analyzing logging data to identify the above-mentioned influencing factors, wherein the identification information of abnormal changes in formation stiffness along the wellbore is a local abnormal protrusion of the gamma logging curve, the identification information of poor cementing quality is a local abnormal cementing quality, and the identification information of construction pressure exceeding the permitted range is a local abnormal protrusion of the construction pressure curve; determining the risk factors of casing deformation induced by fracturing according to the results of logging data analysis, wherein the risk factors include sand plugging peaks in the fracturing construction pressure curve, local abnormal changes in natural gamma, local abnormal changes in cementing homogeneity, and local abnormal natural gamma. The defect points with constant changes overlap with the defect points with abnormal local changes in cementing homogeneity; the risk level of casing deformation induced by fracturing is judged by the number of risk factors existing in the casing, wherein, for casing of the same size, when the casing thickness is less than 11 mm, the number of risk factors is 0, the risk level is none, the number of risk factors is 1, the risk level is the first level (or medium), the number of risk factors is 2, the risk level is the second level (or large), and the number of risks is 3 or 4, the risk level is the third level (or very large); when the casing thickness is greater than 11 mm, the number of risk factors is 0, the risk level is none, the number of risk factors is 1, the risk level is the first level (or medium), the number of risk factors is 2 or 3, the risk level is the second level (or large), and the number of risks is 4, the risk level is the third level (or very large). This is equivalent to judging the risk level of casing deformation induced by fracturing by the number of risk factors existing in the casing. Under the condition of a predetermined casing size and thickness, the greater the number of risk factors, the higher the risk of casing deformation induced by fracturing.

[0010] In an exemplary embodiment of the present invention, when the defect points of the local abnormal change of natural gamma and the defect points of the local abnormal change of cementing homogeneity are located in the formation fracture zone caused by fracturing, the risk level of casing deformation induced by fracturing may increase.

[0011] In an exemplary embodiment of the present invention, the location of the formation fracture zone produced by the fracturing can be determined by geological data before fracturing and / or numerical simulation of reservoir fracturing.

[0012] In an exemplary embodiment of the present invention, the numerical simulation of reservoir fracturing may include the following steps:

[0013] According to the technical method of "well-seismic combination", based on the seismic wave data and combined with the single well layer information, a three-dimensional geological model of the target block is established;

[0014] Calculate rock mechanics parameters based on the logging data of a single well in the target block, perform single well geomechanics analysis based on other logging data and rock mechanics parameters, and obtain single well geological analysis results;

[0015] Comprehensively analyze the information of the world stress map, the single well measurement information of existing wells, and the microseismic monitoring information of horizontal well fracturing in the target block to obtain the maximum horizontal principal stress direction angle in the target block;

[0016] A three-dimensional geological model is introduced to establish a finite element model of the geostress field of the target block. Based on the geological analysis results of a single well and the microseismic measurement results of existing wells during fracturing construction, the simulation results of the geostress field of the target block are verified, and the verified numerical solution of the geostress field is constructed as a fine geostress field of the block.

[0017] Based on the detailed geostress field of the block, a finite element model integrating geology, fracturing engineering, cement sheath and casing was established. The three-dimensional finite element deformation and stress analysis of the casing string in the entire horizontal section of the horizontal well was performed to obtain the initial stress distribution of the casing string before fracturing.

[0018] The three-dimensional finite element deformation and stress analysis of the casing string after the reservoir is fractured is carried out to calculate the changes in the ground stress field caused by fracturing and find out the location distribution of the shear load applied to the casing.

[0019] In an exemplary embodiment of the present invention, the risk factors of the casing include a sand plugging peak in the fracturing construction pressure curve, and when there are multiple risk factors, the risk level of casing deformation induced by fracturing can be reduced by optimizing the fracturing construction parameters.

[0020] In an exemplary embodiment of the present invention, the optimization of the fracturing construction parameters may include controlling the concentration of the sand-carrying fluid, increasing the viscosity of the working fluid, increasing the displacement in steps, and increasing the amount of 100-mesh silt sand with low sand concentration.

[0021] In an exemplary embodiment of the present invention, the determination basis of the abnormal protrusion of the gamma logging curve may be that the local gamma value is greater than 200 GAPI.

[0022] In an exemplary embodiment of the present invention, the judgment basis for determining that the cementing quality evaluation result is poor may be that the acoustic amplitude is higher than the interface with poor cement bonding, and the local evaluation result of the cementing quality is poor.

[0023] In an exemplary embodiment of the present invention, the basis for determining whether the construction pressure curve has a local abnormal protrusion is that the amplitude of a sharp increase or decrease in the pressure curve is greater than 10 MPa / min, and the pressure curve is not a straight line.

[0024] In an exemplary embodiment of the present invention, when the risk level is none, the probability of sleeve deformation can be predicted to be 0; when the risk level is the first level, the probability of sleeve deformation can be predicted to be less than or equal to 20%; when the risk level is the second level, the probability of sleeve deformation can be predicted to be between 20% and 50%; when the risk level is the third level, the probability of sleeve deformation can be predicted to be greater than 50%.

[0025] Compared with the prior art, the beneficial effects and advantages of the present invention include at least one of the following:

[0026] (1) The present invention can predict the risk of casing deformation in the fracturing section before fracturing construction;

[0027] (2) The present invention can timely detect the risk signs of casing deformation and the risk degree of casing deformation during fracturing construction;

[0028] (3) The present invention can qualitatively determine the risk level of casing deformation according to the number of risk factors;

[0029] (4) By identifying the risk level of casing deformation in advance, the fracturing construction parameters can be optimized in a timely manner, the probability of casing deformation can be reduced, and the smooth progress of fracturing construction can be guaranteed to the greatest extent. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 A diagram showing the risk level of casing deformation in an exemplary embodiment of the present invention is shown.

[0031] Figure 2 A casing damage curve and a gamma logging curve diagram in an exemplary embodiment of the present invention are shown.

[0032] Figure 3 A cementing quality acoustic amplitude and evaluation diagram in an exemplary embodiment of the present invention is shown.

[0033] Figure 4 A construction pressure curve diagram in an exemplary embodiment of the present invention is shown. DETAILED DESCRIPTION

[0034] Hereinafter, the method for predicting the risk degree of casing deformation induced by fracturing based on multi-factor analysis of the present invention will be described in detail in conjunction with exemplary embodiments and accompanying drawings.

[0035] In an exemplary embodiment of the present invention, a method for predicting the risk of casing deformation induced by fracturing based on multi-factor analysis includes the following steps:

[0036] S1. Determine the influencing factors of fracturing-induced casing deformation, where the influencing factors include abnormal changes in formation stiffness along the wellbore, poor cementing quality, and construction pressure exceeding the permitted range.

[0037] Here, the abnormal variation of formation stiffness along the wellbore belongs to geological factors, specifically referring to the asymmetric formation stiffness and obvious local variations; poor cementing quality belongs to cementing factors, specifically referring to the large local variations in cementing quality and local poor quality points; construction pressure exceeding the permitted range belongs to construction engineering factors, which may be caused by sand plugging.

[0038] S2. Analyze logging data to identify the above-mentioned influencing factors, among which, the identification information of abnormal changes in formation stiffness along the wellbore is the local abnormal bulge in the gamma logging curve, the identification information of poor cementing quality is the local abnormal cementing quality, and the identification information of construction pressure exceeding the permitted range is the local abnormal bulge in the construction pressure curve.

[0039] For example, the basis for determining an abnormal bulge in the gamma logging curve may be that the local gamma value is greater than 200 GAPI; the basis for determining that the cementing quality evaluation result is poor may be that the acoustic amplitude value is higher than the interface with poor cement bonding, and the local quality evaluation result is poor. The basis for determining a local abnormal bulge in the construction pressure curve may be that the amplitude of the pressure curve surge or drop is greater than 10MPa / min, and the slope of the pressure curve change is consistent with the simulation calculation results and / or microseismic monitoring results.

[0040] S3. Determine the risk factors of casing deformation induced by fracturing based on the results of logging data analysis, where the risk factors include sand plugging peaks in the fracturing operation pressure curve, local abnormal changes in natural gamma, local abnormal changes in cementing homogeneity, and overlap of defect points of local abnormal changes in natural gamma and defect points of local abnormal changes in cementing homogeneity.

[0041] S4. Determine the risk level of casing deformation induced by fracturing based on the number of risk factors existing in the casing.

[0042] Among them, Figure 1As shown, for casings of the same size (for example, the diameter is 127mm to 146.3mm), when the thickness of the casing is less than 11mm, when the number of risk factors is 0, the risk level is none, and the probability of casing deformation is 0; when the number of risk factors is 1, the risk level is the first level (or medium), and the probability of casing deformation is less than or equal to 20%; when the number of risk factors is 2, the risk level is the second level (or large), and the probability of casing deformation is between 20% and 50%; when the number of risks is 3 or 4, the risk level is the third level (or very large), and the probability of casing deformation exceeds 50%. For casings of the same size (for example, the diameter is 127mm to 146.3mm), when the thickness of the casing is greater than 11mm, when the number of risk factors is 0, the risk level is none, and the probability of casing deformation is 0; when the number of risk factors is 1, the risk level is the first level (or medium), and the probability of casing deformation is less than or equal to 20%; when the number of risk factors is 2 or 3, the risk level is the second level (or large), and the probability of casing deformation is between 20% and 50%; when the number of risks is 4, the risk level is the third level (or very large), and the probability of casing deformation exceeds 50%. This is equivalent to judging the risk level of casing deformation induced by fracturing by the number of risk factors existing in the casing. Under the condition of a predetermined casing size and thickness, the more risk factors there are, the higher the risk of casing deformation induced by fracturing.

[0043] Here, it should be noted that when the risk factors of the casing include sand plugging peaks in the fracturing construction pressure curve, and the number of risk factors is multiple, the risk level of casing deformation induced by fracturing can be reduced by optimizing the fracturing construction parameters. For example, when the casing thickness of the target well is less than 11 mm, if the risk factors of the casing of the target well include sand plugging peaks in the fracturing construction pressure curve, local abnormal changes in natural gamma, and local abnormal changes in cementing homogeneity, the number of risk factors is 3, and the risk level is very large (that is, the third level); when in the fracturing construction, the casing is prevented from having sand plugging peaks in the fracturing construction pressure curve by optimizing the fracturing construction parameters, the risk factors of the casing of the target well include local abnormal changes in natural gamma and local abnormal changes in cementing homogeneity, the number of risk factors is 2, and the risk level is large (that is, the second level). In other words, the risk level of casing deformation induced by fracturing can be reduced by optimizing the fracturing construction parameters.

[0044] When the defect points of the local abnormal change of natural gamma and the defect points of the local abnormal change of cementing homogeneity are located in the formation fragmentation zone caused by fracturing, the risk level of casing deformation induced by fracturing can be increased. The location of the formation fragmentation zone caused by fracturing can be determined by geological data before fracturing and / or numerical simulation of reservoir fracturing. For example, when the casing thickness of the target well is less than 11 mm, if the risk factors of the casing of the target well include local abnormal change of natural gamma, the number of risk factors is 1, and the risk level is medium (that is, the second level); but when it is found through numerical simulation that the natural gamma defect point is located in the formation fragmentation zone caused by fracturing (that is, the shear localization zone), the probability of casing deformation increases, and it should be considered that the number of risk factors is 2, and the risk level is large (that is, the third level).

[0045] When the defect points of local abnormal changes in natural gamma and local abnormal changes in cementing homogeneity are located in the formation fragmentation zone caused by fracturing, there are actually dangerous factors. By reducing the construction pressure and scale, the scope of the local shear zone can be controlled and the local shear force can be reduced, which is beneficial to reduce the risk of casing deformation.

[0046] In this embodiment, the numerical simulation of reservoir fracturing may include the following steps:

[0047] (1) Based on the seismic wave data and the single well stratigraphic information, a three-dimensional geological model of the target area is established according to the technical method of "well logging combined with seismic logging".

[0048] Specifically, in combination with the structural undulation characteristics of the target block, on the basis of three-dimensional seismic wave data, the overall geometry and grid size of the target block can be constructed, and then combined with the single well stratigraphic information of the existing wells in the target block, the stratigraphic information of the target block can be delineated, the geometry and grid size of the stratum where the reservoir is located and other strata outside the reservoir can be determined, and a three-dimensional geological model of the target block can be obtained.

[0049] Here, the specific implementation of establishing a three-dimensional geological model of the target block may include: establishing the grid geometry of the geological model according to the three-dimensional seismic wave data, dividing the strata and defining the grid unit size of each stratum, wherein the grid unit of the stratum where the reservoir is located is smaller than the grid unit of other strata. The ratio of the grid unit thickness of the stratum where the reservoir is located to the grid unit thickness of the other strata may be 1:18 to 1:30. For example, the grid unit thickness of other strata may be 20 times the grid unit thickness of the stratum where the reservoir is located.

[0050] (2) Calculate rock mechanical parameters based on the logging data of a single well in the target block, perform single-well geomechanical analysis based on other logging data and rock mechanical parameters, and obtain single-well geological analysis results.

[0051] The other logging data may include gamma rays, compression acoustic wave duration and density of the formation. The rock mechanical parameters include Young's modulus, Poisson's ratio, cohesion (adhesion) and internal friction angle. Using empirical formulas and related calculation principles, rock mechanical parameters such as Young's modulus can be calculated based on acoustic logging data. For example, the rock mechanical parameters such as Young's modulus can be calculated using the following related formulas (Formula (1) to Formula (4)).

[0052] E=10 3 ρ b ·[3(V s / V p ) 2 -4] / Vs 2 [(V s / V p ) 2 -1] Formula (1)

[0053] v=0.5[(V s / V p ) 2 -2] / [(V s / V p ) 2 -1] Formula (2)

[0054] C = 4.69433 × 10 7 V p 4 ρ b [(1+v) / (1-v)](1-2v)(1+0.78V sh ) Formula (3)

[0055]

[0056] Where, E is Young's modulus, MPa; ρ b is the rock density, g / cm 3 ; Vs is longitudinal wave, us / m; Vp is transverse wave, us / m; v is Poisson's ratio, dimensionless; C is cohesion, MPa; V sh is the mud content, %; is the internal friction angle, degrees.

[0057] The single well geological analysis results may include the geostress results obtained by indirect analysis using other well logging data and the geostress results obtained by direct calculation using rock mechanics parameters. The geostress results obtained by indirect analysis using other well logging data may include the maximum horizontal principal stress obtained by indirect analysis using other well logging data, the minimum horizontal principal stress obtained by indirect analysis using other well logging data, the vertical principal stress obtained by indirect analysis using other well logging data, and the formation pore pressure obtained by indirect analysis using other well logging data. The geostress analysis results obtained by direct calculation using rock mechanics parameters include the maximum horizontal principal stress obtained by direct calculation using rock mechanics parameters, the minimum horizontal principal stress obtained by direct calculation using rock mechanics parameters, the vertical principal stress obtained by direct calculation using rock mechanics parameters, and the formation pore pressure obtained by direct calculation using rock mechanics parameters.

[0058] (3) Comprehensively analyze the information of the World Stress Map (WSM), the single well measurement information of existing wells, and the microseismic monitoring information of horizontal well fracturing in the target block to obtain the maximum horizontal principal stress direction angle in the target block.

[0059] Here, the specific implementation method of the comprehensive analysis of the information of the world stress map, the single well measurement information of the existing wells, and the microseismic monitoring information of the horizontal well fracturing in the target block refers to: first, using the world stress map to determine the maximum horizontal principal stress direction angle in the area to which the target block belongs, and clarifying the interval range to which the maximum horizontal principal stress direction angle in the target block belongs; then, based on the information of the single well measurement, determining the interval range to which the maximum horizontal principal stress direction angle in different structural parts in the target block belongs, and clarifying the change law of the maximum horizontal principal stress direction angle in the target block with the terrain; finally, analyzing the microseismic monitoring information, and verifying and correcting the value of the maximum horizontal principal stress direction angle in the target block summarized by the above two types of information in combination with the analysis results of the microseismic monitoring information, or supplementing the value of the maximum horizontal principal stress direction angle in the target block in certain areas omitted by the above two types of information.

[0060] In this embodiment, the analysis of microseismic monitoring information may include: determining the position where a single-color strip distribution appears in the microseismic event points of the horizontal wells in the target block as a fracture network strip generated by the same fracturing stage, and determining the direction angle of the fracture network strip as the direction angle of the maximum horizontal principal stress at the position; determining the position where a color strip composed of multiple colors appears in the microseismic event points of the horizontal wells in the target block and the event point distribution exceeds the reservoir range as the position of a natural fracture; determining the situation where microseismic response points appear in the microseismic event points of the horizontal wells in the target block in a sheet-like or cluster-like distribution as the maximum horizontal principal stress directionality at the position is not obvious, and the minimum horizontal principal stress direction is close to the vertical principal stress direction.

[0061] (4) A three-dimensional geological model is introduced to establish a finite element model of the geostress field of the target block. Based on the geological analysis results of a single well and the microseismic measurement results of existing wells during fracturing construction, the simulation results of the geostress field in the target block are verified, and the verified numerical solution of the geostress field is reconstructed into a fine geostress field of the block.

[0062] Specifically, the triaxial geostress principal components obtained from the single well geological analysis results in step (2) and the maximum horizontal principal stress direction angle obtained from the analysis in step (3) are first input as model setting parameters into the three-dimensional geological model of the target block obtained in step (1), so that a finite element model of the geostress field of the target block can be established; then, a numerical simulation of the geostress field of the target block is performed, and the numerical simulation results of the geostress field are compared and verified with the microseismic measurement results of the existing wells during the fracturing construction and the single well geological analysis results, and the model setting parameters are adjusted, and the verified geostress field finite element model is used as a numerical model that can truly simulate the geostress field of the target block, and the three-dimensional fine geostress field numerical solution of the target block obtained can be used as input data for subsequent fracturing and casing deformation simulation.

[0063] For example, the specific implementation of establishing the finite element model of the geostress field of the target block may include: the unit used in the geological model grid is a three-dimensional 8-node linear unit. Among them, the stratum where the reservoir is located is set as the C3D8RP-pore pressure coupling unit, and other strata are set as the C3D8R displacement unit. Among them, C3D8RP and C3D8R refer to the unit type in the software Abaqus, C represents the solid unit, 3D represents the three-dimensional, 8 is the number of nodes of this unit, R means that this unit is a reduced integration unit, and P refers to the three-line pore pressure. The model load is set as a gravity load. The boundary conditions of the four sides and the bottom of the model are set as normal displacement constraints, and the boundary conditions of the top are set as free boundaries. The initial conditions input the initial geostress parameters and the initial pore pressure parameters, wherein the initial geostress parameters include the triaxial geostress principal components (i.e., the maximum horizontal principal stress, the minimum horizontal principal stress and the vertical principal stress) and the maximum horizontal principal stress direction angle.

[0064] For each single well in the target block, the in-situ stress results obtained by indirect analysis using other logging data and the in-situ stress results obtained by direct calculation using rock mechanics parameters can be input as initial in-situ stress parameters, and numerical simulation of the in-situ stress field of the target block can be performed to obtain the corresponding numerical solution of the in-situ stress field. Then, the errors of the above two numerical solutions of the in-situ stress field and the actual measured values ​​of the in-situ stress field of the existing well fracturing construction are compared, and the numerical solution with the smaller error with the actual measured value of the in-situ stress field is constructed as the fine in-situ stress field of the block, and used as the input data for subsequent fracturing and casing deformation simulation.

[0065] For example, we can compare and analyze whether the maximum horizontal principal stress direction distribution of the reservoir obtained from the two simulations is consistent with the microseismic measurement results of existing wells during fracturing construction, whether the stress format of the reservoir is consistent with the geomechanical analysis results of a single well, and whether the distribution law of the reservoir's geostress field is consistent with the microseismic measurement results of existing wells during fracturing construction. The geostress analysis results with smaller errors in the two simulations are judged to be more suitable for setting as simulation parameters for the block geostress field that reproduces the actual fracturing construction process, and the numerical solution of the geostress field obtained is also more suitable as input data for subsequent fracturing and casing deformation simulation. Considering that the main purpose of the model numerical results is for the subsequent "casing deformation prediction caused by fracturing", the model parameter preparation mainly emphasizes that the minimum principal stress result of the numerical solution is close to the measured value, that is, the principle of "giving priority to ensuring that the minimum principal stress result of the numerical solution is closest to the measured value, and taking into account the trend of the maximum horizontal principal stress direction angle numerical solution and the measured value intermediate value is consistent" is used to ensure the rationality of the model.

[0066] It should be noted that the purpose of single-well geomechanical analysis is to analyze the extension direction of the crack. Since the crack always extends in the direction perpendicular to the minimum horizontal principal stress, the orientation of the crack extension can be predicted by determining the orientation of the geostress. The local geological structural details of different well sections vary to a certain extent, so the geostress analysis results suitable for simulating the vertical well are also different. By using the geostress results obtained by indirect analysis using other logging data and the geostress results obtained by direct calculation using rock mechanics parameters as initial geostress parameters, numerical simulations of the geostress field of the target block are performed respectively, and the simulation accuracy of the two sets of geostress data can be judged, so as to select the initial input parameters of the geostress field simulation that are most suitable for simulating the vertical well. In this way, for all vertical wells in the target block, the geostress analysis results with the most suitable simulation parameters for the block geostress field that are set to reproduce the actual fracturing construction process (i.e., the minimum error) can be repeatedly found, which can improve the overall simulation accuracy of the geostress field model, thereby establishing a fine geostress field, and ensuring that the simulated fracture extension direction is close to the real fracture state during subsequent fracturing and casing deformation simulation.

[0067] (5) Based on the detailed geostress field of the block, an integrated finite element model of geology, fracturing engineering, cement sheath and casing was established. The three-dimensional finite element deformation and stress analysis of the casing string in the entire horizontal section of the horizontal well was performed to obtain the initial stress distribution of the casing string before fracturing.

[0068] Specifically: On the basis of the finite element model of the geostress field of the block in step (4), a geometric model of the well, cement sheath and casing is established, and the model data of the fracturing construction is set to obtain a finite element model of geology-fracturing engineering-cement sheath-casing integration, and the numerical simulation results of the fine geostress field of the block are used as input data for fracturing and casing deformation simulation.

[0069] For example, establishing a finite element model that integrates geology, fracturing engineering, cement sheath and casing may include the following: first, establishing a geometric model of the well, and then setting model data, the model data including reservoir thickness distribution, horizontal section logging data, geostress field distribution, designed fracturing construction parameters, perforation parameters, formation pressure coefficients, geostress parameters, and rock mechanics parameters; finally, considering a variety of materials (including formation materials, cement sheath materials, and casing materials), a variety of geometric shapes (including formation geometry, cement sheath geometry, and casing geometry), two physical fields of structural deformation and physical seepage, fluid pressure loads, geostress loads, gravity loads, elastic mechanics models, and plastic mechanics models, a three-dimensional finite element model of the well is established.

[0070] For the mathematical model of geology-fracturing engineering-cement sheath-casing integration for predicting casing deformation, its basic theoretical model is the plastic loading yield criterion of metal, including the Tresca yield criterion of formula (5) and the von Mises yield criterion of formula (6). Both are yield criteria based on shear strength. In other words, the plastic deformation of metal materials is shear plastic deformation.

[0071] τ max =K Formula (5)

[0072] (σ1-σ2) 2 +(σ2-σ3) 2 +(σ3-σ1) 2 =2σ s 2 =6K 2 Formula (6)

[0073] Among them, σ1, σ2, σ3 are three principal stresses, MPa, σ s is the yield stress, MPa, and K is the shear yield strength of the material, MPa.

[0074] The tensile plasticity of the casing appears to be tensile plastic deformation at a macroscopic level, but the microscopic mechanism is shear plastic slip of metal crystals. Based on this, considering the environment in which the casing is located, it is believed that during fracturing construction, along the horizontal axis, if there are the above two types of defects (for example, defects with gamma anomalies and defects with poor cementing quality) at the places with the largest shear load around the casing, then there is a high risk of casing deformation at these defects. These places should be avoided from falling into the area with the largest shear load.

[0075] The final "geology-fracturing engineering-cement sheath-casing integration" model includes:

[0076] 1) Various materials and geometric shapes;

[0077] 2) Two physical fields: structural deformation and seepage;

[0078] 3) Fluid pressure load, ground stress load, gravity load;

[0079] 4) Elasticity constitutive model and plasticity constitutive model.

[0080] The mechanical behavior of this complex model can be summarized by the following formula:

[0081] K(u)·u=F

[0082] The variables here are defined as:

[0083] K is the system stiffness matrix, which represents the material properties of the model including elastic constitutive and plastic constitutive properties, as well as geometric characteristics; u is the motion vector, including the displacement and pore pressure of each point in the model; F is the load vector, which represents the various loads involved in the model.

[0084] (6) Perform three-dimensional finite element deformation and stress analysis on the casing string after fracturing construction in the target layer of a single well, calculate the changes in the ground stress field caused by fracturing, and find the location distribution of the shear load applied to the casing.

[0085] Specifically, model parameters can be set for the target layer section of the casing string in the finite element model of the geology-fracturing engineering-cement sheath-casing integration according to the designed fracturing construction parameters, and numerical simulation of reservoir fracturing can be performed to calculate the changes in the ground stress field caused by the fracturing construction of the target layer section, and find the position distribution of the shear load applied to the casing.

[0086] In this embodiment, the optimization of the fracturing construction parameters may include controlling the concentration of the sand-carrying fluid, increasing the viscosity of the working fluid, increasing the displacement in steps, and increasing the amount of 100-mesh silt sand with low sand concentration.

[0087] In order to better understand the above exemplary embodiments of the present invention, they are further described below with reference to specific examples.

[0088] Example 1

[0089] In this example, the 204H12-5 well section in Weiyuan area is taken as an example to analyze the risk level of casing deformation (referred to as "casing deformation").

[0090] The following is a curve analysis of the casing damage (i.e. casing deformation) of 204H12-5 in the well with three influencing factors. Figure 2 The casing damage curve and gamma logging curve are shown in Figure 2. Figure 2 Curve a is the maximum inner diameter, curve b is the average inner diameter, and curve c is the minimum inner diameter. Figure 3 It is the sound amplitude and evaluation diagram of cementing quality. Figure 3Curve A is the casing coupling value, curve B is the wellbore value, and curve C is the natural gamma value. Figure 4 is the construction pressure curve. Figure 4 The curves with different symbols represent different construction sections.

[0091] Before fracturing construction, the logging data of well 204H12-5 was analyzed to determine whether the target well (well 204H12-5) had three risk factors: local abnormal changes in natural gamma, local abnormal changes in cementing homogeneity, and overlaps between the defect points of local abnormal changes in natural gamma and the defect points of local abnormal changes in cementing homogeneity.

[0092] Analyze the gamma logging curve of target well 204H12-5 (such as Figure 2 The gamma values ​​at the depths of 3100m and 3200m suddenly increased from 70API to 190API, indicating that these two points are abnormally protruding locations of the gamma curve. In other words, the target well has the risk factor of local abnormal changes in natural gamma.

[0093] Then analyze the cementing quality and acoustic amplitude curve of target well 204H12-5 (such as Figure 3 The results show that: at depths of 3200m or more, the acoustic amplitude shows significant local changes, that is, the acoustic amplitude shows large fluctuations, which indicates that the cementing quality homogeneity of the external interface at this location is poor. In other words, the target well has the risk factor of abnormal local changes in cementing homogeneity.

[0094] At the same time, compare Figure 2 and Figure 3 It was found that the location where the cementing quality was poor and the location where the gamma curve abnormal bulge appeared in the target well 204H12-5 were both located at a depth of 3200m or more. In other words, the target well had a risk factor that the defect point of the local abnormal change of natural gamma overlapped with the defect point of the local abnormal change of cementing homogeneity.

[0095] Finally, during the fracturing construction process, the construction pressure curve of the target well 204H12-5 was analyzed (such as Figure 4 It is found that the construction pressure curve is perfect, and there is no sharp increase in pressure spike value. In other words, the target well does not have the risk factor of sand plugging spike in the fracturing construction pressure curve.

[0096] In addition, the mechanical behavior of the casing string was analyzed, and the stress distribution of the casing string at the initial installation stage was obtained, confirming that the casing is safe under the initial load, and its stress is not the main factor affecting the casing deformation during the later fracturing period. In other words, the location of the formation fracture zone produced by fracturing will not increase the risk of casing deformation.

[0097] Therefore, based on the above information, it can be considered that the target well 204H12-5 includes three risk factors: local abnormal changes in natural gamma, local abnormal changes in cementing homogeneity, and overlapping of defect points of local abnormal changes in natural gamma and defect points of local abnormal changes in cementing homogeneity. The casing thickness of the target well 204H12-5 is less than 11mm, so the casing change risk level of the target well 204H12-5 is predicted to be very high, and the probability of casing deformation is predicted to be greater than 50%.

[0098] During the actual production application of the target well 204H12-5, it was found that the casing string at the predicted position was deformed. Figure 2 As shown in the figure, at a depth of about 3200m, the minimum inner diameter (curve c), average inner diameter (curve b) and maximum inner diameter (curve a) of the casing decrease sharply, that is, 3200m downhole is the location where the casing deformation occurs. Figure 3 It can also be seen that after the depth of 3100m underground, the wellbore curve (i.e., curve B) changes from being flat to fluctuating up and down, which indicates that casing deformation occurs after 3100m underground.

[0099] This verifies that the method of the present invention for predicting the risk degree of casing deformation induced by fracturing based on multi-factor analysis can predict the risk degree and probability of casing deformation induced by fracturing in advance before and during fracturing construction.

[0100] In summary, the beneficial effects and advantages of the present invention include at least one of the following:

[0101] (1) The present invention can predict the risk of casing deformation in the fracturing section before fracturing construction;

[0102] (2) The present invention can timely detect the risk signs of casing deformation and the risk degree of casing deformation during fracturing construction;

[0103] (3) The present invention can qualitatively determine the risk level of casing deformation according to the number of risk factors;

[0104] (4) By identifying the risk level of casing deformation in advance, the fracturing construction parameters can be optimized in a timely manner, the probability of casing deformation can be reduced, and the smooth progress of fracturing construction can be guaranteed to the greatest extent.

[0105] Although the present invention has been described above in conjunction with the exemplary embodiments and the accompanying drawings, it should be apparent to those skilled in the art that various modifications may be made to the above-described embodiments without departing from the spirit and scope of the claims.

Claims

1. A method for predicting the risk of casing deformation induced by fracturing based on multi-factor analysis, characterized in that: The following steps are involved: Determine the factors that influence fracturing-induced casing deformation, including abnormal formation stiffness variation along the wellbore, poor cementing quality, and construction pressure exceeding the permitted range; The above-mentioned influencing factors are identified by analyzing the logging data. Among them, the abnormal change of formation stiffness along the wellbore is indicated by the local abnormal bulge of the gamma logging curve, the poor cementing quality is indicated by the local abnormal cementing quality, and the construction pressure exceeds the permitted range is indicated by the local abnormal bulge of the construction pressure curve. Determine the risk factors of casing deformation induced by fracturing based on the results of logging data analysis, where the risk factors include sand plugging peaks in the fracturing operation pressure curve, local abnormal changes in natural gamma, local abnormal changes in cementing homogeneity, and overlap of defect points of local abnormal changes in natural gamma and defect points of local abnormal changes in cementing homogeneity; The risk level of casing deformation induced by fracturing is determined by the number of risk factors existing in the casing. For casing of the same size, when the thickness of the casing is less than 11 mm, the risk level is zero when the number of risk factors is 0, the risk level is zero, the risk level is 1 when the number of risk factors is 1, the risk level is the first level, the risk level is 2 when the number of risk factors is 2, the risk level is the second level, and the risk level is 3 or 4 when the risk level is the third level, and the third level is higher than the second level and higher than the first level; when the thickness of the casing is greater than 11 mm, the risk level is zero when the number of risk factors is 0, the risk level is zero, the risk level is 1 when the number of risk factors is 1, the risk level is the first level, the risk level is 2 or 3 when the risk level is the second level, and the risk level is 4 when the risk level is the third level, and the third level is higher than the second level and higher than the first level; The basis for determining the abnormal bulge of the gamma logging curve is that the local gamma value is greater than 200 GAPI; The determination basis of the local abnormality of cementing quality is that the acoustic amplitude is higher than the interface of poor cement bonding, and the local evaluation result of cementing quality is poor; The basis for judging the local abnormal bulge of the construction pressure curve is that the amplitude of the pressure curve surge or drop is greater than 10MPa / min, and the pressure curve is not a straight line; When the risk level is none, the probability of casing deformation is predicted to be 0; when the risk level is the first level, the probability of casing deformation is predicted to be less than or equal to 20%; when the risk level is the second level, the probability of casing deformation is predicted to be between 20% and 50%; when the risk level is the third level, the probability of casing deformation is predicted to be greater than 50%.

2. The method for predicting the risk of casing deformation induced by fracturing based on multi-factor analysis according to claim 1, characterized in that: When the defect points of the local abnormal change of natural gamma and the defect points of the local abnormal change of cementing homogeneity are located in the formation fracture zone caused by fracturing, the risk level of casing deformation induced by fracturing increases.

3. The method for predicting the risk of casing deformation induced by fracturing based on multi-factor analysis according to claim 2, characterized in that: The location of the formation fracture zone produced by the fracturing is determined by geological data before the fracturing and / or numerical simulation of the reservoir fracturing.

4. The method for predicting the risk of casing deformation induced by fracturing based on multi-factor analysis according to claim 3, characterized in that: The numerical simulation of reservoir fracturing comprises the following steps: According to the technical method of "well-seismic combination", based on the seismic wave data and combined with the single well layer information, a three-dimensional geological model of the target block is established; Calculate rock mechanics parameters based on the logging data of a single well in the target block, perform single well geomechanics analysis based on other logging data and rock mechanics parameters, and obtain single well geological analysis results; Comprehensively analyze the information of the world stress map, the single well measurement information of existing wells, and the microseismic monitoring information of horizontal well fracturing in the target block to obtain the maximum horizontal principal stress direction angle in the target block; A three-dimensional geological model is introduced to establish a finite element model of the geostress field of the target block. Based on the geological analysis results of a single well and the microseismic measurement results of existing wells during fracturing construction, the simulation results of the geostress field of the target block are verified, and the verified numerical solution of the geostress field is constructed as a fine geostress field of the block. Based on the detailed geostress field of the block, a finite element model integrating geology, fracturing engineering, cement sheath and casing was established. The three-dimensional finite element deformation and stress analysis of the casing string in the entire horizontal section of the horizontal well was performed to obtain the initial stress distribution of the casing string before fracturing. The three-dimensional finite element deformation and stress analysis of the casing string after the reservoir is fractured is carried out to calculate the changes in the ground stress field caused by fracturing and find out the location distribution of the shear load applied to the casing.

5. The method for predicting the risk of casing deformation induced by fracturing based on multi-factor analysis according to claim 1, characterized in that: The risk factors for the casing include a sand plugging peak in a fracturing construction pressure curve, and when there are multiple risk factors, the risk level of casing deformation induced by fracturing can be reduced by optimizing the fracturing construction parameters.

6. The method for predicting the risk of casing deformation induced by fracturing based on multi-factor analysis according to claim 5, characterized in that: The optimized fracturing construction parameters include controlling the concentration of the sand-carrying fluid, increasing the viscosity of the working fluid, increasing the displacement in steps, and increasing the amount of 100-mesh silt sand with low sand concentration.

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