Method and system for widening drilling safety pressure window, and a device and storage medium

Abstract

Provided in the present invention are a method and system for widening a drilling safety pressure window, and a device and a storage medium. The method comprises the following steps: predicting distribution features of underground leakage-prone natural fractures; on the basis of the distribution features of the natural fractures, acquiring the locations and occurrences of the leakage-prone fractures, and predicting the leakage pressure; and respectively predicting fractures and crushed zones, and fracture shear deformation and destruction, optimizing a well location and a well trajectory on the basis of a prediction result, avoiding open-type fracture regions, selecting a region having a relatively high leakage pressure as a well point location and a wellbore trajectory, and using same for widening a safety pressure window. In the present invention, mechanical means are used to reduce the collapse pressure and extend a lower limit, so that broad adaptability and a high success rate are achieved, the problem of drilling safety pressure window widening of ultra-deep, high-pressure and high-stress fractured formations can be effectively solved, and the present invention is conducive to solving the drilling safety problems of kicking, leakage, sticking, etc., and is also conducive to reducing drilling costs, protecting the environment, and effectively avoiding reservoir damage.

Description

A method, system, device and storage medium for widening drilling safety pressure window Technical Field

[0001] The present invention relates to the field of drilling technology, and in particular to a method for widening a drilling safety pressure window, a system for widening a drilling safety pressure window, a computer device, and a computer-readable storage medium. Background Art

[0002] During drilling, a certain density of drilling fluid is used to form a liquid column pressure in the wellbore to balance the formation pore pressure and maintain the stability of the wellbore wall. The accurate selection of the liquid column pressure is very important and can effectively avoid accidents such as blowouts, leaks, collapses, and sticking during drilling. Each different geological layer has its corresponding specific safe drilling pressure window. Among them, the liquid column pressure that avoids drilling overflows and collapses is the lower limit of this window, while the liquid column pressure that prevents formation rupture and leakage is the upper limit. Currently, oil and gas well drilling often faces some narrow pressure window problems caused by factors such as ultra-deep, fractured, high pressure, and high stress. During the implementation of drilling projects, it is easy to have insufficient pressure or exceed the window range, resulting in frequent engineering accidents. Broadening the drilling safety pressure window is an important basic work to ensure the safe, rapid, and high-quality construction of oil and gas wellbores.

[0003] Existing technologies typically employ pressure-bearing plugging to increase formation fracture or leakage pressure, thereby expanding the safe drilling pressure window. This approach primarily increases the upper limit of the window by increasing the formation fracture or leakage pressure. However, due to the limited scope for increasing the upper limit in fractured rock masses, high-pressure, and high-stress formations with well-developed fractures, the existing methods for widening the pressure window are limited in scope. Construction plans are typically determined based on leakage patterns and prior plugging experience, resulting in a lack of quantitative scientific evidence for technical implementation. When leakage is discovered during drilling, the plugging plan is generally determined based on the leakage volume, leakage rate and basic formation characteristics, and there is a lack of comprehensive geomechanical analysis and judgment; as oil and gas drilling develops towards ultra-deep and fractured reservoirs, the industry's overall drilling losses are gradually increasing, and the success rate of pressure plugging is low; pressure plugging requires a large amount of plugging drilling fluid containing multiple chemical components to be injected from the surface into the formation, and the risk of environmental pollution is high during the entire process; the plugging process generally takes a long time, consumes a large amount of drilling fluid and plugging materials, and has high engineering costs; for target layer drilling operations, large-scale pressure plugging may inject high-density or sealing drilling fluid into the formation, which can easily cause reservoir damage, destroy the near-wellbore seepage channel, lead to reduced oil and gas well productivity, and indirectly affect the benefits of oil and gas exploration and development.

[0004] Summary of the Invention

[0005] In response to the problems existing in the prior art, the present invention provides a method, system, equipment and storage medium for widening the drilling safety pressure window, so as to scientifically widen the drilling safety pressure window and effectively solve the leakage prevention and plugging problems in the prior art.

[0006] In order to achieve the above object, the present invention provides a method for widening the drilling safety pressure window, comprising the following steps:

[0007] S1: Predict the distribution characteristics of natural fractures prone to underground leakage;

[0008] S2: according to the distribution characteristics of the natural fractures, obtain the location and occurrence of the fractures prone to leakage, and predict the leakage pressure;

[0009] S3: Predict fracture zones and fracture shear deformation failures separately, optimize well locations and trajectories based on the prediction results, avoid open fracture areas, select areas with higher loss pressure as wellpoint locations and wellbore trajectories, and use this as a means to widen the safe pressure window.

[0010] Furthermore, the prediction of the distribution characteristics of natural fractures prone to underground leakage is carried out based on the evolution of paleo-stress fields.

[0011] Furthermore, the process of predicting the distribution characteristics of underground natural fractures that are prone to leakage is: predicting the parameters of natural fractures based on the regional paleo-stress evolution distribution characteristics and rock mechanical properties.

[0012] Furthermore, the process of predicting natural fracture parameters based on regional paleo-stress evolution distribution characteristics and rock mechanical properties is as follows:

[0013] Based on the Coulomb failure criterion and the basic principle that cracks may occur under triaxial stress conditions, the relationship between crack direction, ground stress and friction coefficient is obtained.

[0014] Based on the relationship between the crack direction, ground stress and friction coefficient, a failure function of crack generation is obtained, and based on the failure function of crack generation, natural crack parameters are obtained.

[0015] Furthermore, the relationship between the crack direction, ground stress and friction coefficient is:

[0016] Where θ is the angle between the maximum principal stress and the fracture surface, and μ is the internal friction coefficient of the rock.

[0017] Furthermore, the damage function F that generates cracks is:

[0018] where σ1, σ2, and σ3 are the maximum, intermediate, and minimum principal stresses, respectively; θ is the angle between the maximum principal stress and the fracture surface; and μ is the internal friction coefficient of the rock.

[0019] Furthermore, in step S2, the process of obtaining the location and occurrence of the leakage-prone fractures according to the distribution characteristics of the natural fractures is as follows:

[0020] Obtain the effective normal stress σ when the current ground stress field acts on the pre-existing natural fracture surface and decomposes it into a vertical fracture surface ne and a shear stress τ parallel to the crack plane;

[0021] Wherein, the effective normal stress σ of the vertical crack surface is ne The shear stress τ parallel to the crack surface satisfies the following when the crack structure surface is in shear failure state:

[0022] Furthermore, the process of predicting the leakage pressure is as follows:

[0023] According to the relationship between the crack structure surface and the principal stress field, the effective normal stress σ perpendicular to the crack surface is defined respectively. ne and the shear stress τ parallel to the crack plane: τ=n 11 n 12 σ1+n 12 n 22 σ2+n 13 n 23 σ3 (4)

[0024] Where σ1, σ2, and σ3 are the maximum, intermediate, and minimum principal stresses, respectively, and are expressed in MPa; γ is the angle between the normal to the crack surface and the minimum principal stress σ3, and is expressed in degrees; λ is the angle between the projection of the crack strike in the σ1-σ2 plane and σ1, and is expressed in degrees; P p is the pore pressure value; n ij is the direction cosine;

[0025] When each fracture reaches the shear failure standard, it corresponds to a specific pore pressure value. The pore pressure value is the rupture or leakage pressure at which fracture leakage occurs. The leakage pressure is the upper limit of the drilling safety pressure window.

[0026] Furthermore, the process of optimizing the well location and trajectory based on the prediction results to avoid the open fracture area is as follows:

[0027] Based on the location, occurrence and leakage pressure of underground fractures prone to leakage, the well point location and wellbore trajectory are selected in the area with higher leakage pressure above the target layer, avoiding the open fracture area and drilling.

[0028] Furthermore, step S4 is also included: based on rock mechanics, ground stress and fracture occurrence characteristics, the wellbore stability under different wellbore conditions at different locations is predicted, multiple wellbore stability prediction results are obtained and the wellbore stability prediction results with higher stability are selected to optimize the well point position and wellbore trajectory.

[0029] Furthermore, the process of predicting wellbore stability at different locations and under different wellbore conditions is as follows:

[0030] Assuming that a set of specific fractures in the formation cut through the wellbore to form a low-strength weak plane, and that the formation strength in other directions is the same, the weak plane failure criterion is used to determine whether the weak plane fails before the rock body. Based on the failure of the weak plane, the failure of the matrix rock, and the sliding failure of the fracture weak plane, the wellbore trajectory with good wellbore stability is selected.

[0031] Furthermore, the weak plane failure criterion is:

[0032] Where σ1 and σ3 are the maximum and minimum principal stresses at the spatial position of the weak structural surface such as the crack, and the unit is MPa; S w is the weak surface cohesion, the unit is MPa; u w is the internal friction coefficient of the weak surface, dimensionless; λ is the angle between the weak surface normal and the maximum stress orientation, unit is °.

[0033] Furthermore, when Or when λ=π / 2, the matrix rock block is destroyed, and the failure criterion of the matrix rock block is:

[0034] Where σ1 and σ3 are still the maximum and minimum principal stresses at the location; S0 is the cohesion of the matrix rock; u0 is the internal friction coefficient of the matrix rock, is the weak internal friction angle;

[0035] in, u w is the internal friction coefficient of the weak surface.

[0036] Furthermore, the sliding failure of the crack weak plane meets the following conditions:

[0037] Where, is the weak surface internal friction angle, and λ is the function of the minimum drilling fluid column pressure to maintain wellbore stability.

[0038] Furthermore, the method further includes step S5: predicting hydration stress according to the chemical properties of the drilling fluid and the mud content of the formation; and adjusting the mud properties according to the hydration stress prediction result.

[0039] Furthermore, the process of predicting hydration stress based on the chemical properties of the drilling fluid and the mud content of the formation is as follows:

[0040] The total stress change value after water absorption is calculated based on the stress change law of the rock after water absorption and the rock water absorption expansion coefficient. The total stress change value after water absorption is used as the predicted hydration stress.

[0041] Furthermore, the stress change law of the rock after absorbing water satisfies:

[0042] Where: p w is the hydration stress generated by rock water absorption; M is the Biot modulus; ε is the volume strain; α is the Biot coefficient, approximately α = 1; c s is the volume expansion coefficient of mudstone due to water absorption.

[0043] Furthermore, the rock water absorption expansion coefficient is: c s =φc sf +(1-φ)c sg (11)

[0044] Where c s is the volume expansion coefficient of mudstone; c sg is the volume expansion coefficient of mudstone after water absorption; φ is the rock volume fraction; c sf is the volume expansion coefficient of rock due to water absorption.

[0045] Furthermore, the total stress change value after water absorption is:

[0046] The hydration stress increment caused by water absorption and expansion is:

[0047] Where c sf is the volume expansion coefficient of salt-gypsum rock absorbing water; c sg is the volume expansion coefficient of mudstone after water absorption; φ is the volume fraction of salt-gypsum rock; ΔW is the rate of change of water absorption;

[0048] The total stress change after water absorption is:

[0049] Where, δ ij is the change in water absorption strain, dimensionless.

[0050] Furthermore, according to the hydration stress prediction result, the process of adjusting the mud properties is: reducing the dynamic hydration stress value during the rock drilling process.

[0051] Furthermore, the method further includes step S6: obtaining a formation pressure bearing capacity model according to shear deformation and failure characteristics of natural fractures, and performing pressure plugging according to the formation pressure bearing capacity model.

[0052] Furthermore, in step S6, a formation pressure bearing capacity model is obtained through the pressure bearing capacity of the fractured formation and the failure pressure of the plugging layer.

[0053] Furthermore, the pressure bearing capacity of the fractured formation is: P c =min{P fd ,P fp} (14)

[0054] Among them, P c is the bearing capacity of the formation, P fd is the failure pressure of the plugging layer, P fp is the crack expansion pressure; P fd =P z +P t (15)

[0055] Among them, P z The pressure value of crack plugging type is determined in the laboratory, P t It is the additional value of the plugging pressure that is jointly influenced by the formation pressure, the permeability of the plugging layer and the wellbore pressure;

[0056] Among them, the crack expansion pressure P fp Based on the influence of background ground stress and specific fracture occurrence, the critical pressure at which natural fractures undergo shear deformation and rupture when the wellbore fluid column pressure acts.

[0057] In a second aspect, the present invention provides a drilling safety pressure window widening system, comprising:

[0058] Prediction module, used to predict the distribution characteristics of natural fractures prone to leakage in the underground;

[0059] A processing module, configured to obtain the location and occurrence of leak-prone fractures based on the distribution characteristics of the natural fractures, and predict the leak-off pressure;

[0060] The output module is used to predict the fracture zone and fracture shear deformation failure respectively, optimize the well location and trajectory according to the prediction results, avoid the open fracture area, select the higher loss pressure area as the well point location and wellbore trajectory, and use this as a way to widen the safe pressure window.

[0061] In a third aspect, the present invention provides a computer device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the steps of a method for widening the drilling safety pressure window when executing the computer program.

[0062] In a fourth aspect, the present invention provides a computer-readable storage medium storing a computer program, which, when executed by a processor, implements the steps of a method for widening the drilling safety pressure window.

[0063] Through the above technical solution, the beneficial effects of the present invention are as follows:

[0064] The present invention provides a method, system, equipment and storage medium for widening the drilling safety pressure window, comprising the following steps: predicting the distribution characteristics of natural fractures prone to leakage underground; obtaining the position and occurrence of the fractures prone to leakage based on the natural fracture distribution characteristics, and predicting the leakage pressure; respectively predicting the fracture fracture zone and the fracture shear deformation and damage, optimizing the well location and trajectory based on the prediction results, avoiding the open fracture area, selecting the area with higher leakage pressure as the well point location and wellbore trajectory, and using this as a means to widen the safety pressure window; the present invention adopts mechanical means to extend the lower limit by reducing the collapse pressure, has wide adaptability and high success rate, can effectively solve the problem of widening the drilling safety pressure window in ultra-deep, high-pressure and high-stress fractured formations, helps to solve the safety problems of drilling gushing, leakage and sticking, helps to reduce drilling costs, protect the environment and effectively avoid reservoir damage.

[0065] Other features and advantages of the embodiments of the present invention will be described in detail in the subsequent detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0066] The accompanying drawings are used to provide a further understanding of the embodiments of the present invention and constitute a part of the specification. Together with the following detailed description, they are used to explain the embodiments of the present invention, but do not constitute a limitation of the embodiments of the present invention. In the accompanying drawings:

[0067] FIG1 is a flow chart of a method for widening a drilling safety pressure window according to an embodiment of the present invention;

[0068] FIG2 is a schematic diagram of the relationship between the fracture surface and stress under the Coulomb failure criterion triaxial stress conditions according to an embodiment of the present invention;

[0069] FIG3 is a schematic diagram of FIG1 showing the optimal well point and well trajectory before drilling to avoid fracture zones prone to leakage in an embodiment of the present invention;

[0070] Figure 4 is a schematic diagram of the widening of the drilling safety pressure window in the embodiment of the present invention, wherein Figure 4(a) is a reservoir stratigraphic map of the area, Figure 4(b) is a reservoir formation pore pressure coefficient of the area, and Figure 4(c) is a schematic diagram of the widening of the safety pressure window. DETAILED DESCRIPTION

[0071] The present invention will be further described in detail below with reference to specific embodiments, which are intended to explain the present invention rather than to limit it.

[0072] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0073] It should be noted that the terms "first", "second", etc. in the description and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that the numbers used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0074] An embodiment of the present invention provides a method for widening the drilling safety pressure window, as shown in FIG1 , comprising the following steps:

[0075] S1: Predict the distribution characteristics of natural fractures prone to underground leakage;

[0076] S2: according to the distribution characteristics of the natural fractures, obtain the location and occurrence of the fractures prone to leakage, and predict the leakage pressure;

[0077] S3: Predict fracture zones and fracture shear deformation failures separately, optimize well locations and trajectories based on the prediction results, avoid open fracture areas, select areas with higher loss pressure as wellpoint locations and wellbore trajectories, and use this as a means to widen the safe pressure window.

[0078] The present invention uses mechanical means to reduce the collapse pressure and extend the lower limit. It has wide adaptability and high success rate. It can effectively solve the problem of widening the drilling safety pressure window in ultra-deep, high-pressure, and high-stress fractured formations, and help solve drilling safety problems such as gushing, leakage, and sticking. It helps to reduce drilling costs, protect the environment, and effectively avoid reservoir damage.

[0079] In one embodiment, the prediction of the distribution characteristics of natural cracks that are prone to leakage underground is performed based on the evolution of paleo-geostress field; specifically, the process of predicting the distribution characteristics of natural cracks that are prone to leakage underground is: predicting the parameters of natural cracks based on the regional paleo-geostress evolution distribution characteristics and rock mechanical properties; it should be noted that the evolution of paleo-geostress field can reveal the stress state and deformation law of strata in the geological period, thereby providing a mechanical mechanism and theoretical support for the formation and distribution of natural cracks; through the evolution of paleo-geostress field, the physical properties and mechanical properties of rocks in the geological period can be understood, thereby providing a material basis for the development of natural cracks; the study of the evolution of paleo-geostress field can also predict the future changing trends of strata and natural cracks, providing a scientific basis for resource development and environmental protection; the study of paleo-geostress field helps to understand the causes and distribution characteristics of natural cracks, thereby providing important theoretical support and guidance for research and practice in related fields.

[0080] In one embodiment, the process of predicting natural fracture parameters based on regional paleo-stress evolution distribution characteristics and rock mechanical properties is as follows:

[0081] Based on the Coulomb failure criterion and the basic principle that cracks may occur under triaxial stress conditions, the relationship between crack direction, ground stress and friction coefficient is obtained.

[0082] Based on the relationship between the crack direction, ground stress and friction coefficient, a failure function of crack generation is obtained, and based on the failure function of crack generation, natural crack parameters are obtained.

[0083] It should be noted that the Coulomb failure criterion assumes that when the shear stress along the potential shear failure surface is equal to or greater than the sum of the cohesive force and the frictional resistance, the compressive material will undergo shear failure. This criterion is usually used to analyze the failure behavior of materials such as rocks and soils; the triaxial stress condition refers to the condition under which stress is applied in different directions. Under triaxial stress conditions, materials such as rocks or soils are subjected to stresses from three directions, which can be normal pressure, shear force, or other types of forces. This stress condition can simulate the complex stress state to which the material is subjected in actual conditions; therefore, when studying the failure behavior of materials such as rocks and soils, it is necessary to consider the Coulomb failure criterion under triaxial stress conditions; by changing the stress conditions and observing the failure behavior of the material, its mechanical properties and failure mechanism can be better understood.

[0084] In one embodiment, the relationship between the crack direction, the ground stress and the friction coefficient is:

[0085] Where θ is the angle between the maximum principal stress and the fracture surface, and μ is the internal friction coefficient of the rock.

[0086] In one embodiment, the damage function F that generates cracks is:

[0087] where σ1, σ2, and σ3 are the maximum, intermediate, and minimum principal stresses, respectively; θ is the angle between the maximum principal stress and the fracture surface; and μ is the internal friction coefficient of the rock.

[0088] In one embodiment, the process of obtaining the location and occurrence of leakage-prone fractures according to the distribution characteristics of the natural fractures in step S2 is as follows:

[0089] Obtain the effective normal stress σ when the current ground stress field acts on the pre-existing natural fracture surface and decomposes it into a vertical fracture surface ne and a shear stress τ parallel to the crack plane;

[0090] Wherein, the effective normal stress σ of the vertical crack surface is ne The shear stress τ parallel to the crack surface satisfies the following when the crack structure surface is in shear failure state:

[0091] It should be noted that the vertical crack surface refers to the interface perpendicular to the crack surface, while the parallel crack surface refers to the interface parallel to the crack surface. Cracks are a common phenomenon in materials such as rocks and soil. They can be caused by a variety of factors, such as crustal movement, temperature changes, groundwater action, etc. The formation and distribution characteristics of these cracks are of great significance for geological exploration and resource development. In oil exploration, the appearance of vertical cracks can indicate the presence of oil to a certain extent, while parallel cracks may affect the stability of the rock formation.

[0092] In one embodiment, the process of predicting the leakage pressure is as follows:

[0093] According to the relationship between the crack structure surface and the principal stress field, the effective normal stress σ perpendicular to the crack surface is defined respectively. ne and the shear stress τ parallel to the crack plane: τ=n 11 n 12 σ1+n 12 n 22 σ2+n 13 n 23 σ3 (4)

[0094] Where σ1, σ2, and σ3 are the maximum, intermediate, and minimum principal stresses, respectively, and are expressed in MPa; γ is the angle between the normal to the crack surface and the minimum principal stress σ3, and is expressed in degrees; λ is the angle between the projection of the crack strike in the σ1-σ2 plane and σ1, and is expressed in degrees; P p is the pore pressure value; n ij is the direction cosine;

[0095] When each fracture reaches the shear failure standard, it corresponds to a specific pore pressure value. The pore pressure value is the rupture or leakage pressure at which fracture leakage occurs. The leakage pressure is the upper limit of the drilling safety pressure window.

[0096] In one embodiment, the process of optimizing the well location and trajectory based on the prediction results to avoid the open fracture area is as follows:

[0097] Based on the location, occurrence and leakage pressure of underground fractures prone to leakage, the well point location and wellbore trajectory are selected in the area with higher leakage pressure above the target layer, avoiding the open fracture area and drilling.

[0098] In one embodiment, step S4 is also included: based on rock mechanics, ground stress and fracture occurrence characteristics, the wellbore stability under different wellbore conditions at different locations is predicted, multiple wellbore stability prediction results are obtained and the wellbore stability prediction results with higher stability are selected to optimize the well point position and wellbore trajectory; it should be noted that, in the deep underground, under the joint action of rock mechanics properties, ground stress field and natural fractures, the mechanical heterogeneity and anisotropy of the formation are very strong, resulting in large differences in drilling wellbore stability at different depths and different locations; in addition, under the same wellbore environment, the wellbore stability at different orientations and different well inclinations is also very different. Therefore, in this embodiment, before drilling, by selecting different locations and different wellbore trajectories, a drilling track with lower wellbore collapse pressure can be found, thereby reducing the lower limit of the pressure window.

[0099] According to the effective stress law, the maximum and minimum principal stresses and angles of the wellbore are all functions of the minimum drilling fluid column pressure required to maintain wellbore stability. Therefore, under the influence of ground stress and natural fractures, the wellbore stability varies along wellbore trajectories in different orientations, and selecting the optimal wellbore trajectory is crucial for safe drilling. Calculations show that under strike-slip stress conditions, the wellbore is more stable along the direction of the horizontal maximum principal stress, and the greater the wellbore inclination, the safer the drilling. When the wellbore is perpendicular to the fracture surface, the shear stress acting on the fracture surface is zero, and the wellbore stability is optimal. By drilling with the optimal wellbore trajectory for good wellbore stability, the collapse pressure can be effectively reduced, thereby widening the safe drilling pressure window for a second time.

[0100] In one embodiment, the process of predicting wellbore stability at different locations and under different wellbore conditions is as follows:

[0101] Assuming that a set of specific fractures in the formation cut through the wellbore to form a low-strength weak plane, and that the formation strength in other directions is the same, the weak plane failure criterion is used to determine whether the weak plane fails before the rock body. Based on the failure of the weak plane, the failure of the matrix rock, and the sliding failure of the fracture weak plane, the wellbore trajectory with good wellbore stability is selected.

[0102] In one embodiment, the weak plane failure criterion is:

[0103] Where σ1 and σ3 are the maximum and minimum principal stresses at the spatial position of the weak structural surface such as the crack, and the unit is MPa; S w is the weak surface cohesion, the unit is MPa; u w is the internal friction coefficient of the weak surface, dimensionless; λ is the angle between the weak surface normal and the maximum stress orientation, unit is °.

[0104] In one embodiment, when Or when λ=π / 2, the matrix rock block is destroyed, and the failure criterion of the matrix rock block is:

[0105] Where σ1 and σ3 are still the maximum and minimum principal stresses at the location; S0 is the cohesion of the matrix rock; u0 is the internal friction coefficient of the matrix rock, is the weak internal friction angle;

[0106] in, u w is the internal friction coefficient of the weak surface.

[0107] In one embodiment, the sliding failure of the crack weak plane meets the following conditions:

[0108] Where, is the weak surface internal friction angle, and λ is the function of the minimum drilling fluid column pressure to maintain wellbore stability.

[0109] In one embodiment, step S5 is also included: predicting hydration stress based on the chemical properties of the drilling fluid and the mud content of the formation; adjusting the mud properties based on the hydration stress prediction result; specifically, during the drilling process, if the drilling fluid enters the formation, special rocks such as salt paste and mudstone will absorb water and expand, generating hydration stress. The entry of the drilling fluid into the formation rock will cause the rock hydration stress to increase, which will directly aggravate the tendency of the well wall to become unstable, causing the formation collapse pressure to rise and the safety pressure window to narrow. Therefore, reducing the dynamic hydration stress value during rock drilling is another means to reduce the collapse pressure and widen the safety pressure window.

[0110] There are two aspects of engineering geological factors that cause drilling fluid to enter the formation and rock to absorb water: one is that the liquid column pressure in the wellbore is greater than the pore pressure of the formation, and the other is the difference between the chemical potential of the drilling fluid in the wellbore and the chemical potential of the shale, or called the activity difference. Among them, the activity difference between the drilling fluid and the formation is the key. In the drilling design, it is necessary to fully understand the chemical activity of the formation and design the drilling fluid parameters accordingly. The application of high-quality drilling fluid performance and appropriate drilling fluid density in drilling can effectively reduce the hydration stress generated by rock absorption. Reducing the hydration stress value can effectively reduce the collapse pressure, thereby lowering the lower limit of the pressure window and achieving the purpose of widening the pressure window.

[0111] In one embodiment, the process of predicting hydration stress based on the chemical properties of the drilling fluid and the mud content of the formation is as follows:

[0112] The total stress change value after water absorption is calculated based on the stress change law of the rock after water absorption and the rock water absorption expansion coefficient. The total stress change value after water absorption is used as the predicted hydration stress.

[0113] In one embodiment, the stress change law of the rock after absorbing water satisfies:

[0114] Where: p w is the hydration stress generated by rock water absorption; M is the Biot modulus; ε is the volume strain; α is the Biot coefficient, approximately α = 1; c s is the volume expansion coefficient of mudstone due to water absorption.

[0115] In one embodiment, the rock water absorption expansion coefficient is: c s =φc sf +(1-φ)c sg (11)

[0116] Where c s is the volume expansion coefficient of mudstone; c sg is the volume expansion coefficient of mudstone after water absorption; φ is the rock volume fraction; c sf is the volume expansion coefficient of rock due to water absorption.

[0117] In one embodiment, the total stress change after water absorption is:

[0118] The hydration stress increment caused by water absorption and expansion is:

[0119] Where c sf is the volume expansion coefficient of salt-gypsum rock absorbing water; c sg is the volume expansion coefficient of mudstone after water absorption; φ is the volume fraction of salt-gypsum rock; ΔW is the rate of change of water absorption;

[0120] The total stress change after water absorption is:

[0121] Where, δ ij is the change in water absorption strain, dimensionless.

[0122] In one embodiment, the process of adjusting mud properties according to the hydration stress prediction result is: reducing the dynamic hydration stress value during rock drilling. It should be noted that the dynamic hydration stress value during rock drilling can be reduced by the following methods:

[0123] Optimize drilling fluid design: By selecting appropriate drilling fluid, the value of dynamic hydration stress can be reduced. For example, using low-solid or solid-free drilling fluid can reduce disturbance and damage to the formation, thereby reducing the occurrence of dynamic hydration stress.

[0124] Controlling the filtration loss of drilling fluid: During the drilling process, controlling the filtration loss of drilling fluid can reduce the entry of water into the formation, thereby reducing the generation of dynamic hydration stress. This can be achieved by optimizing the formulation of the drilling fluid and using filtration reducers.

[0125] Increase formation stability: By taking measures to increase formation stability, the value of dynamic hydration stress can be reduced. For example, the use of soil conditioners or polymers during drilling can improve formation stability.

[0126] Use balanced drilling technology: Balanced drilling technology refers to balancing the formation pressure by controlling the liquid column pressure of the drilling fluid, thereby reducing the disturbance and damage of the formation and reducing the generation of dynamic hydration stress.

[0127] Use low-speed drilling: Low-speed drilling can reduce damage to the formation, thereby reducing the generation of dynamic hydration stress. At the same time, low-speed drilling can also improve drilling efficiency and reduce drilling costs.

[0128] In one embodiment, step S6 is also included: obtaining a formation pressure bearing capacity model based on the shear deformation and failure characteristics of natural fractures, and performing pressure plugging according to the formation pressure bearing capacity model; it should be noted that, compared with intact formations, the leakage pressure of fractured formations is lower, so the upper limit of drilling safety pressure is low and the window is narrow; therefore, it is necessary to design a pressure plugging process according to the characteristics of the fractured formation, increase the pressure upper limit, and widen the pressure window; in this embodiment, according to the pressure instability mechanism of fractured formations, the pressure bearing capacity of the fractured formation is jointly determined by the sealing layer and the fracture stability. When the wellbore pressure exceeds the critical pressure of the sealing layer failure or the fracture expansion, it will cause the fracture to become pressure-instable.

[0129] Fracture propagation pressure is a key parameter for establishing a pressure model. According to geomechanical mechanisms, for ultra-deep, high-pressure, and high-stress formations, it is very difficult for natural fractures to expand openly, and shear deformation and failure are more likely to occur. Therefore, the fracture propagation pressure is determined based on the pore pressure value, that is, the critical pressure at which natural fractures undergo shear deformation and rupture when the wellbore fluid column pressure acts under the influence of background ground stress and specific fracture occurrence. This can more accurately determine the ultimate pressure at which a single or multiple fracture clusters within the formation expand, and can more effectively design pressure-bearing plugging engineering plans. Then, plugging materials with high compressive strength, high density, large elastic deformation rate, and high friction coefficient are used to form a high-strength plugging layer, increase the upper limit of fracture leakage pressure, and further widen the drilling safety pressure window.

[0130] In one embodiment, in step S6, the formation pressure bearing capacity model is obtained by using the fractured formation pressure bearing capacity and the failure pressure of the sealing layer.

[0131] In one embodiment, the pressure bearing capacity of the fractured formation is: P c =min{P fd ,P fp} (14)

[0132] Among them, P c is the bearing capacity of the formation, P fd is the failure pressure of the plugging layer, P fp is the crack expansion pressure; P fd =P z +P t (15)

[0133] Among them, P z The pressure value of crack plugging type is determined in the laboratory, P t It is the additional value of the plugging pressure that is jointly influenced by the formation pressure, the permeability of the plugging layer and the wellbore pressure;

[0134] Among them, the crack expansion pressure P fp Based on the influence of background ground stress and specific fracture occurrence, the critical pressure at which natural fractures undergo shear deformation and rupture when the wellbore fluid column pressure acts.

[0135] The present invention provides a preferred embodiment for jointly applying the steps S1-S6 to widening the drilling safety pressure window, breaking through the limitations of the original pressure-bearing plugging and expansion method of the pressure window being single, poorly applicable to fractured formations, and having a low success rate, and adopting a new method for widening the drilling safety pressure window by four-step widening. First, from the pre-drilling well site design stage, consideration is given to avoiding complex underground areas, laying a geological foundation for widening the drilling safety pressure window. Then, mechanical and chemical techniques are used respectively to extend the lower limit by reducing the collapse pressure, widening the safety pressure window twice. Finally, based on the shear deformation and rupture principle of natural fractures, a pressure-bearing plugging scheme is accurately designed, effectively extending the upper limit of the leakage pressure, and widening the safety pressure window for the fourth time. The scientific basis for widening the pressure window is sufficient, the adaptability is wide, and the success rate is high. The method can effectively solve the problem of widening the drilling safety pressure window in ultra-deep, high-pressure, and high-stress fractured formations, help solve safety problems such as drilling gushing, leakage, and sticking, help reduce drilling costs, protect the environment, and effectively avoid reservoir damage. The method comprises the following steps:

[0136] S1: Based on the evolution of paleo-stress fields, predict the distribution characteristics of natural fractures prone to leakage in the ground and classify them according to the fracture size;

[0137] S2: Based on the relationship between the current regional ground stress field and fractures, and based on the principle of fracture shear deformation and failure, the location and occurrence of fractures prone to leakage are determined, and the leakage pressure is predicted;

[0138] S3: Based on the prediction of fracture zones and fracture shear deformation and failure, the well location and trajectory are optimized to avoid open fracture areas and select areas with higher loss pressure to increase the loss pressure, thus completing the first expansion of the safe pressure window.

[0139] S4: Based on rock mechanics, geostress, and fracture characteristics, predict wellbore stability under different wellbore conditions at different locations, optimize well location and wellbore trajectory, enhance wellbore stability to reduce collapse pressure, and complete the second expansion of the safe pressure window;

[0140] S5: Based on the chemical properties of the drilling fluid and the mud content of the formation, the hydration stress is predicted and the mud properties are adjusted to reduce hydration expansion and collapse pressure, thus completing the third expansion of the pressure window.

[0141] S6: Based on the shear deformation and failure characteristics of natural fractures, a formation pressure bearing capacity model is designed, and pressure-bearing plugging engineering measures are implemented to increase the leakage pressure, completing the fourth expansion of the safe pressure window.

[0142] It should be noted that, in this embodiment, the first widening of the safety pressure window is to optimize the well location and trajectory based on the prediction of the fracture fracture zone and the fracture shear deformation and damage, avoid the open fracture area, select the higher loss pressure area, and increase the loss pressure; the second widening of the safety pressure window is based on rock mechanics, ground stress and fracture occurrence characteristics, predict the wellbore stability under different wellbore conditions at different locations, optimize the well location and wellbore trajectory, enhance the wellbore stability, and reduce the collapse pressure; the third widening of the pressure window is based on the chemical properties of the drilling fluid and the mud content of the formation, predict the hydration stress, adjust the mud properties, reduce hydration expansion, and reduce the collapse pressure; the fourth widening of the safety pressure window is based on the shear deformation and damage characteristics of the natural fracture, design the formation pressure bearing capacity model, implement pressure-bearing plugging engineering measures, and increase the loss pressure. Those skilled in the art can select one or more suitable widening methods for combination according to actual production needs.

[0143] Preferably, step S1 includes the following steps:

[0144] Determining the regional paleo-stress evolution distribution characteristics and rock mechanical properties can predict natural fracture parameters. According to the Coulomb failure criterion, as shown in Figure 1, the basic principle of crack formation under triaxial stress conditions is shown. The relationship between the crack direction, the in-situ stress, and the friction coefficient is:

[0145] The damage function that generates cracks is:

[0146] Where σ1, σ2, and σ3 are the maximum, intermediate, and minimum principal stresses, respectively; θ is the angle between the maximum principal stress and the fracture surface; and μ is the internal friction coefficient of the rock.

[0147] Based on the impact of crack size on leakage, the classification includes micro leakage in cracks with a width of less than micron, leakage in cracks of ten microns, slow leakage in cracks of one hundred microns, normal leakage in cracks of millimeters, rapid leakage in cracks of ten millimeters, ultra-rapid leakage in cracks of one hundred millimeters, and loss and return leakage in large faults or fracture-cavity bodies.

[0148] Preferably, step S2 includes the following steps:

[0149] When each crack structural surface is in shear failure state, it satisfies:

[0150] Among them, σ ne is the effective normal stress perpendicular to the crack surface, τ is the shear stress parallel to the crack surface, and μ is the shear deformation failure coefficient;

[0151] The relationship between normal stress and shear stress through the crack structure surface and the principal stress field is defined as: τ = n 11 n12 σ1+n 12 n 22 σ2+n 13 n 23 σ3 (4)

[0152] Where σ1, σ2, and σ3 are the maximum, intermediate, and minimum principal stresses, respectively, and are expressed in MPa; γ is the angle between the normal to the crack surface and the minimum principal stress σ3, and is expressed in degrees; λ is the angle between the projection of the crack strike in the σ1-σ2 plane and σ1, and is expressed in degrees. p is the pore pressure value; when each crack reaches the shear failure standard, it corresponds to a specific pore pressure value P p , pore pressure value P p is the upper limit of the drilling safety pressure window; specifically, according to the above method, based on the prediction of natural fracture distribution characteristics, the relationship between the current ground stress tensor and fracture occurrence can be used to determine the fracture shear deformation failure possibility (with a high shear stress to normal stress ratio τ / σ ne ) development location and occurrence information, that is, the location and occurrence of natural fractures in the underground space that are more prone to leakage can be obtained in advance. Formulas (3) and (5) show that when each fracture reaches the shear failure standard, it corresponds to a specific pore pressure value P p , this P p The value is exactly the rupture or loss pressure at which fracture leakage occurs, which can be used as the upper limit of the drilling safety pressure window. Therefore, through this step, the location, occurrence and loss pressure of the fractures prone to leakage can be determined before drilling.

[0153] Preferably, in step S3, according to steps S1 and S2, the basic distribution characteristics of natural fractures are clarified, and the location, occurrence and loss pressure of underground fractures prone to leakage are predicted. Then, according to the drilling engineering technical capabilities, the well point location and wellbore trajectory are optimized, and above the target layer, the open fracture area is avoided as much as possible. In the target layer section, drilling is preferably carried out in the area with higher loss pressure to increase the loss pressure at the entire wellbore position, thereby achieving the first widening of the drilling safety pressure window. As shown in Figure 2, the widening of the pressure window in this step increases the upper limit of the safety pressure, which is beneficial to the early deployment of strategies to reduce drilling fluid loss during drilling.

[0154] Preferably, step S4 includes the following steps:

[0155] Deep underground, due to the combined effects of rock mechanical properties, geostress fields, and natural fractures, the formation exhibits strong mechanical heterogeneity and anisotropy, resulting in significant differences in wellbore stability at different depths and locations. Furthermore, within the same wellbore environment, wellbore stability can also vary significantly at different orientations and inclinations. Therefore, before drilling, it is possible to identify drilling trajectories with lower wellbore collapse pressures by selecting different locations and wellbore trajectories, thereby lowering the lower limit of the pressure window.

[0156] Assuming that a set of specific fractures in the formation cuts through the wellbore to form a low-strength weak plane, while the formation strength in other directions is the same, the weak plane failure criterion can be used to determine whether the weak plane fails before the rock body. The failure criterion is:

[0157] Where σ1 and σ3 are the maximum and minimum principal stresses at the spatial position of the weak structural surface such as the crack, and the unit is MPa; S w is the weak surface cohesion, the unit is MPa; u w is the internal friction coefficient of the weak surface, dimensionless; λ is the angle between the normal direction of the weak surface and the maximum stress direction, unit is °;

[0158] because (u w is the weak internal friction angle), so when Or when λ = π / 2, the weak plane will not cause sliding failure, but the failure of the matrix rock. At this time, the failure criterion of the matrix rock is:

[0159] Where σ1 and σ3 are still the maximum and minimum principal stresses at the location; S0 is the cohesion of the matrix rock; u0 is the internal friction coefficient of the matrix rock, is the internal friction angle of the weak surface; the condition for the weak surface of the crack to produce sliding failure is:

[0160] Therefore, under the same mechanical conditions, the occurrence of the crack surface is the key factor in its failure;

[0161] According to the effective stress law, the maximum and minimum principal stresses σ1 and σ3 of the wellbore and the angle λ are all functions of the minimum drilling fluid column pressure Pm (drilling fluid density) required to maintain wellbore stability. Therefore, under the strike-slip stress mechanism (SHmax>SV>Shmin), the wellbore is more stable along the direction of the horizontal maximum principal stress, and the greater the wellbore inclination, the safer the drilling. When the wellbore is perpendicular to the fracture surface, the shear stress acting on the fracture surface is zero, and the wellbore stability is optimal.

[0162] Preferably, step S5 includes the following steps:

[0163] During the drilling process, if the drilling fluid enters the formation, special rocks such as salt paste and mudstone will absorb water and expand, generating hydration stress. The stress change law of special rocks in the formation after absorbing water is as follows:

[0164] Where: p w is the hydration stress generated by rock water absorption; M is the Biot modulus; ε is the volume strain; α is the Biot coefficient, approximately α = 1; c s is the volume expansion coefficient of mudstone;

[0165] Generally, drilling fluid penetrates into the formation, causing the formation rock to absorb water and expand. This process includes two parts: rock absorption and expansion and mudstone absorption and expansion. Therefore, the rock absorption and expansion coefficient c is s is: c s =φc sf +(1-φ)c sg (11)

[0166] The hydration stress increment caused by water absorption and expansion is:

[0167] The total stress change after water absorption is:

[0168] Where c s is the volume expansion coefficient of mudstone; c sf is the volume expansion coefficient of rock absorbing water; c sg is the volume expansion coefficient of mudstone after water absorption; φ is the rock volume fraction; M is the Biot modulus; ΔW is the rate of change of water absorption; δ ij is the change in water absorption strain, dimensionless.

[0169] Drilling fluid parameters are preset and mud properties are adjusted accordingly. Specifically, when drilling fluid enters the formation rock, it increases rock hydration stress, which directly exacerbates wellbore instability, causing formation collapse pressure to rise and narrowing the safe pressure window. Therefore, reducing the dynamic hydration stress value during rock drilling is another means to reduce collapse pressure and widen the safe pressure window.

[0170] There are two engineering geological factors that cause drilling fluid to enter the formation and rock water absorption: one is that the fluid column pressure in the wellbore is greater than the formation pore pressure, and the other is the difference between the chemical potential of the drilling fluid in the wellbore and the chemical potential of the shale, also known as the activity difference. The activity difference between the drilling fluid and the formation is crucial. During drilling design, it is important to fully understand the chemical activity of the formation and design drilling fluid parameters accordingly. Using high-quality drilling fluid and appropriate drilling fluid density during drilling can effectively reduce the hydration stress generated by rock water absorption. Reducing the hydration stress value in Equation (10) can effectively reduce the collapse pressure, thereby lowering the lower limit of the pressure window and achieving the goal of widening the pressure window.

[0171] Preferably, step S5 includes the following steps:

[0172] Compared with intact formations, fractured formations have lower leakage pressure, so the upper limit of drilling safety pressure is low and the window is narrow. Therefore, it is necessary to design a pressure-bearing plugging process based on the characteristics of fractured formations to increase the upper limit of pressure and widen the pressure window. According to the mechanism of pressure instability of fractured formations, the pressure bearing capacity of fractured formations is determined by the sealing layer and the stability of the fractures. When the wellbore pressure exceeds the critical pressure of the sealing layer failure or the expansion of the fracture, it will cause the fracture to become unstable under pressure. Therefore, the pressure bearing capacity of the fractured formation is: P c =min{P fd ,P fp} (14)

[0173] Among them, P c is the bearing capacity of the formation, P fd is the failure pressure of the plugging layer, P fp is the crack expansion pressure; P fd =P z +P t (15)

[0174] Among them, P z The pressure value of crack plugging type is determined in the laboratory, P t It is the additional value of the plugging pressure which is influenced by the formation pressure, the permeability of the plugging layer and the wellbore pressure.

[0175] Furthermore, based on the relationship between the fracture structure surface and the principal stress field, the fracture expansion pressure Pfp is determined, and the critical pressure of shear deformation and rupture of natural fractures is obtained. A plugging material with high compressive strength, high density, large elastic deformation rate and high friction coefficient is used to form a high-strength plugging layer, thereby increasing the upper limit of fracture leakage pressure and completing the fourth expansion of the safety pressure window. Specifically, the fracture expansion pressure Pfp is fp It is a key parameter for establishing a pressure model. According to the geomechanical mechanism, for ultra-deep, high-pressure, and high-stress formations, it is very difficult for natural fractures to expand and expand, and shear deformation and failure are more likely to occur. Therefore, Pfp According to the pore pressure value P in formula (5) p The critical pressure at which natural fractures undergo shear deformation and rupture under the influence of the wellbore fluid column pressure, under the influence of background geostress and specific fracture occurrence, can be determined more accurately. This allows for more accurate determination of the ultimate pressure at which single or multiple fracture clusters within the formation will expand, enabling more effective design of pressure-bearing plugging solutions. Plugging materials with high compressive strength, high density, high elastic deformation rate, and high friction coefficient are then used to form a high-strength plugging layer, raising the upper limit of fracture-induced leakage pressure and further widening the safe drilling pressure window.

[0176] The present invention provides an embodiment:

[0177] Taking drilling in a structure in the Kuqa Depression of the Tarim Basin as an example, as shown in Figure 4(a) and Figure 4(b), the reservoir formation pore pressure coefficient in this area is approximately 1.75. Conventional water-based drilling fluid requires a density of approximately 1.9 g / cm³ to maintain wellbore stability during drilling. However, the equivalent density of the leakage pressure in fractured formations is approximately 2.05 g / cm³, leaving a safe drilling pressure window density equivalent of only 0.1-0.15 g / cm³. This safety window is extremely narrow, resulting in serious leakage and stuck pipe during drilling, high safety risks, and difficulty in reservoir protection. Using the method of the present invention, as shown in Figure 4(c), the well location and wellbore trajectory are first optimized to reduce the drilling collapse pressure to approximately 1.85 g / cm³. By optimizing the drilling fluid properties and density, the collapse pressure is reduced to approximately 1.8 g / cm³. Through the analysis of shear failure and deformation of natural fractures, a reasonable pressure-bearing and plugging plan was formulated, which increased the upper limit of leakage pressure to about 2.15g / cm3 and widened the safe pressure window to 0.4g / cm3, helping to solve the problems of serious leakage and difficulty in reservoir protection during reservoir drilling in this area.

[0178] An embodiment of the present invention provides a system for widening a drilling safety pressure window, comprising:

[0179] Prediction module, used to predict the distribution characteristics of natural fractures prone to leakage in the underground;

[0180] A processing module, configured to obtain the location and occurrence of leak-prone fractures based on the distribution characteristics of the natural fractures, and predict the leak-off pressure;

[0181] The output module is used to predict the fracture zone and fracture shear deformation failure respectively, optimize the well location and trajectory according to the prediction results, avoid the open fracture area, select the higher loss pressure area as the well point location and wellbore trajectory, and use this as a way to widen the safe pressure window.

[0182] It should be noted here that the above-mentioned system provided by the embodiment of the present invention can implement all the method steps implemented by the above-mentioned method embodiment, and can achieve the same technical effects. The parts and beneficial effects that are the same as the method embodiment in this embodiment will not be described in detail here.

[0183] In another embodiment of the present invention, a computer device is provided, comprising a processor and a memory, wherein the memory is used to store a computer program, wherein the computer program includes program instructions, and the processor is used to execute the program instructions stored in the computer storage medium. The processor may be a central processing unit (CPU), or may be other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. It is the computing core and control core of the terminal, which is suitable for implementing one or more instructions, specifically suitable for loading and executing one or more instructions in the computer storage medium to implement the corresponding method flow or corresponding function; the processor described in the embodiment of the present invention can be used for the operation of the drilling safety pressure window widening method.

[0184] In another embodiment of the present invention, the present invention further provides a storage medium, specifically a computer-readable storage medium (Memory), which is a memory device in a computer device for storing programs and data. It is understandable that the computer-readable storage medium here can include both built-in storage media in the computer device and, of course, extended storage media supported by the computer device. The computer-readable storage medium provides a storage space, which stores the operating system of the terminal. In addition, one or more instructions suitable for being loaded and executed by the processor are also stored in the storage space. These instructions can be one or more computer programs (including program codes). It should be noted that the computer-readable storage medium here can be a high-speed RAM memory or a non-volatile memory, such as at least one disk memory. The processor can load and execute one or more instructions stored in the computer-readable storage medium to implement the corresponding steps of the method for widening the drilling safety pressure window in the above embodiment.

[0185] It will be understood by those skilled in the art that embodiments of the present invention may be provided as methods, systems, or computer program products. Thus, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware. Furthermore, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to magnetic disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0186] The present invention is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device produce a device for implementing the functions specified in one or more processes in the flowchart and / or one or more boxes in the block diagram.

[0187] These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce a product including an instruction device that implements the functions specified in one or more processes in the flowchart and / or one or more boxes in the block diagram.

[0188] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, so that the instructions executed on the computer or other programmable device provide steps for implementing the functions specified in one or more processes in the flowchart and / or one or more boxes in the block diagram.

[0189] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for widening a drilling safety pressure window, characterized in that: The following steps are involved: S1: Predict the distribution characteristics of natural fractures prone to leakage in the ground; S2: according to the distribution characteristics of the natural fractures, the location and occurrence of the fractures prone to leakage are obtained, and the leakage pressure is predicted; S3: Predict fracture zones and fracture shear deformation damage respectively, optimize well location and trajectory based on prediction results, avoid open fracture areas, select higher leakage pressure areas as well point locations and wellbore trajectories, and use this as a means to widen the safe pressure window.

2. The method for widening the drilling safety pressure window according to claim 1, characterized in that: The prediction of the distribution characteristics of natural fractures prone to leakage underground is carried out based on the evolution of paleo-geo-stress field.

3. The method for widening the drilling safety pressure window according to claim 1, characterized in that: The process of predicting the distribution characteristics of underground natural fractures that are prone to leakage is: predicting the parameters of natural fractures according to the distribution characteristics of regional paleo-geo-stress evolution and rock mechanical properties.

4. The method for widening the drilling safety pressure window according to claim 3, characterized in that: The process of predicting natural fracture parameters based on regional paleo-geo-stress evolution distribution characteristics and rock mechanical properties is as follows: Based on the Coulomb failure criterion and the basic principle that cracks may occur under triaxial stress conditions, the relationship between the crack direction and the ground stress and friction coefficient is obtained. Based on the relationship between the crack direction, the ground stress and the friction coefficient, the damage function of the crack is obtained, and based on the damage function of the crack, the natural crack parameters are obtained.

5. The method for widening the drilling safety pressure window according to claim 4, characterized in that: The relationship between the crack direction, ground stress and friction coefficient is: Where θ is the angle between the maximum principal stress and the fracture surface, and μ is the internal friction coefficient of the rock.

6. The method for widening the drilling safety pressure window according to claim 4, characterized in that: The damage function F that generates cracks is: Where σ1, σ2, σ3 are the maximum, intermediate and minimum principal stresses respectively, θ is the angle between the maximum principal stress and the fracture surface, and μ is the internal friction coefficient of the rock.

7. The method for widening the drilling safety pressure window according to claim 1, characterized in that: In step S2, the process of obtaining the position and occurrence of the leakage-prone fractures according to the distribution characteristics of the natural fractures is as follows: Obtain the effective normal stress σ when the current geostress field acts on the pre-existing natural fracture surface and decomposes it into a vertical fracture surface ne and a shear stress τ parallel to the crack plane; Wherein, the effective normal stress σ of the vertical crack surface ne The shear stress τ parallel to the crack surface satisfies when the crack structure surface is in a shear failure state: Where μ is the internal friction coefficient of rock.

8. The method for widening the drilling safety pressure window according to claim 7, characterized in that: The process of predicting the leakage pressure is: According to the relationship between the crack structure surface and the principal stress field, the effective normal stress σ perpendicular to the crack surface is defined respectively. ne and the shear stress τ parallel to the crack plane: τ=n 11 n 12 σ1+n 12 n 22 σ2+n 13 n 23 p3 (4) Where, σ1, σ2, and σ3 are the maximum, intermediate, and minimum principal stresses, respectively, and the unit is MPa; γ is the angle between the normal line of the crack surface and the minimum principal stress σ3, in degrees; λ is the angle between the projection of the crack direction in the σ1-σ2 plane and σ1, in degrees; P p is the pore pressure value; n ij is the direction cosine; When each crack reaches the shear failure standard, it corresponds to a specific pore pressure value, and the pore pressure value is the rupture or leakage pressure at which fracture leakage occurs, and the leakage pressure is the upper limit of the drilling safety pressure window.

9. The method for widening the drilling safety pressure window according to claim 1, characterized in that: The process of optimizing the well location and trajectory according to the prediction results to avoid the open fracture area is as follows: According to the location, occurrence and leakage pressure of underground fractures that are prone to leakage, the area with higher leakage pressure is selected as the well point location and wellbore trajectory above the target layer, avoiding the open fracture area and drilling.

10. The method for widening the drilling safety pressure window according to claim 1, characterized in that: It also includes step S4: based on rock mechanics, ground stress and fracture occurrence characteristics, predict the wellbore stability under different wellbore conditions at different locations, obtain multiple wellbore stability prediction results and select the wellbore stability prediction results with higher stability to optimize the well point location and wellbore trajectory.

11. The method for widening the drilling safety pressure window according to claim 10, characterized in that: The process of predicting wellbore stability under different wellbore conditions at different locations is as follows: Assuming that there is a group of specific fractures in the formation that cut the wellbore to form a low-strength weak surface, and the formation strength in other directions is the same, based on the weak surface failure criterion, it is judged whether the weak surface is destroyed before the rock body, and according to the weak surface failure, the matrix rock failure and the sliding failure of the fracture weak surface, the wellbore trajectory with good wellbore stability is selected for drilling.

12. The method for widening the drilling safety pressure window according to claim 11, characterized in that: The weak surface failure criterion is: Where σ1 and σ3 are the maximum and minimum principal stresses at the spatial position of the weak structural surface such as cracks, and the unit is MPa; S w is the weak surface cohesion, the unit is MPa; u w is the internal friction coefficient of the weak surface, dimensionless; λ is the angle between the normal of the weak surface and the direction of maximum stress, in degrees.

13. The method for widening the drilling safety pressure window according to claim 12, characterized in that: when Or when λ=π / 2, the matrix rock block is destroyed, and the failure criterion of the matrix rock block is: In the formula, σ1 and σ3 are still the maximum and minimum principal stresses at the location; S0 is the cohesion of the matrix rock; u0 is the friction coefficient within the matrix rock, is the weak surface internal friction angle; in, u w is the internal friction coefficient of the weak surface.

14. The method for widening the drilling safety pressure window according to claim 11, characterized in that: The sliding failure of the crack weak surface meets the following conditions: In the formula, is the weak surface internal friction angle, and λ is the function of the minimum drilling fluid column pressure to maintain wellbore stability.

15. The method for widening the drilling safety pressure window according to claim 1, characterized in that: The method further comprises step S5: predicting hydration stress according to the chemical properties of the drilling fluid and the mud content of the formation; and adjusting the mud properties according to the hydration stress prediction result.

16. The method for widening the drilling safety pressure window according to claim 15, characterized in that: The process of predicting hydration stress based on the chemical properties of the drilling fluid and the shale content of the formation is as follows: The total stress change value after water absorption is calculated according to the stress change law of rock after water absorption and the rock water absorption expansion coefficient. The total stress change value after water absorption is the predicted hydration stress.

17. The method for widening the drilling safety pressure window according to claim 16, characterized in that: The stress change law of the rock after absorbing water satisfies: Where: p w is the hydration stress generated by rock absorbing water; M is the Biot modulus; ε is the volume strain; α is the Biot coefficient, approximately taking α = 1; c s is the volume expansion coefficient of mudstone due to water absorption.

18. The method for widening the drilling safety pressure window according to claim 16, characterized in that: The rock water absorption expansion coefficient is: c s =φc sf +(1-φ)c sg (11) In the formula, c s is the volume expansion coefficient of mudstone; c sg is the volume expansion coefficient of mudstone; φ is the rock volume fraction; c sf is the volume expansion coefficient of rock due to water absorption.

19. The method for widening the drilling safety pressure window according to claim 16, characterized in that: The total stress change after water absorption is: The hydration stress increment caused by water absorption and expansion is: Δp w =M[φc sf +(1-φ)c sg ]ΔW (12) In the formula, c sf c is the volume expansion coefficient of salt-gypsum rock; sg is the volume expansion coefficient of mudstone after water absorption; φ is the volume fraction of salt-gypsum rock; ΔW is the change rate of water absorption; The total stress change after water absorption is: Board ij =αM[φc sf +(1-φ)c sg ]ΔWδ ij (13); In the formula, δ ij is the water absorption strain change.

20. The method for widening the drilling safety pressure window according to claim 15, characterized in that: According to the hydration stress prediction result, the process of adjusting the mud performance is: reducing the dynamic hydration stress value during rock drilling.

21. The method for widening the drilling safety pressure window according to claim 1, characterized in that: The method further comprises step S6: obtaining a formation pressure bearing capacity model according to the shear deformation and failure characteristics of the natural fractures, and performing pressure-bearing plugging according to the formation pressure bearing capacity model.

22. The method for widening the drilling safety pressure window according to claim 21, characterized in that: In step S6, a formation pressure bearing capacity model is obtained according to the pressure bearing capacity of the fractured formation and the failure pressure of the plugging layer.

23. The method for widening the drilling safety pressure window according to claim 22, characterized in that: The pressure bearing capacity of the fractured formation is: P c =min{P fd ,P fp } (14) Among them, P c is the bearing capacity of the formation, P fd is the failure pressure of the plugging layer, P fp The crack expansion pressure; P fd =P z +P t (15) Among them, P z The pressure value of crack plugging type is determined in the laboratory, P t It is the additional value of the plugging pressure influenced by the formation pressure, the permeability of the plugging layer and the wellbore pressure; The crack extension pressure P fp Based on the influence of background ground stress and specific fracture occurrence, the critical pressure of natural fractures undergoing shear deformation and rupture when the wellbore fluid column pressure acts.

24. A drilling safety pressure window widening system, characterized in that: The method for widening the drilling safety pressure window according to any one of claims 1 to 23 comprises: Prediction module, used to predict the distribution characteristics of natural fractures prone to leakage underground; A processing module, for obtaining the location and occurrence of the fractures prone to leakage according to the distribution characteristics of the natural fractures, and predicting the leakage pressure; The output module is used to predict the fracture zone and fracture shear deformation damage respectively, optimize the well location and trajectory according to the prediction results, avoid the open fracture area, select the higher loss pressure area as the well point location and wellbore trajectory, and use this as a means to widen the safe pressure window.

25. A computer device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the computer program, the steps of the method for widening the drilling safety pressure window as described in any one of claims 1-23 are implemented.

26. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, the steps of the method for widening the drilling safety pressure window as described in any one of claims 1 to 23 are implemented.

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