Well drilling safety pressure window widening method, system and equipment and storage medium

Abstract

The invention provides a well drilling safety pressure window widening method, system and device and a storage medium. The method comprises the following steps that distribution characteristics of underground natural fractures prone to leakage are predicted; according to the natural fracture distribution characteristics, obtaining the position and occurrence of an easy-to-leak fracture, and predicting the leakage pressure; respectively predicting a fracture fracture zone and fracture shear deformation damage, optimizing a well position and a well track according to prediction results, avoiding an open type fracture area, selecting a higher leakage pressure area as a well point position and a well track, and widening a safety pressure window by using the well point position and the well track; according to the method, the collapse pressure is reduced by adopting a mechanical means, the lower limit is extended, the adaptability is wide, the success rate is high, the problem of widening of the drilling safety pressure window of ultra-deep, high-pressure and high-stress fractured formations can be effectively solved, the safety problems of drilling gushing, leakage, jamming and the like can be solved, the drilling cost is reduced, the environment is protected, and reservoir damage is effectively avoided.

Description

Technical Field

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

[0002] In the drilling project, 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, which can effectively avoid accidents such as blowouts, leaks, collapses, and jams during drilling; each different geological layer has its corresponding specific safe drilling pressure window; among them, the liquid column pressure to avoid drilling overflow and collapse is the lower limit of this window, and the liquid column pressure to prevent formation rupture and leakage is the upper limit; at present, oil and gas well drilling often faces some narrow pressure window problems caused by ultra-deep, fractured, high pressure, high stress and other factors. In the implementation of drilling projects, it is easy to have insufficient pressure or exceed the window range, resulting in frequent engineering accidents. Widening the drilling safety pressure window is an important basic work to ensure the safe, rapid and high-quality construction of oil and gas wells.

[0003] In the existing technology, pressure plugging technology is generally used to increase the formation fracture or leakage pressure, thereby expanding the drilling safety pressure window. The pressure plugging method is mainly to increase the formation fracture or leakage pressure and increase the upper limit of the window to achieve the purpose of widening the safety pressure window. Due to the limited space for increasing the upper limit of the broken rock mass, high pressure and high stress formations with developed fractures, the method of widening the pressure window is single and has a limited scope of application; the construction plan is generally determined based on the leakage situation and previous plugging experience, and there is a lack of quantitative scientific basis in the implementation of the technology. When leakage is discovered during drilling, a plugging plan is usually determined based on the amount of leakage, the leakage rate and the basic characteristics of the formation, lacking 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; during pressure plugging, a large amount of plugging drilling fluid containing a variety of chemical components needs 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 plugging drilling fluid into the formation, which can easily cause reservoir damage, destroy the near-wellbore seepage channel, and lead to reduced oil and gas well production capacity, indirectly affecting the benefits of oil and gas exploration and development. Summary of the invention

[0004] In view of 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.

[0005] The present invention is achieved through the following technical solutions:

[0006] A method for widening a drilling safety pressure window comprises the following steps:

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

[0008] 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;

[0009] S3: Predict fracture zones and fracture shear deformation damage respectively, optimize well location and trajectory based on the 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.

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

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

[0012] Furthermore, the process of predicting natural fracture parameters based on regional paleo-geo-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 the crack direction and the ground stress and friction coefficient is obtained.

[0014] 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.

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

[0016]

[0017] Where θ is the angle between the maximum principal stress and the fracture surface, and μ is the internal friction coefficient of the rock.

[0018] Furthermore, the damage function F that generates cracks is:

[0019]

[0020] 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.

[0021] Furthermore, 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:

[0022] 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;

[0023] 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:

[0024]

[0025] Furthermore, the process of predicting the leakage pressure is:

[0026] 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:

[0027] τ=n 11 n 12 σ1+n 12 n 22 σ2+n 13 n 23 σ3 (4)

[0028]

[0029]

[0030] Where σ1, σ2, and σ3 are the maximum, intermediate, and minimum principal stresses, respectively, in MPa; γ is the angle between the normal of the crack surface and the minimum principal stress σ3, in degrees; λ is the angle between the projection of the crack strike in the σ1-σ2 plane and σ1, in degrees; n ij is the direction cosine;

[0031] When each fracture reaches the shear failure standard, it corresponds to a specific liquid column pressure value, and the liquid column 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.

[0032] Furthermore, the process of optimizing the well location and trajectory according to the prediction results to avoid the open fracture area is as follows:

[0033] 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.

[0034] 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.

[0035] Furthermore, the process of predicting the wellbore stability under different wellbore conditions at different locations is as follows:

[0036] 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.

[0037] Furthermore, the weak surface failure criterion is:

[0038]

[0039] 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; μ 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.

[0040] Furthermore, when Or when λ=π / 2, the matrix rock block is destroyed, and the failure criterion of the matrix rock block is:

[0041]

[0042] 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; μ0 is the friction coefficient within the matrix rock, is the weak surface internal friction angle;

[0043] in, The μ w is the internal friction coefficient of the weak surface.

[0044] Furthermore, the sliding failure of the crack weak surface meets the following conditions:

[0045]

[0046] 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.

[0047] Furthermore, 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.

[0048] Furthermore, the process of predicting hydration stress according to the chemical properties of the drilling fluid and the shale content of the formation is:

[0049] 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.

[0050] Furthermore, the stress variation law of the rock after absorbing water satisfies:

[0051]

[0052] 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.

[0053] Furthermore, the rock water absorption expansion coefficient is:

[0054] c s =φc sf +(1-φ)c sg (11)

[0055] 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.

[0056] Furthermore, the total stress change value after water absorption is:

[0057] The hydration stress increment caused by water absorption and expansion is:

[0058]

[0059] 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;

[0060] The total stress change after water absorption is:

[0061]

[0062] Furthermore, according to the hydration stress prediction result, the process of adjusting the mud performance is: reducing the dynamic hydration stress value during rock drilling.

[0063] Furthermore, the method further comprises step S6: obtaining a formation pressure bearing capacity model according to shear deformation and failure characteristics of natural fractures, and performing pressure-bearing plugging according to the formation pressure bearing capacity model.

[0064] 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.

[0065] Furthermore, the pressure bearing capacity of the fractured formation is:

[0066] P c =min{P fd ,P fp} (14)

[0067] 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;

[0068] P fd =P z +P t (15)

[0069] 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;

[0070] 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.

[0071] A drilling safety pressure window widening system, comprising:

[0072] Prediction module, used to predict the distribution characteristics of natural fractures prone to leakage underground;

[0073] 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;

[0074] 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.

[0075] A computer device comprises a memory, a processor and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, the steps of a method for widening a drilling safety pressure window are implemented.

[0076] A computer-readable storage medium stores a computer program, which, when executed by a processor, implements the steps of a method for widening a drilling safety pressure window.

[0077] Compared with the prior art, the present invention has the following beneficial technical effects:

[0078] The present invention provides a method, system, equipment and storage medium for widening a 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 fractures prone to leakage according to the distribution characteristics of natural fractures, and predicting the leakage pressure; respectively predicting the fracture fracture zone and the fracture shear deformation and damage, optimizing the well location and trajectory according to the prediction results, avoiding the open fracture area, selecting the area with higher leakage pressure as the well point location and the wellbore trajectory, and using this as a means to widen the safety pressure window; the application adopts mechanical means to reduce the collapse pressure and extend the lower limit, has wide adaptability and high success rate, can effectively solve the problem of widening the drilling safety pressure window of 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. BRIEF DESCRIPTION OF THE DRAWINGS

[0079] Figure 1 This is a flow chart of a method for widening a drilling safety pressure window in an embodiment of the present invention;

[0080] Figure 2 Schematic diagram of the relationship between the fracture surface and stress under the triaxial stress condition of the Coulomb failure criterion in an embodiment of the present invention;

[0081] Figure 3 for Figure 1 This is a schematic diagram of optimizing well points and well trajectories before drilling to avoid fracture zones prone to leakage in an embodiment of the present invention;

[0082] Figure 4 for Figure 1 Schematic diagram of widening the drilling safety pressure window in an embodiment of the present invention, wherein Figure 4 (a) is the reservoir stratigraphic map of the area. Figure 4 (b) is the reservoir formation pore pressure coefficient in this area, Figure 4 (c) Schematic diagram of widening the safety pressure window. DETAILED DESCRIPTION

[0083] The present invention is further described in detail below in conjunction with specific embodiments, which are intended to explain the present invention rather than to limit it.

[0084] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme 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 described embodiments 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 creative work should fall within the scope of protection of the present invention.

[0085] It should be noted that the terms "first", "second", etc. in the specification 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 data 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 that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0086] An embodiment of the present invention provides a method for widening a drilling safety pressure window, such as Figure 1 As shown, the following steps are included:

[0087] S1: Predict the distribution characteristics of natural fractures prone to leakage in the ground;

[0088] 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;

[0089] S3: Predict fracture zones and fracture shear deformation damage respectively, optimize well location and trajectory based on the 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.

[0090] The present application adopts 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.

[0091] In one embodiment, the prediction of the distribution characteristics of underground natural cracks that are prone to leakage is performed based on the evolution of paleo-geostress field; specifically, the process of predicting the distribution characteristics of underground natural cracks that are prone to leakage is: predicting natural crack parameters 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, and provide 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.

[0092] In one embodiment, the process of predicting natural fracture parameters based on regional paleo-geo-stress evolution distribution characteristics and rock mechanical properties is as follows:

[0093] 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.

[0094] 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.

[0095] 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 compressed 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 of applying stress 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 situations; 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.

[0096] In one embodiment, the relationship between the crack direction and the ground stress and friction coefficient is:

[0097]

[0098] Where θ is the angle between the maximum principal stress and the fracture surface, and μ is the internal friction coefficient of the rock.

[0099] In one embodiment, the damage function F for generating cracks is:

[0100]

[0101] 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.

[0102] In one embodiment, 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:

[0103] 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;

[0104] 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:

[0105]

[0106] 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 soils. 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.

[0107] In one embodiment, the process of predicting the leakage pressure is:

[0108] 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:

[0109] τ=n 11 n 12 σ1+n 12 n 22 σ2+n 13 n 23 σ3 (4)

[0110]

[0111]

[0112] Where σ1, σ2, and σ3 are the maximum, intermediate, and minimum principal stresses, respectively, in MPa; γ is the angle between the normal of the crack surface and the minimum principal stress σ3, in degrees; λ is the angle between the projection of the crack strike in the σ1-σ2 plane and σ1, in degrees; n ij is the direction cosine;

[0113] When each fracture reaches the shear failure standard, it corresponds to a specific liquid column pressure value, and the liquid column 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.

[0114] In one embodiment, the process of optimizing the well location and trajectory according to the prediction results to avoid the open fracture area is:

[0115] 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.

[0116] In one embodiment, step S4 is also included: based on rock mechanics, geostress and fracture occurrence characteristics, the wellbore stability under different wellbore conditions at different positions 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 layer, under the joint action of rock mechanical properties, geostress field and natural fractures, the mechanical heterogeneity and anisotropy of the formation are very strong, resulting in large differences in the wellbore stability at different depths and different positions; 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 positions and different wellbore trajectories, a drilling trajectory with lower wellbore collapse pressure can be found, thereby reducing the lower limit of the pressure window.

[0117] According to the effective stress law, the maximum and minimum principal stresses and angles of the wellbore are functions of the minimum drilling fluid column pressure that maintains the stability of the wellbore. Therefore, under the influence of ground stress and natural fractures, the wellbore stability is different on wellbore trajectories in different orientations, and selecting the best wellbore trajectory is the guarantee of safe drilling. Calculations show that under the strike-slip stress mechanism, the wellbore has better stability along the direction of the horizontal maximum principal stress, and the larger the well inclination angle, the safer the drilling. When the wellbore is perpendicular to the fracture surface, the shear stress acting on the fracture surface is 0, and the wellbore stability is the best. By drilling with the best wellbore trajectory, the collapse pressure can be effectively reduced, thereby widening the drilling safety pressure window for the second time.

[0118] In one embodiment, the process of predicting the wellbore stability under different wellbore conditions at different locations is:

[0119] 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.

[0120] In one embodiment, the weak surface failure criterion is:

[0121]

[0122] 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; μ 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.

[0123] 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:

[0124]

[0125] 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; μ0 is the friction coefficient within the matrix rock, is the weak surface internal friction angle;

[0126] in, The μ w is the internal friction coefficient of the weak surface.

[0127] In one embodiment, the sliding failure of the crack weak surface meets the following conditions:

[0128]

[0129] 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.

[0130] In one embodiment, step S5 is also included: predicting hydration stress according to the chemical properties of the drilling fluid and the mud content of the formation; adjusting the mud properties according to 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 drilling fluid entering 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.

[0131] 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 pressure of the liquid column 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. The chemical activity of the formation should be fully understood in the drilling design, and the drilling fluid parameters should be designed accordingly; the use of high-quality drilling fluid performance and appropriate drilling fluid density in drilling can effectively reduce the hydration stress caused by rock absorption of water, and reducing the hydration stress value can effectively reduce the collapse pressure, thereby reducing the lower limit of the pressure window and achieving the purpose of widening the pressure window.

[0132] In one embodiment, the process of predicting hydration stress based on the chemical properties of the drilling fluid and the shale content of the formation is:

[0133] 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.

[0134] In one embodiment, the stress variation law of the rock after absorbing water satisfies:

[0135]

[0136] 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.

[0137] In one embodiment, the rock water absorption expansion coefficient is:

[0138] c s =φc sf +(1-φ)c sg (11)

[0139] 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; csf is the volume expansion coefficient of rock due to water absorption.

[0140] In one embodiment, the total stress change value after water absorption is:

[0141] The hydration stress increment caused by water absorption and expansion is:

[0142]

[0143] 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;

[0144] The total stress change after water absorption is:

[0145]

[0146] In one embodiment, according to the hydration stress prediction result, the process of adjusting the mud performance 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:

[0147] Optimize drilling fluid design: By selecting suitable 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.

[0148] 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 drilling fluid and using filtration loss reducers.

[0149] Increase formation stability: Dynamic hydration stress can be reduced by taking measures to increase formation stability. For example, using soil conditioners or polymers during drilling can improve formation stability.

[0150] 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.

[0151] 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.

[0152] In one embodiment, step S6 is also included: according to the shear deformation and failure characteristics of natural fractures, a formation pressure bearing capacity model is obtained, and pressure plugging is performed according to the formation pressure bearing capacity model; it should be noted that, compared with the intact formation, the leakage pressure of the fractured formation is lower, so the upper limit of the 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, to increase the pressure upper limit and widen the pressure window; in this embodiment, according to the pressure instability mechanism of the fractured formation, 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.

[0153] Fracture expansion pressure is a key parameter for establishing a pressure model. According to the mechanism of geomechanics, 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 expansion pressure is determined according to the liquid column pressure value, that is, the critical pressure at which natural fractures undergo shear deformation and rupture when the wellbore liquid column pressure acts under the influence of background ground stress and specific fracture occurrence. This can more accurately determine the limit pressure at which a single or multiple fracture clusters in 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 broaden the drilling safety pressure window.

[0154] In one embodiment, in step S6, the formation pressure bearing capacity model is obtained through the pressure bearing capacity of the fractured formation and the failure pressure of the plugging layer.

[0155] In one embodiment, the pressure bearing capacity of the fractured formation is:

[0156] P c =min{P fd ,P fp} (14)

[0157] 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;

[0158] P fd =P z +P t (15)

[0159] 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;

[0160] The crack expansion 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.

[0161] The present invention provides a preferred embodiment for using the steps S1-S6 together in widening the drilling safety pressure window, breaking through the limitations of the original pressure-bearing plugging and expanding the pressure window, which is single, poorly applicable to fractured formations, and low in 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, the means of avoiding underground complex areas are considered to lay a geological foundation for widening the drilling safety pressure window. Then, mechanical and chemical technical means are used respectively to extend the lower limit by reducing the collapse pressure, and the safety pressure window is widened twice. Finally, based on the shear deformation and rupture principle of natural fractures, a pressure-bearing plugging scheme is accurately designed to effectively extend the upper limit of the leakage pressure, and the safety pressure window is widened 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 the safety problems of drilling gushing, leakage, and sticking, and help reduce drilling costs, protect the environment, and effectively avoid reservoir damage. The method comprises the following steps:

[0162] S1: Based on the evolution of paleo-geo-stress field, predict the distribution characteristics of natural fractures prone to leakage underground and classify them according to the fracture scale;

[0163] S2: According to the relationship between the current regional geostress field and cracks, based on the principle of fracture shear deformation failure, the location and occurrence of fractures prone to leakage are determined, and the leakage pressure is predicted;

[0164] S3: Based on the prediction of fracture zones and fracture shear deformation and damage, the well location and trajectory are optimized to avoid open fracture areas, and higher loss pressure areas are selected to increase the loss pressure, thus completing the first widening of the safety pressure window.

[0165] S4: Based on rock mechanics, geostress and fracture characteristics, predict the wellbore stability under different wellbore conditions at different locations, optimize the well location and wellbore trajectory, enhance the wellbore stability to reduce the collapse pressure, and complete the second widening of the safe pressure window;

[0166] 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 widening of the pressure window;

[0167] 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.

[0168] It should be noted that in this embodiment, the first widening of the safety pressure window is to optimize the well location and trajectory according to the prediction of the 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 performance, reduce the 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 natural fractures, 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 of the appropriate widening methods for combination according to actual production needs.

[0169] Preferably, step S1 comprises the following steps:

[0170] Determining the regional paleo-geo-stress evolution distribution characteristics and rock mechanical properties can predict the parameters of natural fractures. According to the Coulomb failure criterion, e.g. Figure 1 As shown in the figure, the basic principle of cracks under triaxial stress conditions, where the relationship between the crack direction and the ground stress and friction coefficient is:

[0171]

[0172] The damage function that generates cracks is:

[0173]

[0174] Among them, 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;

[0175] Based on the impact of crack size on leakage, it is divided into 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 millimeter, fast leakage in cracks of ten millimeters, ultra-fast leakage in cracks of one hundred millimeters and - loss and return loss due to emptying of large faults or fracture-cavity bodies.

[0176] Preferably, step S2 comprises the following steps:

[0177] When each crack structural surface is in shear failure state, it satisfies:

[0178]

[0179] Among them, σne 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;

[0180] The relationship between normal stress and shear stress through the crack structure surface and the principal stress field is defined as:

[0181] τ=n 11 n 12 σ1+n 12 n 22 σ2+n 13 n 23 σ3 (4);

[0182]

[0183] Where nij is the direction cosine:

[0184]

[0185] Among them, σ1, σ2, σ3 are the maximum, intermediate, and minimum principal stresses, respectively, in MPa; γ is the angle between the normal of the crack surface and the minimum principal stress σ3, in degrees; λ is the angle between the projection of the crack strike in the σ1-σ2 plane and σ1, in degrees, P P is the liquid column pressure value; when each crack reaches the shear failure standard, it corresponds to a specific liquid column pressure value P P , liquid column 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 the distribution characteristics of natural fractures, the relationship between the current ground stress tensor and the fracture occurrence can be used to clarify the development location and occurrence information of fractures with high shear deformation failure possibility (with a high shear stress to normal stress ratio τ / σne), that is, the location and occurrence of natural fractures in the underground space that are more likely to cause leakage can be determined in advance. Formulas (3) and (5) show that when each fracture reaches the shear failure standard, it corresponds to a specific liquid column 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 fractures prone to leakage can be determined before drilling.

[0186] Preferably, in step S3, according to steps S1 and S2, after clarifying the basic distribution characteristics of natural fractures, predicting the location, occurrence and loss pressure of fractures prone to leakage in the ground, the well point location and wellbore trajectory are optimized according to the drilling engineering technical capabilities, and above the target layer, the open fracture area is avoided as much as possible, and the target layer section is preferably drilled 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, such as Figure 2 As shown, the pressure window is widened in this step, which increases the upper limit of the safety pressure, and is beneficial to reduce the loss of drilling fluid during drilling from the perspective of early deployment strategy.

[0187] Preferably, step S4 comprises the following steps:

[0188] Deep underground, under the combined effects of rock mechanical properties, geostress fields and natural fractures, the mechanical heterogeneity and anisotropy of the strata are very strong, resulting in large differences in the stability of the wellbore at different depths and locations. In addition, under the same wellbore environment, the wellbore stability at different orientations and different well inclinations also varies greatly. Therefore, before drilling, by selecting different locations and different wellbore trajectories, we can find a drilling track with lower wellbore collapse pressure, thereby reducing the lower limit of the pressure window;

[0189] Assuming that there is a group of specific fractures in the formation that cut the wellbore to form a low-strength weak plane, and the formation strength in other directions is the same, the weak plane failure criterion can be used to determine whether the weak plane is destroyed before the rock body. The failure criterion is:

[0190]

[0191] 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; Sw is the cohesion of the weak surface, and the unit is MPa; μ w is the internal friction coefficient of the weak surface, dimensionless; λ is the angle between the normal of the weak surface and the maximum stress orientation, unit is °;

[0192] because ( 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:

[0193]

[0194] 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; μ0 is the friction coefficient within the matrix rock; then the condition for sliding failure of the weak surface of the crack is:

[0195]

[0196] Therefore, under the same mechanical conditions, the occurrence of the crack surface is the key factor in its failure;

[0197] According to the effective stress law, the maximum and minimum principal stresses σ1, σ3 and the angle λ of the wellbore are functions of the minimum drilling fluid column pressure Pm (drilling fluid density) that maintains the stability of the wellbore; therefore, under the strike-slip stress mechanism conditions (SHmax>SV>Shmin), the stability of the wellbore along the horizontal maximum principal stress direction is better, and the greater the well inclination angle, the safer the drilling; and when the wellbore is perpendicular to the fracture surface, the shear stress acting on the fracture surface is 0, and the wellbore stability is the best.

[0198] Preferably, step S5 comprises the following steps:

[0199] During the drilling process, if the drilling fluid enters the formation, special rocks such as salt gypsum 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:

[0200]

[0201] 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;

[0202] 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 s for:

[0203] c s =φc sf +(1-φ)c sg (11);

[0204] The hydration stress increment caused by water absorption and expansion is:

[0205]

[0206] In the formula, 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; ΔW is the rate of change of water absorption;

[0207] The total stress change after water absorption is:

[0208]

[0209] Based on this, the drilling fluid parameters are preset and the mud properties are adjusted. Specifically, the drilling fluid enters the formation rock, causing the rock hydration stress to increase, which will directly aggravate the tendency of the wellbore instability, 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.

[0210] 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 pressure of the liquid column 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 the activity difference. Among them, the activity difference between the drilling fluid and the formation is the key. In the drilling design, the chemical activity of the formation should be fully understood and the drilling fluid parameters should be designed accordingly. The application of high-quality drilling fluid performance and appropriate drilling fluid density in drilling can effectively reduce the hydration stress caused by rock absorption of water. Reducing the hydration stress value in formula (10) can effectively reduce the collapse pressure, thereby reducing the lower limit of the pressure window and achieving the purpose of widening the pressure window.

[0211] Preferably, step S5 comprises the following steps:

[0212] 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 pressure-bearing plugging technology according to the characteristics of fractured formations, increase the upper limit of pressure, and widen the pressure window. According to the mechanism of fractured formation pressure instability, the pressure bearing capacity of fractured formations is determined by the sealing layer and the stability of the fracture. When the wellbore pressure exceeds the critical pressure of the sealing layer failure or the expansion of the fracture, it will cause the fracture pressure instability. Therefore, the pressure bearing capacity of the fractured formation is:

[0213] P c =min{P fd ,P fp} (14);

[0214] Among them, Pc is the bearing capacity of the formation, P fd is the failure pressure of the plugging layer, P fp The crack expansion pressure;

[0215] P fd =P z +P t (15);

[0216] 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 the combined effect of formation pressure, plugging layer permeability and wellbore pressure.

[0217] Furthermore, based on the relationship between the crack structure surface and the principal stress field, the crack extension pressure P is determined. fp, the critical pressure of shear deformation and rupture of natural fractures is obtained, and 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 complete the fourth widening of the safety pressure window; specifically, the fracture expansion pressure P fp It is the key parameter for establishing the pressure model. According to the mechanism of geomechanics, for ultra-deep, high-pressure, and high-stress formations, it is very difficult for natural fractures to expand and expand, and it is more likely to cause shear deformation and failure. Therefore, P fp According to the liquid column pressure value P in formula (5) p The value is determined by the critical pressure of natural fractures that 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 limit pressure for the expansion of a single or multiple fracture clusters inside the formation, and can more effectively design pressure-bearing plugging engineering solutions. 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.

[0218] The present invention provides an embodiment:

[0219] For example, the drilling of a structure in the Kuche Depression of the Tarim Basin Figure 4 As shown in (a), Figure 4 As shown in (b), the reservoir formation pore pressure coefficient in this area is about 1.75, and the density of conventional water-based drilling fluid in drilling to maintain the stability of the wellbore wall needs to be 1.9g / cm 3 The equivalent density of the leakage pressure in fractured formations is about 2.05 g / cm 3 The density equivalent of the drilling safety pressure window is only 0.1-0.15g / cm 3 , the safety window is extremely narrow, leakage and pipe sticking are serious during drilling, the safety risk is high, and reservoir protection is difficult. Figure 4 As shown in (c), the well location and wellbore trajectory are first optimized to reduce the drilling collapse pressure to 1.85 g / cm 3 By optimizing the performance and density of drilling fluid, the collapse pressure is reduced to 1.8g / cm 3 Through the shear failure deformation analysis of natural fractures, a reasonable pressure-bearing plugging plan was formulated to increase the upper limit of leakage pressure to 2.15g / cm 3 Around, widening the safety pressure window to 0.4g / cm 3 , which helped solve the problems of serious leakage in reservoir drilling and difficulty in reservoir protection in this area.

[0220] An embodiment of the present invention provides a drilling safety pressure window widening system, comprising:

[0221] Prediction module, used to predict the distribution characteristics of natural fractures prone to leakage underground;

[0222] 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;

[0223] 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.

[0224] 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 effect. The parts and beneficial effects that are the same as the method embodiment in this embodiment will not be described in detail here.

[0225] In another embodiment of the present invention, a computer device is provided, the computer device comprising a processor and a memory, the memory being used to store a computer program, the computer program comprising program instructions, and the processor being 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 gates or transistor logic devices, discrete hardware components, etc., which are the computing core and control core of the terminal, which are suitable for implementing one or more instructions, and are specifically suitable for loading and executing one or more instructions in a computer storage medium to implement a 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.

[0226] In another embodiment of the present invention, the present invention also 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 the built-in storage medium in the computer device and the extended storage medium 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, and 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.

[0227] Those skilled in the art will appreciate that embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, 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 disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0228] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks 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 generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0229] These computer program instructions may also be stored in a computer-readable memory capable of directing 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 an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0230] 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, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0231] 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:

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; n ij is the direction cosine; When each fracture reaches the shear failure standard, it corresponds to a specific liquid column pressure value, and the liquid column 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; μ 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; μ0 is the friction coefficient within the matrix rock, is the weak surface internal friction angle; in, The μ 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: 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:

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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