Fractured formation breathing effect loss prediction method and device
By using a dual-hole single-seepage fluid-solid coupling mathematical model to predict the formation breathing effect loss during drilling, the problem of insufficient identification accuracy and wellbore pressure imbalance in existing technologies has been solved. This enables the optimization of drilling fluid density windows and risk control decisions, thereby improving drilling safety.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- CHINA NAT PETROLEUM CORP
- Filing Date
- 2025-12-10
- Publication Date
- 2026-04-14
AI Technical Summary
Existing technologies lack sufficient accuracy in identifying and controlling formation breathing effects during drilling, especially under complex conditions where they are prone to misjudgment. Furthermore, they struggle to adapt to dynamic changes in fracture networks, leading to wellbore pressure imbalances and increasing drilling risks and costs.
A formation breathing effect loss prediction model was established using a dual-pore single-seepage fluid-solid coupling mathematical model. By determining key parameters such as fracture permeability, drilling fluid intrusion degree, fracture width, and geostress, the drilling fluid loss and flowback were calculated using numerical methods. The drilling fluid density window was optimized to guide risk control decisions.
It enables accurate prediction of formation breathing loss during drilling, optimizes drilling fluid density window, distinguishes complex downhole conditions, reduces the risk of misjudgment, and improves the precision and safety of wellbore pressure control.
Smart Images
Figure CN121859531A_ABST
Abstract
Description
Technical Field
[0001] This application belongs to the field of oil and gas well engineering technology, and specifically relates to a method and device for predicting the loss amount of the breathing effect in fractured formations. Background Technology
[0002] With the advancement of deep well, ultra-deep well, and drilling in complex formations, drilling operations face severe challenges. Especially when encountering narrow safety density windows or naturally fractured formations, effectively preventing drilling fluid loss becomes a critical issue. During drilling, wellbore pressure needs to be controlled between pore pressure / collapse pressure and fracture pressure / loss pressure. However, in formations with well-developed microfractures, a "breathing effect" often occurs: continuous, minute leakage of drilling fluid during circulation, and fluid flowing back to the wellhead when the pump is stopped. This phenomenon is easily confused with actual well leakage or well kicks caused by formation fluid intrusion. Misjudgment can lead to incorrect subsequent decisions, such as blindly increasing drilling fluid density, which may exacerbate leakage and flowback, and even trigger serious accidents such as fracture propagation and wellbore integrity failure, significantly increasing drilling risks and costs.
[0003] To address the challenges of identifying and controlling formation breathing effects, existing technologies primarily focus on adjusting drilling fluid density and properties, optimizing drilling hydraulic circulation parameters to reduce wellbore pressure fluctuations, and employing monitoring and diagnostic methods while drilling (such as pressure measurement while drilling and real-time analysis of flowback / leakage) to distinguish breathing effects from actual well kicks / losses. Some methods emphasize adding plugging materials to the drilling fluid to enhance the temporary plugging capacity of microfractures, or controlling tripping speeds and improving pump start-up and shutdown procedures to reduce pressure surges, thereby suppressing fracture opening and closing.
[0004] However, the aforementioned existing technologies still have significant limitations: methods based on pressure and flow monitoring lack sufficient accuracy in identifying the breathing effect in micro-fractured formations, especially prone to misjudgment under complex conditions; while methods relying on drilling fluid density adjustment and plugging materials often lack specificity and are difficult to adapt to the dynamic changes in the fracture network, and excessively high densities can exacerbate leakage and backflow circulation, leading to wellbore pressure imbalance. Furthermore, existing technologies primarily focus on post-event control, with limited ability to actively suppress the causes of the breathing effect, and cannot fundamentally solve the problem of precise wellbore pressure control and fracture behavior prediction under narrow density windows. Summary of the Invention
[0005] To address the aforementioned issues, this application provides a method and apparatus for predicting formation breathing effect loss during drilling, in order to optimize drilling fluid density windows, differentiate complex downhole conditions, and guide drilling risk control decisions.
[0006] The method includes: A prediction model for formation breathing effect loss was established based on a dual-pore single-seepage fluid-solid coupling mathematical model. Based on auxiliary models, key parameters in the formation breathing effect loss prediction model were determined. The auxiliary models include fracture permeability model, drilling fluid invasion degree model, fracture width model, fracture in-situ stress model, and drilling fluid loss model. Key parameters include fracture permeability, drilling fluid invasion depth, fracture width, fracture in-situ stress, and drilling fluid loss. Numerical methods were used to calculate the drilling fluid loss and flowback in the formation breathing effect loss prediction model.
[0007] In this embodiment of the application, before determining the key parameters in the formation breathing effect loss prediction model based on the auxiliary model, the method further includes: Based on the geological characteristics of the target block and the wellbore engineering parameters, the initial boundary conditions of the formation breathing effect loss prediction model are preset. In the initial boundary conditions, the wellbore pressure is the same as the wellbore pressure at the same depth; the initial fracture pressure and the pressure at the farthest point of the fracture are the same as the formation pore pressure in the target block.
[0008] In this embodiment of the application, a prediction model for formation breathing effect loss is established based on a dual-pore single-seepage fluid-solid coupling mathematical model, specifically including: Under preset conditions, establish a set of governing equations for the fracture-matrix dual-pore system. The preset conditions include: the formation is a homogeneous isotropic medium with equal horizontal principal stresses; fluid flows only radially along the wellbore in the fracture network; there is no fluid exchange between the fracture and the matrix; the fracture undergoes elastic deformation under cyclic stress but does not propagate; and the mechanical process is applicable to at least one of the following conditions: plane strain. A model for predicting formation breathing effect loss was established based on the governing equations, fluid flow equations, and auxiliary equations of the fracture-matrix dual-pore system.
[0009] In this embodiment of the application, a formation breathing effect loss prediction model is established based on the governing equations, fluid flow equations, and auxiliary equations of the fracture-matrix dual-pore system, specifically including: Based on the governing equations of the fracture-matrix dual-pore system, the solid skeleton equations controlling formation deformation are determined. By substituting the solid skeleton equation and auxiliary equations into the fluid flow equation, a prediction model for formation breathing effect loss is established. The fluid flow equations include the mass conservation equation and the momentum conservation equation for the fluid. The auxiliary equations include coupled constitutive equations and coupled control equations.
[0010] In the embodiments of this application, the governing equations include the equilibrium equations, constitutive equations, and geometric equations of the fracture-matrix dual-pore system.
[0011] In this embodiment of the application, a numerical method is used to calculate the drilling fluid loss and flowback volume in the formation breathing effect loss prediction model, specifically including: The spatiotemporal data is discretized along the radial direction of the wellbore to establish a spatial-temporal discrete grid. Based on the spatial-temporal discrete grid, the spatiotemporal distribution of drilling fluid pressure in the formation is calculated, and the change of drilling fluid loss at the wellbore wall over time is determined according to the spatiotemporal distribution. Based on the relationship between the amount of drilling fluid loss at the wellbore and time, the amount of drilling fluid loss is determined; it is then determined whether the absolute value of the difference between the amount of drilling fluid loss at the next time step and the amount of drilling fluid loss is less than a first preset threshold; if not, the key parameters are adjusted and iterative execution is performed; if so, the preset conditions are updated to determine the amount of drilling fluid flowback. Determine whether the absolute value of the difference between the drilling fluid return volume and the drilling fluid return volume in the next time step is less than the second preset threshold; if not, adjust the key parameters and iterate; if yes, output the drilling fluid loss and drilling fluid return volume.
[0012] In this embodiment of the application, the first preset threshold is greater than 0.001 times the drilling fluid loss in the next time step, and the first preset threshold is less than 0.005 times the drilling fluid loss in the next time step. and, The second preset threshold is greater than 0.001 times the drilling fluid flowback volume of the next time step, and the second preset threshold is less than 0.005 times the drilling fluid flowback volume of the next time step.
[0013] This application also provides a device for predicting the loss amount due to the breathing effect in fractured formations, the device comprising: The loss calculation module is used to establish a calculation model for the formation breathing effect loss based on the dual-pore single-seepage fluid-solid coupling mechanism. The parameter acquisition module is used to determine the key parameters in the formation breathing effect loss prediction model based on the auxiliary model; the auxiliary model includes a fracture permeability model, a drilling fluid invasion depth model, a fracture width model, a fracture in-situ stress model, and a drilling fluid loss model; the key parameters include fracture permeability, drilling fluid invasion depth, fracture width, fracture in-situ stress, and drilling fluid loss. A loss prediction model is used to calculate the drilling fluid loss and flowback amount in the formation breathing effect loss prediction model using numerical methods.
[0014] This application also provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the method as described in the above embodiments.
[0015] This application also provides an electronic device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the program to implement the steps of the method as described in the above embodiments.
[0016] This method can be used to predict the amount of formation breathing loss during drilling, in order to optimize the drilling fluid density window, distinguish complex downhole conditions, and guide drilling risk control decisions.
[0017] Other features and advantages of this application will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the application. The objectives and other advantages of this application may be realized and obtained by means of the structures pointed out in the description, claims and drawings. Attached Figure Description
[0018] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0019] Figure 1A This is a schematic diagram illustrating the principle of the breathing effect in fractured formations, as provided in an embodiment of this application.
[0020] Figure 1B This is a schematic diagram illustrating the principle of the breathing effect in fractured formations, as provided in an embodiment of this application.
[0021] Figure 1 A flowchart illustrating a method for predicting the loss amount due to the breathing effect in fractured formations, provided in an embodiment of this application.
[0022] Figure 2 A flowchart for calculating the loss due to formation breathing effect is provided in an embodiment of this application.
[0023] Figure 3A This is a schematic diagram illustrating drilling fluid loss under different bottom hole pressure fluctuations, provided as an embodiment of this application.
[0024] Figure 3B This is a schematic diagram illustrating drilling fluid loss under different fracture stiffnesses, provided for embodiments of this application.
[0025] Figure 3C This is a schematic diagram illustrating drilling fluid loss under different initial fracture widths, as provided in the embodiments of this application.
[0026] Figure 3D This is a schematic diagram illustrating drilling fluid loss under different rock elastic moduli, as provided in the embodiments of this application.
[0027] Figure 3E This is a schematic diagram showing the drilling fluid loss flow rate at different times, as provided in the embodiments of this application.
[0028] Figure 4 A schematic diagram of a module for predicting the amount of loss due to the breathing effect in fractured formations, provided in an embodiment of this application. Detailed Implementation
[0029] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.
[0030] With the advancement of deep well, ultra-deep well, and complex formation drilling, drilling operations face severe challenges. In particular, when encountering narrow safety density windows or naturally fractured formations, effectively preventing drilling fluid loss becomes a key problem.
[0031] Figure 1A This is a schematic diagram illustrating the principle of the breathing effect in fractured formations, provided in an embodiment of this application. Figure 1B A schematic diagram illustrating the principle of the breathing effect in fractured formations provided in this application embodiment is shown below. Figures 1A to 1 As shown in Figure B, during drilling, the drilling fluid density needs to be controlled between the pore pressure / collapse pressure and the fracture pressure / loss pressure. However, a "breathing effect" often occurs in formations with well-developed microfractures: a continuous, minute loss of drilling fluid occurs during circulation, and fluid flows back to the wellhead when the pump is stopped. This phenomenon is easily confused with a well kick caused by actual well leakage or formation fluid intrusion, and misjudgment may lead to incorrect subsequent decisions. Blindly increasing the drilling fluid density can exacerbate leakage and flowback, and even cause serious accidents such as fracture propagation and wellbore integrity failure, significantly increasing drilling risks and costs.
[0032] To address the challenges of identifying and controlling formation breathing effects, existing technologies primarily focus on adjusting drilling fluid density and properties, optimizing circulation parameters to reduce wellbore pressure fluctuations, and employing monitoring and diagnostic methods while drilling (such as pressure measurement while drilling and real-time analysis of leakage and backflow rates) to differentiate between breathing effects and actual well kicks. Some methods emphasize adding plugging materials to the drilling fluid to enhance the temporary plugging capacity of microfractures, or controlling tripping speeds and improving pump start-up and shutdown procedures to reduce pressure surges, thereby suppressing fracture opening and closing.
[0033] However, the aforementioned existing technologies still have significant limitations: methods based on pressure and flow monitoring lack sufficient accuracy in identifying the breathing effect in micro-fractured formations, especially prone to misjudgment under complex conditions; while methods relying on drilling fluid density adjustment and plugging materials often lack specificity and are difficult to adapt to the dynamic changes in the fracture network, and excessively high densities can exacerbate leakage and backflow circulation, leading to wellbore pressure imbalance. Furthermore, existing technologies primarily focus on post-event control, with limited ability to actively suppress the causes of the breathing effect, and cannot fundamentally solve the problem of precise wellbore pressure control and fracture behavior prediction under narrow density windows.
[0034] In summary, formation breathing is a high-risk phenomenon in deep drilling. While existing technologies can partially alleviate the problem, they still fall short in terms of precise identification, dynamic control, and accident prevention. Future development requires further advancements in technologies such as precise wellbore pressure control, intelligent fracture network diagnosis, and adaptive plugging to effectively differentiate and proactively control the breathing effect, ensuring the safety and economy of drilling operations.
[0035] Therefore, there is an urgent need in the field for a method and apparatus for predicting the loss amount of fractured formation breathing effect in order to overcome the shortcomings of existing technical solutions.
[0036] Figure 1 A flowchart illustrating a method for predicting the loss amount due to the breathing effect in fractured formations, provided in an embodiment of this application. Figure 2 A flowchart for calculating formation breathing effect loss is provided as an embodiment of this application, such as... Figure 1 and Figure 2 As shown, the method includes: S1. A prediction model for formation breathing effect loss is established based on a dual-pore single-seepage fluid-solid coupling mathematical model.
[0037] S2. Based on auxiliary models, determine the key parameters in the formation breathing effect loss prediction model; the auxiliary models include fracture permeability model, drilling fluid invasion degree model, fracture width model, fracture in-situ stress model, and drilling fluid loss model; the key parameters include fracture permeability, drilling fluid invasion depth, fracture width, fracture in-situ stress, and drilling fluid loss.
[0038] S3. Numerical methods are used to calculate the drilling fluid loss and flowback in the formation breathing effect loss prediction model.
[0039] This method can be used to predict the amount of formation breathing loss during drilling, in order to optimize the drilling fluid density window, distinguish complex downhole conditions, and guide drilling risk control decisions.
[0040] Furthermore, in this embodiment, the equation for the fracture permeability model is:
[0041] in, The permeability of the crack; This represents the width of a single crack after normalization. Indicates the length of the well shaft; Indicates the distance between cracks.
[0042] When the length of the fracture is less than the penetration depth of the drilling fluid, the penetration depth of the drilling fluid... The length of the fracture is equal to the depth of the drilling fluid penetration; when the fracture length is greater than the penetration depth of the drilling fluid, the penetration depth of the drilling fluid is represented by the equation of the drilling fluid penetration degree model: The equation for the drilling fluid invasion rate model is:
[0043] in, This refers to the drilling fluid penetration level. The pressure in the wellbore at the fracture point; The initial pressure at the crack; This represents the drilling fluid yield value (also known as dynamic shear force or yield value, which is the minimum shear force required for the drilling fluid to begin flowing).
[0044] In the embodiments of this application, the width of the crack is an important parameter that determines the crack permeability, and the width of the crack changes with the pressure inside the crack.
[0045] The equation for the crack width model is:
[0046] in, Indicates the crack width; Indicates the initial width of the crack; This indicates the actual pressure inside the crack; This represents the component of the geostress perpendicular to the crack direction; This indicates the deformation stiffness of the crack.
[0047] The equations for the fractured geostress model are:
[0048] in, This represents the stress component perpendicular to the crack surface; It is the vertical principal stress; It is the horizontal principal stress; Indicates the inclination of the crack.
[0049] In this embodiment of the application, after obtaining the pressure change at each moment, the corresponding flow rate at each moment can be obtained. ,right The total volume of drilling fluid loss can be obtained by integration. .
[0050] The equation for the drilling fluid loss model is:
[0051] in, ρ is the drilling fluid loss; p is the pore pressure; μ is the fluid viscosity.
[0052] Furthermore, in this embodiment, before determining the key parameters in the formation breathing effect loss prediction model based on the auxiliary model, the method further includes: presetting the initial boundary conditions of the formation breathing effect loss prediction model based on the geological characteristics of the target block and the wellbore engineering parameters. In the initial boundary conditions, the wellbore pressure is the same as the wellbore pressure at the same depth; the initial fracture pressure and the pressure at the farthest point of the fracture are the same as the pore pressure of the formation in the target block.
[0053] In this embodiment of the application, a prediction model for formation breathing effect loss is established based on a dual-pore single-seepage flow-solid coupling mathematical model, specifically including steps S10 to S20: S10. Under preset conditions, establish the governing equations for the fracture-matrix dual-pore system. The preset conditions include: the formation is a homogeneous isotropic medium with equal horizontal principal stresses; fluid flows only radially along the wellbore in the fracture network; there is no fluid exchange between the fractures and the matrix; the fractures undergo elastic deformation under cyclic stress but do not propagate; and the mechanical process is applicable to at least one of the following conditions: plane strain conditions.
[0054] For example, in one instance, under preset conditions, the governing equations for a fracture-matrix dual-pore system are established. These preset conditions include: the formation is a homogeneous isotropic medium with equal horizontal principal stresses; fluid flows only radially along the wellbore in the fracture network; there is no fluid exchange between the fractures and the matrix; the fractures undergo elastic deformation under cyclic stress but do not propagate; and the mechanical process is applicable to plane strain conditions.
[0055] S20. Based on the governing equations, fluid flow equations, and auxiliary equations of the fracture-matrix dual-pore system, a prediction model for formation breathing effect loss is established.
[0056] Furthermore, in this embodiment of the application, a formation breathing effect loss prediction model is established based on the governing equations, fluid flow equations, and auxiliary equations of the fracture-matrix dual-pore system, specifically including steps S30 to S40: S30. Based on the governing equations of the fracture-matrix dual-pore system, determine the solid skeleton equations that control formation deformation.
[0057] Furthermore, the governing equations include the equilibrium equations, constitutive equations, and geometric equations for the fracture-matrix dual-pore system.
[0058] It should be noted that when studying stratigraphic rocks, inertial forces and the object's own weight are neglected. In this case, the force balance relationship acting on the representative elementary volume (REV) is exactly the same as that obtained from classical elasticity. The equilibrium equation for stratigraphic rocks in a fracture-matrix dual-pore system is as follows:
[0059] in, The comma represents the stress tensor, a physical quantity used to describe the stress state of rocks at a point in the formation; the comma and its subscript indicate differentiation with respect to spatial coordinates; repeated indexes indicate summation.
[0060] Specifically, as shown in the formula, the first subscript i (from left to right) indicates the direction of the force (direction of the stress component); the second subscript j (from left to right) indicates the normal direction of the section on which the stress component acts. This represents the zero vector.
[0061] Similarly, the constitutive equation for the fracture-matrix dual-pore system is:
[0062] in, Indicates the shear modulus of rock; This represents the Poisson's ratio of the rock. Represents the strain tensor components in the i-th row and j-th column; To represent volumetric strain (according to Einstein's summation convention, when two subscripts are the same and repeated, the trace of the strain tensor is: summing the values of those subscripts). That is, the trace of the strain tensor is the sum of the diagonal elements of the strain tensor, which is a scalar and physically corresponds to volumetric strain. The Kronecker exponent (when i=j) represents the Kronecker exponent. =1, i≠j =0); The generalized Biot-Willis constant represents the rock (s = 1 for the rock fracture system and s = 2 for the rock matrix system).
[0063] Similarly, the field equation for the formation rock in the fracture-matrix dual-pore system is:
[0064] It should be noted that the field equations are mathematical equations that describe the geometric relationship between the displacement field and the strain field.
[0065] Substituting the equilibrium equations and constitutive equations into the field equations of the stratigraphy and rocks, we obtain the Navier equations (also called the stratigraphy and rock constitutive equations) which contain coupling and diffusion terms. The Navier equations include the displacement vectors of the solid skeleton (also called the solid phase skeleton). The pressure of the fluid filling the pores of the porous medium, i.e., pore pressure. .
[0066] The constitutive equation for the stratigraphy is as follows:
[0067] It should be noted that the constitutive equation of strata rocks is an equation used to describe the relationship between the stress state and the deformation state (strain) of strata rocks. The word "constitutive" is used to characterize the constituent characteristics of the material, that is, the force-deformation relationship determined by the properties of the material itself, and to reflect the law of deformation and stress transmission of the material under external force or external action.
[0068] S40. Substitute the equations of the constitutive equation of the formation rock and the auxiliary equation into the equation of the fluid flow to establish a prediction model for the loss due to formation breathing effect.
[0069] The fluid flow equations include the mass conservation equation and the momentum conservation equation. Auxiliary equations include coupled constitutive equations and coupled governing equations.
[0070] Specifically, in this embodiment, the equations coupling the constitutive equations are as follows:
[0071] in, The bulk modulus of a composite continuous medium that combines a solid framework and porous fluid. Represents the generalized Skempton coefficient (pore pressure coefficient) under drained matrix / non-drained crack conditions. Represents the generalized Skempton coefficient (pore pressure coefficient) under undrained matrix / drained cracks. This represents the cross-storage coefficient, which describes the ability of a pressure change in one pore system to cause a change in the fluid content of another pore system. This coefficient appears in the off-diagonal position of the constitutive matrix and is used to characterize the coupling terms between variables.
[0072] In summary, the above coefficients can be characterized by functions composed of parameters such as fluid properties, porosity, and fracture properties.
[0073] Similarly, the equations for the coupled control equations are:
[0074] in, It represents the overall equivalent bulk modulus of porous media under two different conditions: drainage matrix and non-drainage cracks. It represents the overall equivalent bulk modulus of porous media under two different conditions: drainage cracks and non-drained matrix.
[0075] In this embodiment, the mass conservation equation for the fluid is:
[0076] Where s takes the value 1 or 2, and is used to characterize cracks or matrix; This indicates the amount of fluid variation in media with different pore sizes; Indicates volumetric flow rate; Represents the coordinate components in three-dimensional space ( It is an index of spatial direction. Indicated along the x-direction, Shown along the y direction, (Indicated along the z-direction).
[0077] Similarly, the equation for the conservation of momentum of a fluid is:
[0078] In this context, the subscript 1 of k represents a rock fracture, and the subscript 2 of k represents the rock matrix. The viscosity is the fluid viscosity.
[0079] By simultaneously solving the mass conservation equation and the momentum conservation equation, and substituting the coupled constitutive equation and the coupled control equation into the mass conservation equation and the momentum conservation equation to make the cross-coupling term zero, the main equation set of the formation breathing effect loss prediction model is obtained.
[0080] In summary, the main equations of the formation respiration effect loss prediction model are as follows:
[0081] This set of equations describes the temporal process and spatial distribution of fluid infiltration / exfiltration into the formation, given the formation mechanics and seepage parameters.
[0082] It should be noted that this set of equations cannot directly calculate drilling fluid loss; instead, the permeability parameter needs to be obtained by solving the set of equations. Pressure variation parameters with distance and flow velocity parameters Then, the flow velocity parameters were... Integrate to obtain the drilling fluid loss.
[0083] In this embodiment of the application, a numerical method is used to calculate the drilling fluid loss and flowback amount in the formation breathing effect loss prediction model, specifically including S50 to S70: S50. Discretize the time and space along the radial direction of the wellbore to establish a spatial-temporal discrete grid; based on the spatial-temporal discrete grid, calculate the spatiotemporal distribution relationship of drilling fluid pressure in the formation, and determine the relationship between the amount of drilling fluid loss at the wellbore and time according to the spatiotemporal distribution relationship.
[0084] S60. Based on the relationship between the amount of drilling fluid loss at the wellbore and time, determine the amount of drilling fluid loss; determine whether the absolute value of the difference between the amount of drilling fluid loss in the next time step and the amount of drilling fluid loss is less than a first preset threshold; if not, adjust the key parameters and iterate; if yes, update the preset conditions to determine the amount of drilling fluid flowback.
[0085] S70. Determine whether the absolute value of the difference between the drilling fluid return volume and the drilling fluid return volume in the next time step is less than the second preset threshold. If not, adjust the key parameters and iterate. If yes, output the drilling fluid loss and drilling fluid return volume.
[0086] like Figure 2 As shown, the drilling fluid loss is V. t The drilling fluid loss in the next time step is V. t+1 The first preset threshold is eps1; the drilling fluid flowback volume is V. t The next step drilling fluid return volume is V. t+1 The second preset threshold is eps2.
[0087] Preferably, the first preset threshold is greater than 0.001 times the drilling fluid loss in the next time step, and the first preset threshold is less than 0.005 times the drilling fluid loss in the next time step; and the second preset threshold is greater than 0.001 times the drilling fluid flowback in the next time step, and the second preset threshold is less than 0.005 times the drilling fluid flowback in the next time step.
[0088] For example, in one example, the first preset threshold can be 0.002 times the drilling fluid loss of the next time step, 0.003 times the drilling fluid loss of the next time step, or 0.004 times the drilling fluid loss of the next time step.
[0089] And / or, the second preset threshold can be 0.002 times the drilling fluid flowback volume of the next time step, 0.003 times the drilling fluid flowback volume of the next time step, or 0.004 times the drilling fluid flowback volume of the next time step.
[0090] In this embodiment, the smaller the ratio of the first preset threshold to the second preset threshold, the higher the accuracy of the predicted drilling fluid loss and flowback. However, this approach places higher demands on hardware, consumes more time for computation, and may introduce numerical noise risks. The range of 0.001 to 0.005 times the target value (drilling fluid loss / flowback) provided in this application represents the optimal balance between accuracy and efficiency in engineering practice. Of course, the specific value can be flexibly adjusted according to the accuracy requirements of the actual scenario.
[0091] An embodiment from engineering practice is provided to explain the method for predicting the loss amount of the breathing effect in fractured formations provided in this application: Actual drilling data from Well X in an oilfield in Xinjiang was applied to the prediction model for the loss of fractured formation breathing effect provided in this application for calculation and analysis. The calculation and analysis results are as follows: Figures 3A to 3E As shown. Among them, Figure 3A This is a schematic diagram illustrating drilling fluid loss under different bottom hole pressure fluctuations, provided in an embodiment of this application. Figure 3B This is a schematic diagram illustrating drilling fluid loss under different fracture stiffnesses, provided in an embodiment of this application. Figure 3C This is a schematic diagram illustrating drilling fluid loss under different initial fracture widths, provided in an embodiment of this application. Figure 3D This is a schematic diagram illustrating drilling fluid loss under different rock elastic moduli, provided in an embodiment of this application. Figure 3E This is a schematic diagram showing the drilling fluid loss flow rate at different times, as provided in the embodiments of this application.
[0092] like Figures 3A to 3E This application provides a method for predicting the loss amount of fractured formation breathing effect, which can realize the simulation calculation of the entire process of drilling fluid loss caused by formation breathing effect due to wellbore pressure fluctuation and the volume at each moment.
[0093] like Figures 3A to 3E As shown, on the time axis, 0 seconds, 150 seconds, 300 seconds, and 450 seconds represent the time points when the pump starts, stops, starts, and stops, respectively.
[0094] according to Figures 3A to 3E The curves show that the formation breathing effect has an overall characteristic of fluctuating up and down with the pressure fluctuations in the wellbore, resulting in continuous fluctuations in the amount of drilling fluid lost.
[0095] Specifically, when the amount of drilling fluid loss increases, the wellbore exhibits a state of drilling fluid leakage; when the amount of drilling fluid loss decreases, the wellbore exhibits a state of drilling fluid kick / overflow.
[0096] Meanwhile, based on the characteristics of the influence of certain fluids and formation parameters on the formation breathing effect, Figures 3A to 3EThe study also showed that the total amount of drilling fluid loss and fluctuation increased with the increase of wellbore fluctuation differential and initial fracture width, and decreased with the increase of fracture stiffness.
[0097] Of course, changes in the elastic modulus of the formation rock will affect the overall time required to achieve the same amount of drilling fluid loss, but will not significantly affect the overall amount of drilling fluid loss. The wellbore will exhibit the speed of drilling fluid leakage and well kick.
[0098] like Figures 3A to 3E As shown, at moments of pressure change such as pump start-up or pump shut-off, the flow rate of drilling fluid loss or increase first reaches its peak and then gradually decreases. This phenomenon is consistent with the gradual decrease in the amount of drilling fluid flowing out of the wellhead after pump shutdown over time.
[0099] Therefore, the method for predicting the loss amount of the breathing effect in fractured formations provided in this application can simulate the entire process of the breathing effect in fractured formations and predict the loss amount of the breathing effect under different conditions, providing an important theoretical basis for in-depth analysis of the full-process characteristics of the breathing effect. At the same time, the method for predicting the loss amount of the breathing effect in fractured formations provided in this application can also analyze and calculate the influence characteristics of different parameters such as fluids, fractures, and rocks, thus providing important guidance for field engineers to identify and handle similar problems.
[0100] Figure 4 A schematic diagram of a module for predicting the loss amount of the breathing effect in fractured formations provided in an embodiment of this application is shown below. Figure 4 As shown, the device includes: a loss calculation module 10, a parameter acquisition module 20, and a loss prediction model 30.
[0101] The loss calculation module 10 is used to establish a calculation model for formation breathing effect loss based on the dual-pore single-seepage fluid-structure interaction mechanism. The parameter acquisition module 20 is used to determine key parameters in the formation breathing effect loss prediction model based on the auxiliary model. The loss prediction model 30 is used to calculate the drilling fluid loss and flowback volume in the formation breathing effect loss prediction model using numerical methods.
[0102] The auxiliary models include a fracture permeability model, a drilling fluid invasion depth model, a fracture width model, a fracture in-situ stress model, and a drilling fluid loss model. Key parameters include fracture permeability, drilling fluid invasion depth, fracture width, fracture in-situ stress, and drilling fluid loss.
[0103] This device can be used to predict the amount of formation breathing loss during drilling, in order to optimize the drilling fluid density window, distinguish complex downhole conditions, and guide drilling risk control decisions.
[0104] This application also provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the method as described in the above embodiments.
[0105] This application also provides an electronic device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the program to implement the steps of the method as described in the above embodiments.
[0106] The above are merely specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.
[0107] Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.
Claims
1. A method for predicting the loss amount due to the breathing effect in fractured formations, characterized in that, The method includes: A prediction model for formation breathing effect loss was established based on a dual-pore single-seepage fluid-solid coupling mathematical model. Based on auxiliary models, key parameters in the formation breathing effect loss prediction model are determined; the auxiliary models include fracture permeability model, drilling fluid invasion degree model, fracture width model, fracture in-situ stress model, and drilling fluid loss model; the key parameters include fracture permeability, drilling fluid invasion depth, fracture width, fracture in-situ stress, and drilling fluid loss. Numerical methods were used to calculate the drilling fluid loss and flowback in the formation breathing effect loss prediction model.
2. The prediction method according to claim 1, characterized in that, Before determining the key parameters in the formation respiration loss prediction model based on the auxiliary model, the following steps are also included: Based on the geological characteristics of the target block and the wellbore engineering parameters, the initial boundary conditions of the formation breathing effect loss prediction model are preset. In the initial boundary conditions, the wellbore pressure is the same as the wellbore pressure at the same depth; the initial fracture pressure and the pressure at the farthest point of the fracture are the same as the formation pore pressure of the target block.
3. The prediction method according to claim 1, characterized in that, A prediction model for formation breathing effect loss was established based on a dual-pore single-seepage fluid-solid coupling mathematical model, specifically including: Under preset conditions, a set of governing equations for a fracture-matrix dual-pore system is established. The preset conditions include: the formation is a homogeneous isotropic medium with equal horizontal principal stresses; fluid flows only radially along the wellbore in the fracture network; there is no fluid exchange between the fractures and the matrix; the fractures undergo elastic deformation under cyclic stress but do not propagate; and the mechanical process is applicable to at least one of the following conditions: plane strain conditions. Based on the governing equations, fluid flow equations, and auxiliary equations of the fracture-matrix dual-pore system, a prediction model for the formation breathing effect loss is established.
4. The prediction method according to claim 3, characterized in that, Based on the governing equations, fluid flow equations, and auxiliary equations of the fracture-matrix dual-pore system, a prediction model for formation breathing effect loss is established, specifically including: Based on the governing equations of the fracture-matrix dual-pore system, the solid skeleton equations controlling formation deformation are determined. Substitute the solid skeleton equation and auxiliary equation into the fluid flow equation to establish the formation breathing effect loss prediction model. The fluid flow equations include the mass conservation equation and the momentum conservation equation for the fluid. The auxiliary equations include coupled constitutive equations and coupled control equations.
5. The prediction method according to claim 4, characterized in that, The governing equations include the equilibrium equations, constitutive equations, and geometric equations for the fracture-matrix dual-pore system.
6. The prediction method according to claim 2, characterized in that, The formation breathing effect loss prediction model is applied numerically to calculate the drilling fluid loss and flowback volume in the model, specifically including: The spatiotemporal data is discretized along the radial direction of the wellbore to establish a spatial-temporal discrete grid. Based on the spatial-temporal discrete grid, the spatiotemporal distribution relationship of drilling fluid pressure in the formation is calculated, and the change relationship of drilling fluid loss at the wellbore wall with time is determined according to the spatiotemporal distribution relationship. Based on the relationship between the amount of drilling fluid loss at the wellbore and time, the amount of drilling fluid loss is determined; it is determined whether the absolute value of the difference between the amount of drilling fluid loss in the next time step and the amount of drilling fluid loss is less than a first preset threshold; if not, the key parameters are adjusted and iteratively executed; if yes, the initial boundary conditions are updated to determine the amount of drilling fluid flowback. Determine whether the absolute value of the difference between the drilling fluid return volume and the drilling fluid return volume in the next time step is less than a second preset threshold; if not, adjust the key parameters and iterate; if yes, output the drilling fluid loss and the drilling fluid return volume.
7. The prediction method according to claim 6, characterized in that, The first preset threshold is greater than 0.001 times the drilling fluid loss in the next time step, and the first preset threshold is less than 0.005 times the drilling fluid loss in the next time step; and, The second preset threshold is greater than 0.001 times the drilling fluid flowback volume of the next time step, and the second preset threshold is less than 0.005 times the drilling fluid flowback volume of the next time step.
8. A device for predicting the amount of loss due to the breathing effect in fractured formations, characterized in that, The device includes: The loss calculation module is used to establish a calculation model for the formation breathing effect loss based on the dual-pore single-seepage fluid-solid coupling mechanism. The parameter acquisition module is used to determine the key parameters in the formation breathing effect loss prediction model based on the auxiliary model; the auxiliary model includes a fracture permeability model, a drilling fluid invasion degree model, a fracture width model, a fracture in-situ stress model, and a drilling fluid loss model; the key parameters include fracture permeability, drilling fluid invasion depth, fracture width, fracture in-situ stress, and drilling fluid loss. A loss prediction model is used to calculate the drilling fluid loss and flowback amount in the formation breathing effect loss prediction model using numerical methods.
9. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the program is executed by the processor, it implements the steps of any one of claims 1 to 7.
10. An electronic 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 program, it implements the steps of any one of claims 1 to 7.