A method and system for designing drilling collapse pressure

Abstract

The present invention discloses a method for designing the collapse pressure of drilling, comprising: obtaining the geomechanical parameters of the target formation to be drilled, and setting the circumferential integrity of the wellbore required for safe drilling construction of the target formation according to the drilling type of the target formation; setting the density of the drilling fluid, based on which, according to the geomechanical parameters, the circumferential stress of the target formation is analyzed to generate wellbore stress information, the wellbore stress information including the wellbore stress characteristics at different positions of the wellbore; according to the wellbore stress information, counting the proportion of the area maintaining the circumferential stress of the wellbore in a stable state to the circumferential area of ​​the wellbore when implementing the safe drilling construction, and determining the corresponding collapse pressure equivalent density when the current proportion reaches the circumferential integrity of the wellbore, thereby calculating the drilling collapse pressure from the collapse pressure equivalent density. The present invention can not only ensure the safety of drilling construction, but also achieve the effect of reducing the density of drilling fluid, increasing the drilling speed, and reducing the drilling cost.

Description

Technical Field

[0001] The invention relates to the technical field of oil and gas drilling, and in particular to a method and system for designing drilling collapse pressure. Background Art

[0002] The stability of the wellbore stress during drilling is directly related to the wellbore fluid column pressure. When the wellbore fluid column pressure is insufficient to maintain the wellbore stress balance, instability and block falling will occur. Furthermore, the smaller the drilling fluid density, the lower the fluid column pressure in the wellbore, and the more instability and block falling of the open hole wellbore will occur. If there are too many blocks, it will cause the downhole drilling tools to encounter obstacles and affect normal construction, and even cause downhole complications such as stuck drill. Therefore, in order to prevent engineering accidents caused by instability and block falling of the wellbore, the drilling fluid column pressure must not be lower than the collapse pressure.

[0003] In the existing drilling collapse pressure design technology, the lower limit of anti-collapse drilling fluid density is often determined based on the principle that no stress collapse occurs at any point on the wellbore wall. However, the effect of this method is that the drilling fluid density is often high. This not only consumes drilling fluid materials, but also affects the mechanical drilling speed and aggravates reservoir damage, which seriously hinders the formation and implementation of the process of increasing the speed and reducing the cost of drilling engineering.

[0004] It can be seen that the requirement of the existing drilling collapse pressure design scheme that the wellbore does not experience stress instability is too harsh and does not conform to the actual situation on site. In actual drilling construction, a certain degree of instability and block loss of the wellbore and expansion of the wellbore diameter can be carried out normally and does not affect drilling safety. As long as the blocks are carried away normally and the wellbore is kept clean, the drilling construction can still operate normally. Because lower drilling fluid density can create conditions for better reservoir protection, drilling speed increase, safety pressure control, and saving drilling material consumption.

[0005] my country is rich in oil and gas resources. In 2019, the oil production was 191 million tons, the natural gas production was 174 billion cubic meters, and about 20,000 wells were drilled annually. The drilling operation volume is huge, and the drillability of the formations in many areas is poor. Therefore, the existing technology needs to form a new drilling collapse pressure design method, so that the designed collapse pressure can not only maintain the safety of drilling operations in the well, but also increase the mechanical drilling speed and reduce the drilling cost by appropriately reducing the density of the drilling fluid, so as to obtain better engineering economic benefits. Summary of the invention

[0006] In order to solve the above technical problems, an embodiment of the present invention provides a method for designing drilling collapse pressure, comprising: step 1, obtaining geomechanical parameters of a target formation to be drilled, and setting the circumferential integrity of the wellbore required for safe drilling construction of the target formation according to the drilling type of the target formation; step 2, setting the drilling fluid density, based on which, according to the geomechanical parameters, analyzing the circumferential stress of the target formation, and generating wellbore stress information, the wellbore stress information including the wellbore stress characteristics at different positions of the wellbore; step 3, according to the wellbore stress information, counting the proportion of the area maintaining a stable state of the circumferential stress of the wellbore to the circumferential area of ​​the wellbore when implementing safe drilling construction, based on which, determining the corresponding collapse pressure equivalent density when the proportion reaches the circumferential integrity of the wellbore, and thereby calculating the drilling collapse pressure from the collapse pressure equivalent density.

[0007] Preferably, the geomechanical parameters include, but are not limited to, geostress parameters, formation pressure parameters, rock elasticity parameters, rock strength parameters and wellbore trajectory parameters.

[0008] Preferably, when calculating the stress state at each circumferential azimuth angle in the wellbore circular stress distribution characteristics, it includes: calculating the in-situ stress components at different azimuths in the wellbore rectangular coordinate system according to the vertical in-situ stress, the maximum horizontal in-situ stress and the minimum horizontal in-situ stress in the in-situ stress parameters, and the well inclination angle and the well inclination azimuth in the wellbore trajectory parameters; calculating the wellbore stress components at different azimuths in the wellbore axis coordinate system according to the in-situ stress components at different azimuths, the Poisson's ratio in the rock elastic parameters, the drilling fluid density and the vertical depth of drilling; calculating the effective principal stress of the wellbore rock at different circumferential azimuths according to the wellbore stress components at different azimuths, the pore elastic coefficient in the rock elastic parameters, and the formation pore fluid pressure in the formation pressure parameters.

[0009] Preferably, the ground stress component, the wellbore stress component and the wellbore rock effective principal stress at the current position are calculated respectively using the following expressions:

[0010]

[0011]

[0012]

[0013] Among them, x, y, and z represent the three directions in the spatial rectangular coordinate system corresponding to the wellbore axis coordinates, σ A , σ B , σ C They represent the effective principal stress of the wellbore rock, g represents the gravitational acceleration, ρ mrepresents the initial drilling fluid density, h v represents the vertical depth of drilling, η represents the poroelastic coefficient, P p represents the formation pore fluid pressure, σ θ , σ z , τ θz They represent the wellbore stress components in the wellbore axis coordinate system, S xx , S yy , S zz , S xy , S xz , S yz represents the in-situ stress component, v represents the Poisson's ratio, θ represents the current wellbore azimuth angle, S v represents the vertical ground stress, S H represents the maximum horizontal ground stress, S h represents the minimum horizontal geostress, β represents the angle between the maximum horizontal geostress azimuth and the wellbore azimuth, and α w Indicates the well inclination angle.

[0014] Preferably, the step three includes: identifying the wellbore stability states at different circumferential angles according to the wellbore stress information; calculating the ratio at the current depth position according to the wellbore stability state identification results at all circumferential angles; comparing the ratio with the wellbore circumferential integrity parameter, if the ratio is greater than the wellbore circumferential integrity parameter, using the current drilling fluid density as the collapse pressure equivalent density, otherwise, adjusting the drilling fluid density; and calculating the drilling collapse pressure at the corresponding depth position according to the collapse pressure equivalent density.

[0015] Preferably, the step of identifying the wellbore stability states at different wellbore azimuth angles according to the wellbore stress information includes: performing stress stability quantification processing on each wellbore azimuth angle according to the Mohr-Coulomb strength analysis principle according to the wellbore stress information; determining the wellbore stability state at each wellbore azimuth angle according to the stress stability quantification result, wherein when the current stress stability quantification parameter is less than or equal to zero, the current wellbore stability state is recorded as 1, and when the current stress stability quantification parameter is greater than zero, the current wellbore stability state is recorded as 0.

[0016] Preferably, according to the wellbore stress information, combined with the rock cohesion and internal friction angle parameters at different azimuth angles, the following expression is used to judge the stress stability of each wellbore azimuth angle:

[0017]

[0018] σ1=max{σ A ,σ B ,σ C}

[0019] σ3=min{σ A ,σ B ,σ C}

[0020] Among them, θ represents the current wellbore azimuth angle, FMC(θ) represents the stress stability judgment result of the current wellbore azimuth angle, σ A , σ B , σ C represents the effective principal stress of the wellbore rock, C represents the cohesion corresponding to the current orientation in the rock strength parameter, and φ represents the internal friction angle corresponding to the current orientation in the rock strength parameter.

[0021] Preferably, when the drilling type is a vertical well, the circumferential integrity of the well wall is greater than 60%; when the drilling type is an inclined well, the circumferential integrity of the well wall is greater than 70%; when the drilling type is a directional well or a horizontal well, the circumferential integrity of the well wall is greater than 80%.

[0022] On the other hand, an embodiment of the present invention further provides a system for designing drilling collapse pressure, comprising: a parameter preparation module, configured to obtain geomechanical parameters of a target formation to be drilled, and, according to the drilling type of the target formation, set the degree of circumferential integrity of the wellbore required for safe drilling construction of the target formation; a wellbore stress distribution module, configured to set the drilling fluid density, based on which, according to the geomechanical parameters, the wellbore stress of the target formation is analyzed to generate wellbore stress information, the wellbore stress information including wellbore stress characteristics at different positions of the wellbore; a collapse pressure generation module, configured to, according to the wellbore stress information, count the proportion of the area in which the wellbore circumferential stress is maintained in a stable state to the circumferential area of ​​the wellbore when implementing safe drilling construction, based on which, determine the corresponding collapse pressure equivalent density when the proportion reaches the degree of circumferential integrity of the wellbore, and thereby calculate the drilling collapse pressure from the collapse pressure equivalent density.

[0023] Preferably, the collapse pressure generation module includes: a wellbore local stability state analysis unit, which is configured to identify the wellbore stability state at different wellbore azimuth angles according to the wellbore stress information; a wellbore stability state preliminary ratio generation unit, which is configured to calculate the ratio at the current depth position according to the wellbore stability state identification results at all wellbore azimuth angles; an equivalent density generation unit, which is configured to compare the ratio with the wellbore circumferential integrity degree, if the ratio is greater than the wellbore circumferential integrity degree parameter, then use the current drilling fluid density as the collapse pressure equivalent density, otherwise, adjust the drilling fluid density; a pressure calculation unit, which is configured to calculate the drilling collapse pressure at the corresponding depth position according to the collapse pressure equivalent density.

[0024] Compared with the prior art, one or more embodiments of the above scheme may have the following advantages or beneficial effects:

[0025] The present invention provides a method and system for designing drilling collapse pressure. The method and system include steps for preparing geomechanical parameters of target formations to be drilled and wellbore parameters, steps for analyzing the stress environment around the well, and steps for calculating drilling fluid equivalent density and collapse pressure. When designing drilling collapse pressure, the present invention fully considers the requirements of safe drilling construction for the integrity of the well wall. The designed collapse pressure can not only ensure the safety of drilling construction, but also create conditions for reducing drilling fluid density, increasing drilling speed, reducing drilling costs, and improving drilling efficiency, thereby obtaining better economic benefits of drilling engineering.

[0026] Other features and advantages of the present invention will be described in the following description, and partly become apparent from the description, or understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures particularly pointed out in the description, claims and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0028] Figure 1 This is a step diagram of a method for designing well collapse pressure according to an embodiment of the present application.

[0029] Figure 2 This is a flow chart of step three in the method for designing drilling collapse pressure in an embodiment of the present application.

[0030] Figure 3 This is a structural block diagram of a system for designing drilling collapse pressure according to an embodiment of the present application. DETAILED DESCRIPTION

[0031] The following will describe the implementation methods of the present invention in detail with reference to the accompanying drawings and embodiments, so that the implementation process of how the present invention applies technical means to solve technical problems and achieve technical effects can be fully understood and implemented accordingly. It should be noted that as long as there is no conflict, the various embodiments of the present invention and the various features in the embodiments can be combined with each other, and the technical solutions formed are all within the protection scope of the present invention.

[0032] The stability of the wellbore stress during drilling is directly related to the wellbore fluid column pressure. When the wellbore fluid column pressure is insufficient to maintain the wellbore stress balance, instability and block falling will occur. Furthermore, the smaller the drilling fluid density, the lower the fluid column pressure in the wellbore, and the more instability and block falling of the open hole wellbore will occur. If there are too many blocks, it will cause the downhole drilling tools to encounter obstacles and affect normal construction, and even cause downhole complications such as stuck drill. Therefore, in order to prevent engineering accidents caused by instability and block falling of the wellbore, the drilling fluid column pressure must not be lower than the collapse pressure.

[0033] In the existing drilling collapse pressure design technology, the lower limit of anti-collapse drilling fluid density is often determined based on the principle that no stress collapse occurs at any point on the wellbore wall. However, the effect of this method is that the drilling fluid density is often high. This not only consumes drilling fluid materials, but also affects the mechanical drilling speed and aggravates reservoir damage, which seriously hinders the formation and implementation of the process of increasing the speed and reducing the cost of drilling engineering.

[0034] It can be seen that the requirement of the existing drilling collapse pressure design scheme that the wellbore does not experience stress instability is too harsh and does not conform to the actual situation on site. In actual drilling construction, a certain degree of instability and block loss of the wellbore and expansion of the wellbore diameter can be carried out normally and does not affect drilling safety. As long as the blocks are carried away normally and the wellbore is kept clean, the drilling construction can still operate normally. Because lower drilling fluid density can create conditions for better reservoir protection, drilling speed increase, safety pressure control, and saving drilling material consumption.

[0035] my country is rich in oil and gas resources. In 2019, the oil production was 191 million tons, the natural gas production was 174 billion cubic meters, and about 20,000 wells were drilled annually. The drilling operation volume is huge, and the drillability of the formations in many areas is poor. Therefore, the existing technology needs to form a new drilling collapse pressure design method, so that the designed collapse pressure can not only maintain the safety of drilling operations in the well, but also increase the mechanical drilling speed and reduce the drilling cost by appropriately reducing the density of the drilling fluid, so as to obtain better engineering economic benefits.

[0036] In order to solve the technical problems that the currently used drilling collapse pressure design method is based on the premise of no wellbore collapse, which limits the drilling density reduction operation space and hinders the formation and application of process technologies such as drilling cost reduction and drilling speed increase within the safe operation range, the present invention provides a method and system for designing drilling collapse pressure. The method and system first need to determine the geomechanical parameters of the target formation to be drilled and set the wellbore circumferential integrity parameters required for safe drilling construction of the target formation to be drilled; then, set the initial drilling fluid density, based on which, according to the geomechanical parameters, analyze the wellbore stress of the target formation to be drilled to obtain the wellbore stress information; then, according to the wellbore stress information, count the first proportion of the area that maintains the wellbore circumferential stress stable state to the wellbore circumferential area when implementing safe drilling construction, and determine the corresponding drilling fluid equivalent density when the first proportion reaches the wellbore integrity, so as to calculate the corresponding drilling collapse pressure from the drilling fluid equivalent density. In this way, the drilling collapse pressure designed by the present invention can not only meet the requirements of safe drilling construction, but also take into account the improvement of mechanical drilling speed and the reduction of drilling costs.

[0037] Figure 1 This is a step diagram of a method for designing a wellbore collapse pressure according to an embodiment of the present application. Figure 1 , the method for designing the drilling collapse pressure of the present invention (hereinafter referred to as "collapse pressure design method") is described in detail.

[0038] like Figure 1 As shown, step S110 obtains the geomechanical parameters of the target formation to be drilled, and sets the circumferential integrity of the wellbore required for safe drilling construction of the target formation to be drilled according to the drilling type of the target formation.

[0039] Specifically, in step S110, the geomechanical parameters of the target stratum to be drilled need to be obtained first. In the embodiment of the present invention, the target stratum to be drilled refers to the stratum area that currently needs to be drilled through the stratum, the area has a certain depth range, and the well in the area is the well to be drilled. Among them, the well to be drilled may include an area of ​​the stratum that has not been drilled through, and may also include an area of ​​the stratum that has not been drilled through and a stratum that has been drilled through.

[0040] Furthermore, in the process of obtaining the geomechanical parameters of the target formation to be drilled, it is necessary to determine the geomechanical parameters of the current target formation to be drilled based on information such as drilling data, mud logging data, well logging data, reservoir distribution data and geological data of the wells that have been drilled in the same reservoir operating unit area as the well to be drilled. In an embodiment of the present invention, the target formation to be drilled is to divide the depth range of the target formation into multiple depth segments according to a preset depth interval, that is, the target formation to be drilled includes multiple depth segments, wherein each depth segment corresponds to a corresponding geomechanical parameter. Therefore, the geomechanical parameters of the target formation to be drilled include: the geomechanical parameters corresponding to each depth segment position within the depth range of the current target formation to be drilled.

[0041] Furthermore, the geomechanical parameters at each depth segment include, but are not limited to, geostress parameters, formation pressure parameters, rock elastic parameters, rock strength parameters, and wellbore trajectory parameters. More specifically, geostress parameters include, but are not limited to, vertical geostress, minimum horizontal geostress, maximum horizontal geostress, and maximum horizontal geostress azimuth. Formation pressure parameters include, but are not limited to, formation pore fluid pressure. Rock elastic parameters include, but are not limited to, Poisson's ratio and pore elastic coefficient. Rock strength parameters include, but are not limited to, pore elastic coefficient, rock cohesion, and rock internal friction angle. Wellbore trajectory parameters include, but are not limited to, well inclination angle, well inclination azimuth, and drilling vertical depth (wherein, drilling vertical depth includes at least: depth data of target formation to be drilled and non-target formation segments).

[0042] Preferably, the geostress parameters at each depth segment in the target formation to be drilled can be obtained through core experiments, imaging logging or fracturing data from wells that have been drilled. The formation pressure parameters at each depth segment in the target formation to be drilled can be obtained through reservoir testing or logging models calibrated by testing. The rock elastic parameters and rock strength parameters at each depth segment in the target formation to be drilled can be obtained by calculation based on core experiments for wells that have been drilled or logging models calibrated by core experiments. The geomechanical parameters for the target formation to be drilled in the embodiment of the present invention can also be obtained by other means, which are not specifically limited in the present invention, and those skilled in the art can make choices based on actual needs.

[0043] After obtaining the geomechanical parameters for the target formation to be drilled, step S110 will also set the circumferential integrity of the wellbore required for safe drilling construction of the current target formation to be drilled according to the drilling type of the current target formation to be drilled. The circumferential integrity of the wellbore is the ratio of the minimum area of ​​the wellbore stability required for safe drilling construction to the overall area of ​​the wellbore surrounding the target formation to be drilled. The circumferential integrity of the wellbore characterizes the minimum degree of wellbore stress stability required to maintain normal operation during drilling. The parameter (circumferential integrity of the wellbore) I required for safe drilling construction is determined based on the drilling type characteristics of the reservoir unit work area where the well is located.

[0044] Specifically, when the drilling type of the well section involved in the target formation to be drilled is a vertical well, the current circumferential integrity of the well wall needs to be greater than 60%, so that safe drilling construction for the target formation to be drilled can be achieved. When the drilling type of the well section involved in the target formation to be drilled is an inclined well, the current circumferential integrity of the well wall needs to be greater than 70%, so that safe drilling construction for the target formation to be drilled can be achieved. When the drilling type of the well section involved in the target formation to be drilled is a directional well or a horizontal well, the current circumferential integrity of the well wall needs to be greater than 80%, so that safe drilling construction for the target formation to be drilled can be achieved.

[0045] After obtaining the geomechanical parameters of the target formation to be drilled and the circumferential integrity of the well wall, step S110 is completed, and then the process proceeds to step S120 to analyze the circumferential stress of the well section involved in the current target formation to be drilled (i.e., the well section to be drilled), and then the corresponding drilling collapse pressure is designed in step S130.

[0046] Step S120 sets the drilling fluid density, based on which, according to step S110, the geomechanical parameters for the current target formation to be drilled are obtained, and the wellbore stress of the current target formation to be drilled is analyzed to generate wellbore stress information. The wellbore stress information includes the wellbore circumferential stress distribution characteristic data at different orientations (circumferential orientation angles) of the wellbore.

[0047] When designing the collapse pressure of the target formation to be drilled, it is necessary to design the corresponding collapse pressure equivalent density and corresponding drilling collapse pressure data that are most suitable for the reservoir conditions and geological conditions of the current depth segment according to the following steps S120 and S130 of the present invention for each depth segment in the current target formation to be drilled, thereby forming a drilling collapse pressure array for the target formation to complete the design of the drilling collapse pressure for the target formation. Since the method adopted by the present invention for the collapse pressure design process for each depth segment is the same, the drilling collapse pressure design process for only one depth segment is used as an example for description.

[0048] Further, step 120 needs to generate corresponding wellbore stress information for each depth segment. In step S120, the drilling fluid density for the current depth segment is set, and then, based on the drilling fluid density of the depth segment, the geomechanical parameters for the current depth segment in the target formation to be drilled are obtained according to step S110, and the wellbore circumferential stress of the well section involved in the current depth segment is analyzed, thereby generating wellbore stress information for the current depth segment. Among them, the wellbore stress information of the current depth segment is a data that characterizes the distribution characteristics of the wellbore circumferential stress of the wellbore section to be drilled involved in the current depth segment, including: wellbore stress state characteristic data (wellbore stress characteristics) at different positions of the wellbore under the current depth segment.

[0049] Specifically, in step S120, it is necessary to calculate the corresponding ground stress component, wellbore stress component and wellbore rock effective principal stress in sequence for each wellbore azimuth angle in the current depth segment, so as to use the wellbore rock effective principal stress as the wellbore stress characteristic corresponding to the corresponding wellbore azimuth angle. It should be noted that in the embodiment of the present invention, the wellbore azimuth angles in each depth segment are preferably 360, ranging from 1° to 360°, with a step length of 1°.

[0050] Furthermore, when calculating the geostress component corresponding to each wellbore azimuth angle in the current depth segment, it is necessary to calculate the geostress component corresponding to different azimuths in the wellbore rectangular coordinate system using the preset geostress component formula according to the vertical geostress, maximum horizontal geostress and minimum horizontal geostress in the geostress parameters (of the current depth segment), and the wellbore inclination angle and wellbore inclination azimuth in the wellbore trajectory parameters (of the current depth segment). In this way, the corresponding geostress component is obtained for each azimuth angle in the current depth segment. Among them, the above geostress component formula is expressed by the following expression:

[0051]

[0052] Among them, x, y, and z represent the three directions in the spatial rectangular coordinate system corresponding to the wellbore axis coordinates; S xx , S yy , S zz , S xy , S xz , S yz represents the ground stress component in the wellbore rectangular coordinate system; S v Indicates the vertical ground stress corresponding to the current orientation, in MPa; S H Indicates the maximum horizontal ground stress corresponding to the current orientation, in MPa; S h Indicates the minimum horizontal geostress corresponding to the current orientation, in MPa; β indicates the angle between the orientation of the maximum horizontal geostress and the orientation of the wellbore trajectory, in degrees; α wrepresents the well inclination angle corresponding to the current azimuth, in degrees. Thus, through the above expression (1), each azimuth angle in the current depth segment corresponds to the ground stress component in the wellbore rectangular coordinate system.

[0053] Further, after completing the calculation of the geostress component corresponding to each wellbore azimuth angle in the current depth segment, it is necessary to calculate the borehole stress components corresponding to different azimuths in the borehole axis coordinate system using the preset borehole stress component formula according to the geostress component corresponding to each azimuth angle in the current depth segment, the Poisson's ratio in the rock elastic parameters (of the current depth segment), the drilling fluid density set in step S110, and the vertical depth of the drilling, so as to convert all the above geostress components into coordinate systems. In this way, the corresponding borehole stress component is obtained for each azimuth angle in the current depth segment. Among them, the above borehole stress component formula is expressed by the following expression:

[0054]

[0055] Among them, σ θ , σ z , τ θz They represent the tangential, longitudinal and radial wellbore stress components corresponding to different orientations in the wellbore axis coordinate system; θ represents the current wellbore azimuth angle (i.e., the tangential coordinate in the wellbore axis coordinate system); v represents the Poisson's ratio; g represents the gravitational acceleration, in m / s 2 ρ m Indicates the density of drilling fluid, unit: g / cm 3 ;h v represents the vertical depth of the well (preferably the depth of the current depth segment). In the embodiment of the present invention, the borehole axis coordinate system is a cylindrical coordinate system established with the borehole axis (the axis of the well to be drilled) as the center. Thus, through the above expression (2), the borehole wall stress component in the borehole axis coordinate system corresponding to each azimuth angle in the current depth segment is obtained.

[0056] Furthermore, after completing the calculation of the borehole wall stress component corresponding to each wellbore azimuth angle in the current depth segment, it is also necessary to calculate the borehole wall rock effective principal stress at different circumferential orientations using the preset effective principal stress formula according to the borehole wall stress component in the wellbore axis coordinate system corresponding to each azimuth angle in the current depth segment, the pore elastic coefficient in the rock elastic parameters (of the current depth segment), and the formation pore fluid pressure in the formation pressure parameters (of the current depth segment), so as to obtain the calculation result of the rock effective stress at the borehole wall position. In this way, the corresponding borehole wall rock effective principal stress is obtained for each azimuth angle in the current depth segment. Among them, the above effective principal stress formula is expressed by the following expression:

[0057]

[0058] Among them, σ A , σ B , σ C It represents the effective principal stress of the wellbore rock in different directions (effective principal stress of the wellbore rock), in MPa; η represents the poroelastic coefficient; P p Represents the formation pore fluid pressure, in MPa. Thus, through the above expression (3), the effective principal stress of the wellbore rock corresponding to each azimuth angle in the current depth segment is obtained.

[0059] In this way, the calculation of the borehole wall stress characteristic data at all circumferential azimuth angles in the same depth segment can be calculated in sequence through expressions (1) to (3), and the borehole circumferential stress analysis of the entire target formation to be drilled can be further completed, thereby ending step S120 and entering step S130.

[0060] Step S130 calculates the (first) ratio of the area where the circumferential stress of the wellbore is maintained in a stable state to the circumferential area of ​​the wellbore (the outer surface area of ​​the circumference of the wellbore) according to the wellbore stress information of all depth sections obtained in step S120, and determines the drilling fluid equivalent density corresponding to the wellbore integrity condition set in step S110 when the first ratio reaches the wellbore integrity condition set in step S110, thereby calculating the drilling collapse pressure from the drilling fluid density.

[0061] Figure 2 This is a flow chart of step 3 of the method for designing the drilling collapse pressure in the embodiment of the present application. Figure 1 and Figure 2 Step S130 will be described in detail.

[0062] Specifically, step 130 needs to calculate the corresponding drilling fluid equivalent density and drilling collapse pressure data for each depth segment that take into account both safe drilling construction and reduced drilling fluid costs. In step S130, according to the well wall stress information of each depth segment obtained in step S120, the (first) ratio of the minimum area that can maintain the well wall circumferential stress stable state to the well wall circumferential outer area when implementing safe drilling construction for the current depth segment is calculated, and when the first ratio for the current depth segment reaches the well wall circumferential integrity condition set in step S110, the corresponding collapse pressure equivalent density is determined, and then, according to the collapse pressure equivalent density, the corresponding drilling collapse pressure is calculated.

[0063] Further, in step S130, the corresponding collapse pressure equivalent density and collapse pressure need to be calculated for each depth segment. In the embodiment of the present invention, since the calculation process of the collapse pressure equivalent density and collapse pressure of each depth segment is the same, the present invention only takes one depth segment as an example for description.

[0064] refer to Figure 2In step S1301, the wellbore stability state at different wellbore azimuth angles is identified according to the wellbore stress information for the current depth segment obtained in step S120. In step S1301, the wellbore stability state at each different wellbore azimuth angle needs to be identified according to the following process:

[0065] The first step is to use the Mohr-Coulomb strength analysis principle to judge the stress stability of each wellbore azimuth angle according to the wellbore stress characteristic data corresponding to different wellbore azimuth angles for the current depth section (wellbore stress information for the current depth section), and calculate the quantitative results of stress stability corresponding to each wellbore azimuth angle. In this way, the wellbore stability at each wellbore azimuth angle is quantitatively represented, thereby completing the quantitative calculation of the local stability of the wellbore at each wellbore azimuth angle.

[0066] Specifically, according to the wellbore stress information of the current depth segment, combined with the rock cohesion and internal friction angle parameters at different azimuth angles in the current depth segment, the following expression is used to judge the stress stability of each wellbore azimuth angle:

[0067]

[0068] Where σ1=max{σ A ,σ B ,σ C},σ3=min{σ A ,σ B ,σ C}, FMC(θ) represents the quantitative result of stress stability at the current wellbore azimuth angle, C represents the rock cohesion corresponding to the current azimuth, in MPa; φ represents the rock internal friction angle corresponding to the current azimuth, in degrees.

[0069] The second step is to determine the (local) stability state of the wellbore at each wellbore azimuth angle according to the stress stability judgment results at each azimuth angle in the current depth segment, and mark it, so that the marking result is used as the wellbore stability state identification result. Among them, the following expression is used to determine the local stability state of the wellbore at each wellbore azimuth angle and complete the marking of the local stability state:

[0070]

[0071] Among them, f(θ) represents the marking result of the local stability state of the wellbore under the current wellbore azimuth angle. Specifically, in one embodiment, when the current stress stability quantification parameter is less than or equal to zero, the current wellbore stability state is recorded as 1, at which time, it indicates that the current wellbore is in a local stable state. In addition, in another embodiment, when the current stress stability quantification parameter is greater than zero, the current wellbore stability state is recorded as 0, at which time, it indicates that the current wellbore is in a local unstable state. In this way, the above-mentioned first and second steps are used to obtain the wellbore stability state identification results corresponding to different wellbore azimuth angles in the current depth segment, thereby entering step S1302.

[0072] Step S1302 calculates the (first) ratio at the current depth position (within the current depth segment) based on the identification results of the wellbore stability state of all wellbore azimuth angles in the same depth segment. The first ratio is the ratio of the minimum area required to maintain the wellbore circumferential stress stability state when implementing safe drilling construction in the current depth segment to the outer area of ​​the wellbore circumference involved in the current depth segment.

[0073] In step S1302, according to the wellbore stability state identification result corresponding to each wellbore circumferential azimuth angle in the current depth section obtained in step S1301, the first proportion corresponding to the wellbore circumferential stress stable area required to be maintained during safe drilling construction in the current depth section is calculated according to the following expression:

[0074]

[0075] Here, ω represents the first ratio. Thus, according to the above expression (6), the first ratio for the current depth segment is obtained, and the process proceeds to step S1303.

[0076] Step S1303 compares the first ratio obtained in step S1302 with the wellbore circumferential integrity data set in step S110, and determines the collapse pressure equivalent density according to the comparison result. The collapse pressure equivalent density is the minimum drilling fluid density corresponding to the need to maintain the wellbore stress stable state when performing safe drilling construction for the current depth section. Among them, in the first embodiment, if the current first ratio is greater than the above-mentioned wellbore circumferential integrity parameter, the initial drilling fluid density set in step S120 is used as the collapse pressure equivalent density that ultimately meets the minimum drilling fluid density condition required for safe drilling construction, thereby entering step S1304. That is to say, only when the above-mentioned first ratio is greater than the wellbore circumferential integrity parameter can the currently set drilling fluid density be used as the final required collapse pressure equivalent density.

[0077] In the second embodiment, if the current first ratio is less than the wellbore circumferential integrity parameter, the process returns to step S120, and the set drilling fluid density is readjusted to form a new drilling fluid density until the first ratio is greater than, and then the process proceeds to step S1304 to determine the collapse pressure equivalent density.

[0078] In addition, in order to take into account the characteristics of safe drilling construction and economical drilling fluid cost, when comparing the first ratio obtained in the above step S1302 with the wellbore circumferential integrity data set in step S110, the comparison basis needs to be greater than the wellbore circumferential integrity parameter and also needs to be close to the wellbore circumferential integrity parameter. Specifically, in the first embodiment, if the current first ratio is greater than the wellbore circumferential integrity parameter and the difference between the current first ratio and the wellbore circumferential integrity parameter is less than the preset ratio comparison threshold, the initial drilling fluid density set in step S120 is used as the collapse pressure equivalent density that ultimately meets the minimum drilling fluid density condition for safe drilling construction, thereby entering step S1304. That is to say, only when the above first ratio is greater than the wellbore circumferential integrity parameter and the first ratio is close to the wellbore circumferential integrity parameter, can the currently set drilling fluid density be used as the final required collapse pressure equivalent density.

[0079] Further, if the current first ratio is less than the wellbore circumferential integrity parameter, or the current first ratio is greater than the wellbore circumferential integrity parameter, and the difference between the current first ratio and the wellbore circumferential integrity parameter is equal to or greater than the ratio comparison threshold, then return to step S120, readjust the set drilling fluid density to form a new drilling fluid density, until the first ratio is greater than, and the difference between the first ratio and the wellbore circumferential integrity parameter is less than the preset ratio comparison threshold, then enter step S1304 to determine the collapse pressure equivalent density.

[0080] Step S1304 calculates the drilling collapse pressure at the corresponding depth position (current depth section) using the collapse pressure formula according to the drilling fluid equivalent density for the current depth section obtained in step S1303. The collapse pressure formula is expressed as follows:

[0081] B p =10 -3 ρ m gh v (7)

[0082] Among them, B pIndicates the drilling collapse pressure. Thus, according to the above expression (7), the design of the drilling collapse pressure for the current depth segment is completed, thereby receiving step S130. Thus, by continuously looping the above steps S1301 to S1304, the design of the drilling collapse pressure for all depth segments in the target formation to be drilled is completed.

[0083] On the other hand, based on the above method for designing the wellbore collapse pressure, the present invention further proposes a system for designing the wellbore collapse pressure. Figure 3 FIG. 1 is a structural block diagram of a system for designing drilling collapse pressure according to an embodiment of the present application. Figure 3 As shown, the system for designing drilling collapse pressure of the present invention comprises: a parameter preparation module 31 , a wellbore stress distribution module 32 and a collapse pressure generation module 33 .

[0084] Specifically, the parameter preparation module 31 is implemented according to the method described in step S110 above, and is configured to obtain the geomechanical parameters of the target formation to be drilled, and according to the drilling type of the current target formation to be drilled, the required circumferential integrity of the wellbore required for safe drilling construction of the target formation to be drilled is set. The wellbore stress distribution module 32 is implemented according to the method described in step S120 above, and is configured to set the drilling fluid density. Based on this, according to the geomechanical parameters obtained by the parameter preparation module 31, the wellbore stress of the current target formation to be drilled is analyzed to generate wellbore stress information. Among them, the wellbore stress information includes the wellbore stress characteristics at different positions of the wellbore. The collapse pressure generation module 33 is implemented according to the method described in step S130 above, and is configured to count the proportion of the area that maintains the stable state of the wellbore circumferential stress to the circumferential area of ​​the wellbore when implementing safe drilling construction, and determine the corresponding collapse pressure equivalent density when the proportion reaches the above-mentioned wellbore integrity, so as to calculate the drilling collapse pressure from the current collapse pressure equivalent density.

[0085] Furthermore, the collapse pressure generation module 33 includes: a wellbore local stability state analysis unit 331, a wellbore stability state preliminary ratio generation unit 332, an equivalent density generation unit 333 and a pressure calculation unit 334. Among them, the wellbore local stability state analysis unit 331 is configured to identify the wellbore stability state at different wellbore azimuth angles according to the wellbore stress information. The wellbore stability state preliminary ratio generation unit 332 is configured to calculate the (first) ratio at the current depth position according to the wellbore stability state identification results at all wellbore azimuth angles. The equivalent density generation unit 333 is configured to compare the current (first) ratio with the wellbore circumference integrity degree. If the current (first) ratio is greater than the wellbore circumference integrity degree, the current drilling fluid density is used as the collapse pressure equivalent density, otherwise, the current drilling fluid density is adjusted. The pressure calculation unit 334 is configured to calculate the drilling collapse pressure at the corresponding depth position according to the collapse pressure equivalent density.

[0086] The present invention discloses a method and system for designing drilling collapse pressure. The method and system include steps for preparing geomechanical parameters of target formations to be drilled and borehole parameters, steps for analyzing the stress environment around the well, and steps for calculating drilling fluid equivalent density and collapse pressure. When designing the drilling collapse pressure, the present invention fully considers the requirements of safe drilling construction for the integrity of the well wall. The designed collapse pressure can not only ensure the safety of drilling construction, but also create conditions for reducing the density of drilling fluid, increasing the drilling speed, reducing the drilling cost, and improving the drilling efficiency, thereby obtaining better economic benefits of the drilling project.

[0087] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by any person familiar with the technology within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

[0088] It should be understood that the embodiments disclosed in the present invention are not limited to the specific structures, processing steps or materials disclosed herein, but should be extended to equivalent substitutions of these features understood by ordinary technicians in the relevant field. It should also be understood that the terms used herein are only used for the purpose of describing specific embodiments and are not meant to be limiting.

[0089] The "one embodiment" or "embodiment" mentioned in the specification means that the specific features, structures or characteristics described in conjunction with the embodiment are included in at least one embodiment of the present invention. Therefore, the phrases "one embodiment" or "embodiment" appearing in various places throughout the specification do not necessarily refer to the same embodiment.

[0090] Although the embodiments disclosed in the present invention are as above, the contents described are only embodiments adopted for facilitating the understanding of the present invention and are not intended to limit the present invention. Any technician in the technical field to which the present invention belongs can make any modifications and changes in the form and details of the implementation without departing from the spirit and scope disclosed in the present invention, but the patent protection scope of the present invention shall still be subject to the scope defined in the attached claims.

Claims

1. A method for designing a wellbore collapse pressure, comprising: Step 1: obtaining geomechanical parameters of the target formation to be drilled, and setting the circumferential integrity of the wellbore required for safe drilling of the target formation according to the drilling type of the target formation; Step 2: setting the drilling fluid density, based on which, according to the geomechanical parameters, analyzing the wellbore stress of the target formation, and generating wellbore stress information, wherein the wellbore stress information includes wellbore stress characteristics at different positions of the wellbore; Step 3: According to the wellbore stress information, the proportion of the area where the wellbore circumferential stress is maintained in a stable state to the circumferential area of ​​the wellbore is counted when the safe drilling construction is implemented, and based on this, the corresponding collapse pressure equivalent density when the proportion reaches the circumferential integrity of the wellbore is determined, so as to calculate the drilling collapse pressure from the collapse pressure equivalent density. Step 3 includes: According to the wellbore stress information, respectively identifying the wellbore stability states at different wellbore azimuth angles; Calculate the ratio at the current depth position according to the wellbore stability state identification results at all wellbore azimuth angles; Comparing the ratio with the circumferential integrity of the wellbore wall, if the ratio is greater than the circumferential integrity parameter of the wellbore wall, taking the current drilling fluid density as the collapse pressure equivalent density, otherwise, adjusting the drilling fluid density; The drilling collapse pressure at a corresponding depth position is calculated according to the collapse pressure equivalent density.

2. The method according to claim 1, characterized in that The geomechanical parameters include, but are not limited to, ground stress parameters, formation pressure parameters, rock elasticity parameters, rock strength parameters and wellbore trajectory parameters.

3. The method according to claim 2, characterized in that When calculating the stress state at each wellbore azimuth angle in the wellbore circumferential stress distribution characteristics, it includes: Calculate the geostress components at different azimuths in the wellbore rectangular coordinate system according to the vertical geostress, the maximum horizontal geostress and the minimum horizontal geostress in the geostress parameters, and the well inclination angle and the well inclination azimuth in the well trajectory parameters; Calculate the borehole wall stress components at different positions in the borehole axis coordinate system according to the in-situ stress components at different positions, the Poisson's ratio in the rock elastic parameters, the drilling fluid density and the vertical depth of the drilling; The effective principal stress of the wellbore rock at different circumferential positions is calculated according to the wellbore stress components at different positions, the pore elastic coefficient in the rock elastic parameters, and the formation pore fluid pressure in the formation pressure parameters.

4. The method according to claim 3, characterized in that The ground stress component, the wellbore stress component and the wellbore rock effective principal stress at the current position are calculated using the following expressions: Among them, x, y, and z represent the three directions in the spatial rectangular coordinate system corresponding to the wellbore axis coordinates, σ A , σ B , σ C They represent the effective principal stress of the wellbore rock, g represents the gravitational acceleration, ρ m represents the initial drilling fluid density, h v represents the vertical depth of drilling, η represents the poroelastic coefficient, P p represents the formation pore fluid pressure, σ θ , σ z , τ θz They represent the wellbore stress components in the wellbore axis coordinate system, S xx , S yy , S zz , S xy , S xz , S yz represents the in-situ stress component, v represents the Poisson's ratio, θ represents the current wellbore azimuth angle, S v represents the vertical ground stress, S H represents the maximum horizontal ground stress, S h represents the minimum horizontal geostress, β represents the angle between the maximum horizontal geostress azimuth and the wellbore azimuth, and α w Indicates the well inclination angle.

5. The method according to claim 1, characterized in that The step of respectively identifying the wellbore stability states at different wellbore azimuth angles according to the wellbore stress information includes: According to the wellbore stress information, the Mohr-Coulomb strength analysis principle is adopted to quantify the stress stability of each wellbore azimuth angle; According to the stress stability quantification results, the wellbore stability state at each wellbore azimuth angle is determined, wherein when the current stress stability quantification parameter is less than or equal to zero, the current wellbore stability state is recorded as 1, and when the current stress stability quantification parameter is greater than zero, the current wellbore stability state is recorded as 0.

6. The method according to claim 5, characterized in that According to the wellbore stress information, combined with the rock cohesion and internal friction angle parameters at different azimuth angles, the stress stability of each wellbore azimuth angle is judged using the following expression: σ1=max{σ A ,s B ,s C } σ3=min{σ A ,s B ,s C } Among them, θ represents the current wellbore azimuth angle, FMC(θ) represents the stress stability judgment result of the current wellbore azimuth angle, σ A , σ B , σ C represents the effective principal stress of the wellbore rock, C represents the cohesion corresponding to the current orientation in the rock strength parameters, and φ represents the internal friction angle corresponding to the current orientation in the rock strength parameters.

7. The method according to any one of claims 1 to 6, characterized in that: When the drilling type is a vertical well, the circumferential integrity of the well wall is greater than 60%; When the drilling type is a deviated well, the circumferential integrity of the well wall is greater than 70%; When the drilling type is a directional well or a horizontal well, the circumferential integrity of the well wall is greater than 80%.

8. A system for designing wellbore collapse pressure, comprising: A parameter preparation module configured to obtain geomechanical parameters of a target formation to be drilled, and to set a circumferential integrity of a wellbore required for safe drilling of the target formation according to a drilling type of the target formation; A wellbore stress distribution module is configured to set the drilling fluid density, based on which, according to the geomechanical parameters, the wellbore stress of the target formation is analyzed to generate wellbore stress information, wherein the wellbore stress information includes wellbore stress characteristics at different positions of the wellbore; A collapse pressure generating module is configured to count the proportion of the area maintaining the stable state of the circumferential stress of the well wall to the circumferential area of ​​the well wall when implementing the safe drilling construction according to the well wall stress information, and based on this, determine the corresponding collapse pressure equivalent density when the proportion reaches the circumferential integrity of the well wall, so as to calculate the drilling collapse pressure from the collapse pressure equivalent density, wherein the collapse pressure generating module includes: A wellbore local stability state analysis unit, configured to respectively identify the wellbore stability states at different wellbore azimuth angles according to the wellbore stress information; A preliminary ratio generation unit for the wellbore stability state is configured to calculate the ratio at the current depth position according to the wellbore stability state identification results at all wellbore azimuth angles; An equivalent density generating unit is configured to compare the ratio with the circumferential integrity of the wellbore wall, and if the ratio is greater than the circumferential integrity parameter of the wellbore wall, use the current drilling fluid density as the collapse pressure equivalent density, otherwise, adjust the drilling fluid density; A pressure calculation unit is configured to calculate the wellbore collapse pressure at a corresponding depth position according to the collapse pressure equivalent density.

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