A drilling leakage quantitative prediction method under rock mechanics and engineering mechanics

Abstract

The present application provides a kind of drilling loss quantitative prediction method under rock mechanics and engineering mechanics, comprising the following steps, preparation of basic data;Additional stress of lithology interface is calculated;Degree and extension scale of mud fracturing are judged to determine the loss scale.The present application combines engineering mechanics and rock mechanics, based on the conventional stratum data of drilling, explains the use of stratum parameters or mineral content and the difference between stratum pressure and mud pressure to determine the stress concentration phenomenon at lithology interface and quantitatively calculate the stress concentration size of lithology interface through the formula derived by test and deduction;Secondly, the fracture development degree and extension scale are determined by combining stratum breakdown pressure and rock crack formation law;And the distance between the broken position determined by seismic data and natural fault is referred to determine the occurrence and scale of loss.The method can quickly determine the loss position in the drilling process, is simple and easy to operate, and has reliable accuracy;This method has small error, good effect and strong timeliness.

Description

Technical Field

[0001] This invention belongs to the field of petroleum exploration and development technology, and in particular relates to a quantitative prediction method for well leakage under rock mechanics and engineering mechanics. Background Technology

[0002] Well leakage is a common drilling phenomenon in oil and gas fields both domestically and internationally, particularly severe in the Bohai Sea region, where the loss rate is approximately 50%. Well leakage not only increases operating costs and delays the project schedule, but in severe cases, it can also increase drilling risks and lead to safety accidents. Furthermore, the plugging fluids used after leakage occurs can contaminate the reservoir, causing logging curves to fail to reflect true formation information, greatly hindering subsequent formation fluid identification, production capacity assessment, and scientific production allocation.

[0003] Currently, the prediction and location of well leakage primarily rely on seismic analysis to identify potential micro-faults for qualitative prediction, followed by fine-tuning of leakage using well logging data. During drilling tracking and well leakage analysis, it has been observed that vertically, lithological leakage zones are often concentrated in areas of interbedded sandstone and mudstone of varying thicknesses, or thin interbedded sandstone and mudstone. Because the formation fracturing pressure interpreted from well logging is much higher than the mud pressure in the wellbore, the leakage zones are often attributed to weak layers (where the fracturing pressure does not show a significant reduction in well logging data). Furthermore, because petroleum geologists generally focus on rock mechanics while neglecting engineering mechanics, the mechanism of lithological leakage is often attributed to the presence of weak lithological layers or lithological slip surfaces causing well leakage.

[0004] Furthermore, because most lithological leaks lack obvious seismic characteristics, their predictability and reliability are low. A new method is needed to reliably predict lithological leaks and accurately locate their sites using existing data, thus addressing these issues. Summary of the Invention

[0005] The problem this invention aims to solve is to provide a quantitative prediction method for drilling leakage under rock mechanics and engineering mechanics. In particular, it applies the phenomenon of stress concentration in layered formations in engineering mechanics. Based on the formation elastic parameters and the pressure difference between the drilling fluid and the formation pores, a new method for calculating the stress distribution at the layer interface is used to obtain a more refined stress distribution. Combined with the formation fracturing pressure, fracture extension scale, and relationship with natural fractures, the location and scale of formation fracturing and leakage can be quantitatively determined.

[0006] This invention provides a method for quantitative prediction of drilling leakage under rock mechanics and engineering mechanics, comprising the following steps: S1: Prepare basic information; S2: Calculate the additional stress at the lithological interface; S3: Determine the extent and scale of mud fracturing; S4: Determine the scale of leakage.

[0007] Furthermore, the basic data includes pre-drilling prediction and monitoring while drilling, and S1 includes the following steps: S1: Prepare basic information; S2: Calculate the additional stress at the lithological interface; S3: Determine the extent and scale of mud fracturing; S4: Determine the scale of leakage.

[0008] Furthermore, the basic data includes pre-drilling prediction and monitoring while drilling, and S1 includes the following steps: S11: Pre-drilling stage, based on predictions, obtain formation lithology, formation P-wave velocity, formation S-wave velocity, formation density, formation fracture pressure, well trajectory, and drilling mud data; S12: During drilling, the actual lithology, clay content, and sand content of the formation are obtained using the drilling-while-drilling (GR) method.

[0009] Furthermore, in step S2, the stress expression of the layer interface is derived using rock mechanics and engineering mechanics for layered strata, and the magnitude and distribution of the additional stress at the lithological interface are calculated. Step S2 includes the following steps: S21: Calculating Poisson's ratio using rock mechanics Young's modulus E, shear modulus G; S22: Before drilling, the P-wave and S-wave time difference and density obtained from seismic inversion are calculated. S23: During the drilling phase, mineral content is calculated using drilling GR data, and then the P-wave and S-wave velocities are replaced by mineral content and formation density.

[0010] Furthermore, by drawing upon the stress distribution and stress test simulation results between interlayer interfaces from rock mechanics and geotechnical engineering mechanics, as well as the formation additional stress transmission mode under positive pressure differential, a new additional stress at the lithological interface of the formation around the wellbore is constructed and expressed by a formula, where the stress magnitude is represented by the pressure equivalent density in drilling engineering: At the mudstone-sandstone interface, i.e., the interface between the relatively plastic and rigid rock layers, stress concentration occurs and is expressed as a positive value. The equivalent density of the stress added by the stress concentration can be expressed by the formula: At the sand-mudstone interface, i.e., the interface between the relatively rigid layer and the plastic layer, stress diffusion occurs and is expressed as a negative value. The magnitude of the stress equivalent density consumed by stress diffusion can be expressed by the formula: in, The magnitude of the additional stress equivalent density at the interface between layers A and B, in g / cm³. 3 ; These are the Young's moduli of layers A and B, respectively, in GPa; , respectively, are the Poisson's ratios of layers A and B, dimensionless; and These are the mud pressure equivalent density and the formation pressure equivalent density, respectively, in g / cm³. 3 ; R is the stress concentration factor, dimensionless; R is the ratio of mudstone to sandstone thickness, dimensionless; H is the interface depth, in meters. 。 Furthermore, S3 includes the following steps: S31: During drilling, a common stress state is that the pressure generated by the drilling mud in the wellbore is greater than the pore pressure of the permeable layer, thus generating a positive pressure differential. S32: When At that time, numerous fractures appeared in the formation, and the drilling fluid showed minor leakage. Density at rock fracture pressure, in g / cm³ 3 ; The effective stress equivalent density of the rock, in g / cm³ 3 ; S33: When At this time, numerous fractures appear in the formation, further increasing the leakage of drilling fluid. The fractures connect to form faults, exacerbating the loss. The half-length of this interconnected fracture can be represented as: Where: L is the length of the maximum connected crack, in meters; Apply the equivalent stress density to the interface between A and B, in g / cm³. 3 ; The effective stress equivalent density of the rock skeleton, in g / cm³ 3 ; The density is the equivalent density of formation fracture pressure, in g / cm³. 3 ; The thickness of the fractured rock layer is m; E is the elastic modulus, GPa. μ Poisson's ratio is dimensionless. b This is the construction factor, dimensionless, and defaults to 200.

[0011] Furthermore, in step S4, the leakage scale is determined by connecting the fracture and crack scale with the leakage space. Step S4 includes the following steps: S41: Obtain the distance from the lost circulation zone in the wellbore to the natural fault using existing conventional depth-domain seismic data or interpretation results. LF ; S42: Determine the scale of leakage.

[0012] Furthermore, S42 includes the following steps: S421: When At that time, a large or serious leak may occur; S422: When At that time, a minor leak occurred; in, LF The distance from the wellbore to the fault is in meters (m). The width of the fault zone can be set to the default value of 0, m; c is a constant, representing the zoning factor, which is dimensionless; H / b is a depth factor, which is dimensionless. P The constants are related to the fault properties: 1 for normal faults, 1.1 for tension-torsional faults, and 1.2 for reverse faults. They are dimensionless. D The fault displacement is expressed in meters (m). θ The fault dip angle is expressed in °. β The magnitude of the fault strike curvature is expressed in degrees. R Due to the brittle nature of the strata, the quantity is dimensionless; h The thickness of the rock strata is in meters (m). Φ Formation porosity, dimensionless.

[0013] Furthermore, the present invention also provides a drilling loss quantitative prediction device under rock mechanics and engineering mechanics, which operates the above-described prediction method.

[0014] Furthermore, the present invention also provides a drilling loss quantitative prediction device under rock mechanics and engineering mechanics, including a memory, a processor, and an algorithm stored in the memory and executable on the processor, wherein the processor implements the prediction method when executing the computer program.

[0015] Furthermore, the present invention also provides a computer-readable storage medium storing a computer algorithm, which, when executed by a processor, implements the method described herein.

[0016] The advantages and positive effects of this invention are: This invention combines engineering mechanics and rock mechanics. Based on existing formation data from conventional drilling, it elucidates how to determine stress concentration phenomena at lithological interfaces and quantitatively calculate their magnitude using formation parameters or mineral content, and the difference between formation pressure and mud pressure, through experimentally derived formulas. Secondly, by combining formation fracturing pressure and rock fracture formation patterns, it determines the degree of fracture development and its extent, and by referring to the distance between the fracture location determined by seismic data and the natural fault, it determines the occurrence and scale of leakage. This method can quickly determine the location of leakage during drilling, is simple and easy to implement, and has reliable accuracy. The predicted and calculated leakage location and magnitude obtained by this method show small errors compared to actual field data, demonstrating good results and strong timeliness. Attached Figure Description

[0017] Figure 1 This is an overall flowchart of an embodiment of the present invention.

[0018] Figure 2 This is a simulation diagram of stress distribution under different thicknesses of sand-mudstone combination mode in the embodiments of the present invention.

[0019] Figure 3 This is a diagram illustrating the additional stress transmission mode in the wellbore according to an embodiment of the present invention.

[0020] Figure 4 This is a quantitative discrimination diagram of well leakage in embodiment X4 of the present invention.

[0021] Figure 5 This is a diagram showing the determination of the distance between the well and the fault in embodiment X4 of the present invention. Detailed Implementation

[0022] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] The embodiments of the present invention will be further described below with reference to the accompanying drawings: like Figure 1 As shown, this invention provides a method for quantitative prediction of drilling leakage under rock mechanics and engineering mechanics, comprising the following steps: S1: Prepare basic data, including pre-drilling predictions and monitoring while drilling. Specifically, S1 includes the following steps. S11: Pre-drilling stage, based on predictions, obtain formation lithology, formation P-wave velocity, formation S-wave velocity, formation density, formation fracture pressure, well trajectory, and drilling mud data.

[0024] S12: During drilling, the actual lithology, mud content, and sand content of the formation are obtained using the drilling-while-drilling (GR) method, which prepares for the subsequent calculation of the stress at the lithological interface.

[0025] S2: Calculate the additional stress at the lithological interface. Using rock mechanics and engineering mechanics, the stress expression for the layered stratigraphy is derived, and the magnitude and distribution of the additional stress at the lithological interface are calculated. Specifically, S2 includes the following steps: S21: Calculating Poisson's ratio using rock mechanics Young's modulus E, shear modulus G, etc.

[0026] S22: Before drilling, the P-wave and S-wave time difference and density obtained from seismic inversion are used for calculation.

[0027] S23: During the drilling phase, mineral content is calculated using drilling GR data, and then the P-wave and S-wave velocities are replaced by mineral content and formation density.

[0028] Based on the results of stress distribution and stress test simulations between interlayer interfaces in rock mechanics and geotechnical engineering mechanics, such as Figure 2 As shown, the formation additional stress transmission mode under positive pressure difference is as follows: Figure 3 As shown, the additional stress at the formation lithology interface around the wellbore can be constructed and expressed by a formula, where the stress magnitude is represented by the pressure equivalent density in drilling engineering: At the mudstone-sandstone interface, i.e., the interface between the relatively plastic and rigid rock layers, stress concentration occurs and is expressed as a positive value. The equivalent density of the stress added by the stress concentration can be expressed by the formula: (Formula 1) At the sand-mudstone interface, i.e., the interface between the relatively rigid layer and the plastic layer, stress diffusion occurs and is expressed as a negative value. The magnitude of the stress equivalent density consumed by stress diffusion can be expressed by the formula: (Formula 2) in, The magnitude of the additional stress equivalent density at the interface between layers A and B, in g / cm³. 3； , These are the Young's moduli of layers A and B, respectively, in GPa; , , respectively, are Poisson's ratios for layers A and B, dimensionless; and These are the mud pressure equivalent density and the formation pressure equivalent density, respectively, in g / cm³. 3； R is the stress concentration factor, dimensionless; R is the ratio of mudstone to sandstone thickness, dimensionless; H Let m be the interface depth. Overall, the formula shows that the additional stress of the thick mud-thin sand lithological combination is the greatest and the risk of well leakage is the greatest. The secondary type is the thick sand-thin mud type, and when mud and sand are of equal thickness, the stress concentration is not obvious and the risk is relatively small.

[0029] S3: Determine the extent and scale of mud fracturing. Specifically, S3 includes the following steps: S31: During drilling, a common stress state is that the pressure generated by the drilling mud in the wellbore is greater than the pore pressure of the permeable layer, thus creating a positive pressure differential.

[0030] S32: When At that time, numerous fractures appeared in the formation, and the drilling fluid showed minor leakage. Density at rock fracture pressure, in g / cm³ 3 ; The effective stress equivalent density of the rock, in g / cm³ 3 .

[0031] S33: When At this time, numerous fractures appear in the formation, further increasing the leakage of drilling fluid. The fractures connect to form faults, exacerbating the loss. The half-length of this interconnected fracture can be represented as: (Formula 3) Where: L is the length of the maximum connected crack, in meters; Apply the equivalent stress density (g / cm³) to the interface between A and B. 3 ; The effective stress equivalent density of the rock skeleton, in g / cm³ 3 ; The density is the equivalent density of formation fracture pressure, in g / cm³. 3 ; The thickness of the fractured rock layer is m; E is the elastic modulus, GPa. μ Poisson's ratio is dimensionless. b This is the construction factor, dimensionless, and defaults to 200.

[0032] S4: Determine the scale of leakage. The core of this method is to determine the scale of leakage by connecting the scale of fractures and cracks with the leakage space. Specifically, S4 includes the following steps: S41: Determine the distance LF between the wellbore and the fault. Specifically, use existing depth-domain seismic data or interpretation results to obtain the distance between the lost circulation zone section in the wellbore and the natural fault. LF .

[0033] S42: Determine the scale of the leakage. Specifically, S42 includes the following steps: S421: When At that time, a large or serious leak may occur.

[0034] S422: When At that time, a minor leak occurred.

[0035] in, LF The distance from the wellbore to the fault is in meters (m). The width of the fault zone can be set to the default value of 0, m; c is a constant, representing the zoning factor, which is dimensionless; H / b is a depth factor, which is dimensionless. P These are constants related to fault properties: 1 for normal faults, 1.1 for tension-torsional faults, and 1.2 for reverse faults. They are dimensionless. D The fault displacement is expressed in meters (m). θ The fault dip angle is expressed in °. β The magnitude of the fault strike curvature is expressed in degrees. R Due to the brittle nature of the strata, the quantity is dimensionless; hThe thickness of the rock strata is in meters (m). Φ Formation porosity, dimensionless.

[0036] By applying the above processes and technologies, and using a progressive method to determine the extent of leakage by going deeper layer by layer after a qualitative assessment of whether leakage has occurred, the quantitative identification of well leakage can be achieved.

[0037] The technical solution of the present invention will be further described below with reference to specific embodiments. Taking the application of the present invention in well leakage analysis while drilling in Bozhong X4 well as an example, the following steps are included: S1: Prepare basic data, specifically, collect data such as sonic logging (AC), GR, density (DEN), resistivity logging (RT), and mud density while drilling.

[0038] S2: Calculation of hierarchical and related parameters. Specifically, using... AC Converted to longitudinal wave velocity V p ;use AC and DEN The longitudinal wave velocity was calculated. V s ;use V p , V s and DEN calculate Young's modulus E, Poisson's ratio Formation pressure, etc. P p Overburden pressure Pv and effective stress of the formation skeleton P eff Formation fracture pressure P f .

[0039] The stratigraphic profile was divided into lithological (brittle and plastic) layers using GR curves, as shown in Table 1. The thickness and average value of each layer were also statistically analyzed. Young's modulus E, Mean Poisson's ratio Minimum rupture pressure P f .

[0040] Table 1. Calculation Results of Loss-Related Parameters for Well X4

[0041] S3: Calculation of additional stress at the lithological interfaces of each sublayer. Specifically, the additional interfacial stress is obtained using formula 1 for the additional stress at the sand-mud interface and formula 2 for the additional stress at the mud-sand interface. The actual interfacial pressure is obtained by adding the additional force to the original skeletal force. P AB .

[0042] S4: Quantitative assessment of formation leakage. Specifically, this is achieved using the formation fracture pressure P. f Subtract the actual pressure on the interface P AB , to obtain P f -P AB Numerical analysis is used to determine the cause: when the value is less than 0, formation fracturing and leakage occur; when the value is less than 0-0.1, it indicates a risk zone for leakage in the working well. Figure 4 A comparison of formation fracture pressure and drilling fluid pressure differential reveals that: conventional logging calculations consistently show formation fracture pressures greater than drilling fluid pressures. However, the new method reveals instances where formation fracture pressures are lower than formation pressures in certain areas. Specifically, in the 2946.7-2948m well section, a thin sandstone layer approximately 1.3m thick is sandwiched between thick mudstone layers, with a mud-to-sand ratio of approximately 4.6. The added stress equivalent density at the sandstone interface is approximately 0.74 g / cm³. 3 The equivalent density of the fracture pressure in the strata at that location is approximately 1.94 g / cm³. 3 Less than the actual interface pressure of 2.11 g / cm³ 3 There was a loss.

[0043] S5: Leakage Rate Determination. Specifically, using seismic substructure maps and isochronous slices of coherent bodies, the leakage point is located 100-150m away from the NE-SW trending main fault and multiple smaller faults. Figure 5 As shown, the calculated length of the crack connection is approximately 190m. Therefore, it is determined to be a large leak.

[0044] The well is located in fine sandstone at a depth of 2948m, with a leakage velocity of 65m / s. 3 / The leakage level is large, with a total leakage of approximately 150 m³ per hour. 3 The plugging fluid is approximately 40m³. 3 The processing time is approximately 3 hours.

[0045] In summary, by effectively identifying the leakage section, rapid, effective, and precise plugging was carried out in that section, ensuring the smooth progress of drilling.

[0046] The foregoing has provided a detailed description of one embodiment of the present invention, but this description is merely a preferred embodiment and should not be construed as limiting the scope of the invention. All equivalent variations and modifications made within the scope of the claims of this invention should still fall within the patent coverage of this invention.

Claims

1. A quantitative prediction method for drilling leakage under rock mechanics and engineering mechanics, characterized in that: Includes the following steps, S1: Prepare basic information; S2: Calculate the additional stress at the lithological interface. Using rock mechanics and engineering mechanics, the stress expression at the layered strata is derived, and the magnitude and distribution of the additional stress at the lithological interface are calculated. S2 includes the following steps: S21: Calculate Poisson's ratio μ, Young's modulus E, and shear modulus G using rock mechanics; S22: Before drilling, the P-wave and S-wave time difference and density obtained from seismic inversion are calculated. S23: During the drilling phase, mineral content is calculated using drilling GR data, and then the P-wave and S-wave velocities are replaced by mineral content and formation density. Based on rock mechanics and the results of stress distribution and stress test simulations at interlayer interfaces, as well as the formation additional stress transmission model under positive pressure differential, the additional stress at the lithological interface of the formation around the wellbore is newly constructed and expressed by a formula, where the stress magnitude is represented by the pressure equivalent density in drilling engineering: At the mudstone-sandstone interface, i.e., the interface between the plastic and rigid rock layers, stress concentration occurs and is expressed as a positive value. The equivalent density of the stress added by the stress concentration can be expressed by the formula: At the sand-mudstone interface, i.e., the interface between the relatively rigid layer and the plastic layer, stress diffusion occurs and is expressed as a negative value. The magnitude of the stress equivalent density consumed by stress diffusion can be expressed by the formula: Where, δ AB The magnitude of the equivalent stress density at the interface between layers A and B, in g / cm³. 3 E A E B The Young's modulus of layers A and B are respectively, in GPa; μ A μ B These are the Poisson's ratios for layers A and B, respectively, dimensionless; ρ w and ρ f These are the mud pressure equivalent density and the formation pressure equivalent density, respectively, in g / cm³. 3 α is the stress concentration factor, which is dimensionless. R The ratio of mudstone to sandstone thickness is dimensionless. H Let m be the interface depth. S3: Determine the extent and scale of mud fracturing; S4: Determine the scale of leakage.

2. The method for quantitative prediction of drilling leakage under rock mechanics and engineering mechanics according to claim 1, characterized in that: The basic data includes pre-drilling prediction and monitoring while drilling. Step S1 includes the following steps: S11: Pre-drilling stage, based on predictions, obtain formation lithology, formation P-wave velocity, formation S-wave velocity, formation density, formation fracture pressure, well trajectory, and drilling mud data; S12: During drilling, the actual lithology, clay content, and sand content of the formation are obtained using the drilling-while-drilling (GR) method.

3. The method for quantitative prediction of drilling leakage under rock mechanics and engineering mechanics according to claim 1 or 2, characterized in that: S3 includes the following steps: S31: During drilling, a common stress state is that the pressure generated by the drilling mud in the wellbore is greater than the pore pressure of the permeable layer, thus generating a positive pressure differential. S32: When At that time, numerous fractures appeared in the formation, and the drilling fluid showed minor leakage, among which P p Density at rock fracture pressure, in g / cm³ 3 ;δ m The effective stress equivalent density of the rock, in g / cm³ 3 ; S33: When At this time, numerous fractures appear in the formation, further increasing the leakage of drilling fluid. The fractures connect to form faults, exacerbating the loss. The half-length of this interconnected fracture can be represented as: Where: L is the length of the maximum connected crack, in meters; P AB Apply the equivalent stress density (g / cm³) to the interface between A and B. 3 ;P m The effective stress equivalent density of the rock skeleton, in g / cm³ 3 ;P f The density is the equivalent density of formation fracture pressure, in g / cm³. 3 Δh is the thickness of the fractured rock layer, in meters; E is the elastic modulus, in GPa. μ Poisson's ratio is dimensionless. b This is the construction factor, dimensionless, and defaults to 200.

4. The method for quantitative prediction of drilling leakage under rock mechanics and engineering mechanics according to claim 1 or 2, characterized in that: In step S4, the leakage scale is determined by connecting the fracture and crack scale with the leakage space. Step S4 includes the following steps: S41: Obtain the distance from the lost circulation zone in the wellbore to the natural fault using existing conventional depth-domain seismic data or interpretation results. LF ; S42: Determine the scale of leakage.

5. The method for quantitative prediction of drilling leakage under rock mechanics and engineering mechanics according to claim 4, characterized in that: S42 includes the following steps: S421: When At that time, a large or serious leak may occur; S422: When At that time, a minor leak occurred; in, LF The distance from the wellbore to the fault is in meters (m). D f The width of the fault zone can be set to the default value of 0, m; c is a constant, representing the zoning factor, which is dimensionless; H / b is a depth factor, which is dimensionless. P These are constants related to fault properties: 1 for normal faults, 1.1 for tension-torsional faults, and 1.2 for reverse faults. They are dimensionless. D The fault displacement is expressed in meters (m). θ The fault dip angle is expressed in °. β The magnitude of the fault strike curvature is expressed in degrees. R Due to the brittle nature of the strata, the quantity is dimensionless; h The thickness of the rock strata is in meters (m). Φ Formation porosity, dimensionless.

6. A quantitative prediction device for drilling loss under rock mechanics and engineering mechanics, characterized in that: Run the prediction method as described in any one of claims 1 to 5.

7. A drilling loss quantitative prediction device based on rock mechanics and engineering mechanics, comprising a memory, a processor, and an algorithm stored in the memory and executable on the processor, characterized in that: When the processor executes the computer program, it implements the prediction method as described in any one of claims 1 to 5.

8. A computer-readable storage medium storing a computer algorithm, characterized in that, When the computer algorithm is executed by the processor, it implements the method for quantitative prediction of drilling leakage under rock mechanics and engineering mechanics as described in any one of claims 1 to 5.

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