Calculation method for fracture width of bedding plane along the invasion direction after drilling fluid invasion

Abstract

The present invention relates to a method for calculating the fracture width of bedding planes along the invasion direction after the invasion of drilling fluid, which includes: conducting a confining pressure core permeability experiment to obtain the bedding plane permeability of laminated shale under different confining pressure conditions, and fitting the relationship between the shale confining pressure and the bedding plane permeability; combining the relationship between the bedding plane permeability and the fracture width to obtain the relationship between the confining pressure and the bedding plane fracture width; assuming that the direction of the maximum principal stress around the wellbore is 0° and the direction of the minimum principal stress is 90°, superimposing the in-situ stress components, pore pressure, and fluid pressure in the wellbore around the well to obtain the stress of the surrounding rock of the well; assuming that the dip angle of the horizontal bedding plane is 0°, calculating the normal stress on the bedding plane according to the stress of the surrounding rock of the well; calculating the effective normal stress on the bedding plane during the drilling process; and calculating the fracture width of the bedding plane according to the effective normal stress on the wellbore bedding plane. The present invention takes into account the differences between the underground confining pressure conditions and the surface environment, and significantly improves the accuracy of the calculation results of the fracture width of the bedding plane along the invasion direction after the invasion of drilling fluid.

Description

Technical Field:

[0001] The present invention relates to the technical fields of rock mechanics and oil and gas well development, and specifically to a method for calculating the seam width of bedding planes along the invasion direction after drilling fluid invasion. Background Art:

[0002] During the drilling process of stratified formations, the interference of engineering activities may cause the bedding planes to further expand or close, which will directly affect the seam width of the bedding planes. Different wellbore trajectories during the drilling process result in different stress components acting on the wellbore, thereby affecting the normal stress acting on the bedding planes around the well and the seam width of the bedding planes; in addition, the drilling fluid invades the formation along the bedding fractures, increasing the fluid pressure in the bedding fractures, which will also have a certain impact on the normal stress and seam width of the bedding planes. Therefore, the seam width of stratified formations is not only related to the original conditions of the formation, but also closely related to the actual drilling conditions. During the drilling of oil and gas wells, in order to prevent the drilling fluid from invading the formation and causing wellbore instability, it is usually necessary to add plugging particles to the drilling fluid. The seam width of the bedding plane is an important basis for the design of the plugging particle size. Accurately calculating the seam width of the bedding plane along the invasion direction after drilling fluid invasion is of great significance for guiding the drilling fluid design of oil and gas wells.

[0003] Currently, there is little research on the seam width of the bedding planes around the well, and the following problems exist:

[0004] 1. Generally, indoor experiments are used to detect the rock seam width. However, due to the differences between the surface environment and the underground overburden conditions, the measured results of the seam width of the bedding planes are different from the actual underground situation, which leads to the fact that direct measurement cannot accurately reflect the actual situation of the formation, and there is a deviation between the measured seam width and the actual value.

[0005] 2. The stress state around the well directly affects the seam width of the bedding planes. As the drilling project progresses, the stress around the well and the fluid pressure in the bedding fractures are constantly changing, and the stress acting on the bedding planes around the well is also constantly changing. Existing technologies often have difficulty comprehensively considering these factors, resulting in inaccurate prediction of the seam width of the bedding planes.

[0006] For the drilling project of stratified formations, the seam width of the bedding planes is crucial for the design of the drilling fluid plugging particles. Accurately calculating the seam width of the bedding plane along the invasion direction after drilling fluid invasion is the key to accurately designing the plugging particles and ensuring the safe and efficient development of stratified reservoirs. Therefore, there is an urgent need for a scientific method to solve the above problems and accurately calculate the seam width of the bedding plane along the invasion direction after drilling fluid invasion, so as to provide accurate guidance for the design of the drilling fluid plugging particles. Summary of the Invention:

[0007] The object of the present invention is to provide a method for calculating the fracture width of bedding planes along the invasion direction after drilling fluid invasion. This method for calculating the fracture width of bedding planes along the invasion direction after drilling fluid invasion is used to solve the problem that the measurement or prediction of the fracture width of bedding planes in the prior art is not accurate enough.

[0008] The technical solution adopted by the present invention to solve its technical problems is as follows: This method for calculating the fracture width of bedding planes along the invasion direction after drilling fluid invasion includes the following steps:

[0009] Step 1: Conduct a confining pressure pore permeability experiment to obtain the bedding plane permeability of laminated shale under different confining pressure conditions, and fit the relationship between the shale confining pressure and the bedding plane permeability:

[0010] K = ae bσ

[0011] In the formula: σ is the confining pressure, MPa; K is the bedding plane permeability, mD; a and b are fitting coefficients;

[0012] Step 2: Combine the relationship between the bedding plane permeability and the fracture width to obtain the relationship between the confining pressure and the bedding plane fracture width:

[0013]

[0014] In the formula: w is the bedding plane fracture width, μm;

[0015] Step 3: Assume that the direction of the maximum principal stress around the wellbore is 0°, and the direction of the minimum principal stress is 90°. According to the generalized plane strain solution method, superimpose the in-situ stress components, pore pressure, and fluid pressure in the wellbore around the well to obtain the stress of the surrounding rock of the well:

[0016]

[0017] In the formula: σ ij (i, j ∈ x, y, z b ) are the respective stress components of [σ B , MPa; σ r and σ θ are the radial stress and circumferential stress around the wellbore, MPa; A = (σ xx + σ yy ) / 2; B = (σ xx - σ yy ) / 2; C = r i 2 / r 2 ; D = r i 4 / r 4 ; θ is the angle between the radial direction of a certain point around the wellbore and the direction of the maximum horizontal principal stress, °; p i is the fluid pressure in the wellbore, MPa; p pis the formation pore pressure, MPa; r i is the wellbore radius, m; r is the distance from the wellbore center, m; α is the Biot coefficient, with a value of 1;

[0018] Step Four: Assume that the dip angle of the horizontal bedding plane is 0°, and calculate the normal stress on the bedding plane according to the rock stress around the well:

[0019]

[0020] In the formula: σ w is the normal stress on the bedding plane, MPa; β is the dip angle of the bedding plane, °;

[0021] Step Five: According to the actual formation temperature and pressure conditions, drilling fluid parameters, rock matrix and bedding fracture parameters, use Darcy's law and fracture flow theory, and through numerical simulation, obtain the bottom hole pressure difference σ wt after the drilling fluid invades along the bedding fracture during the drilling process, and its variation with the drilling cycle and radial distance. The effective normal stress σ w0 on the bedding plane during the drilling process is:

[0022] σ w0 = σ w - σ wt

[0023] Step Six: Calculate the fracture width of the bedding plane according to the effective normal stress on the bedding plane around the well:

[0024]

[0025] Beneficial effects:

[0026] 1. The present invention takes into account the influence of the effective normal stress on the bedding plane around the well, and more truly and accurately reflects the fracture width of the bedding plane at different depths of the bedding fracture during different drilling cycles.

[0027] 2. The present invention takes into account the difference between the underground overburden pressure condition and the surface environment, and significantly improves the accuracy of the calculation result of the fracture width of the bedding plane along the invasion direction after the drilling fluid invades.

[0028] 3. The present invention can adapt to different working conditions, and accurately calculates the fracture width of the bedding plane through the effective normal stress on the bedding plane after engineering disturbance, so it is applicable to the bedded formations under different conditions.

[0029] 4. The present invention takes into account the special bedding characteristics of the bedded formation, and can more truly and accurately predict the fracture width of the bedding plane at different drilling cycles and bedding fracture positions, thus providing an important guidance for the design of on-site drilling fluid plugging particles.

[0030] 5. The present invention takes into account the effective normal stress on the bedding plane along the invasion direction after the invasion of drilling fluid, and proposes a calculation formula for the width of the bedding plane fissure around the wellbore under the condition of considering the effective normal stress of the bedding plane, providing accurate data support for the design of drilling fluid plugging particles in bedded formations. Description of the Drawings:

[0031] Figure 1 is the flow chart of the present invention;

[0032] Figure 2 is the diagram of the stress of the surrounding rock of the wellbore (wellbore angle 10°);

[0033] Figure 3 is the diagram of the normal stress of the bedding plane around the wellbore (wellbore angle 10°);

[0034] Figure 4 is the distribution diagram of the bottom hole pressure difference with the radial distance (wellbore angle 10°);

[0035] Figure 5 is the diagram of the effective normal stress of the bedding plane around the wellbore (wellbore angle 10°);

[0036] Figure 6 is the diagram of the width of the bedding plane fissure around the wellbore (wellbore angle 10°). Detailed Embodiment:

[0037] The following further describes the present invention:

[0038] Refer to Figure 1 , the calculation method for the width of the bedding plane fissure along the invasion direction after the invasion of this drilling fluid is as follows:

[0039] Step 1: Conduct a confining pressure pore permeability experiment to obtain the bedding plane permeability of bedded shale under different confining pressure conditions, and fit the relationship between the confining pressure of shale and the bedding plane permeability:

[0040] K = 0.3441e -0.209σ

[0041] In the formula: σ is the confining pressure, MPa; K is the bedding plane permeability, mD; a = 0.3441, b = -0.209.

[0042] Step 2: Obtain the relationship between the confining pressure and the width of the bedding plane fissure:

[0043]

[0044] In the formula: w is the width of the bedding plane fissure, μm.

[0045] Step 3: Superimpose and calculate the stress of the surrounding rock of the wellbore according to the in-situ stress components, pore pressure, and fluid pressure in the wellbore around the wellbore:

[0046]

[0047] where: σ ij (i, j ∈ x, y, z b ) are the stress components of [σ B , MPa; σ r and σ θ are the radial stress and circumferential stress around the wellbore, MPa; A = (σ xx + σ yy ) / 2; B = (σ xx - σ yy ) / 2; C = r i 2 / r 2 ; D = r i 4 / r 4 ; θ is the angle between the radial direction of a point around the wellbore and the direction of the maximum horizontal principal stress, °; p i is the fluid pressure in the wellbore, MPa; p p is the formation pore pressure, MPa; r i is the wellbore radius, m; r is the distance from the wellbore center, m; α is the Biot coefficient, generally taken as 1;

[0048] The stress diagram of the rock around the well can be seen in Figure 2 , Figure 2 where (a) is the radial stress and (b) is the circumferential stress.

[0049] Step Four: Calculate the normal stress on the bedding plane according to the stress of the rock around the well:

[0050]

[0051] where: σ w is the normal stress on the bedding plane, MPa; β is the dip angle of the bedding plane, °;

[0052] The normal stress diagram of the bedding plane around the well can be seen in Figure 3 .

[0053] Step Five: According to the actual formation temperature and pressure conditions, drilling fluid parameters, rock matrix and bedding fracture parameters, using Darcy's law and fracture flow theory, through numerical simulation, obtain the change of the bottom-hole pressure difference σ wt with the drilling cycle and radial distance during the drilling process. The effective normal stress σ w0 on the bedding plane during the drilling process is:

[0054] σ w0 = σ w - σ wt

[0055] The bottom-hole pressure difference σ wt obtained by numerical simulation after the drilling fluid invades along the bedding fractures during the drilling processThe variation with the drilling cycle and radial distance is shown in the appendix Figure 4 . During the drilling process, the effective normal stress σ of the bedding plane w0 is shown in the appendix Figure 5 .

[0056] Step 6: Calculate the fracture width of the bedding plane according to the effective normal stress on the wellbore periphery bedding plane:

[0057]

[0058] The fracture width diagram of the wellbore periphery bedding plane is shown in Figure 6 .

[0059] The present invention establishes a relationship between the confining pressure of shale and the permeability of the bedding plane through a confining pressure pore pressure experiment; combines the relationship between the permeability of the bedding plane and the fracture width to obtain the relationship between the confining pressure and the fracture width of the bedding plane; uses the in-situ stress components, pore pressure, and fluid pressure in the wellbore around the wellbore to perform superposition calculation of the stress of the surrounding rock of the well; calculates the normal stress on the bedding plane according to the stress of the surrounding rock of the well; through numerical simulation, analyzes the variation of the bottom hole pressure difference with the drilling cycle and radial distance after the invasion of drilling fluid, and then calculates the effective normal stress of the bedding plane during the drilling process; calculates the fracture width of the wellbore periphery bedding plane according to the effective normal stress on the wellbore periphery bedding plane. The present invention considers the influence of the confining pressure condition of the bedding plane and the pressure of the invading fluid after engineering disturbance, and more truly and accurately reflects the fracture width situation of the bedding plane considering the effective normal stress factor of the wellbore periphery bedding plane, solves the problem that the prior art does not consider the continuous change of the stress around the wellbore and the fluid pressure in the bedding fracture with the project, which affects the stress state around the wellbore on the bedding plane and further affects the fracture width of the bedding, and leads to the problem that the prediction of the fracture width of the bedding plane is not accurate enough.

Claims

1. A method for calculating the width of bedding plane fractures along the invasion direction after drilling fluid invasion, characterized in that The steps include: Step 1: Conduct an overburden porosity test to obtain the bedding plane permeability of stratified shale under different confining pressure conditions, and fit the relationship between shale confining pressure and bedding plane permeability: K=yes bσ Where: σ is the confining pressure, MPa; K is the bedding surface permeability, mD; a and b are fitting coefficients; Step 2: Combine the relationship between bedding plane permeability and fracture width to obtain the relationship between confining pressure and bedding plane fracture width: Where: w is the width of the bedding plane crack, μm; Step 3: Assuming that the direction of the maximum principal stress around the well is 0° and the direction of the minimum principal stress is 90°, the ground stress components around the wellbore, pore pressure, and fluid pressure in the wellbore are superimposed to obtain the rock stress around the well: Where: r is the radial stress around the well; σ θ is the circumferential stress around the well, MPa; A=(σ xx +σ yy ) / 2; B=(σ xx -σ yy ) / 2; C = r i 2 / r 2 ; D = r i 4 / r 4 ; θ is the angle between the radial direction of a point around the wellbore and the direction of the maximum horizontal principal stress, °; p i is the fluid pressure in the wellbore, MPa; p p is the formation pore pressure, MPa; r i is the borehole radius, m; r is the distance from the borehole center, m; α is the Biot coefficient, which is 1; Step 4: Assuming the horizontal bedding plane has an inclination angle of 0°, calculate the normal stress on the bedding plane based on the rock stress around the well: Where: w is the normal stress on the bedding plane, MPa; β is the dip angle of the bedding plane; Step 5: According to the actual formation temperature and pressure conditions, drilling fluid parameters, rock matrix and bedding fracture parameters, Darcy's law and fracture flow theory are used to obtain the bottom hole pressure difference σ after the drilling fluid invades the bedding fracture during drilling through numerical simulation. wt With the change of drilling cycle and radial distance, the effective normal stress σ of the bedding plane during drilling w0 That is: s w0 =s w -s wt Step 6: Calculate the bedding plane fracture width based on the effective normal stress on the bedding plane around the well:

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