A method for calculating in-situ fracture width of bedding plane around well in stratigraphic formation

Abstract

The present invention relates to a method for calculating the in-situ fracture width of the bedding surface around a well in a stratified formation, which comprises: step one, performing a pressure-sensitive experiment to obtain the bedding surface permeability of stratified shale under different confining pressure conditions, and fitting the relationship between the shale confining pressure and the bedding surface permeability; step two, calculating the fracture width of the bedding surface when the permeability of the bedding surface is different; step three, combining step one and step two, obtaining the relationship between the confining pressure and the fracture width of the bedding surface; step four, assuming that the maximum principal stress direction around the well is 0°, the minimum principal stress direction is 90°, and the horizontal bedding surface inclination is 0°, and the normal stress on the bedding surface is calculated according to the rock stress around the well; step five, calculating the in-situ fracture width of the bedding surface according to the normal stress on the bedding surface around the well. The present invention takes into account the unique bedding characteristics of the stratified formation, can more truly and accurately predict the fracture width of the bedding surface around the well under different bedding surface inclinations, and is suitable for stratified formations under different working conditions.

Description

Technical field:

[0001] The invention relates to the technical field of rock mechanics and oil and gas well development, and in particular to a method for calculating in-situ fracture width of bedding planes around wells in a stratigraphic formation. Background technology:

[0002] During the drilling process of the stratified formation, the interference of engineering activities will cause the bedding plane to further expand or close, which directly affects the crack width of the bedding plane. Therefore, the crack width of the stratified formation is not only related to the original conditions of the formation, but also closely related to the current stress state of the bedding plane around the well. During the drilling of oil and gas wells, in order to prevent the drilling fluid from invading the formation and causing the well wall to become unstable, it is often necessary to add plugging particles to the drilling fluid. The crack width of the bedding plane is an important basis for the design of the plugging particle size. During the development of oil and gas wells, in order to improve the production efficiency, it is often necessary to perform fracturing and other transformation operations on the stratified formation. The crack width of the bedding plane directly affects the fracturing effect and the flow path of oil and gas. Accurately calculating the in-situ crack width of the bedding plane is of great significance for guiding the design of oil and gas wells, evaluating the transformation effect, and optimizing the production strategy.

[0003] At present, there are few studies on the in-situ fracture width of the wellbore bedding surface, and there are the following problems:

[0004] 1. Indoor experiments are generally used to detect the width of rock fractures. However, due to the difference between the surface environment and the underground pressure conditions, the fracture width measurement results of the bedding surface are different from the actual underground conditions. This results in direct measurement being unable to accurately reflect the actual situation of the stratum, and there is a deviation between the measured fracture width and the actual value.

[0005] 2. The stress state around the oil and gas well has a direct impact on the in-situ fracture width of the bedding plane. However, as the drilling activity proceeds, the stress around the well continues to change, and the stress on the bedding plane around the well also continues to change. Existing technologies often find it difficult to fully consider these factors, resulting in inaccurate prediction of the in-situ fracture width of the bedding plane.

[0006] For drilling projects in stratified formations, the width of the bedding plane is crucial to the design of drilling fluid plugging particles and the effect of fracturing development. Accurately calculating the in-situ width of the bedding plane in stratified formations is the key to accurately design plugging particles, accurately predict fracturing effects, and ensure safe and efficient development of stratified reservoirs. Therefore, a scientific method is urgently needed to solve the above problems, accurately calculate the in-situ width of the bedding plane, and provide accurate guidance for guiding the design of drilling fluid plugging particles and evaluating the effect of fracturing transformation. Summary of the invention:

[0007] The purpose of the present invention is to provide a method for calculating the in-situ fracture width of the bedding surface around the well in a stratigraphic formation. This method for calculating the in-situ fracture width of the bedding surface around the well in a stratigraphic formation is used to solve the problem of inaccurate measurement or prediction of the in-situ fracture width of the bedding surface in the prior art.

[0008] The technical solution adopted by the present invention to solve the technical problem is: the method for calculating the in-situ fracture width of the bedding plane around the well of the bedding formation comprises the following steps:

[0009] Step 1: Conduct pressure-sensitive experiments 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:

[0010] K=ae bσ

[0011] Where: σ is the confining pressure, simulating the normal stress on the bedding plane, MPa; K is the permeability of the bedding plane, mD; a and b are fitting coefficients;

[0012] Step 2: Calculate the width of bedding plane cracks at different bedding plane permeabilities:

[0013]

[0014] Where: w is the width of the bedding plane crack, μm;

[0015] Step 3: Combine steps 1 and 2 to obtain the relationship between confining pressure and bedding plane crack width:

[0016]

[0017] Step 4: Assuming that the direction of the maximum principal stress around the well is 0°, the direction of the minimum principal stress is 90°, and the inclination angle of the horizontal bedding plane is 0°, calculate the normal stress on the bedding plane based on the rock stress around the well:

[0018]

[0019] Where: w is the normal stress on the bedding plane; θ is the angle between the radial direction of a point around the wellbore and the direction of the maximum horizontal principal stress; σ r is the radial effective principal stress of the rock around the well; σ θ is the effective principal stress of the rock around the well; β is the dip angle of the bedding plane;

[0020] Step 5: Calculate the in-situ fracture width of the bedding plane based on the normal stress on the bedding plane around the well:

[0021]

[0022] Beneficial effects:

[0023] 1. The present invention takes into account the influence of the stress of the bedding surface around the well, and more truly and accurately reflects the in-situ fracture width of the bedding surface at different well circumference angles.

[0024] 2. The present invention takes into account the difference between underground overburden conditions and surface environment, and significantly improves the accuracy of the calculation results of the in-situ fracture width of the bedding surface around the well.

[0025] 3. The present invention can adapt to different working conditions and accurately calculate the in-situ crack width of the bedding plane through the normal stress on the bedding plane after engineering disturbance, so it is suitable for stratified strata under different working conditions.

[0026] 4. The present invention takes into account the unique bedding characteristics of the layered strata and can more truly and accurately predict the fracture width of the bedding surface around the well at different bedding surface inclination angles, thereby providing important guidance for the design of on-site drilling fluid plugging particles.

[0027] 5. The present invention takes into account the normal stress on the bedding surface around the well in the stratigraphic formation during drilling engineering, and proposes a calculation formula for the in-situ fracture width of the bedding surface around the well under the condition of the normal stress of the bedding surface, providing effective data support for the design of drilling fluid plugging particles and the evaluation of fracturing effects in stratigraphic formations. Description of the drawings:

[0028] Figure 1 It is a flow chart of a method for calculating in-situ fracture width of bedding plane around a well in a bedding formation disclosed in an embodiment of the present invention;

[0029] Figure 2 is the relationship diagram between bedding plane permeability and confining pressure;

[0030] Figure 3 is the relationship diagram between confining pressure and bedding plane crack width;

[0031] Figure 4 is the rock stress diagram around the well;

[0032] Figure 5 This is the normal stress diagram of the bedding plane around the well;

[0033] Figure 6 This is the in-situ fracture width map of the bedding surface around the well. Specific implementation method:

[0034] The present invention will be further described below:

[0035] See also Figure 1 The in-situ fracture width calculation method of the bedding plane around the well in the stratigraphic formation includes the following steps:

[0036] Step 1: Conduct pressure-sensitive experiments to obtain the bedding plane permeability of stratified shale under different confining pressure conditions. The relationship between bedding plane permeability and confining pressure is shown in Figure 2 , fitting the relationship between shale confining pressure and bedding surface permeability:

[0037] K=0.3441e -0.209σ

[0038] Where: σ is the confining pressure, simulating the normal stress on the bedding plane, MPa; K is the permeability of the bedding plane, mD; a = 0.3441, b = -0.209.

[0039] Step 2: Calculate the width of bedding plane cracks at different bedding plane permeabilities:

[0040]

[0041] Where: w is the width of the bedding plane crack, μm.

[0042] Step 3: Obtain the relationship between confining pressure and bedding plane crack width:

[0043]

[0044] The relationship between confining pressure and bedding plane crack width is shown in Figure 3 .

[0045] Step 4: Calculate the normal stress on the bedding plane based on the rock stress around the well:

[0046]

[0047] Where: w is the normal stress on the bedding plane; θ is the angle between the radial direction of a point around the wellbore and the direction of the maximum horizontal principal stress; σ r is the radial effective principal stress of the rock around the well; σ θ is the effective principal stress of the rock around the well; β is the dip angle of the bedding plane.

[0048] The stress diagram of the rock around the well is shown in Figure 4 , (a) is radial stress, (b) is circumferential stress; the normal stress diagram of the bedding plane around the well is shown in Figure 5 .

[0049] Step 5: Calculate the in-situ fracture width of the bedding plane based on the normal stress on the bedding plane around the well. The calculation formula is as follows:

[0050]

[0051] The in-situ fracture width diagram of the well surrounding bedding plane is shown in Figure 6 .

[0052] The present invention fits the relationship between shale confining pressure and bedding surface permeability through pressure-sensitive experiment; calculates bedding surface crack width according to bedding surface permeability to obtain the relationship between confining pressure and bedding surface crack width; calculates normal stress on bedding surface according to rock stress around the well; calculates in-situ crack width of bedding surface according to normal stress on bedding surface around the well. The present invention takes into account the influence of underground overburden conditions on in-situ crack width of bedding surface after engineering disturbance, and more truly and accurately reflects the in-situ crack width of bedding surface considering stress factors of bedding surface around the well, and solves the problem that the crack width measurement results of bedding surface in indoor experiments are different from the actual underground situation, resulting in the inability of direct measurement to accurately reflect the actual situation of the formation, and the crack width obtained by measurement deviates from the actual value.

Claims

1. A method for calculating the in-situ fracture width of the bedding plane around the well in a stratigraphic formation, characterized in that The steps include: Step 1: Conduct pressure-sensitive experiments 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, simulating the normal stress on the bedding plane, MPa; K is the permeability of the bedding plane, mD; a and b are fitting coefficients; Step 2: Calculate the width of bedding plane cracks at different bedding plane permeabilities: Where: w is the width of the bedding plane crack, μm; Step 3: Combine steps 1 and 2 to obtain the relationship between confining pressure and bedding plane crack width: Step 4: Assuming that the direction of the maximum principal stress around the well is 0°, the direction of the minimum principal stress is 90°, and the inclination angle of the horizontal bedding plane is 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; θ is the angle between the radial direction of a point around the wellbore and the direction of the maximum horizontal principal stress; σ r is the radial effective principal stress of the rock around the well; σ θ is the effective principal stress of the rock around the well; β is the dip angle of the bedding plane; Step 5: Calculate the in-situ fracture width of the bedding plane based on the normal stress on the bedding plane around the well:

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