Disclosure of Invention
The invention mainly overcomes the defects in the prior art and provides a method for calculating the variable of a well casing of a hydraulic fracturing horizontal well in a natural fractured shale stratum.
The technical scheme provided by the invention for solving the technical problems is as follows: the method for calculating the well casing variable of the hydraulic fracturing horizontal well in the natural fractured shale stratum comprises the following steps:
step one, acquiring the ground stress, rock mechanical parameters, natural fracture geometric parameters and logging data of a target work area, and calculating the shear stress tau of the ground stress in the y direction according to the ground stressxyDetermining the distance x from the shaft to the center of the crack length according to the logging data;
secondly, establishing an I-II composite fracture displacement field analytical model of the superposed fluid pressure based on a complex function method;
thirdly, calculating to obtain the tangential relative displacement delta u of the crack according to the I-II composite crack displacement field analytical modelfAnd the normal relative displacement amount Deltavf;
Step four, finally according to the tangential opposition of the cracksDisplacement amount deltaufAnd the normal relative displacement amount DeltavfAnd determining the comprehensive displacement S of the fracture, namely the variable of the wellbore casing.
The further technical scheme is that a calculation formula of the shear stress tau of the ground stress in the y direction in the step one is as follows:
in the formula: τ is the shear stress of the ground stress in the y-direction, MPa; sigmaHMaximum horizontal principal stress, MPa; sigmahMinimum horizontal principal stress, MPa; theta is an included angle between the maximum horizontal main stress direction and the crack surface along the clockwise direction.
The further technical scheme is that the rock mechanical parameters comprise a rock static Young modulus E and a rock static Poisson ratio upsilon; the natural fracture geometry parameters include fracture half-length a.
The further technical scheme is that the I-II composite fracture displacement field analysis model is as follows:
in the formula: τ is the shear stress of the ground stress in the y-direction, MPa; Δ ufIs the tangential relative displacement of the crack, m; Δ vfIs the normal relative displacement of the crack, m; e is the static Young modulus of rock, MPa; upsilon is the static Poisson's ratio of the rock and has no dimension; edThe dynamic Young modulus of rock in the formation acoustic logging data is MPa; upsilon isdThe dynamic Poisson's ratio of the rock in the formation acoustic logging data is dimensionless; a is the half-length of the crack, m; x is the distance from the shaft to the center of the crack length, m; a is1、b1、c1、d1Fitting coefficients for a rock dynamic and static parameter relation curve;σbthe normal stress of the ground stress on the stress unit is MPa; p is a radical offFluid pressure in the fracture, MPa.
The further technical scheme is that the calculation formula of the comprehensive displacement S of the crack is as follows:
in the formula: Δ ufIs the tangential relative displacement of the crack, m; Δ vfIs the normal relative displacement of the crack, m; and S is the comprehensive displacement of the crack, m.
The invention has the following beneficial effects: the method can accurately calculate to obtain the variable of the well casing, can provide an analysis tool and a reference for quickly pre-judging the casing deformation risk and the severity of the horizontal well in the fracturing engineering design, and considers the measures of optimizing the well casing direction, strengthening the well cementation quality, properly reducing the discharge capacity, adopting a temporary plugging technology and the like to reasonably control the fluid pressure in the seam to reduce the casing deformation risk in the area with higher casing deformation risk judgment.
Detailed Description
The present invention will be further described with reference to the following examples and the accompanying drawings.
In the fracturing process of a HX-1 well of a certain horizontal well of a well zone, the 20 th section of bridge plug is blocked due to deformation of a sleeve during perforation linkage. The ant tracing crack prediction graph shows that possible natural cracks (the crack length is 150m, N50 degrees E) are developed near the point of resistance, the distance between the shaft and the center of the crack length is about 30m, the borehole diameter logging shows that three-level casing change occurs at the point of resistance, and the well temperature logging shows that the temperature of the point of resistance is obviously reduced. The stress in the well is relatively stable and the direction of the maximum principal stress is predicted to be 103 deg..
Therefore, the method of the invention is adopted to calculate the variable of the casing of the HX-1, and comprises the following specific steps:
s10, acquiring the ground stress, rock mechanical parameters, natural fracture geometric parameters and logging data of a target work area, wherein the data results are shown in Table 1;
TABLE 1
Length of natural seam, m
|
150
|
Diameter of open hole, mm
|
215.9
|
Diameter of the sleeve, mm
|
139.7
|
Wall thickness of the sleeve pipe mm
|
12.7
|
Poisson ratio
|
0.22
|
Young's modulus, MPa
|
43500
|
Minimum horizontal principal stress, MPa
|
60
|
Maximum horizontal principal stress, MPa
|
72 |
Step S20, calculating the shear stress τ of the ground stress in the y direction,
in the formula: tau isxyIs the shear stress of the ground stress in the y direction, MPa; sigmaHMaximum horizontal principal stress, MPa; sigmahMinimum horizontal principal stress, MPa; theta is an included angle between the maximum horizontal main stress direction and the crack surface along the clockwise direction;
s30, determining the distance x from the shaft to the center of the crack length according to the logging data;
step S40, establishing an I-II composite fracture displacement field analytical model of the superimposed fluid pressure based on a complex function method:
in the formula: τ is the shear stress of the ground stress in the y-direction, MPa; Δ ufIs the tangential relative displacement of the crack, m; Δ vfIs the normal relative displacement of the crack, m; e is the static Young modulus of rock, MPa; upsilon is the static Poisson's ratio of the rock and has no dimension; edThe dynamic Young modulus of rock in the formation acoustic logging data is MPa; upsilon isdThe dynamic Poisson's ratio of the rock in the formation acoustic logging data is dimensionless; a is the half-length of the crack, m; x is the distance from the shaft to the center of the crack length, m; a is1、b1、c1、d1Fitting coefficients for a rock dynamic and static parameter relation curve; sigmabThe normal stress of the ground stress on the stress unit is MPa; p is a radical offFluid pressure, MP, in the fracture;
wherein the above model calculation results are shown in table 2:
parameter(s)
|
E
|
υ
|
Ed |
υd |
a1 |
b1 |
c1 |
d1 |
Data of
|
43500
|
0.22
|
44257
|
0.29
|
7.81
|
-2.0449
|
-0.42
|
62088 |
Step S50, based on the above data and the following formula, HX-1 casing variable (fig. 2) can be calculated, i.e. the wellbore casing variable is 33.5 mm;
in the formula: Δ ufIs the tangential opposition of the crackA displacement amount, m; Δ vfIs the normal relative displacement of the crack, m; and S is the comprehensive displacement of the crack, m.
Comparing the borehole diameter logging results (shown in table 3), the maximum deformation of the casing calculated after the measured inner diameter data is centrally corrected is 31.8mm, the calculation error is 5.3%, and the calculation result of the method is accurate and reliable.
TABLE 3
The process for establishing the I-II compound fracture displacement field analytical model of the superimposed fluid pressure comprises the following steps:
the model assumes that: natural fracture being a superimposed fluid pressure p in the fracturefThe compound type I-II cracks of (1); fluid pressure p in the fracturefThe fracture is completely propped open under the action, the fluid pressure is equal at each position in the fracture, the fracturing fluid is not lost, and the fracture is not expanded. A fracture plane strain model can be established, and the tangential displacement of the fracture is calculated based on a complex function method.
The I-II composite crack Westergaard stress function can be expressed as:
Z(z)=ZI(z)-iZII(z)
in the formula, ZI、ZIIZ is a Westergaard stress function of the compound cracks I, II and I-II respectively;
in the above formula, the Westergaard stress function for the I, II type crack is:
in the formula, σa、σbThe normal stress of the original stress on the stress unit; τ is the shear stress of the ground stress in the y-direction.
As shown in fig. 1, any point z in polar coordinates can be represented by the following formula:
in the formula, a is half crack length m; r, r1、r2The distances m from the z point to the middle point of the long axis of the crack and the two ends of the crack respectively; beta, beta1、β2Is respectively r and r1、r2Angle to the long axis of the crack.
Substituting the formula into formula, by euler's formula, the formula can be written as:
namely, the method comprises the following steps:
wherein Z' is,
Is to differentiate and integrate the Z function.
Based on the fracture displacement calculation method deduced by Muskhellivili and the like, the I-II compound fracture displacement full-field solution can be expressed as follows:
the normal displacement and the tangential displacement of the crack can be calculated by substituting the formula:
on the fracture surface (y is 0), θ is 0 °, θ1+θ2=π,r1=a-x,r2And a + x, the relative displacement of the crack surface is as follows:
in the formula, u and v are I-II compound fracture tangential and normal displacement field full-field solutions, m respectively; u. of+、u-Is the tangential displacement of the upper surface and the lower surface of the I-II composite crack respectively, m; v. of+、v-Is the normal displacement of the upper surface and the lower surface of the I-II composite crack respectively, m; and delta u and delta v are respectively tangential and normal relative displacement of the I-II compound type crack and m.
Fluid pressure p in the fracturefThe Westergaard stress function of (a) can be expressed as:
similarly, the calculation formula of the relative displacement of the fracture surface under the action of the fluid pressure can be obtained:
the I-II composite fracture displacement field and the fluid pressure displacement field are superposed to obtain the following components:
in the formula up、vpThe displacement field full-field solution is the fracture tangential and normal displacement field full-field solution m under the action of fluid pressure; Δ up、ΔvpThe displacement is the tangential and normal relative displacement of the crack under the action of fluid pressure, m; Δ uf、ΔvfThe tangential and normal relative displacement, m, of the I-II composite fracture respectively representing the superimposed fluid pressure.
Although the present invention has been described with reference to the above embodiments, it should be understood that the present invention is not limited to the above embodiments, and those skilled in the art can make various changes and modifications without departing from the scope of the present invention.