JP2787752B2 - 3D crustal stress analysis method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[Industrial application] Analyzing seismic mechanisms and analyzing fracture crustal stress beneath wellbore axis using breakout and drilling induced fractures observed in fracture prediction in hydraulic fracturing About.

2. Description of the Related Art The analysis of underground crustal stress is very important when constructing an underground structure or when excavating deep. To measure crustal stress, stress release method,
There are hydraulic fracturing method, core method, breakout method, etc., but the stress release method makes it difficult to install a strain cage at a large depth, and it is difficult to detect signals from a strain cage at a large depth. Therefore, only in the case near the surface of the ground, only the hydraulic fracturing method is used for underground deeper than several hundred meters. In addition, various methods have been proposed, such as a method of measuring this measurement in one well and a method requiring a plurality of wells. Such various methods have been proposed because it is difficult to simultaneously measure the direction and magnitude of the crustal stress, and it is also important to make some assumptions such as setting some assumptions in the analysis. This is because there is a difference, and this causes a large difference in the analysis result. For example, in the hydraulic fracturing method, the required measuring section of a well is blocked at two places by a plug (packer), and high pressure is applied to this section by a high-pressure pump to hydraulically crush the well wall and crack (crack) ), And the stress is calculated from the time history of the water pressure at this time and the created crack orientation. The crustal stress evaluation method in this method assumes that one of the crustal principal stresses is vertical ( A basic measurement method that evaluates vertical cracks (cracks that occur along well buses) under a vertical assumption, and vertical cracks grow beyond the packer, and water is pressurized from within the pressurized section. A longitudinal crack bypass type measurement method in which leakage is measured outside the section (leakage) and evaluated, or assuming that the crustal stress is distributed in proportion to the depth, There is a depth-proportional measurement method that evaluates from measurement data.

In the measurement of crustal stress by the hydraulic fracturing method exemplified above, the vertical assumption, which is a precondition for the basic type measuring method, and the depth proportional assumption, which is a precondition for the depth proportional measuring method, are used. Does not necessarily indicate the actual underground geological conditions. In particular, it is considered that these preconditions do not hold in geothermal fields where underground tectonic movement is considered active.
This cannot be applied as is. In addition, in the longitudinal crack bypass measurement method, no precondition for assuming the stress state is provided, but in order to completely determine the stress at one depth, each well in two wells with different inclinations is required. It requires enormous cost, time and labor because it requires two pieces of hydraulic fracturing data, and is impractical and impractical except when using a well with a small hole and small depth using a tunnel wall. Things.

Means for Solving the Problems The present invention solves the above-mentioned problems when analyzing the crustal stress, and is particularly useful for designing hydraulic fracturing on site, in terms of speed and ease. The purpose of the present invention is to analyze underground three-dimensional crustal stress from one well logging data. In other words, at least six parameters are required as parameters for determining three-dimensional underground stress, but the borehole televiewer logging (BHTV logging) and the FMI (formation micro imager) logging, etc. Since the state of the crack along the axis can be easily observed, the crack observed at this BHTV logging or FMI logging at one depth has two observation values of θ _m and γ _m . Two observations are obtained.
Therefore, under the condition that the stress ratio is constant in the depth direction, 3
If observation results are obtained under three different well conditions,
Dimensional underground stress can be uniquely determined. Here, the cracks along the well axis are crushing of the well wall due to mud pressure, excessive pump pressure during mud feeding, and thermal stress on the well during excavation. Occurs by a mechanism similar to the cause of However, unlike cracks caused by hydraulic fracturing, these cracks were not created by using a packer and intentionally applying high pressure to the measurement section, and were relatively small at the same level as the rock fracture criteria. has been made in nature by the well drilling, this point is at a place different from the crack of hydraulic fracturing, and for this reason γ _m is easily dominated by the maximum compressive stress, the crack of the wellbore axis The angle (γ _m ) is dominant in stress and rock fracture strength. Further, the crack along the well axis is formed symmetrically in the well axis direction where the tensile stress becomes maximum on the well wall, and then propagates in the direction of the maximum compressive principal stress of the crust. Therefore, three-dimensional crustal stress can be analyzed using the observation results of θ _m and γ _m at three different well conditions. Therefore, in the present invention, as the three different well conditions, the orientation and inclination of the well are focused, and the underground stress at the site is estimated from the observation results at three or more different orientations and inclinations. . In particular, geothermal wells are generally drilled into inclined wells, and the wells are complicated, and the direction and inclination differ depending on the depth. Therefore, the observation results of the position of the crack along the well axis and the angle of the crack with the well axis at three or more different depths in one inclined well drilled in the geothermal field were obtained. If known, the crustal stress at that point can be analyzed. Regardless of the number of depths, a total of six results are obtained by combining the core test results, AE observation results, hydraulic fracturing test results, overcoring measurement / analysis results, breakout analysis results, etc. of the well. By obtaining the above observations, three-dimensional underground stress can be determined. Therefore, the present invention provides, for example, a borehole televiewer (BHTV), an optical scanner (borehole television), a formation microimager (FMI), a formation microscanner (FMS), a molding packer, or the like in one observation well. The position of the crack along the well axis (θ _m ) and the angle of the crack to the well axis (γ _m ) On the other hand, while measuring, the magnitude (σ ₁ ) and its orientation (φ ₁ ) and inclination (θ ₁ ) of the principal stress 1 underground at that site, the principal stress 2 (σ ₂ ) and its orientation (φ ₂ ) and inclination ( θ ₂ ), the magnitude of principal stress 3 (σ
₃ ) and at least six values of its orientation (φ ₃ ) and inclination (θ ₃ ), assuming a unique three-dimensional crustal stress field, and determining the position of the crack along the well axis at each depth (θ _m ) and the angle (γ _m ) between the crack and the well axis are calculated by the following equation.
The three-dimensional crustal stress specified by the six values of the magnitude, orientation, and inclination of each of the principal stresses in which the obtained θ _m and γ _m best approximate the measured values is obtained by trial and error, least square method, Alternatively, analysis is performed by a statistical method.

(Equation 2) Further, for example, in one observation well, the position of a crack along the well axis (θ _m ) and the angle formed by the crack with the well axis (γ _m ) are along the well axis less than 3 depths. If only the position of the crack (θ _m ) and the angle of the crack to the well axis (γ _m ) were measured, the missing measured values were obtained from the same well, core test results, AE Observation results, hydraulic fracturing test results, overcoring measurement / analysis results,
It is characterized in that it is obtained by assuming the three-dimensional crustal stress field by supplementing with at least one or more actually measured values among the breakout analysis results and the like. That is, the position of a crack along one observation well axis (θ _m ) and the angle of the crack with the well axis (γ _m ) along the well axis with a depth of less than 3 depths (γ _m ) θ _m ) and the angle (γ _m ) between the crack and the well axis were measured, the insufficient measured values were used as the core test results, AE observation results, and hydraulic fracturing test results for the well. By combining data such as over-coring measurement / analysis results, break-out analysis results, etc., a total of six or more observations can be obtained and identified by six values of the magnitude, orientation, and inclination of each principal stress The three-dimensional crustal stress field is set, θ _m and γ _m are calculated, and the position of the observed crack (θ _m ) and the angle between the crack and the well axis (γ _m ) are the best. Three-dimensional crustal principal stress specified by the six values of the magnitude, orientation, and inclination of each principal stress set above that is approximated The trial and error, by the least squares legal or statistically determined that, is that analyzing the three-dimensional situ stress. For example, the position (θ _m ) of a crack along the well axis observed from one well and the angle (γ _m ) formed by the crack with the well axis differ in the direction and inclination of the well axis. When obtained at depth, what is necessary for the above analysis is the magnitude (σ ₁ ) of the principal stress 1 and its orientation (φ ₁ ) and inclination (θ ₁ ), the magnitude (σ ₂ ) of the principal stress 2 and its Since there are six directions (φ ₂ ) and the magnitude of the principal stress 3 (σ ₃ ), two observation values are insufficient. Then, it is possible to determine azimuth and inclination of the minimum principal compressive stress from observations AE, when considering this, among the above parameters, the phi ₁ and theta ₁ is known, is intended to determine, sigma _1, σ ₂ , σ ₃ and φ ₂
It becomes four. Therefore, three-dimensional crustal stress can be uniquely determined by changing these four parameters and approximating the set of (θ _m , γ _m ) observed at two depths. Therefore, the invention according to claim 2 is based on observation of a pit wall using a borehole televiewer (BHTV), an optical scanner (borehole television), a formation microimager (FMI), a formation microscanner (FMS), a molding packer, or the like. From the results, the position of the crack along the well axis (θ _m ) and the angle formed by the crack with the well axis (γ _m ) were obtained. Results, hydraulic fracturing test results, over-coring measurement analysis results, break-out analysis results, etc., supplemented with at least one or more results, acquired at least six measured values, and the position of the crack along the well axis (θ _m ) And the angle (γ _m ) formed by the crack with the well axis is calculated by the following equation, and the obtained θ _m and γ _m best approximate the above measured values. By calculating the approximate value, the in-situ three-dimensional crustal stress is analyzed.

(Equation 3)

[Action] Cracks along the pit axis analyzed by BHTV logging and FMI logging, etc., are developed globally along the pit axis, and their orientation (θ _m ) is determined by the orientation core. It is in harmony with the direction of the maximum compressive principal stress of the underground stress estimated by the DSCA method used, and this crack is composed of a set of cracks that are offset from the direction of the pit axis by a certain angle. The shift of the fissure from the pit axis (γ _m ) is considered to have developed under the influence of three-dimensional underground stress and rock strength, so that these (θ _m ) and (γ _m )
However, in a single inclined well, even if the orientation and inclination of the well are different at three or more depths, or even less than three depths, it can be supplemented with actual measurement values obtained from other actual measurements of the same well. If, as a result, the values of the six parameters at three or more depths are determined, it can be estimated that these are data from three different wells, and based on this, it is possible to analyze the three-dimensional underground stress field. Becomes

1 and 2 show cracks along the well axis that appear on the wall of a drilled well. FIG. 1 shows the fracture along the well axis observed by the borehole televiewer (BHTV), and FIG.
The crack along the well axis indicated by 1138.25 m indicates the drilling induced fracture, and the crack along the well axis indicated by the mark indicates the breakout (wall wall). ). FIG. 1B shows a stress distribution at 1137.53 m (cross-sectional view). This example shows that the maximum compressive principal stress is applied in the northwest-southeast direction and the minimum compressive principal stress is applied in the northeast-southwest direction based on true north. However, since the discussion of the maximum principal stress in the breakout assumes that one of the principal stresses is at the well axis, it represents the maximum and minimum compressive principal stresses in a plane perpendicular to the well axis. ing. Also, FIG.
It shows the pit wall at a depth of 1075m to 1077m obtained from one logging, and the wall surface from north (N) to east (E) side, and east (E) side to south (S), respectively, based on true north. The wall surface extending from the west (W) side to the north (N) side, and the wall surface extending from the south (S) side to the west (W) side are shown. In FIG. 2, the wall surface from the east (E) side to the south (S) side and the wall surface from the west (W) side to the north (N) side are each separated by θ _m with respect to true north. The position and also at an angle of γ _m with respect to the well axis indicate that a fracture runs along the well axis longitudinally. like this,
Since the state of the fracture (crack) along the well axis can be observed by BHTV logging or FMI logging, it is assumed that the stress changes linearly in the depth direction, and the above θ _{m at} three or more depths is assumed. And γ _m are obtained, then 3
Dimensional underground stress can be analyzed. FIG. 3 is a conceptual diagram of a method of calculating the orientation and inclination with respect to the pit axis at each depth at three locations at different depths of one inclined well, and analyzing the underground stress by this. In the figure, N, S, W, E are:
Shows north, south, west, and east respectively, 1 indicates the pit, 2,
3, 4 are Depth1, Depth2, Depth3
Fig. 4 shows the concept of a downhole wall in. 5a and 5b show a fracture (crack) appearing on one of the wall surfaces of the pit wall 2 and a fracture (crack) appearing on the other wall surface. Similarly, in the figure, 6a,
6b indicates a crack appearing on one of the wall surfaces of the pit wall 3 and a crack appearing on the other wall surface, and 7a and 7b indicate a crack appearing on one of the wall surfaces of the pit wall 4 and a crack appearing on the other wall surface. Is shown. Θ _m indicates the position of the fracture (crack) with reference to true north, and γ _m indicates the angle between the direction perpendicular to the maximum tensile stress in the wall surface of the fracture and the well axis. Now, a coordinate system as shown in FIG. 4 is used, σ ₃ is set in the vertical direction, σ ₁ and σ ₂ are set in a plane perpendicular to σ ₃ , and at this time, the azimuth inclination, water pressure and vertical stress of the well are changed. Is expressed by the following equation 4 (tangential stress on the wall), σ _m (maximum tensile stress in the wall)
And γ _m (the angle between the direction perpendicular to the maximum tensile stress and the well axis) are simulated.

(Equation 4) The calculation formulas are described in Leeman (1969) and Daneshy (197
Based on the policies and formulas indicated by 3). FIG.
This figure shows a coordinate system based on this concept.
Is a coordinate system when 3 is a vertical direction, and 1 ′, 2 ′,
3 ′ is a coordinate system when 3 ′ is aligned with the well axis (ζ). In the coordinate system of FIG. 4, in a rectangular coordinate system in which the 3 ′ axis is aligned with the well axis (ζ), the stress on the wellbore with respect to the input is expressed as follows using a cylindrical coordinate system.

(Equation 5) Further, in the equation 4, the maximum tensile stress sigma _m and sigma angle gamma _m in a direction perpendicular and wellbore axis _m of Anakabe is expressed as follows.

(Equation 6) The position theta _m when the vertical crack is formed is obtained as follows. That is, in the anti-wall (Shitazeta plane), since sigma _m is given by the position having the maximum value, therefore, obtains the value theta _m of dσ _m / dθ = 0 becomes theta. The obtained theta _m is the position of the longitudinal crack. Also, the angle of the first crack (γ _m ) is the angle between the direction perpendicular to the maximum tensile stress and the well axis when the stress shows the maximum value in the borehole wall surface ((θζ plane). , The angle of the first crack (γ _m ) can be obtained by the following equation.

Equation 7 FIG. 5 illustrates stress and shear, which are parameters in the equation. In the present embodiment, analysis by formula calculation or the like can be obtained by many trials and errors, by the least squares method, or by a statistical method, but can be calculated by a computer according to a flowchart shown in FIG. It is something that may be allowed. That is, FIG. 6 is a flowchart of the stress calculation program. FIG.
As shown in the figure, the initial input values of the program are: a. 3-way stress value, 2-way orientation, 1-way tilt b. Water pressure c. Poisson's ratio d. Well orientation / inclination. The output is the following at arbitrary arbitrary intervals.

(Equation 8) (Stress in the borehole circumferential direction)

[Equation 9] (Stress in the borehole axial direction)

(Equation 10) (Stress on the θζ plane) d · σ _m (Max) (maximum tensile stress in the wall) e · σ _m (Min) (maximum compressive stress in the wall) f · γm (angle between the borehole axis and the fracture) As a check in the calculation process, in tensor rotation, calculate the stress invariant before and after the calculation, it can be confirmed that they match, and when finding the main stress, check the normalized eigenvector Can also. As an example of the present invention, first, we seek Sen City Byi tee due to a change in theta _m and gamma _m due to the change in the change in the stress field and fracture criterion was an overall picture of changes in the theta _m and gamma _m. Next, assuming that the stress ratio is constant in the depth direction, the change of θ _m and γ _m with respect to the depth when the direction and inclination of the well were changed in the depth direction was obtained. Finally, this and theta _m and gamma _m obtained, considering matching of the actual data to determine the approximate value. Hereinafter, a specific method will be described. (Example 1) A simulation in which stress was used as a parameter was performed. A model as shown in FIG. 7 was examined as a basic model. (Case 1) σ ₁ = 216 kg / cm ² σ ₂ = 135 kg / cm ² σ ₃ = 270 kg / cm ² (Case 2) σ ₁ = 162 kg / cm ² σ ₂ = 135 kg / cm ² σ ₃ = 270 kg / cm ² (Case 3) σ ₁ = 270 kg / cm ² σ ₂ = 243 kg / cm ² σ ₃ = 297 kg / cm ^{2 In} this basic model, the effects of the well orientation and the well inclination of γ _m were examined. Assuming that there is no shear,
Furthermore, normal fault type (Normal Fauling Regine: σ ₂ <σ ₁
A stress field of <σ ₃ ) was assumed. It should be noted that the study is performed using γ _m when the rock fracture criterion (σ _m ) at θm becomes 0. FIG. 8A shows the results of plotting γ _m using the well orientation and inclination in the cases 1 to 3 of the above embodiment as parameters. In each case, γ _m also changed as the well orientation and inclination changed. For example, as shown in the case 1 of FIG. 8A, when the well orientation is 60 ° and the inclination of the well is 10 ° and 20 °, there is a difference of about 5 ° in the value of γ _m . You can see that. From this, the difference of 5 ° is
The value of γ _m obtained from the well direction and inclination in the vicinity can be analyzed with relatively high accuracy. However, the 30 ° contours in Case 1 are quite extensive, and the final analysis results are more arbitrary if the γ _m observed in this case is around 30 °. FIG. 8B is a graph plotting changes in water pressure in each case. This shows that as the well approaches the minimum principal stress direction in the plane, the water pressure for pulling out from the well wall increases. (Embodiment 2) Next, the dependence of θ _m and γ _m when the fracture criterion is used as a parameter will be described for Case 1 of Embodiment 1.
The test was performed for two cases where the fracture criterion (σ _m ) was 0 kg / cm ² and 50 kg / cm ² . First, FIG.
And changes in σ _m (the maximum tensile stress in the wall surface) and γ _m (the angle between the borehole axis and the fracture) expressed by Equation 11 when the angle is 30 ° and the inclination is 30 °.

[Equation 11] At the locations indicated by arrows in FIG. 9, σ _m is 0 kg / cm ² and 50 k.
g / cm ² , where destruction of the pit wall will occur, suggesting that θ _m and γ _m must be referenced at this arrow. According to this figure, even if the fracture criterion changes from 0 to 50 kg / cm ² at the location of the arrow,
position of theta _m may know that hardly changed. Therefore, regarding θ _m , the destruction criterion is not so sensitive, and considering the reading error of the actually measured value, 0 kg / cm ² and 50 kg
The level is the same at kg / cm ² . FIG. 10 shows a simulation result of γ _m . FIG. 10 (a) shows that when the fracture criterion is 0 kg / cm ² , the well orientation is 0 to 90 °, and the well inclination is 0 to 9 °.
This is a plot of γm when the angle is changed at intervals of 5 ° within a range of 0 °. Similarly, FIG. 10B is a plot result of γ _m when the fracture criterion is 50 kg / cm ² . 10 (a) and 10 (b) that the destruction criterion is 0 to 50kg.
Increasing the / cm ^2, the value of is unchanged tendency contour gamma _m is day become smaller. This is γ _m
Is changed, and it is shown that γ _m cannot be obtained unless this destruction criterion is uniquely determined. However, the observed cracks were not created under high pressure such as hydraulic fracturing, and γ
The rate of change of _m with respect to the failure criterion changes only in the range of 0 to 7.5 ° even when the failure criterion increases from 0 to 50 kg / cm ² , which is within the error of reading the observed value. Considering both things considered, the destruction criterion is 0 kg
/ cm ² is no problem. Thus, when considered together that there is no change in dependence of theta _m due to changes in the previous failure criterion, the calculation result of the wellbore azimuth, three different depths or more observations inclination (θ _m, γ _m) pairs (Note If the depth is less than 3 depths, it may be supplemented with other data such as a core test). (Embodiment 3) Next, assuming that the stress ratio in the depth direction is constant in case 1 of FIG. 7, θ _m and γ _m with respect to the depth direction when the well orientation and inclination are changed for each depth are described. Seeking change. In this simulation, σ ₃ is set to a rock density (ρ) of 2.7 g / cm ³ and added to the initial value according to the depth difference, and the stress ratio is constant (σ ₃ : σ ₁ : σ ₂ =
1: 0.8: 0.5). The initial value of σ _v is the static rock pressure (ρz = 2.7 g / cm ³ × 1000 m).
FIG. 11 shows the result of plotting γ _m obtained in this simulation. As is clear from FIG. 11, if the stress ratio does not change, there is no significant change in the γ _m contour. That is, it can be seen that γ _m depends only on the bearing and inclination of the well. If the stress ratio does not change with depth, the position of θ _m depends only on the wellbore direction and inclination. Therefore, when approximating (θ _m , γ _m ) measured in the depth direction, one depth If the contours of the calculation results of θ _m and γ _m are prepared, it can be understood that the contours can be referred to even at different depths of the azimuth and inclination of the well. Table 1 shows an example of the analysis. This means that the wellbore direction and inclination are 10 ° at 1000m each, and 5
6 is a table showing changes in γ _{m and the} like when the azimuth and the inclination are increased for each ゜.

[Table 1] FIG. 12 shows a plot of the results of Table 1.
As shown in FIG. 12, it can be understood that γ _m tends to increase in the depth direction, and θ _m shifts from the in-plane maximum compressive principal stress direction in the depth direction and approaches the in-plane minimum pressure principal stress direction. I can know that. Here, when an error is reading theta _m and gamma _m measured values to ± 5 °, the theta _m, 1
300m shallower than, for γ _m, 1200m deeper is, ± 5
°, but for example, 1100m and 1300
m at 200 m intervals, as at a depth of _m
Is 4.6 °, and γ _m is 6.1 °, so that analysis at three depths of 1000 m, 1100 m and 1300 m is possible. Also, for example, at a depth of 1200 m, 13
In the analysis at three depths of 00 m and 1400 _m , there is not much difference between θ _m and γ _m , so that the analysis result becomes more arbitrary. Also, when discussing the magnitude of stress, it is necessary to correctly evaluate the hydraulic pressure during drilling of a well and thermal stress in the case of a geothermal well. , Inclination, can be applied. (Embodiment 4) Next, actual acquired data (Table 2) is shown.
Here, a simulation was performed to approximate the measured values.

[Table 2] The data was obtained by the TG-2 well excavated in the Yunomori area of Matsuo-mura, Iwate-gun, Iwate Prefecture by the NEDO project. I have. The TG-2 well was kicked off at a depth of around 200 m and bored at around 2,000 m.
° (TN), 28 ° 50 ′ inclined well. TG-
The simulation at Well 2 is based on the following assumptions:
It is made up. The maximum compressive principal stress is determined at 240 kg / cm ² at 880 m based on the test results of the core taken around 880 m. The stress ratio in the depth direction does not change. Rate of increase in the depth direction of the stress with respect to what is almost vertically best in each stress is added at about 20kg / cm ² /100m(2.0g/cm ^3). Based on the above assumptions, trial and error calculated result, the orientation of the assumed maximum compressive principal stress were found deviates significantly from theta _m of actual measurement, the measured than to not optimal approximation is obtained, the theta _m It was found that the vicinity of the position became the direction of the maximum compressive principal stress. Table 3 shows an analysis result when the best approximation is obtained between the actually measured value and the calculated value shown in Table 2.

[Table 3] FIG. 13 shows a plot of the comparison between the analysis result and the actually measured value. From this figure, it can be seen that the analysis result and the measured value are extremely similar, and the direction and inclination of each stress in the analysis result are reliable. The analysis results show that the minimum compressive principal stress is closest to the vertical, indicating that the stress field around the TG-2 well is of the reverse fault type, and is consistent with the wide-area stress field, so that the reliability is high. In addition, the results were consistent with the stress analysis results of the core test at TG-2 by the DSCA method (Differential StrainCurve Analysis).

According to the present invention, underground crustal stress can be analyzed only by drilling one well. Especially,
In deep wells, stress analysis at high depths is possible, which greatly contributes to elucidation of the mechanism of earthquake occurrence and prediction of fracture progress in hydraulic fracturing. Also, without the need for large equipment such as packers and pumps,
Since drilling a single well is sufficient, it is also economically efficient, and is particularly excellent in analyzing deep underground crustal stress. In addition, if there is data from a single well, it is possible to easily determine the underground crustal stress, and because it is easy to analyze, analysis at the excavation site is also possible. For wells intended to increase fluid collection, the benefits are very significant.

[Brief description of the drawings]

FIG. 1 is a borehole televiewer (BHTV)
Showing fractures along the well axis observed by SAR

FIG. 2 shows the depth 1075 obtained from the FM1 logging.
The figure which shows the pit wall in m-1077m

[Fig. 3] Fig. 3 is a conceptual diagram of a method for analyzing the underground stress by obtaining the azimuth and inclination of a single inclined well at three different depths with respect to a pit axis at each depth.

FIG. 4 shows that σ ₃ is the vertical direction, σ ₁ and σ ₂ are in a plane perpendicular to σ ₃ , and the azimuth of the well, water pressure and vertical stress are changed to change the tangent to the wall surface. Diagram showing a coordinate system for simulating stress, the maximum tensile stress in the wall, and changes in the angle between the well axis and the direction perpendicular to the maximum tensile stress

FIG. 5 is a diagram illustrating stress and shear.

FIG. 6 is a flowchart of a stress calculation program.

FIG. 7 is a diagram showing a basic model of a simulation using stress as a parameter;

FIG. 8 is a view showing a result of plotting changes in Y _m and P _m using the pressure ratio in the cases 1 to 3 as parameters,

FIG. 9 is a graph showing the equation (11) (stress in the borehole circumferential direction) and σ when the borehole orientation is 50 ° and the inclination is 30 °.
graph showing changes in _m (wall within the maximum tensile stress) and gamma _m (angle between the borehole axis and the fracture)

FIG. 10 (a) shows that the breaking criterion (γ _m ) is 0 kg / cm.
When ^2, the wellbore azimuth 0 to 90 °, Fig diagram 10 showing the results of plotting the gamma _m when went varied 5 ° increments in the range of wellbore inclination 0 to 90 ° (b), the Figure destruction criteria (gamma _m) shows a plot result of gamma _m when the 50 kg / cm ²

FIG. 11 is a graph showing the case where the stress ratio in the depth direction is assumed to be constant for case 1 of the embodiment, and θ _m and γ _m with respect to the depth direction when the well orientation and inclination are changed for each depth. Diagram showing the result of plotting γ _m obtained by simulation of change

FIG. 12 shows wellbore azimuth and inclination of 10
And 10 ° with 00m, shows every 5 ° in the depth direction, the results of plotting the change in the gamma _m like when went increasing orientation and tilt

FIG. 13 is a diagram in which a comparison between an analysis result and an actually measured value is plotted.

[Description of Signs] 1 ... pit mark, 2 ... pit wall at Depth1, 3 ... pit wall at Depth2, 4 ... pit wall at Depth3, 5a, 5b ... wall surface of pit wall 2 6a, 6b: fractures (cracks) appearing on the wall surface of the pit wall 3; 7a, 7b: fractures (cracks) appearing on the wall surface of the pit wall 4 Well axis σ _m・ ・ ・ Maximum tensile stress of the pit wall γ _m・ ・ ・ Angle between the direction perpendicular to the maximum tensile stress of the pit wall and the well axis a ・ ・ ・ Stress in three directions, two directions, one direction Incline b ・ ・ ・ Hydraulic pressure c ・ ・ ・ Poisson's ratio d ・ ・ ・ Bore direction / incline

Continuation of front page (72) Inventor Kazuo Hayashi 2-1-1 Katahira, Aoba-ku, Sendai City Institute of Fluid Science, Tohoku University (58) Fields investigated (Int. Cl. ⁶ , DB name) G01L 5/00

Claims (2)

(57) [Claims] 1. A borehole televiewer (BHTV), an optical scanner (borehole television), and a formation micro for cracks in a wellbore at three or more depths with different well orientations obtained from at least one inclined well. Using an imager (FMI), a formation microscanner (FMS) or a molding packer, the position of a crack along the well axis (θ _m ) and the angle of the crack with the well axis (γ _m ) are measured. In the first step, the magnitude (σ ₁ ), orientation (φ ₁ ), inclination (θ ₁ ), and magnitude (σ ₂ ) of the main stress 1 of the earth's crust are measured with respect to the actually measured crack. ), Its orientation (φ ₂ ) and inclination (θ ₂ ), its principal stress 3 (σ ₃ ), its orientation (φ ₃ ) and its inclination (θ ₃ ) are arbitrarily set and any value is set. 3D ground Using a second step of assuming a shell stress field, and the value of an arbitrary three-dimensional crustal stress field assumed in the second step, the depth of the crack actually measured in the first step by the following equation: Crack location along the well axis at the same depth (θ _m )
And a third step of calculating an angle (γ _m ) between the crack and the well axis, the position (θ _m ) of the crack along the well axis and the crack determined in the third step Angle with the well axis (γ _m )
The above six values are calculated so that the best approximation is made to the actually measured position of the crack along the well axis (θ _m ) and the angle of the crack with the well axis (γ _m ). A three-dimensional crustal stress analysis method, comprising: (Equation 1) 2. When the position (θ _m ) of a crack along the well axis measured from the first step and the angle (γ _m ) formed by the crack with the well axis are less than 3 depths, Insufficient measured values are obtained from at least one of core test results, AE observation results, hydraulic fracturing test results, overcoring measurement / analysis results, breakout analysis results, etc. obtained from the same well. In addition, by obtaining at least the above-mentioned six or more measured values, a three-dimensional crustal stress field is assumed, and using this assumed value, a pit having the same depth as the crack depth actually measured in the first step is used. The position (θ _m ) of the crack along the well axis and the angle (γ _m ) between the crack and the well axis are determined, and the position (θ _m ) of the crack along the well axis and the required The angle (γ _m ) between the crack and the well axis is determined by the position (θ _m ) of the crack along the well axis. 4. The three-dimensional crustal stress analysis method according to claim 3, wherein the six values are calculated and calculated so as to most approximate the angle (γ _m ) between the crack and the well axis.