JPH07301574A - Three-dimensional crustal stress analyzing method - Google Patents

Abstract

PURPOSE:To analyze the underground crustal stress using only one boring by analyzing the three-dimensional crustal stress at more than two points of different depth along the axis of boring based on the observation results of position and angle of cracks thereat. CONSTITUTION:Among six parameters required for determining the three- dimensional underground stress, two observation values, that is, the position of a crack extending along the axis of boring at some depth and the angle thereof with respect to the axis of boring can be acquired by observing a bore hole televiewer detection layer and a formation micro-imager detection layer. When observation results are obtained for three different boring conditions in the depth direction while setting a constant stress, the three-dimensional underground stress can be determined. For example, at three points Depth 1, 2, 3 of different depth in one boring, the position thetam of a crack with reference to the due north for the axis of boring at each depth is determined along with the angle num thereof between the axis of boring and the direction perpendicular to the maximum tensile stress in the wall face thus analyzing the underground crustal stress.

Description

Detailed Description of the Invention

[Industrial application] Recently, a method of analyzing underground crustal stress using breakout and drilling induce fracture along the well axis observed in the elucidation of earthquake generation mechanism and prediction of fracture progress in hydraulic fracturing Regarding

2. Description of the Related Art Underground crustal stress is very important to analyze when constructing an underground structure or when performing deep drilling. To measure crustal stress, the stress release method,
Although there are hydraulic fracturing method, core method, breakout method, etc., the stress release method makes it difficult to install a strain cage at a large depth, and it is difficult to detect a signal from a large depth strain cage. Therefore, the hydraulic fracturing method is only used for underground below a few hundred meters deep only near the surface of the earth. Further, various methods have been proposed, such as a method of measuring this measurement with one well and a method requiring a plurality of wells. Such various methods have been proposed, but it is difficult to measure the direction and magnitude of the stress in the crust at the same time, and the analysis also makes some assumptions. This is because there is a difference, which results in a large difference in the analysis result. For example, in the hydraulic fracturing method, the required measurement section of the well is blocked at two upper and lower locations by a plug (packer), and high pressure is applied to this section by a high-pressure pump to hydraulically fracture the well wall and cause cracks (cracks). ) Is calculated and the stress is calculated from the time history of water pressure at this time and the created crack orientation. In the crustal stress evaluation method in this method, it is assumed that one of the crustal principal stresses is vertical ( A basic measurement method to evaluate vertical cracks (cracks that occur along the bus of a well) under vertical assumptions), and to grow vertical cracks beyond the packer and pressurize water from within the pressurization section. Longitudinal crack bypass type measurement method in which leakage is measured outside the section and evaluation is performed, or crustal stress is assumed to be distributed in proportion to depth, and this proportional coefficient is calculated for many Ps and Psb. There is a depth-proportional measurement method that evaluates from measured data.

Problems to be Solved by the Invention In the measurement of crustal stress by the hydraulic fracturing method illustrated above, the vertical assumption which is a prerequisite for the basic type measuring method and the depth proportional assumption which is a prerequisite for the depth proportional measuring method. Does not necessarily indicate actual underground geological structural conditions. Especially, in the geothermal area where the underground structural movement is recognized to be active, it is considered that these preconditions are not satisfied,
This cannot be applied as it is. In addition, in the vertical crack bypass type measurement method, there is no precondition for assuming the stress state, but in order to completely determine the stress at one depth, two wells with different inclinations should be used. Since hydraulic fracturing data at two locations is required, enormous cost, time, and labor are required, and it is impractical and impractical except when using a well with a small hole diameter and a small depth using a tunnel wall. It is a thing.

This invention solves the above-mentioned problems in the analysis of the crustal stress, and in particular, is designed for hydraulic fracturing in the field, and is practical in terms of speed and ease. Therefore, the present invention intends to analyze the underground three-dimensional crustal stress from one well logging data. That is, at least six parameters are required as parameters for determining the three-dimensional underground stress, but the borehole televiewer logging (BHTV logging) and FMI (formation micro imager) logging, etc. Since the state of cracks along the axis can be easily observed, regarding the cracks that can be observed by this BHTV logging or FMI logging, the observed values of the cracks are 2 _m of θ _m and γ _m at one depth. One observation is acquired.
Therefore, under the condition that the stress ratio is constant in the depth direction, 3
If the observation results under two different well conditions are obtained, then
Dimensional underground stress can be uniquely determined. Here, the crack along the well axis is the crushing of the well wall due to mud pressure, excessive pump pressure during mud sending and thermal stress to the well during excavation, and basically it is hydraulic crushing. Occurs by a mechanism similar to the origin of. However, this crack was not created like a hydraulic fracturing crack by using a packer and intentionally applying a large pressure to the measurement section, and it is relatively small at the same level as the rock fracture standard. It is naturally created by well drilling, and this point is different from the crack of hydraulic fracturing.For this reason, γ _m easily dominates the maximum compressive stress, and that crack is The angle (γ _m ) formed is dominant in stress and fracture strength of rock. The cracks along the well axis are formed symmetrically in the well axis direction in the well wall where the tensile stress is maximum, and then propagate in the direction of maximum compressive principal stress in the crust. Therefore, the three-dimensional crustal stress can be analyzed using the observation results of θ _m and γ _m under three different well conditions. Therefore, in the present invention, focusing on the orientation and inclination of the well as three different well conditions, the in-situ underground stress is estimated from the observation results at three or more different orientations and inclinations. . In particular, geothermal wells are generally excavated in inclined wells, and the well traces are complicated, and the azimuth and inclination differ depending on the depth. Therefore, the observation result of the position of the crack along the well axis and the angle between the crack and the well axis at three or more different depths in one tilted well excavated in the geothermal field is If it becomes clear, the crustal stress at that point can be analyzed. In addition, regardless of the number of depths, a total of 6 data can be obtained by combining data such as core test results, AE observation results, hydraulic fracturing test results, overcoring measurement / analysis results, and breakout analysis results for the same well. By obtaining the above observed values, the three-dimensional underground stress can be determined. Therefore, the present invention uses, for example, a borehole televiewer (BHTV), an optical scanner (borehole television), a formation microimager (FMI), a formation microscanner (FMS), or a molding packer in one observation well. , The crack position along the well axis (θ _m ) and the angle (γ _m ) formed by the crack with respect to the well axis for each well wall at different depths of 3 or more with different well orientation and inclination While actually measuring, the magnitude (σ ₁ ) of the principal stress 1 underground and its orientation (φ ₁ ) and inclination (θ ₁ ) and the principal stress 2 (σ ₂ ) and its orientation (φ ₂ ) and inclination ( θ ₂ ), the magnitude of the principal stress 3 (σ
₃ ), its orientation (φ ₃ ) and inclination (θ ₃ ) are set to at least 6 values to assume a unique three-dimensional crustal stress field, and the position of the crack along the well axis at each depth (θ _m ) and the angle between the crack and the well axis (γ _m )
The three-dimensional crustal stress specified by the six values of the main stresses, the direction, and the inclination, at which the obtained θ _m and γ _m are the best approximation to the above-mentioned measured values, are trial and error, least squares law, Alternatively, it is analyzed by a statistical method.

[Formula 2] Further, for example, in one observation well, the position of the crack along the well axis (θ _m ) and the angle (γ _m ) formed by the crack with the well axis are along the well axis of less than 3 depths. When only the position of the crack (θ _m ) and the angle of the crack with respect to the well axis (γ _m ) are measured, the insufficient measured value is obtained from the same well, core test results, AE Observation results, hydraulic fracturing test results, overcoring measurement / analysis results,
It is characterized in that the three-dimensional crustal stress field is assumed and obtained by supplementing it with at least one measured value out of the breakout analysis result and the like. That is, the position (θ _m ) of a crack along the axis of one observation well and the position (θ _m ) of the crack with the axis of the well (γ _m ) along the axis of the well below 3 depth ( θ _m ) and the angle (γ _m ) formed by the crack with respect to the well axis are measured, the insufficient actual measurement value is used as the core test result, AE observation result, hydraulic fracturing test result of the well. By combining data such as measurement results of overcoring and analysis, and breakout analysis results, a total of 6 or more observation values can be acquired and specified by 6 values of each main stress magnitude, direction, and inclination. The three-dimensional crustal stress field is set, and θ _m and γ _m are calculated, and the observed position of the crack (θ _m ) and the angle (γ _m ) between the crack and the well axis are the best Three-dimensional crustal principal stress specified by the magnitude, direction, and inclination of each of the above-set principal stresses that are 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 a well axis observed from one well and the angle (γ _m ) formed with the well axis of the crack are different in the direction and inclination of the well axis. When the depth is obtained, what is necessary for the above analysis is the magnitude of the principal stress 1 (σ ₁ ) and its orientation (φ ₁ ) and inclination (θ ₁ ), and the magnitude of the principal stress 2 (σ ₂ ) and its Since there are six directions (φ ₂ ) and the magnitude of the principal stress 3 (σ ₃ ), two observation values will be insufficient. Since the azimuth and inclination of the minimum compressive principal stress can be obtained from the AE observation result, if this is taken into consideration, φ ₁ and θ ₁ are known among the above parameters, so that the one to be obtained is σ ₁ , σ ₂ , σ ₃ and φ ₂
It will be four. Therefore, the 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 to observe the pit wall by a borehole televiewer (BHTV), an optical scanner (borehole television), a formation microimager (FMI), a formation microscanner (FMS), or a molding packer. From the results, the position of the crack along the well axis (θ _m ) and the angle of the crack with the well axis (γ _m ) were obtained, and the lacking data was obtained from the same well Core test results, AE observation Results, hydraulic fracturing test results, overcoring measurement analysis results, breakout analysis results, etc. are supplemented with at least one result, and at least six measured values are acquired, and the position of the crack along the well axis (θ _m ). And the angle (γ _m ) that the crack makes with the well axis are calculated by the following formula, and the calculated θ _m and γ _m are the closest to the above measured values. By obtaining an approximate value, in-situ three-dimensional crustal stress is analyzed.

[Formula 3]

The cracks along the shaft analyzed by BHTV logging and FMI logging are developing along the shaft, and the orientation (θ _m ) is 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 shaft by a certain angle. The gap (γ _m ) from the mine axis is considered to have developed under the influence of three-dimensional underground stress and the strength of rock, so these (θ _m ) and (γ _m )
However, in one inclined well, it is possible to make up for it by using the measured values obtained from other measured values of the same well even if the depths are less than 3 or more than 3 locations with different well orientations and inclinations. If, as a result, the values of 6 parameters of 3 depths or more are determined, it can be estimated that these are the data in 3 different wells, and therefore the analysis of the underground 3D stress field is possible based on this. Becomes

EXAMPLES FIGS. 1 and 2 show a crack along the well axis that appeared on the wall of an excavated well. FIG. 1 shows the fracture along the well axis observed by a borehole televiewer (BHTV), and FIG.
The crack portion along the well axis indicated by indicates the drilling induce fracture, and the crack along the well axis indicated by indicates the breakout (well wall). Fig. 3 shows continuous shear failure in the axial direction of the well). Moreover, FIG.1 (b) shows the stress distribution in 1137.53m (cross section). In this example, it is shown 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 with respect to true north. However, here, the discussion of the maximum principal stress in the breakout assumes that one of the principal stresses is in the well axis, so the maximum and minimum compressive principal stresses in the plane orthogonal to the well axis are expressed. ing. In addition, FIG.
It shows the mine wall surface at the depth of 1075m to 1077m obtained from one logging, and the wall surface from north (N) to east (E) side, east (E) side to south (S) with true north as the reference. It shows a wall surface from the side, a wall surface from the south (S) side to the west (W) side, and a wall surface from the west (W) side to the north (N) side. 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 separated by θ _m with respect to true north. It shows that a fracture runs longitudinally along the well axis at a position and at an angle of γ _m with respect to the well axis. like this,
The fracture (crack) condition along the well axis can be observed by BHTV logging and FMI logging, so it is assumed that the stress linearly changes in the depth direction, and the above-mentioned θ _{m at} three or more depths is assumed. If γ _m and γ _m are obtained, then 3
Dimensional underground stress can be analyzed. FIG. 3 is a conceptual diagram of a method of analyzing the stress in the underground by obtaining the azimuth and inclination with respect to the shaft at each depth at three different depths of one inclined well. In the figure, N, S, W and E are
Shows north, south, west, and east, respectively, 1 is a mine site, 2,
3 and 4 are Depth1, Depth2, and Depth3
The mine wall concept in is shown. 5a and 5b show a fracture (crack) that appears on one of the wall surfaces of the mine wall 2 and a fracture (crack) that appears on the other wall surface. Similarly, in the figure, 6a,
6b is a crack appearing on one of the wall surfaces of the mine wall 3 and a crack appearing on the other wall surface, and 7a and 7b are cracks appearing on one of the wall surfaces of the mine wall 4 and a crack appearing on the other wall surface. Indicates. Further, θ _m is the position of the fracture (crack) with reference to true north, and γ _m is the angle between the direction perpendicular to the maximum tensile stress in the wall of the fracture and the well axis. Now, take the coordinate system as shown in Fig. 4, set σ ₃ to the vertical direction, and set σ ₁ and σ ₂ in the plane perpendicular to σ ₃ , and change the azimuth inclination of the well, water pressure and vertical stress at this time. Equation (4) (wall tangential stress), σ _m (maximum tensile stress in the wall)
And γ _m (angle between the direction perpendicular to the maximum tensile stress and the well axis) are simulated.

[Formula 4] The calculation formulas are based on Leeman (1969) and Daneshy (197
Based on the policies and formulas set out by 3). Figure 4
This figure shows the coordinate system of this way of thinking.
Is the coordinate system when 3 is the vertical direction, 1 ', 2',
3 ′ is a coordinate system when 3 ′ is aligned with the well axis (ζ). In the coordinate system of FIG. 4, in the orthogonal coordinate system in which the 3 ′ axis is aligned with the well axis (ζ), the stress in the well wall against the input is expressed as follows using the cylindrical coordinate system.

[Formula 5] Further, in the equation 4, the maximum tensile stress σ _m of the well wall and the angle γ _m formed by the well axis and the direction perpendicular to the σ _m are expressed as follows.

[Formula 6] Here, the position θ _m when a vertical crack is formed is obtained as follows. That is, on the pit wall surface (θζ surface), σ _m is given at the position where it takes the maximum value. Therefore, the value θ _m of θ such that dσ _m / dθ = 0 is obtained. The obtained θ _m is the position of the vertical crack. The angle of the first-lived crack (γ _m ) is the angle formed by the well axis and the direction orthogonal to the maximum tensile stress when the stress reaches its maximum value in the borehole wall surface ((θζ plane). , The angle of the first-lived crack (γ _m ) can be obtained by the following equation.

[Formula 7] FIG. 5 shows the stress and shear as the parameters in the equation. In the present embodiment, the analysis by the formula calculation or the like can be obtained by many trial and error, the least squares method, or the statistical method, but the calculation is performed by the computer according to the flowchart shown in FIG. You can let me do it. That is, FIG. 6 is a flowchart of the stress calculation program. Figure 6
As shown in, the initial input value of the program is a. 3-direction stress value, 2-direction azimuth, 1-direction tilt b. Water pressure c. Poisson's ratio d. Well orientation / tilt. The output is a step width with an arbitrary equal interval, and the following is output.

[Formula 8] (Stress in the circumferential direction of the borehole)

[Formula 9] (Stress in borehole axial direction)

[Formula 10] (Stress of θζ surface) d · σ _m (Max) (maximum tensile stress in the wall surface) e · σ _m (Min) (maximum compressive stress in the wall surface) f · γm (angle between the borehole axis and the fracture) As a check in the calculation process, in the tensor rotation, stress invariants are calculated before and after the calculation, and it can be confirmed that the two match, and when obtaining the principal stress, check the normalized eigenvectors. You can also As an example of the present invention, first, the sensitivities due to changes in θ _m and γ _m due to changes in stress field and changes in fracture standard were obtained, and an overall image of changes in θ _m and γ _m was grasped. Next, assuming that the stress ratio is constant in the depth direction, changes in θ _m and γ _m with respect to the depth when the orientation and inclination of the well were changed in the depth direction were obtained. Finally, the matching between the obtained θ _m and γ _m and the actual data was examined, and the approximate value was obtained. Hereinafter, a specific method will be described. (Example 1) A simulation was performed using stress as a parameter. A model as shown in FIG. 7 was examined as a basic model. (Case 1) σ ₁ = 216kg / cm ² σ ₂ = 135kg / cm ² σ ₃ = 270kg / cm ² (Case 2) σ ₁ = 162kg / cm ² σ ₂ = 135kg / cm ² σ ₃ = 270kg / 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 well orientation and well inclination of γ _m were examined. Assuming that there is no shear,
Furthermore, Normal Fauling Regine: σ ₂ <σ ₁
A stress field of <σ ₃ ) was assumed. Note that γ _m when the rock fracture criterion (σ _m ) at θ _m becomes 0 is examined. FIG. 8A shows the result of plotting γ _m using the well direction and inclination in the cases 1 to 3 of the above-described embodiment as parameters. In each case, γ _m also changes as the well direction and tilt change. For example, as shown in the case 1 of FIG. 8A, when the well orientation is 60 ° and the well inclination is 10 ° and 20 °, there is a difference of about 5 ° in the value of γ _m . I understand. From this, the difference of 5 ° is
It is possible to discriminate from the observed values, and therefore, the value of γ _m obtained by the well orientation and inclination in this vicinity can be analyzed with relatively high accuracy. However, the 30 ° contour in case 1 covers a fairly wide range, and if the observed γ _m in this case is around 30 °, the final analysis result becomes highly arbitrary. Further, FIG. 8 (b) plots changes in water pressure in each case. This indicates that the water pressure for pulling out from the well wall increases as the well approaches the in-plane minimum principal stress direction. (Example 2) Next, regarding the case 1 of Example 1, the dependence of θ _m and γ _m when the destruction criterion is used as a parameter is described.
Failure Criteria (sigma _m) is performed for two cases of 0 kg / cm ² and 50 kg / cm ^2. First, in Fig. 9, the well direction 50
When the angle is 30 ° and the inclination is 30 °, the changes of (stress in the circumferential direction of the borehole), σ _m (maximum tensile stress in the wall surface) and γ _m (angle formed by the borehole axis and the fracture) are shown.

[Formula 11] Σ _m is 0 kg / cm ² and 50 k at the position of the arrow in FIG.
It is shown that g / cm ² is shown, where failure of the pit wall will occur and θ _m and γ _m must be referenced at the location of this arrow. According to this figure, even if the fracture standard changes from 0 to 50 kg / cm ² at the arrow,
It can be seen that the position of θ _m has hardly changed. Therefore, regarding θ _m , the destruction criterion is not so sensitive, and considering the reading error of the measured value, it is 0 kg / cm ² and 50
It is the same level at kg / cm ² . Further, 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 changing in steps of 5 ° in the range of 0 °. Similarly, FIG. 10B is a plot result of γ _m when the fracture criterion is 50 kg / cm ² . From Figure 10 (a) and (b), the destruction criterion is 0 to 50 kg.
When it is increased to / cm ² , the tendency of contour is not changed, but the value of γ _m becomes smaller. This is γ _m
Indicates that γ _m cannot be obtained unless the destruction criterion is uniquely determined. However, the observed cracks were not created by large pressure such as hydraulic fracturing, and γ
The rate of change of _m with respect to the fracture criterion changes only within the range of 0 to 7.5 ° even if the fracture criterion increases from 0 to 50 kg / cm ² , which is within the range of observation reading error. Considering that both are considered, the destruction criterion is 0 kg.
You can safely think of it as / cm ² . Therefore, considering that there is no dependence on the change in θ _m due to the change in the failure criterion, the calculation result shows that the set of observation values (θ _m , γ _m ) at three or more depths with different well orientations and inclinations ( When the depth is less than 3 depths, the crustal stress and its orientation / tilt can be obtained by matching (approximation) with other data such as core test. (Example 3) Next, in case 1 of FIG. 7, assuming that the stress ratio is constant in the depth direction, θ _m and γ _m with respect to the depth direction when the well direction and inclination are changed for each depth. I asked for change. In this simulation, σ ₃ is assumed to be the rock density (ρ) of 2.7 g / cm ³ and is added to the initial value due 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, the contour of γ _m does not change significantly. In other words, it can be seen that γ _m depends only on the well direction and inclination. The position of θ _m also depends only on the well direction and inclination if the stress ratio does not change with depth. Therefore, when approximating (θ _m , γ _m ) measured in the depth direction, one depth It can be seen that if the contours of the calculated results of θ _m and γ _m at are created, this contour can be referred to even at the depths of different well orientations and inclinations. Table 1 shows an example of the analysis. This is 5 m in the depth direction, with well bearing and inclination of 10 m at 1000 m each.
9 is a table showing changes in γ _{m and the} like when the azimuth and the tilt are increased for each degree.

[Table 1] Moreover, what plotted the result of Table 1 is shown in FIG.
As shown in FIG. 12, it can be understood that γ _m tends to increase in the depth direction, and θ _m deviates from the in-plane maximum compression principal stress direction in the depth direction and approaches the in-plane minimum pressure principal stress direction. You can know that. Here, assuming that the reading errors of the measured values of θ _m and γ _m are ± 5 °, θ _m is 1
For depths less than 300 m and γ _m , depths greater than 1200 m are ± 5
Although it is within °, for example, 1100m and 1300
Looking at 200m intervals such as in depth of _m, θ m
It is possible to make a difference of 4.6 ° at γ _m and 6.1 ° at γ _m , and it is possible to analyze at three depths of 1000 m, 1100 m and 1300 m. Also, for example, depths of 1200 m and 13
In the analysis at three depths of 00 m and 1400 _m , θ _m and γ _m are not so different from each other, and therefore the analysis result is highly arbitrary. Also, when discussing the magnitude of stress, it is necessary to correctly evaluate the water pressure during well drilling and thermal stress in the case of geothermal wells. , Can be applied to obtain the slope. (Example 4) Next, actual acquired data (Table 2) is shown.
Here, a simulation was performed to approximate the measured value.

[Table 2] The data was obtained by the TG-2 well excavated in the Yunomori area of Matsuo-mura, Iwate-gun, by the NEDO project. In this well, BHTV and FMI logging were actually performed. There is. The TG-2 well was kicked off at a depth of around 200 m and the well heading 216 at a depth of around 1000 m.
It is an inclined well with an inclination of 28 ° and 50 ° (TN). TG-
The simulation in 2 wells is based on the following assumptions:
It is made up. The maximum compressive principal stress is 240 kg / cm ² at 880 m based on the test results of the core taken at 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 is the direction of the maximum compressive principal stress. Table 3 shows the analysis result when the best approximation is obtained between the measured value and the calculated value shown in Table 2.

[Table 3] Further, FIG. 13 shows a plot of comparison between the analysis result and the actual measurement value. From this figure, it can be seen that the analysis results and the measured values are very close, and the azimuth and inclination of each stress in the analysis results are reliable. From the analysis results, it is shown that the stress field around the TG-2 well is a reverse fault type because the minimum compressive principal stress is closest to the vertical, and it is reliable because it matches the wide area stress field. Further, it was in harmony with the stress analysis result of the DSCA method (Differential Strain Curve Analysis) of the core test in the TG-2 well.

According to the present invention, underground crustal stress can be analyzed by excavating one well. In particular,
Since it enables stress analysis at high depths in wells with large depth, it greatly contributes to the elucidation of the earthquake generation mechanism and the prediction of fracture progress in hydraulic fracturing. Also, without the need for large-scale devices such as packers and pumps,
Since it is sufficient to excavate one well, it is excellent in economic efficiency, and particularly excellent in the analysis of deep underground crustal stress. Also, if there is data from one well, underground crustal stress can be easily obtained, and analysis is easy, so analysis at the excavation site is also possible, especially by hydraulic fracturing. Wells that aim to increase the amount of fluid harvested have significant advantages.

[Brief description of drawings]

FIG. 1 is a borehole televiewer (BHTV).
Of fracture along the well axis observed by

FIG. 2 is a depth 1075 obtained from FM1 logging.
Figure showing the mine wall surface at m-1077m

[Fig. 3] Fig. 3 is a conceptual diagram of a method of analyzing underground stress by obtaining orientations and inclinations with respect to the shaft of each well at three different depths of one inclined well.

[Fig. 4] Fig. 4 shows σ ₃ in the vertical direction, σ ₁ and σ ₂ in a plane perpendicular to σ ₃ , and the azimuth inclination of the well, water pressure, and vertical stress at this time are changed to tangent to the wall surface. Diagram showing a coordinate system for simulating stress, maximum tensile stress in the wall surface, and changes in the direction perpendicular to the maximum tensile stress and the angle formed by the well axis.

FIG. 5 shows a graphical representation of 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 (a) shows the result of plotting γ _m with the well direction / inclination as a parameter in Cases 1 to 3; FIG. 8 (b) shows the change in water pressure in each case. Figure showing the result of plotting

FIG. 9 is represented by Equation 11 (stress in the circumferential direction of the borehole), σ, when the well direction 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 fracture criterion (γ _m ) is 0 kg / cm.
Fig. 10 (b) showing the result of plotting γ _m when the well orientation is changed in increments of 5 ° in the range of 0 to 90 ° and well inclination of 0 to 90 ° at the time of ² The figure which shows the plot result of γ _m when the destruction criterion (γ _m ) is 50 kg / cm ² .

FIG. 11 is a graph showing the relationship between the depth direction θ _m and γ _m when the well orientation / inclination is changed for each depth assuming that the stress ratio is constant in the depth direction in case 1 of the embodiment. Diagram showing the result of plotting γ _m obtained by the change simulation

FIG. 12 shows a well orientation and a dip of 10
The figure which shows the result of plotting the change of γ _m, etc. when the azimuth and inclination are increased every 5 ° in the depth direction with 10 ° at 00 _m .

FIG. 13 is a diagram in which a comparison between analysis results and actual measurement values is plotted.

[Explanation of symbols]

1 ... Well trace, 2 ... Well wall at depth 1, 3 ... Well wall at depth 2, 4 ... Well wall at depth 3, 5a, 5b ... Fracture appearing on wall surface of well wall 2 cleft), 6a, fracture (crack appearing on the wall surface of 6b · · · Anakabe 3), 7a, appear on the wall surface of 7b · · · Anakabe 4 fracture (crack) zeta · · · Koijiku sigma _m ·・ ・ Maximum tensile stress of well wall γ _m・ ・ ・ Angle between direction perpendicular to maximum tensile stress of well wall and well axis a ・ ・ ・ 3-direction stress value, 2-way direction, 1-direction tilt b ・ ・ ・Water pressure c ・ ・ ・ Poisson's ratio d ・ ・ ・ Well bearing / tilt

─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] August 12, 1994

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] Figure 8

[Correction method] Change

[Correction content]

FIG. 8 is a diagram showing a result of plotting changes in Y _m and P _m with a pressure ratio in Cases 1 to 3 as a parameter.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuo Hayashi 2-1-1 Katahira, Aoba-ku, Sendai City Institute of Fluid Science, Tohoku University

Claims (4)

[Claims] 1. The location of a crack along a well axis at three or more different depths in one inclined well and the observation result of the angle between the crack and the well axis. 3D crustal stress analysis method for analyzing the 3D crustal stresses of 2. The above observation results are obtained from data such as core test results of the same well, AE observation results, hydraulic fracturing test results, overcoring measurement / analysis results, breakout analysis results, etc., regardless of the number of depths. The three-dimensional crustal stress analysis method according to claim 1, characterized in that the three-dimensional underground stress at that point is analyzed from a total of six or more observed values obtained. 3. A borehole televiewer (BHTV), an optical scanner (borehole television), a formation micro, for cracks in a well wall with different well orientation inclinations of 3 or more depths obtained from at least one inclined well. Measure the position (θ _m ) of the crack along the well axis and the angle (γ _m ) formed by the crack with the well axis using an imager (FMI), formation microscanner (FMS), or mold packer. In the first step, the magnitude of the crustal principal stress 1 (σ ₁ ), its orientation (φ ₁ ), the inclination (θ ₁ ), and the magnitude of its principal stress 2 (σ ₂ ) are applied to the actually measured crack. ) And its orientation (φ ₂ ) and tilt (θ ₂ ),
Its principal stress 3 (σ ₃ ) and its orientation (φ ₃ ) and inclination (θ ₃ )
Using the second step of arbitrarily setting at least six values among them to assume an arbitrary three-dimensional crustal stress field and the value of the arbitrary three-dimensional crustal stress field assumed in the second step, The position of the crack along the well axis (θ _m ) at the same depth as the depth of the crack actually measured in the first process
And a third step of calculating an angle (γ _m ) formed between the crack and the well axis, and the position (θ _m ) of the crack along the well axis and the crack obtained in the third step. The angle (γ _m ) with the well axis of
The six values are calculated so as to best approximate the measured position of the crack along the well axis (θ _m ) and the angle formed by the crack with the well axis (γ _m ). A three-dimensional crustal stress analysis method comprising: a fourth step. [Formula 1] 4. When the position (θ _m ) of the 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 value is obtained from at least one of the core test result, AE observation result, hydraulic fracturing test result, overcoring measurement / analysis result, breakout analysis result, etc. obtained from the same well. In addition, a three-dimensional crustal stress field is assumed by obtaining at least the above-mentioned six or more measured values, and using this assumed value, the 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 ) formed by the crack with respect to the well axis are obtained, and the position (θ _m ) of the crack along the well axis and the crack position of a crack along the wellbore axis angle (gamma _m) formed by the wellbore axis crack (theta _m) and its To best approximate the angle between the borehole axis Crack (gamma _m), 3-dimensional crustal stress analysis method according to claim 3, wherein the determination by calculating the six values.