CN115163037A

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Info

Publication number: CN115163037A
Application number: CN202210884908.8A
Authority: CN
Inventors: 任强
Original assignee: Chengdu Hexin Hengtai Engineering Technology Co ltd
Current assignee: Chengdu Hexin Hengtai Engineering Technology Co ltd
Priority date: 2022-07-26
Filing date: 2022-07-26
Publication date: 2022-10-11

Abstract

The invention discloses a method for causing well wall fracture by artificial heating, which comprises the following two steps: s1, adding a heater to a drilling bottom; s2, manually heating to cause the well wall of the well to break, wherein the analysis method of the method for manually heating to cause the well wall to break comprises two aspects of deterministic analysis and data analysis. The method makes up the defect that the well wall fracture naturally occurs in the traditional maximum horizontal main stress measurement and expands the application range of the measurement method. The modeling analysis includes: deterministic analysis of the thermally induced annulus pressure around the borehole; evaluating the relationship among the maximum horizontal main stress, the width of a well wall fracture angle and the temperature rise; data analysis of the accuracy and sensitivity of the method for measuring the maximum horizontal principal stress by thermally induced borehole wall fracture; and (4) carrying out data analysis on the probability estimation of success of the maximum level main stress measurement under different specific conditions. The data analysis comprehensively proves the feasibility of the method for causing the borehole wall to break by artificial heating, and analyzes the condition range required by the method.

Description

Method for causing well wall to break through artificial heating and analysis method thereof

Technical Field

The invention relates to the technical field of measurement of hot-pressing fracturing ground stress, in particular to a method for causing well wall fracture by artificial heating and an analysis method thereof.

Background

The current maximum horizontal principal stress measurement process comprises a series of tests such as well wall fracture observation, drilling induced fracture test, hydraulic fracturing test and the like. This technique has found widespread use in the oil and gas industry, but it has some drawbacks that prevent the measurement of the maximum principal stress, such as the uncontrolled breaking of the well wall that occurs naturally. As a direct measurement index of the maximum horizontal main stress, if well wall breakage does not occur, data loss of the maximum horizontal main stress measurement can be caused.

The prior art measures the minimum horizontal principal stress by a hydraulic fracturing method (when a well wall crack is opened or closed, the current hydraulic pressure is measured, namely the minimum principal stress is measured). Then, the stress distribution around the drill hole is deduced by applying the linear elasticity theory, and the maximum horizontal principal stress is estimated based on the minimum horizontal principal stress and the fracture re-tensioning pressure. Finally, the orientation of the fracture, i.e. the orientation of the maximum horizontal principal stress, is measured by borehole imaging logging. But the accuracy of the method is poor due to factors such as difficult crack orientation detection, uncontrollable crack formation, well pressure effect on the results, etc. Until the borehole imaging technology and the directional borehole diameter measurement technology are developed, the borehole wall breakage is not promoted to become an important index for the ground stress measurement. The measurement data of well wall fracture and hydraulic fracture are combined, so that the maximum horizontal principal stress and the functional relation between the minimum horizontal principal stress and the depth can be accurately measured.

When the maximum horizontal principal stress is sufficiently large and the ratio thereof to the minimum horizontal principal stress is sufficiently large, stress concentration exceeds the rock compressive coefficient, and borehole wall fracture occurs. Thus well wall fractures are difficult to occur in most cases. The prior art can not artificially induce the occurrence of well wall fracture, so that the traditional stress measurement method can not be applied to all regions.

In recent studies, a downhole resistance heating device for melting backfill materials to seal a borehole has been developed and suggested that the device may cause compression and tensile fractures in the borehole when heated irregularly. However, the experiment is carried out in an isotropic medium, and the relationship between the thermal-induced borehole wall fracture and the ground stress is not strict.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provides a method for cracking a well wall by artificial heating and an analysis method thereof.

In order to achieve the purpose, the invention provides the following technical scheme: a method of artificially fracturing a well wall, comprising: the method comprises the following two steps:

s1, adding a heater to a drilling bottom:

s2, manually heating to break the well wall of the well.

An analysis method of a method for breaking a well wall by artificial heating comprises both deterministic analysis and data analysis.

As a further aspect of the present invention, wherein the deterministic analysis comprises:

(1) The method comprises the following steps of (1) carrying out deterministic analysis on the circumferential pressure induced by the heat force around the drilling well, and estimating the possibility of the generation of the well wall fracture by solving the circumferential pressure around the drilling well under different temperature conditions and comparing the circumferential pressure with the unconfined compressive strength;

(2) And solving the temperature difference which enables the ring pressure to exceed the unconfined compressive strength under the condition of different maximum horizontal main stress values, and evaluating the relation among the maximum horizontal main stress, the width of the well wall fracture angle and the temperature rise.

As a further aspect of the present invention, the data analysis comprises:

(1) Solving a maximum horizontal principal stress distribution curve under the conditions of limiting temperature difference, well wall fracture angle width and material characteristic parameters, and performing data analysis on the precision and sensitivity of the method for measuring the maximum horizontal principal stress by thermally induced well wall fracture;

(2) And carrying out Monte Carlo simulation under different specific conditions, and solving an accumulated probability curve of well wall fracture, thereby carrying out data analysis on the probability estimation of the success of the maximum horizontal main stress measurement.

Compared with the prior art, the method for causing the well wall to break by artificial heating has the following beneficial effects:

the method makes up the defect of uncontrollable well wall fracture naturally occurring in the traditional maximum horizontal main stress measurement, and expands the application range of the measurement method. The modeling analysis includes: deterministic analysis of the thermally induced annulus pressure around the borehole; evaluating the relationship among the maximum horizontal main stress, the width of a well wall fracture angle and the temperature rise; data analysis of the accuracy and sensitivity of the method for measuring the maximum horizontal principal stress by thermally induced borehole wall fracture; and (4) carrying out data analysis on the probability estimation of success of the maximum level main stress measurement under different specific conditions. The data analysis comprehensively proves the feasibility of the method for causing the borehole wall to break by artificial heating, analyzes the condition range required by the method and provides a theoretical basis for the method.

Drawings

FIG. 1 is a normal distribution curve fitted to (a) coefficient of thermal expansion, (b) Young's modulus, (c) Bonus index, (d) UCS;

FIG. 2 is a graph of calculated wellbore annulus pressures at two different temperature conditions;

FIG. 3 is a contour plot of the relationship between maximum horizontal principal stress, angular width, and temperature differential;

FIG. 4 is a maximum horizontal principal stress measurement distribution based on numerical errors of modeling parameters at 30 degrees angular width with 30 degrees temperature differential;

FIG. 5 is a graph of the sensitivity of maximum horizontal principal stress to the amount of change in the standard deviation of the material property distribution. The dashed line reflects the baseline of the maximum horizontal principal stress standard deviation.

FIG. 6 is a cumulative success rate for inducing borehole wall fractures of at least 0 ° angular width;

FIG. 7 is a cumulative success rate for inducing borehole wall fractures of angular width up to 50 deg.;

FIG. 8 is a comparison of cumulative probabilities at a temperature difference of 30 ℃.

Detailed Description

The principles and features of this invention are described below in conjunction with the following drawings, which are set forth to illustrate, but are not to be construed to limit the scope of the invention.

The modeling analysis is based on the classical Kirsch solution. While the classical Kirsch resolution requires that the borehole be circular, recent studies have extended its analysis range to elliptical, i.e., the borehole shape before collapse typically occurs. Compared to elliptical well analysis, the classical Kirsch solution tends to underestimate the maximum level principal stress due to some surface shape differences, but the difference is small. For simplicity of analysis, the classical Kirsch solution is used herein and is consistent with conventional borehole wall fracture analysis. FIG. 1 shows the horizontal stress composition, azimuthal orientation, and borehole wall fracture schematic for a vertical borehole.

From fig. 1 and the Kirsch solution, the well circumferential pressure can be obtained with constant temperature difference:

σ_θθ ＝S_{h min} +S_{H max} +2(S_{H max} -S_{h min} )cos2θ-P₀ -P_m +α_T EΔT/(1-ν) (1)

σ_θθ in order to realize the circumferential pressure of the well,

S_{h min} in order to achieve the minimum level of principal stress,

S_{H max} in order to be the maximum horizontal principal stress,

theta is the azimuth angle of the minimum horizontal principal stress direction as the polar axis,

P₀ in order to be able to measure the drilling pressure,

P_m the pressure is the self weight of the soil or the pressure of the inner wall of the drilled well,

α_T e and v are respectively rock thermal expansion related density coefficient, young modulus and Poisson ratio, and delta T is the change quantity of the surface temperature of the well wall.

In order for the borehole wall to crack, the borehole surface must be compressed beyond the compressive strength of the rock. According to the formula (1), the induced borehole wall temperature rise can cause the borehole wall annular pressure to increase, and a controllable method is provided for inducing borehole wall fracture. The thermoelastic effect of borehole wall annular pressure has long been an important factor in the calculation of well safety. This patent is greater than unconfined compressive strength with the ring crush and breaks as the wall of a well and takes place the basis. Namely that

σ_θθ ≥UC S

(2)

The unconfined compressive strength of field scale rock is often 2 to 10 units less than that of laboratory scale rock. In order to theoretically prove that the method for artificially inducing the well wall fracture to occur obtains the conservative temperature difference of the theoretically generated well wall fracture, the patent adopts the unconfined compressive strength of the rock in the laboratory scale. For simplicity, equation (1) only considers smooth heat transfer and borehole wall surface temperature differences. While transient heat transfer can provide more accurate estimates of thermal pressure variations, the patent ignores transient heat transfer effects in order to represent the theoretical basis and its limitations.

In equation (1), the patent introduces and defines physical parameters such as stress, pressure and material density to calculate the annular pressure of the surface of the well wall, and considers that the stress and the pressure can be accurately determined through actual conditions. In contrast, due to geological complexity, material properties often exhibit inherent variable characteristics that are difficult to accurately determine. Due to uncertainty in practical application, the patent estimates material characteristics from existing data materials.

The method utilizes geophysical wireline logging data in a typical well drilling area and theoretical relationships and empirical relationships to obtain deviations of material properties. Based on these deviations, to obtain reasonable data expectations of material properties, the patent fitted a normal distribution curve for each material property. Table 1 lists the modeling parameters used in this study, and FIG. 1 lists the normal distribution curves fitted to each material property parameter.

TABLE 1 modeling parameters

Detailed description of the invention

S1: and (3) deterministic analysis: the data modeling analysis carries out the following two deterministic analyses:

a: a thermodynamically induced annular pressure is determined around the borehole. During this process, the patent solves equation (1) with the determined average parameter values listed in Table 1 to obtain the likelihood of borehole wall fracture.

b: and (3) clearly evaluating the relationship among the maximum horizontal main stress, the width of the well wall fracture angle and the temperature rise. In the process, the patent utilizes equation (1) to solve the temperature difference which enables the ring pressure to exceed the unconfined compressive strength under the condition of different maximum level main stress values.

S2: and (3) data analysis: the modeling data analysis carries out the following two data analyses:

a: and carrying out data analysis on the precision and the sensitivity of the method for measuring the maximum horizontal principal stress by thermally induced borehole wall fracture. Under the conditions that the temperature difference and the width of a well wall fracture angle are known and the material characteristic parameters are sampled based on normal distribution curve data in the figure 1, the Monte Carlo method is adopted by the method to solve the equation (1) so as to solve the maximum horizontal main stress.

b: and carrying out data analysis on the estimation of the success probability of the maximum level main stress measurement under different specific conditions. Based on the normal distribution of the material characteristic numerical value, the method further utilizes a Monte Carlo simulation method to evaluate the accumulation success probability of the maximum level main stress measurement. In this process, the patent performed 500000 replicates to obtain a representative data set.

The modeling analysis results are as follows:

a: and (3) determinacy evaluation: the deterministic evaluation result of the modeling analysis is as follows:

(1) the method comprises the following steps Based on the average values of the parameters in table 1, the magnitude of the annulus pressure in equation (1) is solved under the conditions of a heating drilling temperature difference of 0 ℃ (no temperature rise) and 30 ℃. As shown in figure 2, the ring pressure can not exceed the unconfined compressive strength at the temperature difference of 0 ℃, and the well wall can not crack. In contrast, when the well is heated to 30 ℃, the magnitude of the annular pressure exceeds the unconfined compressive strength limit, and the well wall fracture phenomenon of about 35-degree angle width is generated. In practical application, the measured fracture angle width of the well wall and the temperature difference are substituted into equation (1) to reversely calculate the maximum horizontal principal stress. When the temperature difference is 0 ℃, the well wall is not broken, and the maximum horizontal main stress cannot be estimated.

(2) The method comprises the following steps The method further generalizes the deterministic analysis method to the process of evaluating the thermal induced borehole wall fracture. FIG. 3 shows a contour plot of the relationship between maximum horizontal principal stress, borehole wall fracture angle width and temperature differential.

Based on fig. 3, the following important conclusions can be drawn:

1, under the condition of not artificially heating to cause the temperature rise of the well wall, the maximum horizontal main stress of at least about 45MPa is required for the phenomenon of well wall fracture.

2 under the condition that the maximum horizontal principal stress and the minimum horizontal principal stress are both approximately 20MPa (the horizontal stress ratio is close to 1.0), the induced borehole wall fracture generation needs to make the borehole wall temperature rise by about 100 ℃. Meanwhile, when the maximum horizontal principal stress and the minimum horizontal principal stress are small, the width of the well wall fracture angle is obviously sensitive to small temperature difference change. This temperature differential sensitivity at very small horizontal stress ratios is consistent with the opinion of the challenge of the ONKALO thermally induced borehole wall fracture experiment (Sinen et al 2015).

3: it is sometimes not necessary to precisely control the temperature differential heated by the borehole heater to achieve a borehole wall rupture condition. For example, when the maximum horizontal principal stress is 40MPa, the heating temperature difference between 20 ℃ and 70 ℃ can induce the generation of well wall fracture with the angular width of 0-90 degrees.

b: and (3) data evaluation: the data evaluation results of the modeling analysis are as follows:

(1) the method comprises the following steps In consideration of the inherent uncertainty of geological materials, the method applies material characteristic normal distribution to evaluate the thermal induced well wall fracture process in a datamation mode. For simplicity, this patent only considers material property errors and characterizes the errors by a normal distribution fit curve in FIG. 1. Based on the material characteristic error, the value distribution of the maximum level main stress is estimated by applying equation (1) to Monte Carlo simulation.

The modeling parameters were simulated using the values listed in table 1 (except for the maximum horizontal principal stress) using an angular width of 30 ° and a temperature difference of 30 ℃. Fig. 4 shows the maximum horizontal principal stress results from this. The maximum level of principal stress obtained is expected to be about 39MPa for the parameters employed and the material property errors, consistent with the results shown in fig. 3. The standard deviation obtained was 3.8MPa. The probability of the maximum horizontal principal stress measurement in the range of 33MPa to 45MPa is approximately 90% based on a normal distribution curve fitted to the maximum horizontal principal stress simulation result.

(2) The method comprises the following steps In order to evaluate the influence of each material characteristic on the measurement of the maximum level principal stress distribution, the patent develops a sensitivity test, and the standard deviation of each material characteristic is considered separately to obtain the corresponding maximum level principal stress standard deviation. As shown in fig. 5, young's modulus, poisson's index and coefficient of thermal expansion have relatively little effect on the maximum horizontal principal stress standard deviation. Therefore, in the field of thermally induced borehole wall fracture technology, if the uncertainty of the maximum level principal stress measurement is to be reduced, then the unconfined compressive strength standard description (or other applicable fracture standard) needs to be improved.

The traditional method of using natural borehole wall fracture is also subject to the same accuracy of non-closed compressive strength. Therefore, the sensitivity of maximum horizontal principal stress to unconfined compressive strength in thermally induced borehole wall fracture methods should be consistent with conventional methods. In the Kirsch solution, which introduces thermal stresses, the maximum horizontal principal stress likewise does not exhibit sensitivity to other material-specific parameters (coefficient of thermal expansion, young's modulus, poisson's coefficient). Thus, the application of thermally induced wall-cracking techniques does not introduce much uncertainty in the measurement of the maximum horizontal principal stress as compared to the application of conventional well-induced wall-cracking techniques.

(3) The method comprises the following steps In order to know the accumulated success rate of thermally induced well wall fracture under the conditions of different heating temperatures and different maximum horizontal main stresses, the Monte Carlo simulation is further developed by adopting the material characteristic parameter distribution shown in FIG. 1. FIG. 6 shows the cumulative probability of a borehole wall fracture angular width of at least 0 (the minimum condition for borehole wall fracture to occur). Based on fig. 6, the following conclusions can be drawn:

1 maximum horizontal principal stress greater than about 45MPa at a temperature differential of 0 ℃ (without elevated temperature), with the probability of inducing borehole wall cracking within reasonable limits.

2, under the condition that the temperature difference is 60 ℃, the maximum horizontal main stress is more than about 30MPa, and the possibility of inducing the occurrence of well wall fracture is in a reasonable range.

And 3, based on inherent errors of material characteristics and moderate heating temperature (60 ℃ at most), under the maximum level main stress between 30MPa and 45MPa and corresponding modeling parameters, the thermal induced well wall fracture technology is feasible.

(4) The method comprises the following steps Fig. 6 only shows the success probability of successfully inducing borehole wall fracture, but does not consider the potential instability caused by the excessive borehole wall fracture angular width and the possibility of complete collapse of the borehole wall. Therefore, monte Carlo simulations were performed to evaluate the cumulative probability that the borehole wall fracture angle width does not exceed 50 ° (the borehole wall fracture angle width is not sufficient to compromise drilling stability). Fig. 7 shows the simulation results of the possibilities.

Based on fig. 7, the following conclusions can be drawn:

1, when the temperature difference is 0 ℃, in order to ensure that the width of a well wall fracture angle is not too large, the maximum horizontal main stress is less than about 55MPa.

2 when the temperature difference is 60 ℃, in order to ensure that the width of the well wall fracture angle is not too large, the maximum horizontal principal stress is less than about 35MPa.

And 3, based on inherent errors of material characteristics and moderate heating temperature difference (60 ℃ at most), in order to avoid unstable drilling, proper temperature needs to be considered when the thermal induced well wall cracking technology is applied to obtain a determined maximum horizontal main stress value.

(5) The method comprises the following steps In conclusion with reference to fig. 6 and 7, the present patent, which compares the possibilities of raising the temperature by 30 ℃, roughly evaluates the possibility of successfully inducing borehole wall fracture without generating an excessive angular width. The results are shown in FIG. 8.

Based on fig. 8, the following conclusions can be drawn:

1 the probability of the width of the well wall fracture angle between 0 and 50 degrees is about 75 percent when the maximum horizontal principal stress is 40 MPa.

2: relatively, the probability of borehole wall failure not occurring (angular width less than 0 °) or of the angular width being too large is 25%.

3. As shown by the dotted line in FIG. 8, if the maximum horizontal principal stress magnitude is between 37MPa and 43MPa, the probability of occurrence of borehole wall fracture with an angular width in the range of 0 to 50 is about 50%.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.

Claims

1. A method of artificially fracturing a well wall, comprising: the method comprises the following two steps:

s1, adding a heater to a drilling bottom:

s2, manually heating to break the well wall of the well.

2. The method of claim 1, further comprising both deterministic analysis and data analysis.

3. The method of claim 2, wherein the deterministic analysis comprises:

4. The method of claim 2, wherein the data analysis comprises:

(1) Solving a maximum horizontal main stress distribution curve under the conditions of limiting temperature difference, well wall fracture angle width and material characteristic parameters, and thus carrying out data analysis on the precision and sensitivity of the method for measuring the maximum horizontal main stress by thermally induced well wall fracture;

(2) And carrying out Monte Carlo simulation under different specific conditions, and solving an accumulated probability curve of well wall fracture occurrence so as to carry out data analysis on the probability estimation of the success of the maximum horizontal main stress measurement.