The way to determine the local stresses in the rock

 

The invention relates to the field of study of rocks and can be used to determine the stresses acting in the rock. Rock drill hole, which is filled with wash liquid, providing an adjustable pressure on the borehole wall, which in a certain area rocks first local voltage is replaced by other voltage-dependent named the regulated pressure acting on the borehole wall. From this region to extract a sample having first, second and third base direction coinciding with the direction of the first, second and third local stresses, respectively, acting on the sample before it is extracted from rocks. Do it tests for each of which he undergoes regulated voltages along the reference lines to determine the surface of the sample is destroyed, the value of the regulated voltage along the first baseline direction is equal to the value specified another voltage. On the surface of the fracture is determined by at least one local voltage - second or third. The direction of the first local voltage vertically and napravlenije below the bottom of the drill hole, and the primary voltage is determined by the pressure of the liquid column in the well and the weight of the total rock volume that is located between the bottom of the drill hole and the place from which the extracted sample of the breed. The sample can be retrieved from the downhole region of the drill hole. When performing each test point on the surface of the fracture can be identified by acoustic emission emanating from the sample. The invention improves the accuracy of determining the stresses acting in the rock. 4 C.p. f-crystals, 2 Il.

The present invention relates to a method of determining the local stress in the rock, and the rock is in a state of stress, which is generated first, second and third principal stresses. These three principal stresses are called respectively the first, second and third local voltage. When the extraction of hydrocarbons from the rock formation it is necessary to know the magnitude and direction of the local stresses in this breed, or at least, a signaling information. Such information is needed, for example, to ensure the stability of the wellbore, performing hydraulic fracturing, geological modelling or preduprava, among them differential deformation analysis, a variety of acoustic methods or so-called minimally destructive testing. It should be remembered that one of the local stress has a generally vertical direction and its magnitude is determined by the pressure of overlying rocks. Therefore, research should be carried out only for the two horizontal local stresses to determine for each direction and magnitude. Known attempts to determine the values of the horizontal local stresses by measuring deformations and accounting constitutive properties of the rock to determine the stresses. However, the constitutive properties of the rocks in most cases are not known precisely.

Based on the foregoing the present invention aims to provide a more accurate way of determining values of one or more local stresses in the rock.

In accordance with this invention proposes a method of determining the local stress rocks, facing the first, second, and third local voltage, provided that the rock drilled borehole, the borehole filled with drilling fluid, providing adjustable giving the correspondingly substituted for the voltage, the value of which depends from the named regulated pressure produced on the walls of the well, and this method consists of the following operations: - selection of the sample extracted from the named region, the sample has a label first, second and third basic directions corresponding to the directions of the first, second and third local stress acting on the sample before extraction from the rock, and the execution of several test sample, for each of which a sample is exposed to certain stresses in the base areas to determine the surface of the destruction of the sample and to determine the surface destruction, at least one of the second or the third voltage, whereby in the first baseline direction generates a voltage which is, in essence, is called to another voltage.

It should be clear that in the context of the present invention assumes that the borehole wall includes a cylindrical part of the borehole and the borehole bottom. A significant aspect of the present invention is that is considered the most stress state, which is exposed to the material sample when determining the surface destruction. is W most fully. For example, if the sample is taken from the borehole bottom, the stress state corresponds directly before removing the sample from the rocks, and therefore local vertical stress in the area of location of the sample it is necessary to replace the vertical stress, which is equal to the sum of the hydrostatic pressure of drilling fluid in the borehole bottom and the weights of the rocks, referred to the unit area, between the well bottom and the location of the sample. If the sample material contains the pore fluid, the pressure of the pore fluid necessary to subtract from the value of the named local vertical voltage to determine the effective vertical stress (which is the voltage experienced by the grains of the rock).

During the lifetime of most of the stress state of the sample material the ratio of the difference between the local horizontal stress and vertical stress to the average voltage has a maximum value.

Fracture surface of (or, in other words, the shell of destruction) form in three-dimensional space to points where there is more destruction of the sample material when the load increases. Powerade additional destruction. What is happening is for this reason that acoustic emission is called the Kaiser effect, which is described, for example, in "a Study of acoustic emission during the development of the fracture and the aftereffect stress Sandstone", B. J. Pestman and other international refereed journal "rock Mechanics and geomechanics", T. 33, 6, S. 585-593, 1996.

Below is given a detailed description of the present invention a specific example with reference to the attached figures.

Fig. 1 is a schematic depiction of the cross section of the wells drilled in the rock by the method corresponding to the present invention.

Fig. 1A is a schematic depiction of the local stresses present in the rock.

Fig. 1B is a schematic representation of the test sample, extracted from the rocks.

Fig. 2 is a schematic depiction of a local chart of voltages used in the implementation of the method corresponding to the present invention.

The following detailed description is made for the case when the rock is missing the pore fluid, which means that under the stresses in the text implies it is the effective stress experienced by the particles of the breed. In Fig.1 shows a well 1, the imp is real directions, namely, the vertical compressive stress1and two horizontal compressive stresses2and3Fig.1A these stresses are depicted in force at the cuboid element 5 rock 3. Well 1 is filled mud 7 of a certain specific gravity, which creates a pressure P on the bottom 11 of the well. Below the bottom of the hole is a region 14 of breed 3, in which the vertical local voltage1at any one point is equal to the voltagewhich is the sum of the vertical pressure P produced mud 7 and weight, referred to the unit area of rock that is located between the bottom of the well and the considered point. Horizontal local voltage2and3in region 14 does not change (or change very little) after the construction of the borehole.

Core drilling tool (not shown) is lowered into the borehole 1 for selection of the cylindrical core 16 in the sample (Fig.1B) from the field 14 rocks 3. In Fig.1 test sample is depicted by the dashed lines, to the base direction 18, the second baseline direction 20 and the third base direction 22, and these basic directions correspond to the directions of the local stresses, which experienced the core 16 to the extraction of rocks 3. Thus, to extract the core 16 of rocks 3 core 18 coincides with the vertical direction, the base 20 in the direction of the local voltage2and the base 22 in the direction of the local voltage3. In the process, and after removing the core 16 of the rock compressive stresses acting in the basic directions change if the core is stored in a container (not shown) filled with liquid under moderate hydrostatic pressure.

The core 16 is subjected to test pressure with which the core is applied compressive stresses S1, S2 and S3 in basic areas 18, 20 and 22, respectively. The purpose of this test is to determine the extent of the damage that has undergone the material of the core 16 to the extraction of rock 3, and a numerical evaluation of horizontal local stresses caused this destruction. The degree of destruction can be represented in the form over which the material of the core is determined by the condition of maximum tension (so that is the state of tension that is drawing the greatest degree of destruction), it can be argued that an important feature of the present invention is the fact that the state of maximum tension the material sample is exposed when it is in the well 1 and the extraction of the core 16 of the rocks. Therefore, in a state of maximum tension the principal stresses are equal:basic direction 18,2basic direction 20 and3basic direction 22.

As can be seen in Fig.2, the surface profile of destruction for S1=determined by conducting a series of tests, the purpose of which is the horizontal dimension of the local stress2and3. When performing these tests, the compressive stress support 31 is equal towhile the voltage S2 and S3 change before more destruction. As illustrated exemplary chart of Fig.2, the core 16 has applied the force along the path 24 of loading to point a, from which began more destruction. Acoommodate with the Kaiser effect. Then changed the voltage S2 and S3 along paths 26, 28 of loading to point B, along the paths 28, 30, 32 loading to the point With, along paths 32, 34, 36 loading to the point D and along paths 36, 38, 40 of loading to the point E, and the points b, C, D, E, was determined by the beginning of the additional destruction in accordance with the Kaiser effect. The curve drawn through the points a, b, C, D, E, forms a surface profile of destruction when S1=To obtain the surface profile of destruction, just the most appropriate stress condition, which was the core 16 to the extraction of rock 3, when performing the tests necessary to ensure that the generated voltage is exceeded only very marginally the most stress state of the core 16 to retrieve it.

Profile of destruction on graph S2, S3 (S1=) gives a set of points (32, 33), each of which, in principle, can represent a local stress state (1,2,3). Known in the art of these points is sampled to determine the actual condition local tensions; brazennose.

If a rock contains interstitial liquid, the total intensity at any given point of the rock is equal to the sum of the effective tension (feel the grains of the rock) and the pressure of the pore fluid. Given this, the above-described method can be successfully used to determine the effective local stress1E,2Eand3E. Vertical effective local voltage1Eat a specific point needs to be replaced for a voltageequal to the pressure P produced mud 7, increased by the weight of the rocks located between the bottom 11 of the wells and the specific point, and the reduced pressure of the pore fluid. Values of the horizontal effective local stress2Eand3Edetermine in fact, according to the method described above with reference to2and3.and

Claims

1. The way to determine the local stresses in the rock are exposed first, second, and third local awn, providing adjustable pressure on the walls of the well, resulting in a certain area rocks first local voltage is replaced by other voltage-dependent named the regulated pressure acting on the borehole wall, the method consists of the following operations: perform the selection of the sample extracted from the named region and having a first, second and third basic directions which coincide with the directions of the first, second and third local stresses, respectively, acting on the sample prior to its extraction from rocks; perform a variety of tests on the sample, when conducting each of which a sample is subjected to controlled stress along the reference lines to determine the surface of the destruction of the sample and definitions on the surface of the destruction of at least one of the second or third local voltage, the value of the regulated voltage along the first baseline direction essentially equal to the value of the named another voltage.

2. The method according to p. 1, characterized in that the direction of the first local voltage essentially vertically and the direction of the second and third local napire downhole borehole and the primary voltage is determined by the pressure of the liquid column in the well and the weight of the total rock volume, located between the bottom of the drill hole and the place from which the extracted sample of the breed.

4. The method according to any one of paragraphs.1-3, characterized in that the sample is removed from the downhole region of the drill hole.

5. The method according to any one of paragraphs.1-4, characterized in that when performing each test point on the surface of the fracture is determined by acoustic emission emanating from the sample.

 

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SUBSTANCE: method includes recording signals of electromagnetic radiation in time, measuring amplitudes thereof as well as durations from load start and building spectral-time matrix of spectral amplitude of said signals on basis of results, with growth of frequency and time. On said matrix frequency sub-ranges are marked with growth of frequencies, in each of which equal spectral amplitudes of signals are marked, area taken by these is contoured with closed line and its size is determined, then relation of dimensions of area of Sn n frequency sub-range (n=2, 3, 4,…) to area S1 of first frequency sub-range is determined. With growth of relations of these areas start of intensive crack forming process is detected. Critical relation, at which transfer from intensive cracks forming process to rock massif splitting process occurs, is relation Sn=(2-4)S1, on basis of which splitting of areas on said matrix is predicted in greater frequency sub-ranges, to characterize destruction of rock massif.

EFFECT: higher precision.

1 dwg

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