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Rock brittleness evaluation method based on stress strain curve and scratch test

A technology of scratch testing and evaluation method, which is applied in the direction of applying stable tension/pressure to test the strength of materials, measuring devices, strength characteristics, etc., to achieve the effect of wide applicability, strong reliability and high accuracy

Active Publication Date: 2019-07-12
CHINA UNIV OF PETROLEUM (BEIJING)
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  • Description
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Problems solved by technology

[0004] In order to solve the technical problem in the prior art that there is no scientific evaluation method for the brittleness of fractured rocks, the present invention provides a rock brittleness evaluation method based on stress-strain curves and scratch tests, which is based on rock triaxial compression experiments Analysis of the whole process of the full stress-strain curve and the scratch test can obtain the brittleness evaluation results of the rock conveniently and accurately

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  • Rock brittleness evaluation method based on stress strain curve and scratch test
  • Rock brittleness evaluation method based on stress strain curve and scratch test
  • Rock brittleness evaluation method based on stress strain curve and scratch test

Examples

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Embodiment 1

[0036] To evaluate the brittleness index of tight carbonate rocks with different buried depths, the steps of the method are as follows: figure 1 As shown, the details are as follows:

[0037] (1) Evaluate the rock from the stress environment and pore pressure of the rock: evaluate the geological environment of the tight carbonate rock: the buried depth is widely distributed, from the surface to 4000 meters underground, the rock is extremely dense, and the interior is almost Does not contain fluid;

[0038] (2) Select a rock mechanics experiment that conforms to the environment of the rock sample to be tested: Since the geological environment of the rock sample is in which the main influencing factor is the in-situ stress, the conventional triaxial compression experiment is selected, the number of experiments is 4, and the confining pressure is set 10MPa, 20MPa, 30MPa and 40MPa respectively. For extremely tight reservoirs, the effective stress coefficient is taken as 0. The ...

Embodiment 2

[0052] For a low porosity and low permeability reservoir in a certain area (porosity between 10-15%, permeability 5-50*10 -3 μm 2 ) shale for brittleness index evaluation, such as figure 1 As shown, the method for calculating the brittleness index provided by the embodiments of the present invention has the following steps:

[0053] (1) Evaluation of the geological environment in which the mud shale is located: the buried depth is between 4,000 and 4,200 meters, and the rock has low porosity and low permeability. The regional pore pressure varies greatly, and the pressure coefficient varies from 1.1 to 1.5.

[0054] (2) Since the rock sample is located in the geological environment, the main influencing factors are in-situ stress and pore pressure, so the triaxial compression experiment is selected, the number of experiments is 4, the confining pressure is set to 80MPa, and the pore pressure is 45MPa, 50MPa, 55MPa respectively and 60MPa. For low porosity and low permeabilit...

Embodiment 3

[0067] To evaluate the brittleness index of tight carbonate rock, the steps of the method are as follows: figure 1 As shown, the details are as follows:

[0068] (1) Evaluate the geological environment of the carbonate rock: the carbonate rock in this section is relatively compact, and there is no fluid in the underground environment, and its buried depth is about 4000m;

[0069] (2) The condition setting of the triaxial compression test according to the rock environment: Since there is no fluid in the geological environment of the rock sample, there is no need to consider the influence of the fluid pore pressure. The main influencing factor is the in-situ stress, so the conventional Triaxial compression experiments.

[0070] In this example, the number of experiments is 1, and the confining pressure is set to 40MPa according to the buried depth of the rock. In this example, since there is no fluid, the pore pressure is zero, so the effective stress coefficient is 0. The co...

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Abstract

The invention provides a rock brittleness evaluation method based on a stress strain curve and a scratch test. The method comprises the following steps that: evaluating rock from a crustal stress environment where the rock is positioned, and pore pressure, and obtaining the stratum condition of the rock; selecting a rock mechanical experiment of the environment where a rock sample to be tested ispositioned, wherein the experiment includes a conventional triaxial compression test or a triaxial compression test which considers pore pressure, and a scratch test; obtaining a pre-peak strain energy density value, a crack initiation stress value, a peak value stress value, a residual stress value as well as corresponding strain size and crack linear density; and determining the value range of an effective stress coefficient [Alpha] from the pore pressure of a tested rock sample, and substituting the pre-peak strain energy density value, the crack initiation stress value, the peak value stress value, the residual stress value as well as the corresponding strain size and crack linear density into a brittleness index calculation formula to obtain the brittleness index of the rock to be tested. By use of the brittleness evaluation method, the accuracy and the applicability of the rock brittleness evaluation can be improved.

Description

technical field [0001] The invention relates to the technical field of deep rock mechanics, in particular to a method for evaluating rock brittleness based on stress-strain curves and scratch tests. Background technique [0002] The classical point of view is that there is no or little permanent deformation of the rock before it breaks into brittle fracture. For deep rocks, they generally have high brittleness and are often accompanied by a complex environment of high temperature and high pressure. Brittleness is a very important property of rock, and its evaluation has important guiding significance for rock engineering. For example, in petroleum engineering, brittleness is an important index for evaluating the geomechanical characteristics of reservoirs and the evaluation of hydraulic fracture expansion; while in deep rock mass engineering under complex stress conditions, the brittleness of rock mass is the key factor affecting engineering disasters such as rockbursts. i...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): G01N3/00G01N3/08
CPCG01N3/00G01N3/08G01N2203/0019G01N2203/0075G01N2203/0218G01N2203/0256G01N2203/0676G01N2203/0682
Inventor 陈勉金衍周舟考佳玮侯冰林伯韬卢运虎
Owner CHINA UNIV OF PETROLEUM (BEIJING)
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