Method and device for measuring thermal stress of rock test piece under action of liquid nitrogen

Abstract

The invention provides a method and device for measuring thermal stress of a rock test piece under the action of liquid nitrogen. The method comprises the following steps of: acquiring tensile strength of the rock test piece under a room temperature condition; presetting a first shaft and a second shaft for the rock test piece; applying three-dimensional confining pressure stress with different sizes to the rock test piece, injecting water into the first shaft, and plugging the second shaft, so that the rock test piece is subjected to hydraulic fracturing, and a main crack perpendicular to thedirection of the minimum confining pressure stress is obtained; and applying preset three-dimensional confining pressure stress with the same sizes to the rock test piece, injecting liquid nitrogen into the first shaft, enabling the liquid nitrogen to flow out of the second shaft, gradually reducing the confining pressure stress parallel to the direction of the main crack, and measuring the confining pressure stress corresponding to a first fracture signal when the fracture signal in the rock test piece is sharply increased, wherein the confining pressure stress is critical confining pressurestress. The thermal stress of the rock test piece is the sum of the critical confining pressure stress and the tensile strength. The method and the device can make up the blank that the thermal stress of rock cannot be effectively measured in a liquid nitrogen environment.

Description

technical field [0001] The application belongs to the field of rock thermal stress measurement, in particular to a method and device for measuring the thermal stress of a rock test piece under the action of liquid nitrogen. Background technique [0002] my country is rich in unconventional oil and gas resources with great development potential. Due to the extremely low permeability of unconventional oil and gas reservoirs, special engineering techniques are required for exploitation. At present, conventional hydraulic fracturing technology is difficult to effectively stimulate unconventional oil and gas reservoirs. Cryogenic fluids such as liquid nitrogen and liquid carbon dioxide are gradually applied to fracturing operations in unconventional oil and gas reservoirs, which is expected to increase the production of unconventional oil and gas resources. The study of the mechanism of liquid nitrogen ultra-low temperature rock breaking is very important for the design of liqui...

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Problems solved by technology

[0003] At present, the conventional method of measuring thermal stress is mainly to measure the deformation of the rock specimen by pasting sensors such as strain gauges or optical fibers on the surface of the rock specimen to calculate the thermal stress. However, due to the extremely low temperature of liquid nitrogen, the conventional method of measuring thermal stress in There are two main problems when measuring the thermal stress of rock under the ultra-low temperature of liquid nitrogen. First, the properties of sensors such as strain gauges and optical fibers will change greatly under the action of ultra-low temperature of liquid nitrogen, which makes them unable to measure deformation normally. The adhesive of the specimen will also undergo a large deformation under the ultra-low temperature of liquid nitrogen, which will interfere with the sensor to measure the strain of the specimen. Therefore, the conventional method of measuring thermal stress will fail when measuring the thermal stress of rock under the ultra-low temperature of liquid nitrogen. Resulting in ineffective measurement of rock thermal stress

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