Method for measuring permeability of ultra-low permeability rocks under tri-axial stress effect

Abstract

The invention discloses a method for measuring permeability of ultra-low permeability rocks under a tri-axial stress effect. The method comprises the following steps of: selecting an ultra-low permeability rock, and preparing a test sample; wrapping water permeable liner plates at the upper end and the lower end of the test sample and the test sample between an upstream porous pressure cushion block and confining pressure chamber base by using a rubber sleeve; applying confining pressure and axial pressure to the test sample to a given value, simultaneously applying permeation pressure to the test sample, and saturating the test sample; after the osmotic pressure saturation of the test sample, applying a sinusoidal pressure wave with a known amplitude and a known frequency to the test sample, recording a downstream pore pressure wave situation, and transmitting the data to a data measurement and acquisition system in real time; changing the confining pressure and the axial pressure, measuring the permeability by using a waveform correlation method, analyzing the permeability of the test sample under different confining pressure and axial pressure situations, and obtaining the permeability under different confining pressure and axial pressure conditions. By adopting the method for measuring the permeability of the ultra-low permeability rocks under the tri-axial stress effect, the weaknesses of the prior art that the measurement precision is poor, only the confining pressure can be provided, and the stress state of the deep rock under the tri-axial stress effect cannot be actually simulated can be overcome.

Description

technical field [0001] The invention relates to the field of rock mechanics testing in geotechnical engineering technology, in particular to a method for measuring ultra-low permeability rock permeability under the action of triaxial stress. Background technique [0002] Permeability is one of the important physical parameters of rocks, and it is especially important for understanding the physical characteristics of deep rock masses stored in unconventional oil and gas fields and nuclear waste. With the exploitation of shale gas and tight sandstone oil and gas in recent years, there is an urgent need to A device for measuring the permeability of ultra-low-permeable rock mass under triaxial stress state, which poses a big challenge to the current experimental principles and experimental instruments. [0003] At present, most of the experimental instruments for measuring rock permeability adopt the principle of steady state method or pressure pulse method. For ultra-low permea...

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Problems solved by technology

[0003] At present, most of the experimental instruments for measuring rock permeability adopt the principle of steady state method or pressure pulse method. For ultra-low permeability rock mass in unconventional oil and gas field reservoirs, this test method has the disadvantages of backward measurement principle and poor measurement accuracy. , so it is not applicable to the measurement of the permeability of this ultra-low permeability rock mass; the more popular method for measuring the permeability of ultra-low permeability rock is the pressure oscillation method. Wave, the corresponding seepage pressure wave is measured downstream, and the ultra-low permeability rock permeability is obtained by comparing the waveforms between the two

[0004] At present, there are some shortcomings in a small number of domestic instruments that use the pressure oscillation method to measure the permeability of ultra-low permeability rock mass; The pressure oscillation method is used to measure the permeability of ultra-low permeability rocks, but this device can only provide confining pressure, not the test state of triaxial stress, and cannot truly simulate the stress state of deep rock mass under triaxial stress

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