CN103528934A - Mutual correlation technology for measuring permeability stress sensitivity of ultra-low permeability rocks - Google Patents

Abstract

The invention provides a cross-correlation technique for measuring the stress sensitivity of ultra-low permeability rock permeability. The technology includes the following steps: a) select ultra-low permeability cores such as shale or tight sandstone, and process them into cylindrical specimens; b) process a cylindrical steel block standard specimen for system calibration; c) use periodic Oscillation method is used to measure ultra-low permeability, and the porous medium can be gas or water. The measurement results of the steel block are used to calibrate the system; d) Put the core in the holder, apply confining pressure and pore pressure, saturate the core, apply the upstream sinusoidal pressure wave and keep it constant, and measure the downstream pressure wave of different confining pressure Response; e) Perform cross-correlation analysis on the downstream pressure waveforms of different confining pressures to obtain the variation of permeability with confining pressure. The present invention combines the periodic oscillation method of ultra-low permeability rock permeability measurement to perform cross-correlation analysis on the pressure waveform of permeability measurement, improves the accuracy of permeability change measurement, and solves the problem of ultra-low permeability stress sensitivity measurement.

Description

A cross-correlation technique for measuring the stress sensitivity of ultra-low permeability rock permeability

technical field

The invention relates to a technology for testing stress sensitivity of ultra-low permeability materials, in particular to a cross-correlation testing technology for ultra-low permeability rock permeability stress sensitivity. The invention can provide technical support for the permeability stress sensitivity test of unconventional oil and gas reservoirs and nuclear waste reservoirs.

Background technique

Permeability is the most important physical parameter of reservoir and the basis of oil and gas development. In recent years, with the development of unconventional oil and gas such as shale gas and tight sandstone oil and gas, there is an urgent need to carry out ultra-low permeability (<0.1×10 ^-3 μm ² ) testing, which poses challenges to both testing methods and instruments, and is unconventional. Difficulties in oil and gas development research. At present, the steady-state method and pulse decay method are mainly used in my country's petroleum industry to test ultra-low permeability, but there are still shortcomings in test accuracy, stability and test cycle. It is very important to develop high-precision ultra-low permeability methods.

The factors affecting the measurement of permeability can be mainly divided into two categories: external factors and internal factors. The internal factors are the mineral composition, pore structure, and particle size of rocks. External factors mainly include pressure, temperature and fluid properties. For ultra-low permeability cores in the laboratory, especially for core samples with a permeability lower than 0.1×10 ^-3 μm ² , the measurement of permeability takes a long time, some as long as several weeks to several months, so the pressure of the press Instruments such as pumps and pore pressure pumps put forward higher requirements. The instruments need to have high precision and good stability, and can maintain a certain stress state for several days to several months to measure the permeability value under a certain stress state. Second, the perturbation of the pore pressure, whether due to the pore pressure pump or the method of measuring the permeability, should be very small. During the experiment, there are noises in both the input pore pressure and the output test pressure, such as low-frequency temperature disturbance, high-frequency pump and pressure sensor noise, and other high-frequency electrical signals and other high- and low-frequency noises. The results have significant effects, which increase with decreasing permeability of the test sample. Especially for cores with ultra-low permeability, the constant temperature of the instrument is very important. Otherwise, small temperature and environmental disturbances may make it difficult to fit the pore pressure curve. The commonly used steady-state method and pulse decay method are not stable enough to measure ultra-low permeability, and the accuracy is also affected by temperature noise, which makes it more difficult to measure the stress sensitivity of permeability.

Compared with the pulse attenuation method widely used at present, the periodic oscillation method has lower requirements on experimental conditions and environment, and has the advantages of short time, stable results and high precision. The periodic oscillation method only uses the amplitude ratio and phase difference of the pore pressure signals at both ends of the rock, and does not require absolute values, so the influence of environmental changes on the measurement results is reduced to a certain extent. Moreover, the pore pressure wave of the periodic oscillation method has waveform characteristics, and digital signal processing methods such as fast Fourier transform (FFT) and cross-spectrum method can be used to process the data of the periodic oscillation method, so that the signal-to-noise ratio can be greatly improved to achieve fine Measuring ultra-low permeability requirements. The present invention combines the periodic oscillation method of ultra-low permeability rock permeability measurement, uses the waveform cross-correlation method for permeability change measurement, greatly improves the accuracy and stability of permeability change measurement, and solves the ultra-low permeability rock permeability stress sensitivity Measurement conundrum. The principle of the method is: the cross-correlation of two columns of waveforms can obtain the waveform phase difference with high precision, which belongs to waveform interferometry and is widely used in the field of signal detection. The invention uses the waveform cross-correlation method for permeability change measurement, carries out cross-correlation analysis on the pressure waveform of permeability measurement, obtains the change of permeability with confining pressure, and evaluates the stress sensitivity of ultra-low permeability rock permeability. Provide technical support for the permeability stress sensitivity test of unconventional oil and gas reservoirs and nuclear waste reservoirs

Contents of the invention

The purpose of the present invention is to provide a cross-correlation technology for measuring the stress sensitivity of ultra-low permeability rock permeability. Innovative invention. In order to monitor the stress sensitivity of ultra-low permeability core permeability.

In order to achieve the above object, the present invention provides a cross-correlation technology of ultra-low permeability rock permeability stress sensitivity, which comprises the following steps: a) select ultra-low permeability rock cores such as shale or tight sandstone, and process them into cylindrical b) process a cylindrical steel block standard sample for system calibration; c) use periodic oscillation method for ultra-low permeability measurement, and the porous medium can be gas or water. First, the steel block specimen is placed in the core holder, and the holder uses two servo pressure pumps to respectively apply confining pressure and sinusoidal pore pressure wave to the core through the valve. The measurement results of the steel block are used to calibrate the system; d) Put the core in the holder, apply confining pressure and pore pressure, and saturate the core with water or gas. After the core is saturated, an upstream sinusoidal pressure wave is applied and the downstream sinusoidal pressure wave response is measured. Keep the upstream sinusoidal pressure wave unchanged, change the confining pressure, and measure the response of the downstream pressure wave at different confining pressures; e) use the waveform cross-correlation method for the measurement of permeability changes, and perform cross-correlation on the pressure waveforms of permeability measurements under different confining pressures. Through correlation analysis, the change of permeability with confining pressure is obtained, and the stress sensitivity of ultra-low permeability rock permeability is evaluated.

Further, in step a), the selected cores such as shale and tight sandstone are taken from full-diameter cores of the developed reservoir or outcrops of the same horizon, and have ultra-low permeability. The core is processed into a standard cylinder with a diameter of 2.5 cm and a height of 3-4 cm.

Further, in step b), a cylindrical steel block specimen with the same scale as the core is processed. The porosity and permeability of steel blocks are theoretically zero.

Further, in step c), the steel block test piece is placed in the holder, and the confining pressure and pore pressure are respectively applied to the steel block test piece. A sinusoidal pore pressure wave is applied upstream of the steel block specimen, and the downstream pore pressure wave response is measured. The measurement results are used to calibrate the system specific storage rate equivalent.

Further, in step d), the periodic oscillation method is used to measure the permeability of ultra-low permeability cores such as shale and tight sandstone. After applying confining pressure and pore pressure to saturate the core, an upstream sinusoidal pressure wave is applied, and the downstream sinusoidal pressure wave response is measured. Keep the upstream sinusoidal pressure wave constant, change the confining pressure, and measure the response of the downstream pressure wave with different confining pressure.

Further, in step e), the cross-correlation technique is adopted in the data processing of the periodic oscillation method, and the downstream pore pressure wave of a certain confining pressure is selected as the reference pressure waveform, and the correlation between the downstream pressure wave and the reference pressure wave under different confining pressures is used to Correlation processing to obtain the relative pressure waveform amplitude ratio and phase difference.

Further, the inner diameter of the pipe transporting the pore fluid in the holder is very small, about 0.7 mm, and after exiting the holder, the pipe is connected to a large pipe with an inner diameter of 3 mm through a valve. In order to reduce the impact of the specific storage rate on the ultra-low permeability core permeability test.

Further, keep the waveform of the upstream pore pressure unchanged, that is, keep the same amplitude and frequency of the upstream pore pressure waveform.

Further, the downstream pressure wave under a certain confining pressure is selected as the reference waveform, and the permeability under a certain confining pressure is selected as the reference permeability.

The beneficial effect of the present invention is that, in combination with the periodical oscillation method of ultra-low permeability rock permeability measurement, the waveform cross-correlation method is used for the permeability change measurement, and the cross-correlation analysis is performed on the pressure waveform of the permeability measurement, which greatly improves the permeability change. The accuracy and stability of the measurement can obtain the change of permeability with the confining pressure, and solve the problem of stress sensitivity measurement of ultra-low permeability rock permeability, so as to evaluate the stress sensitivity of ultra-low permeability rock permeability. This method will have great stress potential in unconventional oil and gas development and nuclear waste reservoir research.

Description of drawings

In order to illustrate the embodiments of the present invention more clearly, the following briefly introduces the accompanying drawings that are used in the description of the embodiments. In the attached picture:

Fig. 1 is an experimental flow chart of a cross-correlation technique for measuring ultra-low permeability rock permeability stress sensitivity in an embodiment of the present invention;

Fig. 2 is a schematic diagram of the experimental device structure of a cross-correlation technique for measuring the stress sensitivity of ultra-low permeability rock permeability in an embodiment of the present invention;

3 is a cross-correlation technical schematic diagram of ultra-low permeability rock permeability stress sensitivity measurement in an embodiment of the present invention;

Detailed ways

In order to make the purpose, technical solutions and advantages of the embodiments of the present invention more clear, the embodiments of the present invention will be further described in detail below in conjunction with the accompanying drawings. Here, the exemplary embodiments and descriptions of the present invention are used to explain the present invention, but not to limit the present invention.

The main problems of existing technologies for measuring ultra-low permeability are long measurement time, low precision, and poor stability. Therefore, it is more difficult to measure the permeability stress sensitivity of ultra-low permeability cores. In order to overcome the above difficulties, the present invention provides a cross-correlation technique for measuring the stress sensitivity of ultra-low permeability rock permeability. As shown in Figure 1, the method includes the following steps:

Step S101: select ultra-low permeability cores such as shale or tight sandstone, and process them into cylindrical specimens;

Step S102: Process a cylindrical steel block standard test piece for system calibration;

Step S103: The periodical oscillation method is used to measure the ultra-low permeability, and the porous medium can be gas or water. First, the steel block specimen is placed in the core holder, and the holder uses two servo pressure pumps to respectively apply confining pressure and sinusoidal pore pressure wave to the core through the valve. The steel block measurement results are used to calibrate the system;

Step S104: Put the core in the holder, apply confining pressure and pore pressure, and saturate the core with water or gas. After the core is saturated, an upstream sinusoidal pressure wave is applied and the downstream sinusoidal pressure wave response is measured. Keep the upstream sinusoidal pressure wave unchanged, change the confining pressure, and measure the response of the downstream pressure wave with different confining pressure;

Step S105: Apply the waveform cross-correlation method to the measurement of permeability change, perform cross-correlation analysis on the pressure waveforms of permeability measurements under different confining pressures, obtain the change of permeability with confining pressure, and evaluate the stress sensitivity of ultra-low permeability rock permeability sex.

As mentioned above, for unconventional reservoirs with ultra-low permeability, the specific storage flow rate of the system can be calibrated and corrected through this instrument and equipment, thereby greatly improving the measurement accuracy of permeability. Combined with the periodic oscillation method of ultra-low permeability rock permeability measurement, the waveform cross-correlation method is used to measure the permeability change, and the cross-correlation analysis of the pressure waveform of the permeability measurement can obtain the change of the permeability with the confining pressure, and evaluate the ultra-low permeability. Stress Sensitivity of Permeable Rock Permeability.

For ultra-low permeability cores in the laboratory, especially for core samples with a permeability lower than 0.1×10 ^-3 μm ² , the measurement of permeability takes a long time, and the pressure pump of the press and the pore pressure pump and other instruments have higher requirements. The requirement of the instrument requires high precision and good stability, and it can maintain a certain stress state for several days to several months to measure the permeability value under a certain stress state. In addition, due to the extremely low permeability of unconventional reservoirs, the specific storage flow rate of the pipeline transporting pore fluids has a great influence on the measurement results of permeability. , the inner diameter of the pipe in the holder is about 0.7mm, and the pipe is connected to a large pipe with an inner diameter of 3mm through a valve after exiting the holder. As shown in Figure 2, 1 is the core chamber, 2 and 3 are the pore pressure servo pump and the confining pressure control pump respectively, which apply pore pressure and confining pressure to the core. 4, 5, and 6 are the upstream pore pressure sensor, the downstream pore pressure sensor, and the confining pressure sensor respectively. When the periodic oscillation method is used to test the permeability of the core, a sinusoidal pore pressure wave is applied upstream of the core, and the response of the pore pressure downstream of the core is observed. 7 is a control valve, 8 is a pipeline with an inner diameter of 0.7 mm for transporting pore fluid, and 9 is a pipeline with an inner diameter of 3 mm for transporting pore fluid. The tested rock core is processed into a standard cylinder with a diameter of 2.5 cm and a height of 3-4 cm, and placed in the core chamber 1. The experimental equipment can measure the variable confining pressure. In order to solve the influence of the specific storage rate of the core holder on the accuracy of ultra-low permeability, a cylindrical steel block specimen with the same scale as the core was processed. The porosity and permeability of steel blocks are theoretically zero. Put the steel block specimen in the holder, respectively apply confining pressure and pore pressure to the steel block, apply a sinusoidal pore pressure wave to the upstream of the steel block, and measure the downstream pressure wave response. The measurement results are used to measure the core permeability. The results are calibrated.

To measure the relative change in permeability, the waveform data from the periodic oscillation method were analyzed using cross-correlation techniques. The principle of this technology is: the cross-correlation of two columns of waveforms can obtain the waveform phase difference with high precision, which belongs to waveform interferometry and has been widely used in the field of signal detection. The cross-correlation function is defined as:

${\mathrm{<span\; class="notranslate">\; R</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; w</span>}}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; S</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&equiv;</span>\frac{{<span\; class="notranslate">\; \&Integral;</span>}_{\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; w</span>}}}^{\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; w</span>}}}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; unp</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; t</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; per</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; t</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; d</span>}{\mathrm{<span\; class="notranslate">\; t</span>}}^{<span\; class="notranslate">\; \&prime;</span>}}{{<span\; class="notranslate">\; (</span>{<span\; class="notranslate">\; \&Integral;</span>}_{\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; w</span>}}}^{\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; w</span>}}}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; unp</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; t</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; d</span>}{\mathrm{<span\; class="notranslate">\; t</span>}}^{<span\; class="notranslate">\; \&prime;</span>}{<span\; class="notranslate">\; \&Integral;</span>}_{\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; w</span>}}}^{\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; w</span>}}}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; per</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; t</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; d</span>}{\mathrm{<span\; class="notranslate">\; t</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; )</span>}^{\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}}}$

In the formula, the length of the time window is 2t ^w , and t is the center position of the window. t ^s is the moving time used in cross-correlation, uunp represents the reference wave field, and uper represents the wave field under different confining pressures. The maximum value (R _max ) of the cross-correlation function represents the similarity of two waves, and the time delay (δ _t ) corresponding to R _max represents the change of different phases.

The invention combines the periodic oscillation method of ultra-low permeability rock permeability measurement, and uses waveform cross-correlation technology for permeability change measurement. Using cross-correlation techniques, the phase differences of two similar wave trains are compared to obtain high-precision measurements of permeability changes. The cross-correlation technique of the periodic oscillation method for permeability change measurement is to use the cross-correlation of downstream waveforms to obtain the phase difference under different stress states. As shown in Fig. 3, 1 is the upstream pore pressure wave of the core, no matter how the confining pressure changes, the upstream pressure waveform always remains the same, with the same amplitude and frequency. 2 is a core with ultra-low permeability. 3 is the response waveform of the downstream pore pressure of the core under different confining pressures. Since the upstream pore pressure waves have the same amplitude and frequency, the amplitude ratio and phase difference under different confining pressure conditions can be obtained by cross-correlating the downstream pore pressure waves. In Fig. 3, 4 is the phase difference of downstream pore pressure waves under different confining pressure conditions, and 5 is the amplitude ratio of downstream pore pressure waves under different confining pressure conditions. The variation of permeability with confining pressure is obtained from the amplitude ratio and phase difference of downstream pore pressure waveforms under different confining pressure conditions, and the stress sensitivity of ultra-low permeability rock permeability is evaluated.

The specific embodiments described above have further described the purpose, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above descriptions are only specific embodiments of the present invention and are not intended to limit the scope of the present invention. Protection scope, within the spirit and principles of the present invention, any modification, equivalent replacement, improvement, etc., shall be included in the protection scope of the present invention.

Claims (10)

1. A cross-correlation technology for measuring the stress sensitivity of ultra-low permeability rock permeability. It is characterized in that the waveform cross-correlation method is used for the measurement of permeability change, which greatly improves the accuracy and stability of permeability change measurement, and solves the problem of ultra-low permeability. Difficulties in measuring the stress sensitivity of permeability rock permeability. The principle of the method is: the cross-correlation of two columns of waveforms can obtain the waveform phase difference with high precision, which belongs to waveform interferometry and is widely used in the field of signal detection. The present invention combines the periodic oscillation method of ultra-low permeability rock permeability measurement, uses the waveform cross-correlation method for the permeability change measurement, and performs cross-correlation analysis on the pressure waveform of the permeability measurement to obtain the change of the permeability with the confining pressure, and evaluate the ultra-low permeability. Stress Sensitivity of Low Permeability Rock Permeability. The technique includes the following steps: a) select ultra-low permeability cores such as shale or tight sandstone, and process them into cylindrical specimens; b) Process a cylindrical steel block standard test piece for system calibration; c) The periodical oscillation method is used to measure the ultra-low permeability, and the porous medium can be gas or water. First, the steel block specimen is placed in the core holder, and the holder uses two servo pressure pumps to respectively apply confining pressure and sinusoidal pore pressure wave to the core through the valve. The steel block measurement results are used to calibrate the system; d) Put the core in the holder, apply confining pressure and pore pressure, and saturate the core with water or gas. After the core is saturated, an upstream sinusoidal pressure wave is applied and the downstream sinusoidal pressure wave response is measured. Keep the upstream sinusoidal pressure wave unchanged, change the confining pressure, and measure the response of the downstream pressure wave with different confining pressure; e) Apply the waveform cross-correlation method to the measurement of permeability change, conduct cross-correlation analysis on the pressure waveforms of permeability measurements under different confining pressures, obtain the change of permeability with confining pressure, and evaluate the stress sensitivity of ultra-low permeability rock permeability . 2. the cross-correlation technique of measuring ultra-low permeability rock permeability stress sensitivity as claimed in claim 1, is characterized in that, in step a), the rock cores such as selected shale, tight sandstone are taken from the developed reservoir Full-diameter cores or outcrops of the same horizon, with ultra-low permeability, are machined into standard cylinders with a diameter of 2.5 cm and a height of 3-4 cm. 3. the cross-correlation technique of measuring ultra-low permeability rock permeability stress sensitivity as claimed in claim 1, is characterized in that, in step b), process a cylindrical steel block specimen with the same scale as rock core, steel block The porosity and permeability are theoretically zero. 4. the cross-correlation technique of measuring ultra-low permeability rock permeability stress sensitivity as claimed in claim 1, is characterized in that, in step c), steel block specimen is placed in the holder, respectively gives steel block Confining pressure and pore pressure are applied to the specimen, and a sinusoidal pore pressure wave is applied upstream of the steel block specimen, and the response of the downstream pore pressure wave is measured. The measurement results are used to calibrate the equivalent value of the system specific storage flow rate. 5. the cross-correlation technique of measuring ultra-low permeability rock permeability stress sensitivity as claimed in claim 1, is characterized in that, in step c), in the holder, the two pipe inner diameters of transporting upper and lower pore media It is very small, about 0.7mm, to reduce the influence of the specific storage rate on the ultra-low permeability core permeability test. 6. the cross-correlation technique of measuring ultra-low permeability rock permeability stress sensitivity as claimed in claim 1, is characterized in that, in step d), adopts periodic oscillation method to carry out ultra-low permeability rock cores such as shale, tight sandstone infiltration Rate measurement, apply confining pressure and pore pressure to saturate the core, apply upstream sinusoidal pressure wave, measure downstream sinusoidal pressure wave response, keep upstream sinusoidal pressure wave unchanged, change confining pressure, measure downstream pressure wave of different confining pressure response. 7. the cross-correlation technology of measuring ultra-low permeability rock permeability stress sensitivity as claimed in claim 1, is characterized in that, in step e), adopts cross-correlation technology in period oscillation method data processing, selects a certain range The downstream pore pressure wave under different confining pressures is the reference pressure waveform, and the relative pressure waveform amplitude ratio and phase difference are obtained through cross-correlation processing between the downstream pressure wave and the reference pressure wave under different confining pressures. 8. The cross-correlation technique for measuring the stress sensitivity of ultra-low permeability rock permeability as claimed in claim 5, characterized in that, the internal diameter of the pipe transporting pore fluid in the holder is very small, about 0.7mm, The holder is then connected to a large pipe with an inner diameter of 3 mm through a valve. 9. The cross-correlation technique for measuring the stress sensitivity of ultra-low permeability rock permeability as claimed in claim 6, wherein the upstream pore pressure waveform is kept constant, that is, the same amplitude and frequency of the upstream pore pressure waveform are kept. 10. the cross-correlation technique of measuring ultra-low permeability rock permeability stress sensitivity as claimed in claim 7, is characterized in that, selects the downstream pressure wave under a certain confining pressure condition as reference waveform, selects under a certain confining pressure condition The permeability is the reference permeability.

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