Study On Measurement Methods Of Porosity And Permeability For High Thermal Maturity Longmaxi Shale Reservoir,Southern Sichuan

Shale reservoirs are unconventional oil and gas reservoirs.Their pore system is small in size,and their porosity and permeability measurements are different from conventional reservoirs.In order to clarify the differences in different shale permeability measurement methods and compare the advantages and disadvantages of each method with the difference in test results,an evaluation method for pore permeability characteristics that is more consistent with marine shale reservoirs was obtained.This paper uses the Longmaxi high in the Xingwen area in the southern part of the Sichuan Basin.The evolutionary shale is the research object.Through the principle analysis of the pore permeability measurement method and the comparison of the test results,the advantages,disadvantages and applicable scope of different pore permeability measurement methods are obtained,which provides a strong basis for the physical evaluation of shale reservoirs.Combined with environmental scanning electron microscopy,X-ray diffraction(whole rock)mineral analysis,organic texture test analysis(TOC,Ro,kerogen microscopy)and other experimental analysis,obtained shale rock structure characteristics,mineral composition characteristics,organic petrological characteristics,etc.Comprehensive analysis of petrological characteristics.Through alcohol porosity measurement on 16 samples(post samples),conventional gas porosity measurements on 13 samples(pillar samples),clad porosity measurements on 18samples(post samples),and 16 Block samples(pillar samples)were subjected to NMR porosity measurements,and the measured porosity was compared and analyzed.The results were as follows:(1)Conventional gas measurement methods resulted in smaller test results due to the smaller inlet pressure P_k.Cannot be used for dense shale tests.(2)Alcohol method,since the G₂ value reading results vary with the reading time,the best reading time is about 90s.The conventional alcohol saturation method cannot fully saturate the shale,and under the saturation pressure of 15MPa,the shale can be fully saturated.saturation.(3)NMR method,because the presence of crystal water in shale will affect the accurate measurement of nuclear magnetic porosity,therefore,the crystal water content in shale can be deducted from the measurement results of saturated samples to obtain more accurate results.(4)The clad pressure method,because the experimental confining pressure is too high will make the sample broken or the pore is closed,should test under the low confining pressure(3.5MPa?12MPa).(5)One-way analysis of variance was performed on the porosity parameters obtained by different methods.The results also showed that there was no significant difference among the three parameters and they were consistent.The shale porosity of the Longmaxi formation in the Xingwen area measured by the three methods are:alcohol method(3.77%?13.77%),clad pressure method(3.83%?13.5%),and nuclear magnetic method(3.84%?5.74%).The average porosity is 7.36%.(6)The pulse attenuation method was used to test 14 samples with a permeability of 0.0004056m D?0.0067068m D and an average of 0.0018478m D.Comparing the permeability differences between the horizontal and vertical bedding directions,it was found that the permeability in the parallel bedding direction was much higher than that in the vertical bedding direction,and the former was 2?9 times the same for the same sample.(7)The permeability calculated by the inversion empirical value C is 1.5?10 times smaller than the permeability calculated by the conventional region empirical value,but it is nevertheless quite large compared with the permeability obtained by the pressure pulse method.The Coates calculation formula for the particle accumulation model is not suitable for calculating the permeability of dense shales.