Study On Influence Of Mineral Components On The Properties Of Shale Reservoirs In The Northern Guizhou

The unconventional natural gas in the northern Guizhou province is one of the key areas for exploration and development,and its efficient exploitation with enormous significance for China’s high-quality and sustainable development in accelerating the achievement of"peak carbon and carbon neutrality",restructuring the energy industry,optimizing the strategic reserve of energy supply and demand,deepening the structural reform of the energy supply side,and promoting the national economy,science and technology,R&D innovation,and people’s livelihood needs.The mineral components play an indispensable role in shale reservoirs,this paper takes shale reservoirs of northern Guizhou province as the research object and based on the field survey,geological and logging data collection,and theoretical literature as a starting point.The geochemical parameters such as mineral components,physical parameters such as porosity,and mechanical parameters such as elastic modulus are obtained through the combination of geochemical,material property,physical,numerical test,and theoretical research methods to study the influence of mineral components on the reservoir characteristics,mechanical properties,and stress sensitivity of shale reservoirs in northern Guizhou province,and the following research results were obtained1)The clay mineral contents of wells FC-1,TM-1,TMY-1,TX-1,CY-1,and outcrop samples are negatively correlated with the cumulative quartz,feldspar,and pyrite contents,which are not significantly correlated with carbonate minerals.The clay mineral composition is dominated by illite,and the illite content is negatively correlated with the mixed layer mineral content.The carbonate mineral content is negatively correlated with both R₀ and depth of burial,with correlations of 0.6 to 0.8,which is not significantly correlated with TOC.The brittle mineral content is positively correlated with TOC,R_0,and depth of burial,with correlations ranging from 0.2 to 0.8.The clay mineral content is negatively correlated with TOC,R_0,and depth of burial,with correlations ranging from 0.5 to 0.8.The depth of burial is positively correlated with R₀,with correlations of 0.8 to 1.0,but not with TOC content.The high correlation between wells TM-1,TX-1,and CY-1 with common pooling domains,is mainly influenced by pyrite,carbonates,and clay mineral content.The well FC-1 has no common pool area with wells TM-1,TX-1,and CY-1 is poorly correlated and mainly influenced by the cumulative quartz,feldspar,and pyrite contents,depth of burial,and organic maturity R₀.2)When shale has a low brittleness index and a high clay mineral content,the stress-time variation curve is flat,the compressive strength,tensile strength,and modulus of elasticity are small,and the acoustic emission signal is low and of low intensity.Conversely,a large slope of the stress-time variation curve,the compressive strength,tensile strength,and modulus of elasticity are high,and a high number and intensity of acoustic emission signals.Under the Brazilian splitting test,the yy-1,2,and3 series fracture extension patterns can be categorized as axial penetration,lateral slip,and lateral slip+bottom rupture.Under uniaxial compression testing,the fracture expansion pattern of the yy-1,2,and 3 series can be generally summarized as an axial penetration type,with primary rupture accompanied by secondary rupture,secondary rupture shifting to primary rupture,and with primary rupture increasing with increasing brittleness index.Numerical simulations show that the paths of fracture extension are divided into emergence,extension,and destruction,all of which occur at the junction of the shale matrix or quartz and shale matrix.An overall increase in the proportion of fractures with increasing quartz content,with a fit of 0.684.3)The permeability impairment rate and stress sensitivity of shale reservoirs in the study area is judged to be moderately strong and strong,respectively,and the permeability impairment rate and stress sensitivity factor are positively and negatively correlated with the effective stress,respectively.When the effective stress is 7MPa,it is the inflection point value affecting the stress sensitivity factor and permeability impairment rate of the shale reservoir in northern Guizhou province.Analyzed from the perspective of quartz content,quartz content of 65%is the critical value affecting the stress sensitivity factor and permeability impairment rate of shale reservoirs.The permeability impairment rate and stress sensitivity factor decrease with increasing quartz content and modulus of elasticity,increase with increasing feldspar and clay mineral content,increase and then decrease with increasing calcite and ankerite content,while the effect of pyrite content on the permeability impairment rate and stress sensitivity coefficient is not significant.The greater the brittle mineral content of shale,the more likely it is to undergo brittle damage and more crack extension during compression with predominantly elastic deformation,resulting in a lower stress sensitivity factor.Conversely,the higher the stress sensitivity factor.