Research On Rock Physics Experiments And Numerical Simulation Of Marine Shale In South Of China

Shale is observed to have strong anisotropy due to its unique mineralogy and microstructure,and this anisotropy property has significant impact on seismic and well-log data.The organic-rich marine shale in the southern and eastern Sichuan Basin is one of the most important shale-gas target reservoir formations in China.This paper performed a series of systematic rock physical experiments on shale in Wulong county and Yushan in Pengshui county.We obtained the velocity ? mineral and elastic characteristics of shale in south of China by comparing the different rock physics data of domestic and foreign regions,then analyzed the influencing factors and verified the research results by theoretical model.The results provide an important rock-physics basis and data support for seismic anisotropy exploration,quantitative interpretation,and resource evaluation of the shale in southern China.The main results of this paper can be summarized as follows:(1)More than 30 field samples were collected,the mineral composition and clay type were measured by X-ray diffraction.The organic matter content,organic matter types,organic matter maturity,and vitrinite reflectance were observed using rock-eval pyrolysis,kerogen microscopic examination,and vitrinite reflectance measurement,respectively.About 20 plug samples were prepared for elastic wave velocities measuring by a pulse system,and the elastic parameters were calculated according to the measured data.Density and porosity were measured by high-precision densitometer.Microstructure of samples were analyzed by SEM image.(2)The shale characteristics of mineral distribution?organic matter?porous?elastics?microstructure were obtained:(1)All Mineral types were obtained including quartz?clay?feldspar?pyrite.The major mineral content is Quartz and followed by clay content.Clay types includes illite?smectite?kaolinite and chlorite,illite content was the highest.(2)The organic matter with types?showed overmature feature and distributed randomly and discretely among other minerals in shale.(3)The reservior space are mainly solution pores?organic pores and Intergranular pores.(4)The velocity anisotropy of the shale varies from 10% to 50%,and most samples have strong anisotropy because of the clay's distribution.(3)The influence factors of velocity and elastic were analyzed,the results showed that organic matter was positively correlated with quartz and negatively with clay.These relations and overmature characteristics indicated that organic matter has not been associated with velocity.The relation between quartz and velocity impedance were also analyzed,the results showed a V-trend between quartz and velocity impedance which indicated the change of rock skeleton(quartz or clay).Based on the above study we also studied the relationships between quartz?organic matter and elastic property.(4)The Backus model was introduced to analysis the relation between organic matter and elastic anisotropy in different regions,the results showed that organic matter also has no relevance to elastic anisotropy.The elastic?distribution and relation with quartz of organic matter are the main reason.Clay orientation?content and Thomsen parameters were used to analysis the impact of clay orientation on clay content and Thomsen parameters.On the basis of positive correlation between clay content and anisotropy,compaction degree and pore structure should be considered for anisotropy.(5)The anisotropic DEM model was used to study the rock physics characteristics of marine shale in South China ccording to the results.Two results were discussed:(1)The influence of Quartz and clay as rock skeleton respectively.(2)The influence of organic matter's distribution and overmature characteristic on elastic property.