Subsidence feature of Qishen area Sha Ⅲ member and its relationship with tectonic evolution

Carrying on the subsidence history simulation in Qishen area key exploration stratigraphic interval,understand the space and time distribution characteristic of its subsidence rate,simultaneously study the subsidence characteristic and its relationships with the basin structure evolutionary.Take Qishen area's three dimensional seismic data as a foundation,select each simulation parameter reasonably,carry on the subsidence history simulation on Sha III member by using the EBM basin simulation software.The analogue result indicates that subsidence features of each sub-member of the Sha III member depositional stage have the characteristics of both obvious succession and certain difference.Further analysis reveals: Sha III member stage,subsidence features of Qishen area is related to its tectonic evolution,its tectonic stress condition experiences successively by the initial intense extension stress condition two evolutions of obviously weakening and the small scale weakening.Which means Sha III member sedimentary basin experienced three evolutionary phases as the fault depression initial period,accelerating period and weakening period.The analogue result also indicates: Qishen area subsidence characteristic and the tectonism are controlling the sedimentary sand body distribution of each sub-member of Sha III member.According to the comprehensive study of Qishen high speed subsidence features and reservoir forming law,it is thought overpressure oil and gas reservoir existed in Sha II member of Qishen area.The subsidence history simulator study has revealed Sha III member basin sedimentation rate characteristic and its relationship with tectonic evolution,meanwhile discussed the subsidence characteristic and its relationship with the deposition and formation,thus established the good foundation for the research area fine oil-gas exploration.