Accumulation Mechanism And Enrichment Regulation Of Upper Paleozoic Tight Gas Reservoirs In Jingbian Area, Ordos Basin

Using the existing data of drilling,borehole log,well logging,testing,core observation,thin section examination and fluid inclusion in this area,combined with latest theoretical methods and measures of hydrocarbon accumulation geology,reservoir geology,petroleum geochemistry,dynamics of petroleum accumulation and the theory of petroleum system,the geological characteristics,migration and accumulation characteristics,accumulation model and key reservoir-forming factors of the Upper Paleozoic gas reservoirs in Jingbian area are systematically analyzed.Upper Paleozoic strata are gentle and simple,which mainly dominated by the barrier coast system and delta sedimentary system in Jingbian area.As a whole,it belongs to ultra low porosity and low-ultra low permeability reservoir,and gas mainly comes from the C-P coal-bearing source rock,which is mainly dry gas that has higher methane content.Most present gas reservoirs have ultra low pressure or low pressure,which is mainly caused by the lifting and erosion of strata,the decrease of formation temperature and gas dissipation.Late Jurassic to Early Cretaceous,especially in Early Cretaceous period,the source rocks entered the peak period of hydrocarbon generation and expulsion.And the hydrocarbon generation pressurization provided the main driving force for the primary migration of gas.In addition,tight sandstone gas had no dominant pathways of gas migration which mainly migrated and charged in a larger scale.The main reservoir-forming period is later than the reservoir densification period,and it is mainly “tight first and then accumulated” reservoir.There are 2 kinds of hydrocarbon accumulation models:“self-generated and self-stored gas in source rock” and “lower-generated and upper-stored gas near source rock”,and the reservoirs are typical “quasi-continuous tight sandstone gas reservoirs”.The Upper Paleozoic gas reservoirs in Jingbian area have the characteristics of quasi-continuous and widespread distribution,which mainly distributed in single factor relatively superior position,rather than the optimal area.And the accumulation is controlled by multi-factor coupling relationship of source,reservoir,caprock and construct that single factor has no significant effects.Based on accumulation mechanism,distribution characteristics and main controlling factors of the Upper Paleozoic gas reservoirs in Jingbian area,it can provide reference for the study of tight sandstone gas reservoirs and guide the exploration and development of Upper Paleozoic gas in the central and southern Ordos Basin.