Study On Hydrocarbon Accumulation Process In Paleogene Low-permeability Area In Wushi 16-1/17-2 Target Area Of Beibuwan Basin

Wushi 16-1/17-2 target area is located in the central uplift belt in Wushi sag of Beibuwan Basin,oil-bearing series and low permeability oil resource are rich,but the pore structure characteristics of low permeability reservoir are unknown,abnormal high pressure of low permeability reservoir formation mechanism is not clear and the influence on the hydrocarbon accumulation process is not yet clear,at the same time,the region's oil and gas accumulation time remains to be further defined.Focusing on Wushi 16-1/17-2 target area as the research object and on the basis of comprehensive analysis of regional geological background,this study uses nitrogen adsorption,high-pressure mercury injection experiments to quantitatively characterize the pore structure of low permeability reservoir rocks,applies one-dimensional physical simulation experiments to reveal the hydrocarbon filling process within low-permeability reservoirs,conducts fluid inclusion analysis to clarify the hydrocarbon accumulation period and finally establishes the hydrocarbon accumulation model.The results show that the low-permeability reservoirs in the study area have strong heterogeneity,and many pore types,such as dissolution pores,microfractures and intergranular pores,are developed.The pore volume is mainly provided by macropores.The formation mechanism of overpressure is mainly due to the under-compaction of mudstone,and the formation period of overpressure in the target area is earlier than the most recent oil-gas filling event,which is not conducive to oil-gas filling.Target hydrocarbon expulsion and tectonic movement period time-space matching relations as well as the physical properties of reservoir rocks are the main factors affecting hydrocarbon accumulation,the hydrocarbon accumulation within reservoirs is mainly controlled by source reservoir pressure difference.The physical properties of reservoir rocks mainly control the hydrocarbon accumulation process within source rocks.The hydrocarbon accumulation model within source rock is that differential pressure leads to hydrocarbon filling reservoirs,physical properties of reservoir rocks control hydrocarbon accumulation.Consequently,the future exploration direction of Wushi target area is looking for high quality reservoirs.