Oil Accumulation Rule Research On Low-permeability Lithologic Reservoirs

The large and medium-sized oil and gas fields which have been found in Ordos Basin are mostly in the low permeable lithologic stratigraphic trap,so,analysing the low-permeability lithologic reservoir accumulation of Yanchang formation in Ordos Basin has very important significance.According to the coring,field observation and the log interpretation,through the physical property test,thin section identification,scanning election microscopy and other research methods,this paper researches the sedimentary facies,reservoir rock characteristics,diagenesis and physical property of Chang 6 reservoir in Ordos Basin,and it emphasizes on hydrocarbon transporting systems,petroleum migration and accumulation dynamic,discusses and sums up the enrichment regularity of low permeability lithologic reservoir.This article is based on the bentonite layer,Chang 6 reservoir is divided into four oil sub-groups:Chang 61,Chang 62,Chang 63,Chang 64,and the key research is Chang 63,Chang 64.In the study area,Chang 6 reservoir belongs to low permeability reservoir,its primary porosity is mainly between 11%?14%and permeability is mainly(0.2-0.4)×10-3?m2.The dominant diagenesis types mainly include compaction,cementation and dissolution,compaction and cementation have important effects on the porosity of the reservoir.The mainly hydrocarbon transporting system types are cracks and the permeable sand body,the natural structural cracks and micro cracks developed with different degrees in the study area,with "small cutting depth,small open degree,small spacing" as the main character.The excess pressure is the main mainspring in the study area.The study area developed nosed-shaped uplifts which are favorable area for oil and gas gathering,at the same time,the purpose layer has good reservoir properties,which combines with the underlying Chang 7 hydrocarbon source rocks,has favorable hydrocarbon accumulation conditions.Comprehensive hydrocarbon source distribution,sand body distribution rules and reservoir-cap combination factors,we conclude that the low-permeable lithologic stratigraphic reservoirs have good prospective in the exploration.