Reservoir-forming Conditions&Resource Potential Of Paleogene Shale Oil From The South Of Bohai Bay Basin

Based on the research of the situation of exploration and development of the shale oil in the domestic and overseas,this paper choose the Jiyang Depression and Dongpu Depression which located at the southern part of Bohai Bay Basin as the study area.Based on the research of the shale deposition geological conditions and the distribution characteristics of shale,this paper analyzed the reservoir forming conditions and the main controlling factors.In the end,this paper cinfirmed the shale oil accumulation types and modes of occurrence,computed the potential resources,predictted the range of profitability and drilling targets of shale oil.The main results are as follows:The major layers of shale oils occur at upper ES4,lower ES3 and ES1 in Jiyang Depression and ES3 and ES1 in Dongpu Depression.Paleogene lacustrine shale in the studied area has high thickness and organic abundance,which entered into matured oil generation stage.The shale has high content of brittle minerals,moderate porosity and micro-fractures to act as a good shale oil reservoir.And also those shales have lower quartz contents,higher carbonate contents and pool-forming conditions,which made the shale oil reservoirs with high specificity and complexity.The major controlling factors of the shale oil reservoir are high maturity,high organic content,high pressure and high permeability,low clay contents and high brittle mineral contents.The fluid properties and the poor reservoir stimulation prospect currently constrain the shale-oil exploration in the syudy area.This area has multiple shale reservoirs which can be divided into pure-shale reservoir.intra-salt reservoir and shale inter-bedded with brittle layers,which can be even divided into six sub-type reservoirs.Only shale-oils in dissociative state are movable and these oils accumulated in shale diagenetic or structure fractures and fractures in over-beddings can be developed effectively.This paper suggests that choose the type of shale with silt and carbonate inter-beddings and the shale content in intra-salt reservoir with high pressure and more fissure as the exploration targets.And alos this paper suggests to perform shale-oil exploration nearing delta front source areas where develops multiple silt and carbonate inter-beddings in the studied area,try to find intervals with higher diagenesis and ultra high pressure in the vertical sequences and those shale inter-bedded by brittle layers,intra-salt,and high pressure fractured reservoirs should be put into prior exploration.This paper preliminarily calculates Paleogene shale-oil resources in the study area are 82.56×108tons.Jiyang Depression has a high number 72.54×108tons,and Dongpu Depression is 10.02×108ton.The shale-oil resources mostly exist at lower ES3 and upper ES4 at Dongying Depression and Zhanhua Depression with a buried depth of 3500m to 4500m.The most prospective areas of shale oil in Jiyang Depression lie in lower ES3 and upper ES4 at Dongying Depression and lower ES3 and ES1 at Zhanhua Depression which are 502km2.The most prospective areas of shale oil in Dongpu Depressio lie in the upper-middle ES3 at northern Wenliu,Wennan and Mazhai-Liutun-Huzhuangji which are 225km2.