Petroleum Pool Formation Conditions And Models Of The East Slope Area In The Chengdao Oilfield

The East Slope Area of the Chengdao Oilfield is located at the eastern-south part of the Chengbei Lowuplift. It is a covered structure evoluted from the pre-Tertiary Chengdao Hidden Hill, with rich petroleum resources. There have been many questions about the petroleum pool formation conditions and models for this area since the first well was drilled in 1988, which has had an great influence on the further petroleum exploration and development. In this study, a method with the combination of petroleum geology, sequence stratigrapy, organic geochemistry and geophysics, based on drilled core analysis data, well data and seismic sections, has been applied to investigate the petroleum pool formation conditions and models in this area , and the following results and recognition have been obtained:(1). The Lower Tertiary strata are subdivided into two sequences and seven systems. The strata of ES, to middle ED3 belong to Sequence I and upper ED3 to ED, to Sequence II.(2). The diagenesis of the ED3 and ES, sandstone has been evoluted to late diagenesis A and B stage, with mainly primary pores and secondary solved pores. Most of the sandstones belong to middle porosity and middle permeability reservoirs.(3). There are three types of crude oils in the East Slope Area and three sets of source rocks in the Bozhong Depression. Oil-source correlation analysis has shown that the oils were mostly from ED2 source rocks from the Bozhong Depression, and the oils occurred in the Slope Hidden Hill Belt were from ES3 or/and ES, source rocks in the Bozhong Depression.(4). The main stage of oil generation of the source rocks occurred during 9 my to present, which can match with trap formation in the East Slope Area. With the combination of good migration conditions, it has been believed that the slope area of the Bozhong Depression is the main source area.(5). There are two types of fluid inclusions: petroleum inclusions and aqueous inclusions in the reservoir sandstones. The homogenization temperatures of the aqueous inclusions associated with petroleum inclusions range from 107 to 141 . According to the burial history of this area, it has been deduced the petroleum pools formed after 2.5 My.(6) Three petroleum pool formation models have been established and three important targetting areas have been evaluated, with total petroleum resources of 1200 x 104 ton.These results have not only provided a case study of hidden petroleum pools, but also given an important guide to the exploration evaluation of this area.