Hydrocarbon Accumulation Model of Big Depression Ramp Area——As Putaohua Reservoir in the Sanzhao Depression

Using 4 079 log curves,10 well cores,as well as the initial deliverability data of production wells,the authors comprehensively analyze the chief factors that control hydrocarbon accumulation in Putaohua reservoirs of the Sanzhao depression in the Songliao Basin,including the buried history of the source rocks,the palaeotectonics evolution history,the migration and accumulation field of hydrocarbon,the reservoir sedimentary character and oil-water distribution rule.The scenario is thought as the follows:the hydrocarbon of the Putaohua reservoir was derived from the underlying source rocks of the Ⅱ+Ⅲ segment of the Qingshankou Group,the initial migration period of hydrocarbon began from the final stage of the Nenjiang Group,the key stage of hydrocarbon accumulation was at the end of the Mingshui Group;the Putaohua reservoir top has undergone four stages of paleotectonics evolution,and the major hydrocarbon migration direction was along the axis of some large nose structure that dumps to depression center,some hydrocarbon migration direction seems to be rotating,namely,they was in northwest direction at the end of the Nenjiang Group,became near east-west at the end of Mingshui Group;The Putaohua reservoir is identified as the single northern source,with well development of distributary channel sand bodies that controlled by shallow water delta dominated river sediment and that are intensively located and have long extension.The combination of these channel sand bodies arranged in northwest direction and faults makes up the most favorable passageways for hydrocarbon lateral migration;initial deliverability data of production wells and detailed analysis of reservoir traps indicate that oil-water distribution is controlled by local structures,and a single trap has a unified oil-water interface.Based on above research,2 types of accumulation mode are recognized in the Putaohua reservoir in the Sanzhao depression:inheritance nose structure accumulation mode and the overlying mudstone shielding of the reverse normal fault down-throwing block in depression gentle slope.Under the guidance of these accumulation models,101 favorable drilling traps containing 2 800×104 t reserves are forecasted.This forecast could direct the next step of exploration and development of the Putaohua reservoir in the Sanzhao depression.