Integrated Study Of Source Rock From Shiwu And Changling Depressions In Southern Songliao Basin

The study area of my thesis is Shiwu and Changling depressions in southern Songliao Basin, which is leased by Sinopec. It is critical to perform source rock assessment in the study area because of low exploration degree. On the base of sample analysis and data interpretation, coupled with source rock log inversion, sequence stratigraphy, seismic facies analysis and basin modeling, source rock organic richness, thermal maturity and hydrocarbon generation potential were thoroughly investigated.The main source rock in the Shiwu Depression occurs in the Yingcheng Formation, which is organic rich and dominated by typeⅢandⅡ2 kerogen. The Shahezi Formation could serve as minor source rock, while the Huoshiling and Denglouku formations are only locally distributed source rocks due to less organic matter contents and inert organic matter nature (dominated by TypeⅢkerogen). The main source rock in the Changling Depression is derived from Shahezi Formation, which is organic rich and dominated by typeⅢandⅡ2 kerogen. The Yingcheng and Huoshiling formations are minor source rocks, which have low organic contents and TypeⅢkerogen. The Denglouku Formation has no hydrocarbon generation potential in the study area and is regarded as non source rock interval. All source rocks in the study area are highly matured, mainly approached gas generation stage.Source rock assessment and prediction was carried out through“point - line - surface– body”strategy on the basis of geochemical analysis coupled with geology, well logging information, seismic reflection and seismic facies analysis, structural and depositional system interpretations. Source rocks distribution in the Shiwu Depression, a typical half graben, is largely controlled by structural features which is thickening toward west and thinning toward east. Source rocks distribution in the Changling Depression is controlled by multiple sub-depocenters. It is well developed at deep depocenters of the Changling Depression and Chaganhua Sub-depression. Source rocks are poor developed at Yaoyingtai and Dongling regions due to uplift influence. There are some differences between two depressions in terms of source rock nature and development. The Shiwu Depression has higher hydrocarbon generation potential than that of the Changling Depression. The former contains more C27 steranes while the later is dominated by C29 steranes, reflecting more algae sourced material contribution in the Shiwu Depression. Depositional environment in the Changling Depression is mainly characterized by fresh water lacustrine facies and weak reducing regime. It shows partially oxidizing nature during the deposition of the Denglouku Formation. The source rock depositional facies in the Shiwu Depression is characterized by brackish water lacustrine and weak reducing environment. The "V"-shaped sterane distribution indicates that organic source materials are derived from both terrestrial and aquatic organisms.Source rock development in the study area is mainly controlled by tectonic settings. The faulted structural nature controls the depositional system distribution and source rock lateral distribution; while the tectonic evolution controls vertical source rocks development. The freshwater - brackish water and weak reducing environment in southern Songliao Basin is moderately faire for source rock development. The source rocks in the Shahezi and Yingcheng formations are organic rich and gas prone.