Heterogeneities in Fine-Grained Lacustrine Sediments and Implications for Shale Oil Mobility: A Case Study in the Zhanhua Depression, Bohai Bay Basin

Maowen Li, Zhiming Li, Qiqui Jiang, Peng Liu, Tingting Cao, and Zhenkai Huang
Sinopec Key Laboratory for Petroleum Accumulation Mechanisms, Sinopec Petroleum Exploration & Production Research Institute, Beijing, China

Fine-grained Paleogene lacustrine sediments in eastern China have been the focal point for shale oil exploration recently, as the thermal maturity levels of the Eocene-Oligocene organic-rich black shales are currently within the conventional oil window. The organic rich shales in fault bound rift basin setting display large heterogeneities both vertically and laterally, potentially exerting major influence on shale oil occurrence. Earlier study identified four potential types of shale oil accumulations, occurring in sandwiched thin shale/sandstone interbeds, in highly fractured shale/mudstones commonly associated with larger faults, in over-pressured shale/mudstones within the evaporates, or in limestone and argillaceous carbonate interbeds within the shale/mudstone sequence. In this study, we examine the oil resource potentials, reservoir characteristics and oil chemistry/physical properties of the Es3 and Es4 sections of Eocene-Oligocene Shahejie Formation in the Zhanhua Depression, Jiyang Superdepression, Bohai Bay Basin. A litho-stratigraphic comparison with the marine shale sequences in North America (e.g. Bakken and Eagle Ford shales) reveals critical controls for hydrocarbon mobility and likely shale oil production “sweetspots” within the shale dominated sequences. More importantly, several significant differences between the lacustrine and marine shale systems become apparent. These include (1) the greater sensitivity to climate and more frequent change in lake levels within lacustrine systems that tend to produce greater heterogeneities in lacustrine sediments and more limited connectivity between source and conventional reservoirs in the distal portions of lacustrine systems; (2) the close proximity to terrestrial source that creates opportunity for higher plant contribution and more waxy oils from lacustrine source rocks in oil window; (3) the relatively narrow but generally higher activation energy range in the kinetics of hydrocarbon generation from type I kerogens in carbonate-rich lacustrine kinetics that have clear implications for kerogen-oil interaction behaviour, oil flow characteristics, GOR and thermochemical sulphate reduction within the lacustrine system. We will review the production test results, correlate them with the oil geochemistry and shale reaction kinetics data from available Sinopec shale oil wells, and comment on future directions of lacustrine shale oil exploration in eastern China.

AAPG Datapages/Search and Discovery Article #90180©AAPG/SEPM/China University of Petroleum/PetroChina-RIPED Joint Research Conference, Beijing, China, September 23-28, 2013