Reservoir Quality, Hydrocarbon Mobility and Implications for Lacustrine Shale Oil Productivity in the Paleogene Sequence, Bohai Bay Basin

Li, Maowen; Li, Zhiming; Jiang, Qigui

The Paleogene lacustrine sequences in rift basins in eastern China has been the focal point for exploration of shale oils and tight oils recently, due to the wide spread occurrence of organic-rich black shales, moderate to high maturity levels, association with natural fractures, overpressure zones, or high percentage of brittle minerals. 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 Jiyang Superdepression, Bohai Bay Basin. A litho-stratigraphic comparison with the marine shale sequence in the Devonian-Mississippian Bakken Formation of the Williston Basin 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 (i) the greater heterogeneities in lacustrine sediments and more limited connectivity between source and conventional reservoirs in the distal portions of lacustrine systems; (ii) the close proximity to terrestrial source that creates opportunity for higher plant contribution and more waxy oils from lacustrine source rocks in oil window; (iii) 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, and gas to oil ratio within the lacustrine system; (iv) high temperature thermochemical sulphate reduction that tend to form significant amounts of hydrogen sulphide, with various undesirable effects. 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 Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013