HYBRID PLAYS OF SOURCE ROCK INTERVAL IN CHINA LACUSTRINE BASINS

Lacustrine basins were widely developed in China since later Permian. 90% oil production in China is from lacustrine basins and this oil is sourced from organic rich lacustrine shale. This lacustrine shale deposit is associated with thin sandstone, siltstone and dolomite interbeds within source rock interval. Its lithologic and stratigraphic context is similar to that of many US producing shale plays (Bakken, Niobrara, etc.) to some extent, e.g. Bakken play interval consists of dolomite reservoir and its overlying and underlying shale, Niobrara shale play interval includes alternate chalk and marl layers. Historical production, current exploration and research for lacustrine shale in China show that the lacustrine shale in China is potential shale oil and shale gas play even clay content in lacustrine shale is higher than marine shale. Due to current shale exploration focus, the thin sandstone, siltstone and dolomite interbeds within lacustrine shale seem to be ignored. But these interbeds usually have better reservoir quality, are relatively easy to be hydraulically fractured and can produce more efficiently than lacustrine shale. The petroleum system characteristics for the lacustrine source rock interval is that the interbeds are charged with hydrocarbons migrated from their neighboring organic rich shale and this shale can also be self-sourced reservoir. Generally, besides the lacustrine shale in the source rock interval is emerging unconventional shale play, the thin sandstone, siltstone and dolomite interbeds are conventional plays if they have high porosity and permeability and they are unconventional tight plays if their porosity and permeability are low. These interbed plays and shale play within the lacustrine source rock interval form the hybrid plays and provide the new frontier for many lacustrine basins in China. These hybrid plays should be targeted together in the near future instead of current shale reservoir only exploration focus in China lacustrine basins.