Hydrocarbon Plays and Unconventional Hydrocarbon Distribution in Lacustrine Basins, China

There are three types of lacustrine basins in China: rifted basin, depression basin and foreland basin. Rifted basins were mainly formed during Cenozoic era, such as the Bohai Bay Basin (E) in eastern China. Depression basins were mainly developed during Mesozoic era, such as the Songliao Basin (K) in eastern China, the Ordos Basin (K) in central China. Foreland basins were dominantly formed during Mesozoic era and late Paleozoic era, such as the western area of the Sichuan Basin (T). Because of the differences in their tectonic background and basin structure, different depositional systems were developed in these three types of lacustrine basins, forming plays with dominant lithology of muddy shale, coal measures and sandstone. They have similarities in petroleum system constitutions. The effective source rocks in lacustrine basin are widely distributed, usually accounting for more than 50% of the lacustrine basin area. The frequent contacts between sandbodies and source rocks can assure effective hydrocarbon accumulations in various sand bodies, and can control the development and wide distribution of tight sandstone gas and tight oil. They have various features in hydrocarbon reservoir types and accumulations. Rifted basins have structure features of multiple uplifts and multiple sags, small individual sags and well developed faults, developing various of sandbodies (such as alluvial fan, fan delta, braided river delta, underwater fan and beach bar, etc.). Each small sag constitutes a relatively independent petroleum system, with high hydrocarbon generation efficiency in source rocks. In the past exploration, the discovered hydrocarbon reservoirs in structural traps are large scale conventional reservoirs. In recent explorations, large scale unconventional oil and gas have been found in deep mudstone and tight sandstone, which shows that oil and gas accumulation efficiencies in rifted basins are very high. Depression basins and foreland basins that were developed in large craton background have big areas of lacustrine basins. Their structures are extremely gentle, mainly developing large delta sandbodies. Their source rocks widely contact with sandbodies, with low porosity, low permeability and strong heterogeneity in reservoirs, which is favorable for forming massive tight oil and gas. They are distributed in the whole basin, with huge hydrocarbon resource potentials.