Main controlling factors for tight oil accumulation in continental lacustrine basins in China

Tight oils refer to the oils accumulated in tight reservoirs. The tight reservoirs mainly include tight sandstones and carbonate rocks, with in-situ permeability less than 0.1×10^-3 μm². There is no natural production normally, and commercial oil flows can be obtained through technical reconstructions. In China, the tight oil reservoirs in continental lacustrine basins are developed, and four controlling factors for tight oil accumulation have been concluded as followed: developing superior hydrocarbon source rocks, being preferable reservoirs, possessing original driving forces and accumulating near to source rocks. Two types of high-quality hydrocarbon source rocks developed in the continental lacustrine basins in China. The source rocks of type Ⅰ have superior organic type, high organic content, high maturity, and big hydrocarbon generation potential. The source rocks of type Ⅱ are outstanding in hydrocarbon transformation ratio. Tight sandstones and carbonate rocks work as the main reservoirs for tight oils, and are featured by strong heterogeneity (discontinuous in transverse and superimposed in vertical). Generated hydrocarbon pressurization is the main driving force for tight oils in China. Powerful pressure differential between source rocks and reservoirs displaced the generated oils to fill the tight reservoirs continuously which were close to high-quality hydrocarbons. Micro-crack in communication and micro-nanometer pore development were the key conditions for tight oil gathering. Micro-nanometer pore development increased the effective reservoir space and micro-crack in communication provided the effective channel for tight oil gathering. The tight oil resources are rich in China. The favorable exploration area is about 16×10⁴ km², and the geological resources are about (160-200)×10⁸ t. The favorable exploration areas mainly distribute in the Ordos, Junggar, Songliao, Bohai Bay, Qaidam and Sichuan basins, and so on.