Connotation analysis, source-reservoir assemblage types and development potential of unconventional hydrocarbons in China

Through analysis of the connotation of unconventional hydrocarbons, the source-reservoir assemblages of unconventional hydrocarbons are divided into three types, i.e., source-reservoir neighboring type, source-reservoir integration type, and source-reservoir separation type. The source-reservoir neighboring type resources mainly include tight oil and tight gas with the following formation conditions and characteristics: (1) efficient near-source accumulation close to high-quality source rocks with the pressure difference between source and reservoir as the dynamic force; (2) large-area tight reservoirs with certain porosity, dominated by micro-nanopores of inorganic origin; (3) distributed in depressions and slopes with large hydrocarbon-bearing area and great resource quantity, low abundance and local development of “sweet spots”; (4) weak tectonism. The source-reservoir integration type resources mainly include coalbed methane, shale gas, shale oil and oil shale. The formation conditions and characteristics are: (1) high abundance of organic matter, different types of organic matter and thermal evolution grades leading to formation of different resources types; (2) organic-rich sections are distributed continuously in the reservoiring space which is dominated by nanometer organic pores, interparticle pores and microfissures; (3) hydrocarbons mainly occur in free or adsorbed state, varying much with resource type; (4) the resources are self-conserved, and enriched in depressions and slopes, the conservation conditions are controlled by tectonics, temperature and pressure; (5) the production per well can be enhanced by volume fracturing, which increases the permeability of the reservoirs. The source-reservoir separation type resources are more special, mainly including (1) transformed conventional resources such as oil sand and heavy oil; (2) unsteady resources formed under special conditions of temperature and pressure, among which natural gas hydrate is a representative. These three types of resources in China are different in both development prospect and current situation: (1) the source-reservoir neighboring type is most practical and will develop fast in the next 5 years; (2) the source-reservoir integration type needs continuous exploration and technical breakthrough, and is expected to develop rapidly in the coming decade; (3) in the source-reservoir separation type resources, natural gas hydrates have the greatest development potential, on which technical tests are being conducted.