A thorough understanding of seals is needed for petroleum exploration in marine carbonate strata in Tarim basin

Ordos basin and southern China. A concept of ″petroleum preservation unit″ is presented. It is a petroliferous geological unit with fluids being sealed in 3D space within a sedimentary basin. According to their spatial structures and evolution in geologic history

hydrocarbon preservation units can be classified into three basic types

succession

modification and reconstruction types.Hydrocarbon preservation unit can be delineated based on analysis of cap rocks

sealing capacity and sealing time of faults

as well as some key events

such as volcanic activities

earthquake and hydrogeological process.In combination with the study of basin and petroleum system

pool-forming elements and processes can further be analysed

and comprehensive evaluation of hydrocarbon preservation units can then be made.In the case of Chuxiong basin

seven hydrocarbon preservation units have been analyzed and evaluated

and Dongshan

Zhonghe-Dayao and Yongren have finally been selected to be the three favorable hydrocarbon preservation units.