Paleokarst reservoirs in the oil and gas fields of China

摘要

Discovered during oil and gas exploration in China, there exists widely distributed carbonate paleokarst reservoirs associated with regional unconformities. Based on analysis of the main paleokarst reservoirs in China the following characteristics are common: (1) The surface karst zone, the vadose zone and the phreatic zone are present throughout in China. (2) The reservoir volume is composed of remnant solution pores, vugs, and fissures. The most favorable reservoir for oil and gas accumulation is the solution-fissure vug reservoir. (3) The distribution of paleokarst reservoirs is controlled by paleokarst morphology and fault fissures. The most favorable place for reservoir development is on karst slopes and in fault belts. (4) Dissolution during deep burial coincides with the maturation of source rocks, and hydrocarbon evolution and migration. Porosity enhancement related to buried organic dissolution takes place just prior to the arrival of hydrocarbons in the reservoir, and hence is of economic significance. (5) Karstification and buried organic dissolution are the most important diagenetic processes in paleokarst reservoir development. The former is a prerequesite factor, while the latter is the dominant process in reservoir construction.