Types of abnormal high-pressure gas reservoir in foreland basins of China

Abstract

Abnormal pressure commonly exists in foreland basins that are closely related to the oil and gas reservoir. A deep understanding of the distribution of the said kind of pressure in various reservoirs and characteristic types of abnormally high-pressure gas reservoirs are supplementary to the theory of the fluid storage tank. This paper analyzed in detail the characteristics of this atypical distribution of high-pressure in typical local and foreign foreland basins, as well as their relationship with gas reservoirs. The three types of abnormal high-pressure gas reservoirs are identified as follows: box type, top seal type, and pressure transfer type. The box type is mainly characterized by the reservoir of a source reservoir superposition with a stable structure. The unusual high pressure occurs in the reservoir and the cap rock, which are mainly results of hydrocarbon supercharging and under-compacting deposition. The top seal type is predominated by the high pressure in the cap rock, while the pressure in the reservoir may be normal or not. The abnormally high pressure may be caused by under-compacted deposition, strong oil and gas filling, as well as tectonic compression. It is also worth noting that the pressure transfer type is dominated by secondary gas reservoirs with active tectonics. The pressure has a decreasing trend from the deep to the shallow area due to the formation of pressure conduction caused by pressure relief or deterioration of storage conditions, as well as lithological changes brought by fractures. Determining the types of abnormal high-pressure gas reservoirs have a great significance to the exploration of the said gas reservoirs themselves. Moreover, their classification can avoid accidental drillings in the foreland basin.