Accumulation And Distribution Of Oil And Gas At Larger Depths In The Bohai Bay Basin

This thesis is based on collection and analyses to a great number of original data from exploration practice. Beginning with the study on the regional geology of the Bohai Bay basin, in conjunction with the features of source rocks, reservoir rocks, and seal layers as well as their assemblage at depth, a detailed analysis is made for typical reservoirs at larger depths. The purpose is to probe into the generation conditions of oil-gas reservoirs and the accumulation rules of oil and gas at larger depths in the basin. It is suggested that in the lower Tertiary deep reservoir system, the source rocks developed well, the supply of oil and gas is sufficient and the seal conditions are good. Therefore, the oil and gas accumulation and high production depend on scales of deep reservoirs and the quality of their physical properties, hi this system, due to wide existence of abnormal high pressure in deep strata, the threshold of the hydrocarbon generation window shifted down, and the position of secondary pore zones also became deeper. Both the changes are favorable to oil-gas accumulation at depth. As for the buried hill reservoirs of the "Young generation and old storage" type, their oil-gas accumulation relies on the size and porosity-permeability of their reservoir bodies, as well as a sufficient supply from the Cenozoic Erathem. For the buried hills covered with Cenozoic hydrocarbon source rocks, the extent of oil-gas accumulation depends on their source rocks. While for those buried hills without cover of source rocks, it needs enough fault offset to constitute the oil supply window of Tertiary system or unconformities to provide conduits for oil-gas supply. The lower parts of deep slope and gentle slope in a dustpan-like sag, and the pre-Tertiary strata are quite favorable to forming deep oil-gas reservoirs. Their structural deformation, styles and sediment features control the basic types of deep oil-gas reservoirs which distribute in a pattern.After analyzing the great potential of deep-depth petroleum resources in the Bohai Bay Basin, 34 favorable deep-depth exploration zones are evaluated, among which 13 are the most favorable zones with a total potential of 990 million tons, 9 are more favorable zones(total potential resources: 340 million tons). Moreover, 7 favorable exploration zones in the Paleozoic are chosen out with a total resources of 300 million tons.