Terrestrial sequence stratigraphy and lithological deposit group of sandstone in the faulted lacustrine Jiyang basin

摘要

The violently-faulted Eocene-to-Oligocene terrestrial Jiyang basin, area 26000 km2, in which the discovery ratio of proved geological reserves reaches 50% above of the total hydrocarbon resource, entered the conceived deposit exploration stage by the time of the mid 90's of the 20th century, and the lithological reservoirs of sandstones had been sort of the chief targets. In terms of the sequence stratigraphical principles, the Tertiary Shahejie and Dongying Formations can be divided into six third-band sequences with integral system tract construction and can be sorted into two categories, i.e., deep-faulted and shallow-faulted sequences. Oilshale within the expansion system tract (EST) in the deep-faulted third-band sequence is the excellent source rock, for it is rich in organic matter with high hydrocarbon conversion ratio. The sandstone complexes, so-called lower-stand fan, within the lower system tract (LST) in deep-faulted third-band sequences mainly include turbidite fan and fan-delta, and due to ideal collocation with the oilshale of the transgressive system tract, 90% of them are oil-bearing. These lower-stand fans exist along fault slope break, in the appearance of group and belt, forming conceived lithological sandstone deposits with the prospect of 700 million barrels above. During recent years in the faulted lacustrine Jiyang basin, based on the theory of "the exploration of the lithological lower-stand fan deposit group along the fault slope break", 1640 million barrels of geological crude oil reserves have be-en proved, and 20 million barrels are the products.