Abstract:

Various types of subtle reservoirs are developed in the northern steep slope zone of Dongying depression during different periods. During fault subsidence, various lithologic reservoirs and relevant compound reservoirs, including lenticular reservoirs, structural-lithologic reservoirs and updip pinch out reservoirs, are developed. During the transitional period from fault subsidence to downwarping, stratigraphic reservoirs as well as lithologic and structural reservoirs controlled by stratigraphy are developed, including unconformity reservoirs, fault-lithologic reservoirs, strati-graphic overlap-fault reservoirs, and fault-lithologic and stratigraphic reservoirs controlled by unconformities. Various types of hydrocarbons accumulated in different subtle reservoirs. On the periphery of the northern steep slope zone, hydrocarbons accumulated in the structure-controlled stratigraphic-lithologic reservoirs in the 3^rd member of Shahejie Formation that have been formed during fault subsidence period, and in the stratigraphic reservoirs formed during the transitional period from fault subsidence to downwarping have mainly been sourced from the 4^th member of Shahejie Formation. While in the inner part near hydrocarbon-generating center, hydrocarbons accumulated in the lenticular lithologic reservoirs and other lithology-related reservoirs in the 3^rd member of Shahejie Formation, and fault-lithologic reservoirs in the upper part of the 3^rd member of Shahejie Formation have mainly been sourced by the source rocks in the 3^rd member of Shahejie Formation. The formation of subtle reservoirs and the distributional characteristics of petroleum have been controlled by various factors, such as paleo-tectonic setting, hydrocarbon migration pathways, combination of source, reservoir and cap rocks, and the timing of hydrocarbon generation and accumulation.

Key words: subtle reservoirs, genetic type of hydrocarbon, hydrocarbon migration pathway, northern steep slope zone