Lithologic Charateristics And Significance Of Petroleum Geology Of The Lower K₁bt¹ In A’nan Subsag,Erlian Basin

In recent development of petroleum exploration, tight reservoir has attracted more and more attentions. A’nan subsag in the Erlian basin exhibits potential of tight oil. However, the degree of prospecting is still at the beginning, the lithology of reservoir rock and the development of petroleum system have not been recognized. Based on observation of drilling cores, petrologic analysis, electron microprobe analysis of diagenetic minerals, scanning electron microscope observation, as well as elemental geochemical analysis and logging data analysis, this thesis performed systematic petroleum geological studies.The lower section of Member 1 of Tenger group (Klbtl) mainly composed by grey dolomitic mudstone, argillaceous dolostone, gray green massive tuff, sedimentary stuff and calcareous fine sandstone. The sedimentary stuff and calcareous fine sandstone are the reservoir rocks because of high porosity and intensive alteration. Compared with other mudstones, sedimentary stuff has the higher ∑REE/∑REE, which is attributed to interaction with diagenetic fluid. Such interaction resulted in the development of secondary porosity, and improves its physical properties.The lower Klbtl in A’nan subsag is mainly composed by dark mudstone deposited in shallow lake, occasionally interrupted by the formation of slip turbidite fans. Sedimentary stuff and channel sandstone were formed in slip turbidite fan. The organic geochemical analysis shows that the dark mudstone are the medium or above medium source rocks in this area. But their maturity is generally low, the highest Ro is only 0.95% which was detected in the mudstone occurred in the center of depression. The main channels of secondary migration includes unconformity surface and fault planes, and the vertical migration of oil and gas was not preferred. Sedimentary stuff can act as the lens-type reservoir in dolomitic mudstone. The dolomitic mudstone may be both source rock and cap-rocks. The channel sandstone reservoir is mainly lithologic stratigraphic reservoir, which can accommodate the oil and gas from the underlain source rocks, and was sealed by the overlying mudstone.