Sedimentary Sequence of Ordovician Majiagou Formation in Central and Eastern Part of Ordos Basin and Its Control over Reservoir Development

Abstract

Abstract: Based on analysis of sedimentation and lithofacies paleogeography of Ordovician Majiagou Formation in the central and eastern part of Ordos Basin, this paper, for the first time, defines the 3rd and 4th sequential stratigraphic configuration of Majiagou Formation and divides Majiagou Formation into three 3rd sequences and 11 4th sequences. The study is focused on lithofacies paleogeographic evolution of the 4th sequences of Ma5, a gas-producing horizon, fully analyzing the controlling role of sedimentary sequences on distribution of dolomite reservoirs. (1) Fluctuations of sea level and ejection of central paleo-uplift caused the differences in dolomitisation – penecontemporaneous dolomite in the regressive period and mixing dolomite in the transgressive period. (2) The differences in dolomitisation led to a vertically cycled distribution of reservoirs with development of gypsum-dissolved dolomite reservoirs in the regressive period and intercrystal pore dolomite reservoirs in the transgressive period. (3) Distribution of reservoirs is controlled by sedimentary facies in the sedimentary sequences. Intertidal gypsum-bearing dolomite flat is the favorable sedimentary microfacies in the regressive sedimentary cycle and intertidal algae-clastic beach is the favorable sedimentary microfacies in the transgressive sedimentary cycle.

Huang Zhengliang, Wu Chunying, Ma Zhanrong, Ren Junfeng, Bao Hongping. Sedimentary Sequence of Ordovician Majiagou Formation in Central and Eastern Part of Ordos Basin and Its Control over Reservoir Development[J]. China Petroleum Exploration, 2015, 20(5): 20-29.

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