Recently, Well Ketan 1 in the Keping area of the Tarim Basin achieved an industrial gas flow from the diamict of Wusonggeer Formation, Lower and Middle Cambrian, which breaks through the "restricted zone" of diamict exploration. So far, however, the sedimentary characteristics and oil and gas exploration potential of the diamict in this area have not been understood clearly. In order to promote further study on the Cambrian diamict in the whole basin and the evaluation on oil and gas exploration potential, this paper took the massive diamict of Shayilike–Wusonggeer Formations, Lower and Middle Cambrian in the Akesu outcrop next to the Keping area as the research object. Based on the previous research results on regional structures, sedimentary facies and reservoirs, combined with the data of outcrop observation, thin section analysis and geochemical analysis, the sedimentary facies of Wusonggeer–Shayilike Formations were analyzed using a combination method of sequence stratigraphy, petrology and sedimentation–microfacies study. Then, the oil and gas exploration potential of the diamict in this area was evaluated. And the following research results were obtained. First, sedimentary environments of Lower and Middle Cambrian in the Akesu outcrop area are mainly evaporative platform, semi-restricted platform and neritic shelf, including 19 diamict lithofacies, 3 carbonate lithofacies, and 2 clastic lithofacies. Besides, 5 types of microfacies assemblages are recognized, including 4 types of reservoirs with low to ultralow porosity and permeability. In addition, high-quality reservoirs are developed in regional intervals. Second, the sedimentary environments of Lower and Middle Cambrian in the Akesu area experience a transition process from open to close and then sallification, including 3 major sedimentary structural layers, i.e., gentle slope of carbonate rock, restricted platform of evaporite and diamict, and restricted platform of evaporite. And the development mode of the diamict in the restricted platform of evaporite and diamict is controlled by the property and the location of provenance, the condition and the change rate of climate, the depth and the temperature of evaporative gypsum-salt lake water body, the paleogeomorphology of platform basin, and the interface change rate of different levels of sequences. Third, gypsum-salt bearing dolomitic mudstone with higher total organic content (TOC) and mudstone of tidal flat facies, which are the potential source rocks, are developed in the massive diamict of Lower and Middle Cambrian in the Akesu area. And among them, the source–reservoir–caprock assemblages of Wusonggeer–Shayilike diamict are better in configuration, and their oil and gas exploration potential shall not be ignored.
白莹,徐安娜,刘伟,赵振宇,罗平. 塔里木盆地西北部中下寒武统混积岩沉积特征[J]. 天然气工业, 2019, 39(12): 46-57.
Bai Ying, Xu Anna, Liu Wei, Zhao Zhenyu & Luo Ping. Sedimentary characteristics of Lower and Middle Cambrian diamict in the northwestern Tarim Basin. NATURAL GAS INDUSTRY, 2019, 39(12): 46-57.