| Jimsar sag is located in the eastern part of the Junggar Basin. To its east is Guxi raised, west is Beisantai raised, north is Shaqi raised and south is Fukang fault zone. Currently, the three main oil area (X7well area, X17well area and X19well area) of the study area is located in the eastern slopes of the Jimsar sag and administratively belongs to Jimsar county, Xinjiang Uygur Autonomous Region. The ground of the research area are most covered with grassland and gobi, with flat surface, rare vegetation, and the altitude of the ground is650meters to680meters above the sea level. It is belongs to inland climate. The highest and lowest temperature has exceeded40℃and-40℃respectively. The average annual precipitation is less than200mm.Jimsar sag experienced Hercynian, Indo-china, Yanshan, Himalayan tectonic movement. In early Mid-Permian, Jimsar sag experienced strong tectonic subsidence, accepted thinner Jiangjunmiao formation sedimentary on the Carboniferous basment. In late Mid-Permian, it developed of a set of delta-lake deposits, formed the most important hydrocarbon source rocks of Lucaogou formation in this area. In the late Permian, Jimsar sag deposited the Upper Permian Wutonggou formation to Triassic Jiucaiyuan formation stratas, in which the Wutonggou formation is the major reservior of Jimsar sag. n the late Indosinian movement, Qitai ridges of Jimsar Sag rapid uplift with being sequeezed. The result of that movement is the stratigraphic of the eastern slope of the Jimsar Sag rised to the place which above the base level of deposition, included of the Triassic stratigraphic and the Permian stratigrapic and become a denudation area. The contact relationship between the Jurassic Badaowan group and the Permian Wutonggou formation is unconformity. The stratigraphy of Jurassic was sharply eroded with the Yan Mountain movement (Ⅱ), the deposition area of the Jimsar Sag was gradually reduced from east to west. Finally, the formation retain only the lower part of the layers of Badaowan group. During the Creaceous (K), along with the end of the Jurassic period Yan Mountain movement (Ⅲ), Jimsar Sag is no longer a single sedimentary unit. The south-east of the layers rise to be eroded by squeezed.The drilled formation in the east slope of Jimsar sag, in which, bottom-up there are Batamayineishan formation in Carboniferous (C2b), Jiangjunmiao formation (P2j), Lucaogou formation (P2l), Wutonggou formation (P3wt) in Permian, Badaowan formation (J1b), Sangonghe formation(J1s), Xishanyao formation (J2x), Toutunhe formation (J2t) in Jurassic, Paleogene (E),Neogene (N), Quaternaru (Q), missing Tugulu Group (K1tg) in Caretaceous, Haojiagou formation (T3hj), Huangshanjie formation (T3h), Kelamayi formation (T2k), Shaofanggou formation (T1s), Jiucaiyuan formation (T1j) in Triassic. And the more farther to the east, the more stratigraphic miss.Because the Wutonggou formation and the overburden and underlying strata showed unconformity, the coal in the bottom of the overlying strata Badaowan formation is the divided logo layer and the lime mudstone of top of the underlying strata Lucaogou formation is the boundary with the bottom of Wutongou formation. And according to those what mentioned above we devided Wutonggou formation (P3wt) into two segments, P3wt1and P3wt2. Further devided both of them into four sand sets, P3et11、P3wt12、P3wt21、P3wt22, Devided four of them into eleven sands, P3wt11-1、P3wt11-2、 P3wt12-1、P3wt12-2、P3wt12-3、P3wt21-1、P3wt21-2、P3wt21-3、P3wt22-1、P3wt22-2、P3wt22-3.According to the characteristics of stable heavy mineral assemblages (ZTR) and the distribution of the ratio of the sandstone and stratigraphic and the ratio of the conglomerate and stratigraphic, combination of the features of the ancient geomorphological of the sag, we determined that the Jimsar sag has two sediment source, X7well area and X19well area’s sediment source is southwest and the X17well area’s sediment source is north.The predecessors conducted some research on the Permian Wutonggou formation in the eastern of Jimsar sag and some of them believed that it desosited alluvial fan-fan delta-lacustrine depositional system and delta-lacustrine depositional system, some believed that the fully developed braided river delta (including three sub-phase)-lacustrine depositional system, while others think that the alluvial fan, braided river delta, tuibidite phase deposited. Several views of the same show obvious differences. In this paper, according to the core observation and logging data, analysis of laboratory data, logging curve characteristics data analysis, we believe that it developed a braided river delta-lacurrine depositional system in eastern of Jimsar sag in Wutonggou formation. In that system, braided river delta plain subfacies did not exist but braided river front subfacies and front braided riverl delta subfacies developed, development of sedimentary six microfacies including the underwater distributary channel, Tributary bay, estuarine dam, distal bar, front delta mud and shallow lake mud microfacies.Underwater distributary channel is the continuation fo the part of the braided river in the plains environment into the lake basin, and the overall showed a bedded distri-bution and pebbly sandstone, conglomerate, sandstone lenticular sand bodies superposed with each other. The sandstone lens takes the shape of the rough bottom to thin top. A single river lenticular sand body shows thinning pich-out by extends laterally several meters. Lateral accretion cross-bedding is the main sedimentary structure type, formed by the frequently lateral migration of the underwater distributary channel. In addition, usually parallel to bedding and erosion filling structure developed. The tributaru bay composited of gray-dark mudstone, and it usually is distributed lenticular, lotus shaped in the channel sand body because of mostly erosion by frequently lateral migration of the underwater river. The estuarine dam usually composed on mid-sandstone, thin sandstone, coarsening-upward reverse grading, development parallel to bedding small and medium-sized staggered bedding. Distal bar was mostly consist of fine sandstone, siltstone, and thin-bedded, but extends farther. Front braided river delta located in the braided river delta front slope with direction to the center of the basin and usually deposition was gradual transition associated with shallow lake mud, mainly with dark gray, gray and black mudstone-based, developmental horizontal bedding.It generally shows rising lake level during the period of Wutonggou formation, and junior lake level fluctuations was included. It mainly deposited delta front in P3Wt1and P3wt22, folded prodelta mud, which formed through subprime lake level lift. And shallow lake and prodelta depostition developed in P3wt21, locally foldered braided river front sand body. In the late P3Wt1, a thick mudstone formed by a large-scale lake invasion existed all around of the sag, and forming the marker layer fo hierarchical between the P3wt1and P3Wt2.Comparative and analysis of the drilled testing and production testing data and the corresponding layer of sedimentary microfacies, it was found that the best oil sedimentary microfacies is the braided river front underwater distributary channel microfacies, accounted for95,45of the total number of statistical reservior and followed by the mouth bar microfacies, accounting for4.55of the total number of statistical reservior. |
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