Research On Sedimentary Facies Of The Fourth Sand Section The Second Sand Group In138Area Of Bamianhe Oifiled

Bamianhe oil field is located in the eastern part of south slope of Dongying sag in Jiyang depression, Bohai Bay Basin. Shahejie formation in the Lower Tertiary is the major oil reservoir of Bamianhe oil field. According to the region’s character of complex structures, many faults but small flocks, small oil-bearing area,and complicated sedimentary facies, gas and water distribution’s regularity is irregular to find. The exploration and development become more difficult. Because of the limitation of exploration data, the Shahejie formation’s development project is hard to be formulated. Many people studied on the types of sedimentary facies in Shahejie formation, but there was no unified view to be reach. In view of this, it is thought that the more study is indispensable on the types of Shahejie formation’s sedimentary characteristics.Mian138block is the major oil and gas accumulation belt in Bamianhe oil field. The second sand group of the forth section of the Shahejie formation in Lower Tertiary is the major oil layer, also is the key formation of our research on. The sand group is divided into two single-sand layers. The paper does systemic studies on each of the sand layer’s sedimentary micro facies.In this study, by combining drilling with logging, core data and seismic inversion and employing the theory of base-level cycle, sedimentary cycle division was performed for the second sandstone group in the fourth member of Shahejie Formation (Cenozoic-Pleogene) of Bamianhe Area under the control of isochronous marker bed. Furthermore, a systematic study on the sedimentary facies of the second sandstone group in the fourth Shahejie member was also conducted.Stratigraphic framework was constructed for the strata in this area. In particular, meticulous comparison and division were conducted on the controversial second sandstone group in the fourth Shahejie member, so as to amend the original plan of stratigraphic division, to provide reliable stratigraphic division data for the research on the sedimentary reservoir in this area, and to complete a new dada sheet of stratigraphic division. Under the control of isochronous marker bed, meticulous stratigraphic division and framework comparison were conducted for the sandstone of the second group in the fourth Shahejie member, which contained122wells. The results suggested the sandstone in this area was vertically overlapped and horizontally contiguous; NO.1sand body in the first thin layer of second sandstone group was the thickest. According to the core observation and description, the collection of all kinds of sedimentary facies marks, and the analysis of single well facies, three types of sedimentary facies in the forth section formation was recognized:delta facies, beach dam facies, lakes facies. Then, each face was divided into many subphase and micro facies. After summarized the typical recognition feature and sedimentary characteristics, the paper built three sedimentary facies models of coastal shallow-lake, delta, beach dam.During the sedimentary period, Second sandstone group in the fourth Shahejie member has experienced the sedimentary cycle of lake-level fluctuations. Based on the rounded analysis of sedimentary environment, character and vertical evolution, it is considered that the second sand group of the forth section formation mainly developes coastal shallow-lake sand body, beach dam sand body and delta front sand body.The sedimentary period of the second sand group of the forth section formation experienced the sedimentary cycle of the lake plane’s increase and decrease. At early sedimentary, the lake plane began to rise, until it submerged the region. The sand and shale deposition covered the sedimentary discontinuity, and formed some overlap deposition. But when the lake water submerged the region, the lake plane was close to the maximum value. In other words, the region was not submerged at early period when the lake plane rose up at low or high speed, and it exposed at surface and was denudated until the lake plane rose to the top basically. Then, it developed a mass of delta front sediment. So the lake water receded temporary and the deposition exposed at surface again, at the sedimentary period of the second sand group. Afterwards, the area was submerged to lake-bay, and formed beach dam sand body sediment.The result proves that, the shallow-lake sand body, beach dam sand body developed at the second sand group of the forth section formation in Mian138block are dominated by fine sandstones. The fine sandstone is well-sorted, and has good physical property, shale cementation and pore development character. The fine sandstone reservoir is the most ideal place to store oil and gas. The block is adjacent to deep lacustrine facies source rock,so it provides good reservoir space for the hydrocarbon accumulation.Combining to maps of the single well facies, profile facies, sandstone content, sandstone thickness and seismic reflection characteristics, the paper works out the sedimentary facies plane distribution map about the second sand group of the forth section in Mian138block, Bamianhe oil field. It does system analysis on sedimentary facies about distribution characteristics and space-time evolution regularities, and builds the sedimentary facies models of shallow-lake sand body and beach dam sand body.