Study On Reservoir Sedimentary Characteristics Of Ⅱ、Ⅲ Sand Series Of Zhuhai Formation In Liwan 3-1 Gasfield

The Studied area, Liwan 3-1 gas field was located in the southeast edge of Baiyun Sag, which was located in the eastern part of ZhuⅡdepression of the Pearl River Mouth Basin. The drilling wells encountered high-yield industrial oil and gas flow, and also it had good reservoir properties. As the lithology and sedimentary structures were very rich in the core, so it was a typical representative of the reservoir of Zhuhai formation in the South China Sea. But Sand body distribution and vertical stacking relationship was unclear, and sand controlled factors were unknown, and it was needed to determine microfacies distribution law, and also it was required further research on the vertical heterogeneity of reservoir characteristics and interlayer distribution and so on. So this paper fine studied the depositional facies distribution law and sand distribution, and also analyzed the reservoir characteristics, in order to have those as basis for the foundation of later geological modeling.There were only four wells in the study area, and the core wells were only LW3-1-1 well and LW3-1-3 well, so the basic data was weak, and it was difficult to find out the phase boundary. By four well core data, well logging and seismic data, using the research ideas of points (wells)→line (section)→face (plan)→domain (time evolution and spatial distribution), this paper studied the sedimentary characteristics of the reservoir in the objective interval including UNIT3 and UNIT4 to determine the sedimentary facies and analyzed the reservoir characteristics. The Paper was obtained the main results as follows:(1) Using detailed description and observation of the core in the objective interval, founding that from coarse to fine sandstone were developed, and the main color of sandstone were linen or dark gray, and that of mudstone was black, with gray for supplemented. Sedimentary structures were rich, that is to say, the traction current bedding and internal tide bedding were developed, and plant debris, carbon dust, biological medium crumbs were also developed; and also pyrite nodules were visible.(2) Constrained by sequence stratigraphic framework, integrated core, logging and seismic data, the paper identified deposition system of UNIT3 (SAND2 sand series) and UNIT4 (SAND3 sand series) in Zhuhai formation was obviously under the control of the slope break belt, that is to say, above which it was shallow delta deposits, and below which it was slump turbidite fan deposits. The main types of sedimentary microfacies were distributary channel of delta front, mouth bar, sheet sand, streaming sedimented.(3) Through the reservoir property analysis, finding the Low Limit of favorable reservoir: porosity was 12% and permeability was 30md. According to the porosity found in the value, UNIT4 had better reservoir properties, and UNIT3 was relatively poor.(4) Through the analysis of intercalation, rhythm features and the permeability parameters of the heterogeneity of the mobile unit to determine the heterogeneity of characteristics, finding that based on the whole UNIT3 was heterogeneity, and the local sand of UNIT4 was strongly heterogeneity.(5) Using physical parameters and permeability parameters and interbed parameters as the evaluation parameters of reservoir, finding that distributary channel and mouth bar were the favorable reservoir. Combined WGC, finding that the favorable reservoir zone were located around the four drilling wells.