Characteristics of Sedimentary Facies in Lower Part of Xingouzui Formation in Mawangmiao Area of Qianjiang Depression

Key words: 
• Mawangmiao area /
• lower part of Xingouzui Formation /
• shallow water delta /
• sedimentary facies

Abstract: The lower part of Xingouzui Formation of Mawangmiao area is an important producing pay and profitable range to find lithologic hydrocarbon reservoir in the future. Based on the synthetical analysis of cores description, thin section analysis and logs, and combined with sedimentary marks of lithology, paleoclimate, sedimentary structure, and so on,
the lower segment of Xingouzui Formation is ascertained shallow water deltashoreshallow lacus depositional system, and is further divided into subfacies as follows: delta front, prodelta, shoreshallow lacus, etc. and several microfacies. Provenance analysis results indicate that the study area is controlled by northeastern Hanchuan provenance and northwestern Hanshui provenance, the study area develops two lobate deltas of NESW and NWES distribution, especially the NESW delta develop more widely. During the Ⅱoil group depositional stage, depositional water depth is the most deep, and the delta develop most widely, Ⅲoil group takes second place. And during the Ⅰoil group depositional stage, depositional water depth is the most shallow and the delta develop most shallowly. Most of all, the underwater distributary channel microfacies develop most widely. Through analyzing sedimentary facies distribution and reservoir sands distributing rule of three oil groups and important sections of Xia31,Xia25 and Xia13, indicate that the underwater distributary channel microfacies of Xia25 has most wide scale and most thick sand, the sand distribution rule according to underwater distributary channel distribution. The sedimentary facies distribution of Xia31 and Xia13 coincide with the Xia25 and northwestern delta front sand of Xia31 develop more wide. The result of analyzing every microfacies reservoir physical property indicates that underwater distributary channel has highest porosity. Thus underwater distributary channel microfacies and thicker sand distribution region of each section should be optimum reservoir facies and beneficial region to seek for lithologic hydrocarbon reservoirs.