Analysis of lithofacies and evaluation of effective reservoirs of member 2 of Xujiahe Formation in the Xinchang area in Western Sichuan

Abstract

In the Xinchang area in western Sichuan Basin, a total of 121.12 billion cubic meters of proved reserves of natural gas are discovered in Member 2 of Xujiahe Formation, but only 7.739 billion cubic meters of proved reserves of natural gas are produced. The main reason is that sandstones in Member 2 of Xujiahe Formation in the Xinchang area are generally tight, with strong heterogeneity, only intervals with relatively good physical properties have a certain production capacity; therefore, it is very necessary and important to evaluate effective reservoirs in Member 2 of Xujiahe Formation. Through analysis of cores, with consideration of color, sedimentary texture and grain size, lithofacies of Member 2 of Xujiahe Formation in the Xinchang area can be divided into 12 types. According to data of physical properties and thin section analysis, it can be concluded that the favorable lithofacies in the upper submember of Member 2 of Xujiahe Formation are the massive medium-coarse sandstone, the medium-coarse sandstone with cross bedding, and the medium-coarse sandstone with carbonaceous fragments. On the basis of electrical characteristics, well-logging interpretation standards for favorable lithofacies are established, in addition, favorable lithofacies and effective reservoir in the Xinchang area are determined, and distribution of favorable lithofacies (effective reservoir) is identified, which lay a solid foundation for next deployment of appraisal well and development of effective reserves.