Assessing the Gas Potential of the Lower Paleozoic Shale System in the Yichang Area, Middle Yangtze Region

摘要

This study aims to characterize the geological properties and to evaluate the gas potential of the lower Paleozoic shales in the Yichang area by integrating a series of analyses on geology and geochemistry, well logging data, and 2D seismic interpretation. The thickness of the lower Cambrian Shuijingtuo shale is less than 10 m in the southeast but may exceed 120 m in the southwest area. The thickness of the upper Ordovician Wufeng shale and the lower Silurian Longmaxi shale (hereafter referred to as the Wufeng-Longmaxi shale) gradually increases in thickness from 2% is more than 10–20 m, commonly located at the bottom of the shale intervals. Black shales near the Huangling anticline have low thermal maturity due to its relatively shallow burial. The predominant minerals are quartz and clay minerals. Carbonate contents of the Shuijingtuo shale are relatively high compared to the Wufeng-Longmaxi shale. Pores are more developed in the Wufeng-Longmaxi shale than those in the Shuijingtuo shale. Natural fractures are common in the Shuijingtuo shale but are rare in the Wufeng-Longmaxi shale. The well logging and lab analytical results both indicate that the natural gas content in the black shales is relatively high. The prospective area of the Shuijingtuo interval for shale gas production is nearly 670 km~(2), located in the southwestern region. In contrast, the prospective area of the Wufeng-Longmaxi interval for shale gas production is approximately 1590 km~(2), situated in the eastern area.