WELL LOGGING RESPONSE CHARACTERISTICS AND ITS GEOLOGICAL SIGNIFICANCE OF SHALE GAS IN THE SHUIJINGTUO FORMATION OF THE CAMBRIAN IN YICHANG SLOPE, CHINA

摘要

In this paper, taking the Cambrian Shuijingtuo Formation shale in Well YYI and Well YYIHF in the Yichang Slope Zone as examples, we have sys- tematically analyzed the vertical and horizontal mudgas measured values. vertical and horizontal changesof gas components and their relationship with drill- ing time, TOC content and shale gas content. The measured value of shale gas reservoir in ShuijingtuoFormation in Yichang area has a high linear correla- tion with shale gas content. It is less affected by the drilling time and background value, and the gas measurement value can better reflect the gas-bearing characteristics of the reservoir. The analysis results show that the No. 4 and No. 5 layers of the lower Cambrian Shuijingtuo Formation in Yichang area are high-quality shale gas reservoirs. In high-quality res- ervoirs, the methane content of shale gas is nega- tively correlated with the total gas content in the ver- tical direction, and the hydrocarbons have the char-acteristic of being enriched in the high part of the structure in the lateral direction. There are two stages of continuous lateral migration of oil and gas in high- quality shale reservoirs. The first is the Early Silu- rian-Middle Triassic oil generation stage. The shale oil migrated laterally from the slope facies to the platform facies, which caused the TOC content in the shale reservoir to reverse in local areas of the slope facies, and formed the "side-generating lateral stor- age type"paleo-oil reservoir of the Dengying For- mation. The other stage is the dry gas generation stage since the Late Triassic. Shale gas continues to undergo lateral diffusion and fractionation, formingatmospheric shale gas reservoirs with different dis- tributions of shale gas hydrocarbon components.