Abstract:

Based on a comparison of geological and surface conditions for shale gas in China and America, we conclude that marine strata in South China having similar properties to those of America are targets for shale gas exploration, and the Sichuan Basin and its surroundings are favorable exploration areas. After six years of research and exploration, the Fuling Shale Gas field, which is the first major commercial shale gas play in China, was finally found in the Sichuan Basin in 2012 and then successfully developed. The shale gas enrichment and high productivity in the WufengLongmaxi Formation is mainly controlled by the original depositional environment which determines organic matter content and postdepositional conditions that promote shale preservation and gas retention within the shale after thermal maturation. Deposition and distribution of the shales are controlled by the platform depression environment. Thickness and TOC content are the evaluation parameters for play. The late preservation conditions control the enrichment of shale gas. There are favorable preservation conditions and high degree of shale gas enrichment in the internal of Sichuan Basin, which are characterized by widely distributed Triassic gypsolyte layers and high pressure coefficient. The areas where both original depositional environment and preservation conditions are favorable should be given priority in play evaluation. Comprehensive analysis of the shale gas reservoir indicates that organic matter content is the principal control on shale gas enrichment, the organic micropores are the main reservoir space, horizontal bedding fractures ensure horizontal seepage, and that the high siliceous mineral content ensures good fracturing effect, high pressure coefficient indicates high degree of shale gas enrichment. These five properties have genetic relationships and statistical correlation and are characterized by “five properties in one position” distribution features in vertical. The high quality shales with “five properties in one position” feature is conducive to the enrichment of shale gas and benefit for its development, which is the main development of shale gas layer and key objectives of horizontal well trajectory.

Key words: Sichuan Basin, evaluation parameters, enrichment of shale gas, five properties in one position