Geological Characteristics Of The Black Shale And Prospective Eevaluation Of The Shale Gas In Lower Cambrian Of Upper Yangtze Area

The lower Cambrian of upper Yangtze area has the good hydrocarbon genesis conditionsand exploration prospect.Based on the field profiles observation, chip identification,scanning electron microscope and other research test, from sedimentary facies, mineralcomposition, through the systematic comparative study of lower Cambrian Qiongzhusiformation black shale to divide the key blocks.After the original, ancient and new eastern Tethyan tectonic and sedimenrary evolution,these tectonic movements caused the development of high-angle fracture in Qiongzhusiformation, and increased the mudstone and shale reservoir space, while promoting thedesorption of adsorbed gas in shale.The Qiongzhusi formation in lower Cambrian of upper Yangtze area is mainlycontinental shelf environment, bottom-up the deep water shelf transition to shallow shelf. Thelithology changes from phosphate rock to chert when the area changes from north west tosouth east. The black shale of upper stratum thickening from north west to south east;Sedimentary facies transition from shallow shelf to deep-water shelf. The bottom-uplithology is phosphate/chert, black shale, sility shale/carbonate rock shale andsiltstone/carbonates. Favorable sedimentary facies are deep basin and deep water shelfenvironment.The lower Qiongzhusi formation is mainly black shale, especially near the site of contactwith the Dengying formation, type of organic matter is mainly type I, most organic matter istoo mature stage(generally Ro>2).30%of the thickness of the Qiongzhusi formantion isblack shale, some up to40%, the organic matter abundance of this group is too high, themajority of between1.5to2.5%, evolution of the organic matters and maturation are high.Vertically, organic carbon has a smaller tendency upward, TOC>2.0%is mainly concentratedin the35m of the bottom Qiongzhusi formantion; The high organic carbon mainly in southernSichuan to east Chongqing and western Hubei, Sichuan and Southeast Sichuan to becomelow.Through a comprehensive analysis of information and data, divided into six keyevaluation blocks, the Qiongzhusi formation in lower Cambrian includes Zunyi-Fenggang block, Sinan-Shiqian block and Yanhe block, and estimate the effective area andresources ofeach block, the shale of the Qiongzhusi formation in lower Cambrian of upper Yangtze area ispreliminary forecast.