Abstract:

W ith focus on the sedimentary，geoˉchem istry，reservoir，and gas potential，a prelim inary study is perˉformed on the form ing conditions and characteristics of the shale gas in the Lower Silurian Longmaxi Formation and the Lower Cambrian Qiongzhu Formation in the Upper Yangtze region by using outcrop，drilling，and core data.The results indicate that an Early Paleozoic shallowˉdeep water shelf sedimentary environment controlled the development and distribution of the organicˉrich black shale in the formations.The black shale is the thickest in the depocenter on the deep water shelf.TheirTOC values are generally high.Horizontally，the distribution of organic rich black shale（TOC>2%）is in accordance with that of the shelf.In contrast，vertically，theymainly occur in the m iddleˉlower and bottom parts of the formations and have a continuous thickness of30-50m and a TOC value over4%.Being sim ilar to the gasˉbearing shale in America，the black shale is rich in brittlem ineˉrals，but unitary in clay m ineral type，and contains no smectite.The matrix contains wellˉdeveloped pores and m icroˉfissures，occurring in threadlike，netted and honeycomb shapes.The measured porosity of core samples ranges from2%to16%，indicatingmoderate poroperm characteristics.Active gas shows occur during drilling in the black shale.Gas content of core samples is above the industrial development threshold.Isothermal adsorption simulation of the samples also shows a high methane adsorption capacity.The overall gas potential is sim ilar to

Key words: organicˉrich black shale, shale gas reservoir, form ing condition for shale gas, Lower Paleozoic, Upper Yangtze region