Tectonic And Lithofacies Paleogeography Research Of The Early Cambrian In Middle Yangtze Region

As the basis of the research of shale gas reservoir, it’s necessary to analyze and discuss the lithofacies and paleogeography. Understanding the development and distribution characteristics of lithofacies and paleogeography is helpful to the study of the geological conditions of shale gas accumulation and the evaluation of favorable zones, In recent years, there is great progress in the shale gas reservoir characteristics, hydrocarbon generation conditions and gas bearing analysis in Cambrian Niutitang Formation in Yangtze area, but the study of lithofacies and paleogeography still needs to be improved. So it’s urgent to study the lithofacies palaeogeography systematically and comprehensively, so as to make a strong support for the shale gas exploration and exploitation work.The thesis is divided into seven parts, introduction, regional geological survey, the types and characteristics of rocks, sedimentary environment analysis and lithofacies palaeogeography study, shale reservoir geology condition analysis and conclusions. There are about 30000 words,23 illustrations and 7 tables. The main conclusions are as follows:1. We discussed the shale formed in continental shelf and slope facies sedimentary environment in early Cambrian Niutitang stage through field outcrop survey and previous data analysis. Niutitang formation is in a continuous development of shale and the thickness is betweem 20 and 120 meters, trending in North East.2. The shale gas in Niutitang formation has good quality of generating conditions, its organic matter abundance is high, the TOC value is between 0.15% and 13.13%, and the average value is 2.34%; its organic matter maturity distribution is between 2.31% and 4.46%, the average value is 3.52%, and it’s in the high-mature stage; its TI value is mainly between 0 and 40,δ13C value is less than-29 per thousand and the type of organic matter is a type Ⅱ.3. The shale gas in Niutitang formation has good quality of reservoir conditions, the quartz content value is between 11% and 71%, the clay mineral content value is between 3% and 28%, the carbonate content value is between 5% and 55%, and the brittle mineral content is high, which is easy to make crack; the porosity and permeability of the shale gas in Niutitang formation is not good, the porosity value is between 0.4% and 21.3%, the permeability value of shale is between 0.006×10-3 and 0.496×10-3μm2; it developped the large organic pore, intragranular pore, intergranular pore, and is good for the accumulation of shale gas.4. Combining the shale thickness, TOC content, organic matter maturation and shale depth in Niutitang formation, we chose two favorable area by analysising the hydrocarbon generating condition, reservoir properties and preservation condition, the three areas are northwest of Hubei-Hunan and Mayang basin.