Geological Conditions And Assessment Of Lower Cambrian Gas Shale Around Sichuan Basin

Lower Cambrian formation around Sichuan basin presents geological characteristics such as wide distribution with favorable stability,high content of organic carbon etc,which is a vital respect in shale gas exploration of China.Based on geological analysis,Guangyuan area in the northwest edge,South east Chongqing area and Northwest of Guizhou area in the southeast edge of this basin is established as the main targets in relative research.Geological favorability of shale gas accumulation is assessed in quantificational methodology which is also researched thoroughly.Some recognitions re acquired consequently.In the respect of geological features,it is believed organic matter type of lower Cambrian shale is typically marine,of which the main contribution is from alga and plankton as low forms of life.The abundance of organic matter is relatively high,which can be connected to contents of quartz,which presents a positive correlation.High maturity of organic matter is a quite obvious characteristic,which is negative to existence of hydrocarbon in shale.Illite is the main content of clay mineral,which presents a negative relationship with a porosity and permeability of lower Cambrian shale.There is a relative difference between different typical areas.Shale of Niutitang formation in the southeast edge is more favorable than Shale of Qiujiahe formation in the Northwest edge in the capability of gas adsorption of shale,which indicates that the intensity of tectonic movement after the deposition is quite influential to gas detaining capability of shale.In the respect of geological assessment,parameter standardization and its technological process are innovated.From applying treatments including multiple regression and cluster analysis etc,dimensionality reduction in parameters and multivariate statistics are established as basic methodology.Parameters are accordingly divided into monotone type,complex type and background type.The processes of nondimensionalization and standardization are separated as independent ones.Multiple geological parameters are treated through conventional and commonly used mathematical geological and statistical methods.Relative weightiness are calculated and distributed to researched parameters according to analytical results of multivariate statistics and clustering analysis,from which univariate and nondimensional value containing general information in petroleum geology can be acquired.The aim of dimensionality reduction then can be achieved to assess and represent the geological favorability quantitatively.Comprehensive geological assessment is implemented aiming at Lower Cambrian shalein different typical sub areas of Peripheral area of Sichuan basin in this dissertation.The result of assessing the geological favorability of shale gas development indicates all of typical sub areas surpassing the threshold of geological favorability of shale gas development.Geological favorability of Lower Cambrian Niutitang shale in Southeast Chongqing is 0.534 on average.Geological favorability of Lower Cambrian Niutitang shale in Northwest Guizhou is 0.435 on average.Geological favorability of Lower Cambrian Qiujiahe shale in Southeast Chongqing is0.307 on average.It can be discovered through quantitative geological assessment that there is a sequence from high influential effect to low influential effect of the parameters to gas adsorption in Lower Cambrian shale of peripheral area of Sichuan basin,which is abundance of organic matter,specific surface area,maturity of organic matter,content of clay mineral,permeability,content of quartz and porosity.