Integrated Study of Reservoir Characteristics of a Shale Gas Reservoir: A Case Study from Sichuan Basin of China

摘要

The Lower Cambrian Niutitang Formation is an organic-rich siliceous mudrocks which is widely considered to be a potential shale gas reservoir in Sichuan Basin of southwest China. An integrated study was performed to characterize the reservoir characteristics. A series of tests were conducted on core samples including organic geochemistry, mineralogical, petrophysical and mechanical properties. A deep insight into the characterization of pore structure in shale reservoir was analyzed by field emission scanning electron microscope, gas adsorption and high-pressure mercury injection. The results show that Niutitang Formation shale reservoir has the potential for gas exploration and production due to organic matter rich, moderate porosity and high brittleness. The Niutitang formation is of great thickness and the total organic carbon content ranges from 0.16% to 9.15% with average of 3.56%. The porosity of shale samples is from 1.26% to 9.85% with average of 5.78%, and the pulse permeability of matrix is from 320 nD to 890 nD. The total content of brittle minerals (quartz, feldspar and carbonate) is over 70%, and the formation is characterized as rigid and brittle for high elastic modulus and low Poisson’s ratio. There are five types of pores in shale: organic nanopores, pores of clay minerals, intraparticle pores of matrix minerals, intragranular pores from microfossils, and microfractures, and the chief are organic nanopores and pores of clay minerals. Nanopores with pore diameter less than 50nm provide the main pore surface area and pore volume, which indicates they are the main place for hydrocarbon adsorption and storage. These results will provide a basis for further evaluation of the hydrocarbon potential of the Lower Cambrian Niutitang Formation shale in the Sichuan Basin.