Study On Methane Adsorption Capacity Of Organic-rich Shale

Shale gas, which exists in the organic-rich shale, is an important kind of the unconventional natural gas resource. Shale gas has been widely concerned as a new type of clean energy. Shale gas resource is extremely rich in the world, especially in North America, East Asia, South America, North Africa and Australia. World rankings on shale gas recoverable resources are China, Argentina, Algeria, Russia and the United states.Shale gas development has a good start now in China. With the beginning of large-scale development, this clean and efficient resource will gradually become an important part of China’s energy. In 2014, shale gas demonstrated reserves increased from 0 to 106.75 billion cubic meters because of the first submitted reserves. In 2015, shale gas demonstrated reserves sharply increased 437.379 billion cubic meters. Shale gas demonstrated reserves has cumulatively increased 544.129 billion cubic meters and the total output has reached 5.718 billion cubic meters during China’s 12 th FivePyrites Year Plan.In this study, the samples are taken from the southeast of Chongqing Lower Cambrian Niutitang Formation. In order to study the adsorption capacity of shale of Lower Cambrian Niutitang Formation, we get continuous Niutitang Formation shale cores from the Well Yuke 1. Varieties of tests, such as SEM, Isothermal Adsorption and Organic carbon content testing, are conducted on 10 shale samples of the cores to analyze their surface and pore characters and find out how these characters influence the adsorption capacity.Various types of pores and microcracks, such as large numbers of 10 nm pores in the organic carbon, pores among the pyrite particles and microcracks in minerals, are observed by SEM in the shale samples. Nitrogen adsorption/desorption results indicate that the pore size of these 10 shale samples is concentrated in 1 nm and 4 nm, the pores from 1 to 2 nm and 3 to 4 nm provide most of the pore volume(under 10 nm). The mesopore volume is larger in the total pore volume and the micropore surface area is larger in the total surface area. The mesopore volume plays a decisive role in shale samples’ adsorption capacity of N2. Hysteresis loop is obvious in the isotherm, and its closing point’s relative pressure is about 0.45 which is in line with the law(0.42-0.5). These shale samples have good fractal characterization. Most of the fractal dimensions are between 2.7 and 2.8, which means the surface is rougher and micropore widespreads. Carbon dioxide adsorption results indicate that most of the pores are between 0.3 and 0.7 nm when the pore size is under 2 nm. This pore size distribution tends to provide more surface area. The adsorption isotherm of methane conforms to the I-type adsorption isotherm and the Langmuir Equation. Combined with these adsorption data and organic carbon content test, we find out that most of the shale samples’ pore volume of the 0-5 nm pores is positively correlated with the TOC content when the TOC content is under 6%, and the methane adsorption capacity is positively correlated with pore volume of 10-15 nm pores when the TOC content is above 6%.