Abstract
Currently, many adsorption experiments of methane on shale have been done to understand adsorption characteristics of methane on shale, but those experiments’ pressure and temperature are far less than reservoir pressure and temperature; therefore, we carried out the experiments of methane adsorption on shale at 75.6°C and 95.6°C with 0–50 MPa pressure range to study the adsorption characteristics of shale under reservoir condition. We also build a new method to calculate the real (absolute) adsorption of methane on shale. Results present that the characteristics of excess adsorption isotherm under high pressure is different from the characteristics of excess isotherm under low pressure; adsorption obtained by adsorption experiment increases with pressure going up until reaching a peak and then declines with further increase in pressure. We build a new method to calculate the absolute adsorption by assuming that the adsorption phase volume approximately equals to the total volume occupied by adsorbed molecule, and the results calculated by our method show this method is reasonable and effective.
Highlights
As the development of shale gas is expanding, it attracts many researchers’ attention and makes them start to research some mechanism of developing shale gas
Strapoc et al (2010) and Wang et al (2009) reported that minerals, organic matter, vitrinite reflectance (Ro), and micro-pore volume of shale have impact on adsorption characteristics; monolayer adsorption theory may not be suitable to calculate the total gas content of shale precisely; it is reported that kerogen in Posidonia shales plays an important role in methane adsorption while sorption of CO2 is mainly due to non-organic materials (Hartman et al, 2011; Rexer et al, 2014)
We assume the volume of adsorption phase (Va) approximately equals to the total volume occupied by adsorbed molecule (Vt), and Vt can be calculated by multiplying each adsorbed molecule’s volume with the molecular amount which corresponds to the adsorption obtained by general adsorption experiment
Summary
As the development of shale gas is expanding, it attracts many researchers’ attention and makes them start to research some mechanism of developing shale gas. Schettler and Parmely (1990, 1991) studied the characteristics of methane adsorption on shale through adsorption experiments, which indicates that methane is adsorbed by kerogen and various clay minerals and adsorbents have different sorption capacities for their different specific surface areas; the adsorption capacity of some Devonian shale has positive correlation with total organic carbon (TOC; Schettler and and Parmely, 1990, 1991). Strapoc et al (2010) and Wang et al (2009) reported that minerals, organic matter, vitrinite reflectance (Ro), and micro-pore volume of shale have impact on adsorption characteristics; monolayer adsorption theory may not be suitable to calculate the total gas content of shale precisely; it is reported that kerogen in Posidonia shales plays an important role in methane adsorption while sorption of CO2 is mainly due to non-organic materials (Hartman et al, 2011; Rexer et al, 2014). Adsorption experiments on shale were carried out under pressure from 1.0 to 25 MPa at 46C, and results showed that methane sorption capacity increased with TOC content and moisture content can reduce sorption capacity of shale (Tan et al, 2014)
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