Abstract
Shale gas has become an important source of natural gas, and a significant portion of gas in the reservoir exists in an adsorbed state. Thus, knowledge of gas adsorption behavior is important to estimate original gas in place and shale gas production. In this paper, shale gas adsorption affecting factors which include temperature, pressure, pore type, and diameters were studied quantitatively and systematically using simplified local density model. It was found that the main affecting factors were temperature, pore type, diameter, and pressure; type I kerogen has the lowest and type III kerogen has the largest excess adsorption gas capacity; due to the interaction energy between gas molecules and pore wall molecules, gas has the highest local density near the pore wall and the lowest density in the middle of the pore under a certain pressure and temperature; the increment of gas density as temperature decreases near the pore wall is significant, but the bulk methane gas density shows a very small change due to temperature change; the ratio of excess adsorption gas to free gas declines and its rate slows down as pressure increases; when the pore diameter increased from 1.5 to 5 nm, the ratio of excess adsorption gas to the total gas amount decreases rapidly; the excess adsorption gas of type III kerogen takes up 89% of the total gas amount with diameter of 1.5 nm and takes 70% of the total gas amount with diameter increases to 5 nm; the excess adsorption gas of type I kerogen takes 71% of the total gas amount with diameter of 1.5 nm and takes up 43% of the total gas amount with diameter increases to 5 nm. Local gas density in different kinds of pores under different conditions also provided a way to calculate gas transport in pores that take adsorption gas into consideration.
Highlights
Shale gas reservoir has become an important source of natural gas, and a significant portion of the gas in this reservoir exists in an adsorbed state
Liming et al (2012) studied the methane adsorption of clay rocks which is the main components of shale and the results show that clay mineral type greatly affects CH4 sorption capacity under experimental conditions
We study shale gas adsorption influence factors quantitatively and systematically using simplified local density (SLD) model, including temperature, pressure, pore type, diameters, and so on
Summary
Shale gas reservoir has become an important source of natural gas, and a significant portion of the gas in this reservoir exists in an adsorbed state. We study shale gas adsorption influence factors quantitatively and systematically using simplified local density (SLD) model, including temperature, pressure, pore type, diameters, and so on. The SLD model which was first developed by Rangarajan et al (1995) can be used to describe the adsorption behavior of pure gases It has been successfully used in several studies on gas adsorption on activated carbon and coal (Fitzgerald et al, 2003, 2006; Mohammad et al, 2011). The SLD model accounts for both fluid–fluid and fluid–solid interactions in the slit-shaped pore. The lower limit in equation (8) is 1/2ff, which is 1/2 of the diameter of an adsorbed molecule touching the left plane surface. Zhang et al (2012) Zhang et al (2012) Zhang et al (2012) Zhang et al (2012) Zhang et al (2012) Zhang et al (2012) Zhang et al (2012) Zhang et al (2012) Zhang et al (2012) Hartman et al (2008) Hartman et al (2008) Liming et al (2012) Liming et al (2012) Liming et al (2012) Liming et al (2012) Liming et al (2012) Liming et al (2012) Liming et al (2012) Liming et al (2012)
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