Shale gas adsorption and desorption characteristics and its effects on shale permeability

Wei Guo,Rongze Yu,Xiaowei Zhang,Zhiming Hu,Li Wang

doi:10.1177/0144598716684306

Wei Guo, Rongze Yu + Show 3 more

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https://doi.org/10.1177/0144598716684306

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Abstract

A large proportion of shale gas is in adsorbed state. However, in the process of shale gas development, adsorbed gas in the shale pores will gradually desorb, which results in the permeability change of shale. This study aims to find out the adsorption and desorption characteristics of shale and whether there exists certain impact of desorption effects on shale permeability by experiments. Isothermal adsorption and desorption curves of shale gas are not coincident and the desorption curves are in hysteresis. Langmuir equation can be used to calculate the shale isothermal adsorption curve and desorption equation can be used to calculate the shale gas isothermal desorption curve. The permeability of shale was measured, respectively, under low pressure and high pressure, with methane and helium as experimental gas. Then, the comparison was made between the results of shale and the similar experiment results of tight gas sandstone. The results are showed as follows: adsorption effects will break the linear relationship between the shale permeability and the reciprocal of average pore pressure under low pressure; under high pressure, when gas desorption enhances, shale permeability significantly increases. Therefore, adsorption effects can impact the shale permeability under low pressure as well as under high pressure, which should be taken into consideration in the shale gas development.

Highlights

In China, there are various kinds of shale gas resources, distributing in large areas.our shale gas has a great potential for exploitation
Adsorption effects can impact the shale permeability under low pressure as well as under high pressure, which should be taken into consideration in the shale gas development
It is found that desorption and adsorption curves were not coincident and desorption curve overruns the adsorption curve.In our previous work (Wei et al, 2013a, 2013b), we have explained why the desorption curve and adsorption curve did not coincide; we have proposed that Langmuir equation can be used to calculate the adsorption curve and the desorption equation can be used to calculate the desorption curve

Summary

Introduction

In China, there are various kinds of shale gas resources, distributing in large areas.our shale gas has a great potential for exploitation. In China, there are various kinds of shale gas resources, distributing in large areas. China’s shale gas resource that can be exploited is about 31 1012 m3 (Wang and Wang, 2011). Gas exists in three states: as free gas in cracks, as free gas in matrix pore, and as absorption gas (Lane et al, 1989). The quantity of high organic matter is closely related to natural gas adsorption (Lu et al, 1995). Its pore structure provides it with large specific surface area. Those advantages are beneficial for matrix pore to adsorb a good deal of natural gas, with its content changing in the range of 20–85% (Lane et al, 1995). The existence of nanopores in shale has been revealed recently by ultra-high pressure mercury injection (Curtis et al, 2010, 2011a; Elgmati et al, 2011; Sondergeld et al, 2010) and back-scattered scanning electron microscopy (Ambrose et al, 2012; Curtis et al, 2011b; Milner et al, 2010; Schieber, 2010)

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