Simulation of methane adsorption in diverse organic pores in shale reservoirs with multi-period geological evolution

Shangbin Chen,Yingkun Zhang,Xiaoqi Wang,Xueyuan Li,Chu Zhang

doi:10.1007/s40789-021-00431-7

Shangbin Chen, Yingkun Zhang + Show 3 more

Open Access

https://doi.org/10.1007/s40789-021-00431-7

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Abstract

In shale reservoirs, the organic pores with various structures formed during the thermal evolution of organic matter are the main storage site for adsorbed methane. However, in the process of thermal evolution, the adsorption characteristics of methane in multi type and multi-scale organic matter pores have not been sufficiently studied. In this study, the molecular simulation method was used to study the adsorption characteristics of methane based on the geological conditions of Longmaxi Formation shale reservoir in Sichuan Basin, China. The results show that the characteristics of pore structure will affect the methane adsorption characteristics. The adsorption capacity of slit-pores for methane is much higher than that of cylindrical pores. The groove space inside the pore will change the density distribution of methane molecules in the pore, greatly improve the adsorption capacity of the pore, and increase the pressure sensitivity of the adsorption process. Although the variation of methane adsorption characteristics of different shapes is not consistent with pore size, all pores have the strongest methane adsorption capacity when the pore size is about 2 nm. In addition, the changes of temperature and pressure during the thermal evolution are also important factors to control the methane adsorption characteristics. The pore adsorption capacity first increases and then decreases with the increase of pressure, and increases with the increase of temperature. In the early stage of thermal evolution, pore adsorption capacity is strong and pressure sensitivity is weak; while in the late stage, it is on the contrary.

Highlights

China has become the third-largest shale gas producer in the world, establishing commercial mining in Fuling, Changning–Weiyuan, Zhaotong, and other districts (Dong et al 2016a, b; Dong et al 2016a, b; Zou et al 2015, 2016, 2018)
In shale reservoirs, the organic pores with various structures formed during the thermal evolution of organic matter are the main storage site for adsorbed methane
The molecular simulation method was used to study the adsorption characteristics of methane based on the geological conditions of Longmaxi Formation shale reservoir in Sichuan Basin, China

Summary

Introduction

China has become the third-largest shale gas producer in the world, establishing commercial mining in Fuling, Changning–Weiyuan, Zhaotong, and other districts (Dong et al 2016a, b; Dong et al 2016a, b; Zou et al 2015, 2016, 2018). Shale gas reservoirs exhibit significant heterogeneity in space–time after through multi-stage and multi-type geological transformation (Pandey et al 2018). Thermal evolution experiments with rich organic matter have shown that pore volume and surface area increase with thermal maturity. Thermal simulation experiments on oil shale samples suggest that the main diameter range first decreases and increases with maturity. They indicate that the generation of nanoscale cylindrical pores within organic matter is the primary cause of added porosity during mature hydrocarbon generation. Slit porosity at contacts between the organic matter and the skeleton particles, interlayer pores in clay minerals and dissolution pores began to grow in the mature stage (Xue et al 2015)

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