Quantitative characterization of pore network and influencing factors of methane adsorption capacity of transitional shale from the southern North China Basin

Abstract

Quantitative characterization of pore structure and analysis of influencing factors of methane adsorption are important segments in shale gas reservoir and resources evaluation and have not been systematically carried out in marine–continental shale series. A series of integrated methods, including total organic carbon (TOC) contents, Rock-Eval pyrolysis, mineral composition analysis, pore structure measurement, high-pressure CH4 adsorption analysis and FE-SEM observation, were conducted on 12 transitional shale samples of well WBC-1 in the southern North China Basin (SNCB). The results indicate that TOC contents of the transitional shales range from 1.03 to 8.06% with an average of 2.39%. The transitional shale consists chiefly of quartz, white mica and clay minerals. Interparticle pore, intraparticle pore, dissolution pore and microfracture were observed in the FE-SEM images. The specific surface area (SSA) of BET for the samples ranges from 3.3612 to 12.1217 m2/g (average: 6.9320 m2/g), whereas the DR SSA for the samples ranges from 12.9844 to 35.4267 m2/g (average: 19.67 m2/g). The Langmuir volume (VL) ranges from 2.05 to 4.75 cm3/g (average = 2.43 cm3/g). There is unobvious correction between BET and DR SSA with TOC contents, which means inorganic pores are the main component of pore space in the transitional shale from the SNCB. The relationship of SSA and pore volume shows that micropore has a greater impact on the CH4 adsorption capacity than mesopore–macropore in the transitional shale. Different from shales in other petroliferous basin, clay minerals are the primary factor affecting adsorption capacity of CH4 for transitional shale in this study. The pore structure of the transitional shale for this study is characterized by higher fractal dimension and more heterogeneous pore structure compared to shale in other petroliferous basin. This study provides an example and new revelation for the influencing factors of pore structure and methane adsorption capacity of marine–continental transitional shale.

Methane Adsorption Equilibrium on Marine Gas-Bearing Shale Matrices: The Polanyi Potential Theory Approach

“…The micropores of shale matrices mainly accommodate adsorbed CH 4 . − The adsorption mechanism of CH 4 on shale matrices typically consists of surface coverage and micropore filling. , Hence, the correlation analysis between the micropore structure parameters and CH 4 adsorpiton capabilites of shale matrices was conducted to reveal the possible adsorption mechanism. The pore classification method raised by the International Union of Pure and Applied Chemistry (IUPAC) was adopted.…”

Review of the Effect of Diagenetic Evolution of Shale Reservoir on the Pore Structure and Adsorption Capacity of Clay Minerals

“…demonstrated that micropores developed in clay provided a considerable specific surface area, which was conducive to the adsorption capacity of shale. Liu et al also reported a similar conclusion and stated that clay content was the primary influencing factor of shale adsorption capacity. However, more studies suggested that shale adsorption capacity was dominated by organic matter content. − Jiang et al and Xie et al normalized the CH 4 adsorption amount by TOC to avoid the influence of organic matter pores and found a linear positive correlation of clay content versus normalized value.…”

“…Liu et al 34 demonstrated that micropores developed in clay provided a considerable specific surface area, which was conducive to the adsorption capacity of shale. Liu et al 35 also reported a similar conclusion and stated that clay content was the primary influencing factor of shale adsorption capacity. However, more studies suggested that shale adsorption capacity was dominated by organic matter content.…”

“…In period A of the middle diagenetic stage, V L versus clay content shows a clear positive linear correlation (R 2 = 0.9117), and V L increases much with higher clay content (Figure 3b). Liu et al 35 concluded that clay minerals were the primary contributors of reservoir pore space and adsorption capacity, even higher than that of organic matter. In this stage, the free water in clay minerals is discharged, and only structural water remains.…”

“…Nevertheless, the extent of the effect of clay content in shale on CH 4 adsorption is still controversial. Some researchers argued that the inner surface of the micropores provided a large number of CH 4 adsorption sites. − However, others stated that CH 4 in shale was mainly adsorbed in kerogen structure and pores, and that not much in clay minerals. − Although clay minerals may block the pore throat or lack significant positive correlation with CH 4 adsorption capacity, they are still considered to play a role in the adsorption capacity of shale, besides that of organic matter. ,, …”