Differences in the distribution and occurrence phases of pore water in various nanopores of marine-terrestrial transitional shales in the Yangquan area of the northeast Qinshui Basin, China

Gas-In-Place Content of Deep Shales and Its Main Controlling Factors: A Case Study on the Wufeng-Longmaxi Shales in the Middle Luzhou Block of the Southern Sichuan Basin, China

“…Although most pore water of shales has been expelled from shale reservoirs during diagenetic and thermal evolution stages, shales generally contain certain amounts of pore water under geological conditions, even for deep shales. ,− Because pore water and shale gas are competitively stored in shale nanopores, the water-bearing characteristics of shales can significantly affect the accumulation and enrichment of shale gas. The C PW of the deep WF-LMX shales ranges from 2.06 to 11.31 mg/g, with an average value of 7.17 mg/g, and it progressively decreases with increasing burial depth (Table and Figure a).…”

A Modified Dent-Fractal Mathematical Model to Investigate the Water Vapor Adsorption on Nanopore Structure Heterogeneity from the Longmaxi Shale, Sichuan Basin, China

“…Recently, an increasing number of scholars have been employing the water vapor isothermal adsorption methods to study the water-bearing capacity of shales, such as Marcellus, Shanxi Formation, and Wufeng-Longmaxi Formation Shale, and a series of results have also been obtained. − It is believed that the adsorption behavior of water vapor in shale is affected by the clay minerals, brittle minerals, organic matter content, pore structure characteristics, mineral surface wettability, environmental conditions (adsorption temperature, relative pressure), and other factors. ,,− Because shale mainly consists of inorganic minerals and organic matter (OM), the water distribution characteristics in the different components is significant. Water molecules are believed to mainly reside in the pores of inorganic minerals, especially clay minerals that are usually negatively charged and can strongly interact with water molecules (e.g., highly negatively charged montmorillonite). ,,,, Water molecules can form a water film on the surface of clay-rich shale, which is strongly adsorbed on the inner and outer surface by electrostatic forces and hydrogen bonds. ,, For the OM pore, hydrocarbons are primarily found in the kerogen pores, and the interior of kerogen pores have almost no water molecules. , However, some scholars disagree that the oxygen-containing functional groups within OM have certain hydrophilic properties. ,,− Furthermore, the internal pore structure characteristics of shale are important factors for measuring and evaluating the quality of shale reservoirs, including storage capacity and fracturability. − WVA describes the relationship between the activity of water molecules and the saturation of water content on the surface and inside of a solid material at the constant pressure and temperature .…”

Effect of Water Saturation on Gas-Accessible Effective Pore Space in Gas Shales

“…There are many factors affecting the development of effective pores in shales, and the water content of shales is one of the most important factors [14,15,[23][24][25][26][27][28]. For example, Li et al [25] studied the water distribution characteristic in shale clay and found that under a certain humidity condition (such as 0.98), the water distributes in different sized pores mainly as (1) capillary water in the small pores (<6 nm) and (2) water film in the larger pores.…”

“…Specific surface area is more susceptible to water than pore volume due to its smaller variation range of pore size distribution (2.5-20 nm). Cheng et al [23] studied the differences in the distribution and occurrence phases of pore water in various nanopores of marine-terrestrial transitional shales in the Yangquan area of the northeast Qinshui Basin and pointed out that the pore water takes up the majority of the inorganic-matter hosted pore structures, especially for the inorganic-matter hosted nonmicropore surfaces; however, it only occupies a few of the organic-matter hosted micropore structures and fails to occupy the organic-matter hosted nonmicropore structures. Xu et al [27] studied the storing characteristics of connate water in lower Paleozoic shales in southeast Chongqing and pointed out that connate water occurs in shale micropores and nonmicropores, and adsorption and filing states simultaneously exist and are distributed in <10 nm mesopores and 0.4-0.6 nm micropores; this distribution reduces the pore structure parameters of inorganic matter in shale, especially the nonmicropore surface area.…”