Modeling Gas Adsorption in Marcellus Shale With Langmuir and BET Isotherms

Abstract

Production from shale-gas reservoirs plays an important role in natural-gas supply in the United States. Horizontal drilling and multistage hydraulic fracturing are the two key enabling technologies for the economic development of these shale-gas reservoirs. It is believed that gas in shale reservoirs is mainly composed of free gas within fractures and pores and adsorbed gas in organic matter (kerogen). It is generally assumed in the literature that the monolayer Langmuir isotherm describes gas-adsorption behavior in shale-gas reservoirs. However, in this work, we analyzed four experimental measurements of methane adsorption from the Marcellus Shale core samples that deviate from the Langmuir isotherm, but obey the Brunauer-Emmett-Teller (BET) isotherm. To the best of our knowledge, it is the first time to find that methane adsorption in a shale-gas reservoir behaves similar to multilayer adsorption. Consequently, investigation of this specific gasdesorption effect is important for accurate evaluation of well performance and completion effectiveness in shale-gas reservoirs on the basis of the BET isotherm. The difference in calculating original gas in place (OGIP) on the basis of both isotherms is discussed. We also performed history matching with one production well from the Marcellus Shale and evaluated the contribution of gas desorption to the well's performance. History matching shows that gas adsorption obeying the BET isotherm contributes more to overall gas recovery than gas adsorption obeying the Langmuir isotherm, especially at early time in production. This work provides better understanding of gas desorption in shale-gas reservoirs and updates our current analytical and numerical models for simulation of shale-gas production.

Simulation of shale gas transport and production with complex fractures using embedded discrete fracture model

“…In our previous studies, it was found that four experimental measurements of methane adsorption from the Marcellus Shale core samples deviate from the Langmuir isotherm, but obey the BET isotherm . The standard BET isotherm assumes that the number of adsorption layers is infinite.…”

“…Gas transport in shale formation involves complex gas transport mechanisms due to the presence of a large amount of nanopores and organic matter, which include gas desorption, adsorbed gas porosity, gas slippage, and Knudsen diffusion, and so forth . Yu et al reported that the adsorbed gas porosity can be up to as high as 3.8% based on the experimental measurements of gas adsorption isotherm in some area of Marcellus shale. However, this important effect has not yet been well documented and clearly understood in the literature.…”

Applicability of various adsorption isotherm models on adsorption of methane and CO2 on Indian shales

“…In case of shales, previous studies mostly focused on application of Langmuir model to the experimental methane and CO 2 adsorption data [9][10][11][12][13][18][19][20][21][22][23]. Some researchers have also reported the applicability of BET and D-P models that are based on the mechanism of multilayer adsorption or pore-volume filling, respectively [24][25][26][27]. Recently few authors have applied the Ono-Kondo model to describe methane adsorption data on shales [27,28].…”

A review of carbon dioxide adsorption to unconventional shale rocks methodology, measurement, and calculation

“…They found that the simple Langmuir and Dubinin-Radushkevich models were the most adequate for modeling supercritical single component adsorption on coal and shale as long as the density value is adjusted on the simulator for the CO 2 since it has a direct effect on the compressibility value. Yu [16] used BET Isotherm rather than Langmuir Isotherm to model gas adsorption in Marcellus Shale. They observed that the Langmuir isotherm does not accurately model adsorption in all cases in the Marcellus shale, and hence a combination of BET and Langmuir isotherm should be applied.…”