Methane Adsorption In Illite By Molecular Simulation

The prospect of shale gas brings much more attention on evaluating theamount of the adsorbed gas. With the deepening understanding of the adsorptionmechanism of shale gas, many scholars tended to focus on the clay minerals inshale,especially on illite. Being the most common clay minerals within oil andgas basin, illite plays an important role in forming reservoirs for its fine crystalsand large specific surface area. Many experiments were done in order to revealthe adsorption capacity of illite. However, it was hard to tell in the clay-organiccomplex. This research aimed to find out the adsorption capacity that illiteplayed in shale, as well as the methane distribution in illite. The process ofmethane adsorption in illite were simulated from a microscopic view, whichwould play a significant role in estimating and evaluating the shale gasresources.By use of the software Materials Studio6.0, this work simulated themethane adsorption in illite. Firstly, based on the general formula of illite,1M-tv and1M-cv models were built. Using the Molecular Mechanism method, themost stable configurations which were updated on basis of the structuresconstructed. Secondly, XRD were modeled to match the standard phase. Theresult turned out to be a good agreement with the characteristics found byresearch before, as well as the match result with the standard card. The values ofd001d002were also calculated, which agreed well with the theoretical andexperimental values contrasted. All these proved our models reasonable.Monte Carol method was used to simulate the methane adsorption underthe actual reservoir conditions. The amount of methane adsorbed results in1M-illite tended to be first increase then decrease along with the deepeningburial depth, and the summits appeared to be at the depth of2-3km.It made a difference in the amount of methane adsorbed as a result ofdifferent isomorphism in structures.1M-cv configuration tured out to adsorbmore gas than in tv, which showed that illite with rich Fe、Al circumstancewould be beneficial to methane adsorption.To deepen understanding the reason why different above methane amountoccurred as well as the diffusion rule methane followed, Molecular DynamicMethod was used. The results were listed as follows:1) The methane adsorbed in1M-illite accumulated two positions,one was the middle of the layers,while the other nearside the clay sheets. Theinterlayer K ion also had the same tendency, however, with the changingtemperature and pressure，K ion in tv configuration happened to have a localized vibration.2) The methane accumulated was mainly due to the attractive interactioncreated by ion K and T-sheets of the clay, among which, interaction by T-sheet isthe reason why the adsorption difference appeared.3) As a result of radial distribution function and self-diffusion coefficientof the interlayer particles,1-M illite had a stronger constrain interaction tomethane at2-3km depth which was most suitable for the shale gas exploration.