Fundamental Understanding of Methane-Carbon Dioxide-Water (CH4-CO2- H2O) Interactions in Shale Nanopores under Reservoir Conditions Yifeng Wang, Tuan Anh Ho, Yongliang Xiong, Louise J. Criscenti, Philippe Weck, Edward Matteo and Jessica Kruichak (Sandia National Laboratories) Objectives: Extraction of CH4 from nanopores in kerogen 1.0 Understand two important processes that control gas-in-place(GIP) & well 250 production: 0.8 • Methane partitioning in the nanopores of mudstone matrices. 200 • Methane transport from low-permeability matrices to fracking-induced fracture 0.6 150 networks. 0.4 100 Pressure (atm) Pressure 0.2 50 Field observations Molecular dynamic (MD) 0.0 0 • (# molecules/ps) rate Extraction Core/outcrop sample 0 200 400 600 800 1000 collection modeling Time (ps) • Quantification of • Binding energies of methane heterogeneities sorption Methane release from kerogen matrix is • Diffusion rates characterized by a fast release of pressurized free Synthesis of nanoporous materials gas followed by a slow release of adsorbed gas. Material characterization A B Nanoscience • Pore structures: SANS, BET, • Effects of nanopore TEM, SEM, etc confinement on fluid • Chemistry & mineralogy: XRD, Gas disposition & release thermodynamic properties XRF, etc • Gas in place (GIP) • Effects of nanopore • Gas migration from matrix confinement on methane into fractures transport (microfluidics in Sorption/desorption • Stimulated volume shale) measurements • Gas for secondary recoveryC • Methane sorption/desorption on model materials Upscaling • Methane sorption/desorption • Percolation theory under high P & high T • Fractal representation • Chemical/physical • Lattice Boltzmann modeling stimulations Predictive models Column experiments • Constitutive relationships • Diffusive fluxes • Continuum models High pressure/high temperature • Advective fluxes sorption/desorption measurements • Reactive transport modeling Adsorption isotherm of CH4 in kerogen: Total uptake of CH4 in kerogen 4 • At low pressure gas present Total-1 3 Excess-1 Total-2 in kerogen is mainly Excess-2 adsorbed gas 2 • At high pressure more gas fills into the free volume (mmol/g) Uptake 1 inside kerogen matrix. 0 0 50 100 150 200 250 300 Pressure (atm) Grand Canonical or Gibbs-NPT Excess adsorption of CH4 in kerogen Monte Carlo Simulations 푛푒푥푐푒푠푠 = 푛푡표푡푎푙 − 휌푃,푇푉푓푟푒푒 Our excess adsorption is of the same order of magnitude with actual measurements on Conclusions: Barnett and Haynesville shales. • Our kerogen model can reproduce the experimental results such as the kerogen density, pore size distribution, and methane adsorption isotherm in organic shales. • Methane diffusion in kerogen nanopores behaves significantly different from the bulk phase. • We found that methane release from kerogen matrix is characterized by a fast release of pressurized free gas followed by a slow release of adsorbed gas. • Significant amount of gas deposited in kerogen can be trapped in isolated pores and thus not recoverable. • Significant fraction methane can sorb onto clay minerals. • A new kerogen model is needed to reproduce FTIR data. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000. SAND No. 2011-4582P.