Experimental Determination of P-V-T-X Properties and Adsorption Kinetics in the CO2-CH4 System under Shale Gas Reservoir Conditions

Shale gas production via hydrofracturing has profoundly changed the energy portfolio in the USA and other parts of the world. Under the shale gas reservior conditions, CO₂ and H₂O, either in residence or being injected during hydrofracturing or both, co-exist with CH₄. One important feature characteristic of shale is the presence of nanometer-scale (1-100 nm) pores in shale or mudstone. The interactions among CH₄, CO₂ and H₂O in those nano-sized pores directly impact shale gas storage and gas release from the shale matrix. Therefore, a fundamental understanding of interactions among CH₄, CO₂ and H₂O in nanopore confinement would provide guidance in addressing a number of problems such as rapid decline in production after a few years and low recovery rates. We are systematically investigating the P-V-T-X properties and adsorption kinetics in the CH₄-CO₂-H₂O system under the reservior conditions.

We have designed and constructed a unique high temperature and pressure experimental system that can measure both of the P-V-T-X properties and adsorption kinetics sequentially. We measure the P-V-T-X properties of CH₄-CO₂ mixtures with CH₄ up to 95 vol. %, and adsorption kinetics of various materials, under the conditions relevant to shale gas reservoir. We use three types of materials: (I) model materials, (II) single solid phases separated from shale samples, and (III) crushed shale samples from both the known shale gas producing formations and the shale gas barren formations. The model materials are well characterized in terms of pore sizes. Therefore, the results associated with the model material serve as benchmarks for our model development.

Sandia National Laboratories is a multi-program laboratory 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. This research is supported by a Geoscience Foundation LDRD.