Project personnel will systematically study CH4-CO2-H2O interactions in shale nanopores under high-pressure and -temperature reservoir conditions, with the ultimate goal of developing new stimulation strategies to enable efficient and less environmentally harmful resource recovery from fewer wells.
Sandia National Laboratories (SNL), Albuquerque, NM 87123
Shale is characterized by the predominant presence of nanometer-scale (1-100 nm) pores. The behavior of fluids in those pores directly controls shale gas storage and release in the shale matrix and, ultimately, the wellbore production in unconventional reservoirs. It has been recognized that a fluid confined in nanopores can behave dramatically differently from the corresponding bulk phase due to nanopore confinement. CO2 and H2O (either preexisting or introduced) are two major components that coexist with shale gas (predominately CH4) during hydrofracturing and gas extraction. Liquid or supercritical CO2 has been suggested as an alternative fluid for subsurface fracturing such that CO2 enhanced gas recovery can also serve as a CO2 sequestration process. Limited data indicate that CO2 may preferentially adsorb in nanopores (particularly those in kerogen) and displace CH4 in shale. Similarly, the presence of moisture seems able to displace or trap CH4 in the shale matrix. Therefore, fundamental understanding of CH4-CO2-H2O behavior and their interactions in shale nanopores is vitally important for gas production and related CO2 sequestration.
The proposed work will address the following knowledge gaps:
Project personnel propose to bridge these gaps by using an integrated experimental and modeling approach to systematically study CH4-CO2-H2O interactions in shale nanopores under high-pressure and -temperature reservoir conditions.
The proposed research will (1) significantly advance fundamental understanding of hydrocarbon storage, release, and flow in shale; (2) provide more accurate predictions of gas-in-place and gas mobility in reservoirs; (3) help to develop new stimulation strategies to enable efficient and less environmentally harmful resource recovery from fewer wells; and (4) provide the basic data set to test the concept of using supercritical CO2 as an alternative fracturing fluid for simultaneous CH4 extraction and CO2 sequestration. The work will leverage unique SNL capabilities: nanogeochemistry, high-pressure and -temperature geochemistry, numerical modeling, nanoscience, and neutron scattering.
Project researchers obtained 10 shale core samples (including samples from Mancos, Woodford, and Marcellus) and model materials. They also obtained one relatively pure kerogen isolate from Mancos shale. Additional kerogen extractions from Woodford shale (immature) and Marcellus shale (mature) were prepared using solvent extraction, acid demineralization, and critical point drying. Low angle neutron scattering analysis was performed on Mancos shale samples. The team 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. Researchers completed the first set high-temperature high-pressure (HTHP) measurement for a gas mixture of 90% CH4 and 10% CO2. More measurements for other mixtures with different CH4 and CO2 concentrations are currently underway. Complementary to the HTHP experiments, researchers have completed a set of high-temperature and low-pressure CH4 adsorption measurements using a thermal gravimetric analyzer. Significant progress has been made on molecular dynamics modeling. The major findings up to date include:
The project is also working on the effects of gas extraction on water-kerogen contact angles. Molecular dynamics (MD) simulations were performed to investigate the wettability alteration of kerogen and mineral upon CH4 extraction and CO2 injection. The results indicate that contact angle of a water droplet changes significantly with a changing gas pressure for kerogen and pyrophyllite surfaces. This means that upon CH4 extraction, the gas pressure decreases and so does the contact angle of water droplet, suggesting that more water can move into the kerogen matrix during the gas extraction process. However, during CO2 injection, the CO2 gas pressure increases upon injection. The surface becomes more hydrophobic, indicating that water would move away from the kerogen surface and make the surface available for CO2 gas adsorption. The results have a significant implication to reservoir-scale simulations for shale gas extraction and CO2 injection.
Fundamental Understanding of Methane-Carbon Dioxide-Water (CH4-CO2-H2O) Interactions in Shale Nanopores under Reservoir Conditions (Aug 2017)
Presented by Yifeng Wang, Sandia National Laboratories, 2017 Carbon Storage and Oil and Natural Gas Technologies Review Meeting, Pittsburgh, PA
1.The original FWP was designated FWP 14-017608, which was replaced by FWP 16-019347 in FY17, followed by FWP 18-021410 and FWP 19-021410. The present FWP is 20-021410.