Assessing CO2 adsorption capacities onto shales through gravimetric experiments : a first step in the feasibility study of coupling "fracking" with carbon storage
Résumé
Oil and gas production from shale formations stimulated by hydraulic fracturing (or « fracking ») is an abundant source of domestically available energy for the United States of America. Today, shale formations are mostly fracked using fresh water or brine which induces large volumes of water to manage. Industry face issues related to containment, transport, recycling, reuse, treatment and disposal of wastewaters (wastewaters are defined as mixture of drilling fluids, hydraulic fracturing fluids and formation water). Some alternative fracking options are proposed by oil and gas companies to reduce the quantity of water that is used. Among these options, fracking with carbon dioxide appears to have several benefits compare to hydraulic fracking, as (1) it does not require water but carbon dioxide ; as (2) injection of carbon dioxide could enhance the gas recovery ; and as (3) carbon dioxide could be adsorb onto the shale surface to be permanently stored in the formation. Here, we will present and discuss our results from laboratory experiments in order to assess adsorption capacities of carbon dioxide onto shales. Adsorptions experiments were carried out using a gravimetric sorption system based on magnetic suspension balance, which measures under controlled pressure and temperature conditions the changes in mass which act on solid samples during gas adsorption process. Results will be presented as adsorption isotherms giving sorption capacities at different values of pressure for a given temperature.We will see that our experimental results can also be easily fitted to model adsorption processes in numerical codes. Beyond the assessment of the carbon dioxide adsorption capacities, other topics should be discussed in further details as : What could be the impacts of changes in shale nanoporous structure through CO2/water/rock interactions on gas adsorption and recovery ? Is there any competitive adsorption between carbon dioxide and methane onto shale as it is the case of gas adsorption onto coal ? How can we model replacement of adsorbed methane by adsorbed carbon dioxide onto shale ? Future studies will help to answer these questions, but we will give here first answers through our present experimental data.