CO2 Injection in Shales for CCUS

Abstract

Shale gas production has had great impact on energy supply and fuel prices. Due to low permeability and reservoir complexity the recovery factors are still very low. A promising alternative to pressure depletion is injection of CO2 with alternate pressure depletion (huff-and-puff). CO2 is able to adsorb onto shale and release trapped methane and thus increase recovery efficiency while providing a viable option for carbon sequestration. The world is combating global warming and one of the main causes is carbon emission; safe sequestration of carbon dioxide in shales could help mitigate this problem. The aim of this thesis work will hence be to study injection of carbon dioxide for 〖CO〗_2-EGR and CCS purposes in hydraulic-fractured shale gas reservoirs. A multicomponent adsorption isotherm with application to 〖CH〗_4- 〖CO〗_2 substitution is coupled with a flow model for evaluation of injection-production scenarios. Compaction behavior related to changes in effective stress and resulting impact on porosity and permeability will be explored. 〖CO〗_2-EGR is considered first in a matrix model, then at larger scale in a fracture-matrix model. Huff and puff is the considered scheme where injection and production occurs at the same well. Key parameters such as fracture and matrix properties, well pressure or rate, diffusion time and injection-production intervals during shale-gas production are investigated.