Investigation of CO_2-CH_4 Displacement and Transport in Shale for Enhanced Shale Gas Recovery and CO_2 Sequestration

摘要

To gain a better understanding of the enhanced shale gas recovery by CO_2 gas injection (CO_2-ESGR) technique, the dynamic displacement mechanism of CO_2-CH_4, the CO_2 enhanced shale gas recovery (R_(CH_4))< and CO_2 storage capacity (V_(CO_2) were studied based on transport properties of CO_2 and CH4. Experiments of CO_2 injection into shale gas reservoir preadsorbed by CH_4 were performed in a fixed bed. Breakthrough curves were obtained under different test conditions and simulated by one-dimension advection-dispersion (AD) model. It was found that dispersion coefficient (K_1) rather than molecular diffusivity of CO_2 dominated its transport in shale. K_1 together with advection velocity (v) of CO_2 during CH_4 displacement controls R_(CH_4) and V_(CO_2), When transporting in shale gas reservoir, CO_2 had larger dynamic adsorption amount and v, but smaller K_1 than CH_4. The competitive transport and adsorption behavior of CO_2 and CH_4 made it possible for CO_2 to store in shale reservoir and to drive the in-place CH_4 out of shale reservoir. The transfer zone of CO_2-CH_4 displacement (CCD) was very wide. High R_(CH_4) and V_(CO_2) were reached at low injection CO_2 gas pressure and for small shale particles. Higher injection flow rates of CO_2 and temperatures ranging from 298 K to 338 K had a little effect on R_(CH_4) and V_(CO_2), For field conditions, high CO_2 injection pressure has to be used because the pore pressure of shale reservoir and adsorption amount of CH_4 increase with the increase in depth of shale gas reservoir, but R_(CH_4) is still not high.