Analysis of reservoir confinement potential for Carbon Dioxide geological storage at Mae Moh Mine

Abstract

Fossil power plants, like Mae Moh coal-fired power plant in Lampang, are known to have released great amount of carbon dioxide (CO2) into atmosphere, which has been a significant contributor to climate change problem since an industrial revolution. One of the effective solutions to sustainably reduce CO2 from atmosphere is net-zero emission process, namely CO2 capture and storage (CCS). The current thesis focuses on downstream section of CCS, CO2 geological storage (CGS), aiming to investigate potential CO2 confinement in storage formations in Mae Moh basin, hence a decarbonized electrical generation for Mae Moh power plant. The current study includes: (i) select suitable CGS storage formations; (ii) examine reservoir rock and other relevant properties as a result of geochemical reaction induced by CO2; and (iii) evaluate potential of CO2 confinement. Prospect formations (i.e. structural trap with sediments) and site location in Mae Moh mine (cross section line N30.5) were selected and the rock core samples were sampled. The structural trap for CGS consists of fine-particle claystone (NK) acting as seal that covers limestone (TR4) storage formation located underneath. As a result of geochemical reaction, seal (NK) rock average pore size was increased from 5.72 nm to 6.11 nm due to dissolution in a cementing carbonate mineral, while reservoir rock (TR4) average pore size was decreased from 4.04 nm to 3.53 nm due to CaCO3 precipitation within pore. These consequently altered bulk porosity of the rocks, with both found a reduction. For CO2-brine-rock interactions, the three-phase contact angle measured on seal thin slice were 11.2°C and increased to be 16.6°C when exposed to CO2, while the CO2-brine interfacial tension was reduced from 87.1 mN/m to 78.9 mN/m due to dissolved CO2 in the formation brine. Potential confinement of CO2 storage was thus determined using CO2 column height (h), a balance between capillary and gravitational forces, with those investigated rock and fluid properties. The CO2 column height was considered into two approaches: non- relative and 'seal-reservoir' relative capillary equations. When considering non-relative capillary-controlled column height (only seal rock pore was considered), resulted h were positive (~2.9 to 3.6 km) even exposed to CO2 (i.e. geochemical effects were minima). On the contrary, with additional contribution from reservoir rock the calculated h from relative capillary equation were negative (-1.5 to -2.1 km for without and with CO2 exposure, respectively). This was due to relative pore size between seal and reservoir rocks, with smaller reservoir pore the capillary suction reversing to suck the non-wetting phase (i.e. CO2) upward. The current findings imply weak structural trapping with possible '1eakage' through such structural seal-reservoir trapping (NK and TR4). CGS confinement in this formation would thus be less potential and further modification is a challenge to functionalize this storage site to be more CGS feasible.