The objective is to demonstrate effective sequestration of CO2 in coalbeds via injection of dissolved gas. We have developed a laboratory-scale apparatus to simulate processes involved in coalbed sequestration: 1)Preparation of injection fluid, 2) Flow of fluid through coal, 3) Recovery of displaced coal fluid for recycling at Step 1. The apparatus consists of three clear polycarbonate pressure compartments: a mixing tank, tubing packed with coal, and a recovery tank. These represent respectively the injection well, the coalbed, and peripheral production wells. Flow is driven by a single pump with valving to select for and simulate the three phases of sequestration. First, the pump moves headspace gas through a sparging stone in the mixing tank. Second, gas-saturated water is passed through coal packed in polycarbonate tubes and into the recovery tank. Third, the coal is isolated, and water is pumped from the recovery tank to the mixing tank. This effectively closes the loop so additional injection fluid can be prepared and cycled through the coal. Partitioning of CO2 in the system is monitored with pressure, temperature, and pH sensors, as well as Raman spectroscopy.
In fluid saturated with CO2, the Raman signature of dissolved CO2 is observed. After passing through coal, lower CO2 is observed in recovered fluid, even after replacing the entire volume of water in the pore-space of the coal several times over. Furthermore, when recovered fluid is returned to the mixing tank, the pressure drops immediately as residual CO2 in the headspace dissolves into fresh fluid. Another indication of CO2 retention in the coal is observed when the mixing and recovery tanks are vented to atmosphere post injection: much more gas exsolves from the mixing tank fluid as compared to recovered water. A final dramatic demonstration of sequestered CO2 is observed when the coal is then vented. Microscopic gas bubbles in the coal expand rapidly, driving most of the water out of the coal and large amounts of gas also bubble out.
