Geologic CO2 storage in arkosic sandstones with CaCl2-rich formation water

The feasibility of geologic CO2 storage in deeply buried arkosic sandstones has been tested using high -temperature, high-pressure short-term laboratory experiments and long-term numerical simulations with CO2-saturated solution rich in CaCl2. These conditions mimic the conditions found today in the Eocene reservoir sandstones of depleted oilfields in the Dongying Sag, Bohai Bay Basin, China. Experiments at 100 degrees C and 150 degrees C and PCO2 of 4 MPa were conducted on sandstones rich in K-feldspar and albite without anorthite. During the experiments, calcite and kaolinite precipitated while albite and K-feldspar partly dissolved. Ca2+ in formation water is shown to be critical for mineral trapping of CO2. The continuous dissolution of K-feldspar and albite at a slow rate for a long time period can prolong duration time of calcite precipitation and increase geologic CO2 storage capability by mineral trapping. Addition of NaCl, KCl and MgCl2 can prolong the dissolution time of K feldspar and albite and precipitation duration of calcite. It also increased the mass of sequestered CO2 by mineral trapping. The process of geologic CO2 storage can be divided into 3 stages. In stage I, calcite precipitates rapidly, and geologic CO2 storage is dominated by solubility trapping within 100 years. Stage II lasts up to 300 years in the solution without NaCl, KCl and MgCl2 and 900 years with addition of NaCl, KCl and MgCl2 into the solution. The precipitation rate of calcite decreases abruptly and the mass of mineral trapping of CO2 increases with increasing time, because dissolution of K-feldspar and albite causes decrease of Ca activity and prolongs calcite precipitation time. The geologic CO2 storage is dominated by mineral trapping. In stage III, reactions reach equilibrium and the mass of geologic CO2 storage reaches the maximum. The calculated mass of CO2 by mineral trapping in sandstones of the Es4x to Es3z in the Dongying Sag is about 3.61Gt.