A Theoretical Study of the Effect of Salt Precipitation on CO2 Injectivity

Abstract

Adequate well injectivity is required to successfully inject large volumes of CO2 through a minimum number of wells. Brine vaporization in the wellbore vicinity has been identified as a major CO2 injectivity impairment mechanism especially in deep saline reservoirs. A bundle-of-tubes model was developed to investigate basic mechanisms of salt precipitation and to quantify injectivity loss induced by precipitated salts during CO2 injection into saline formations. A Berea sandstone rock was reconstructed with a bundle-of-tubes model. A correlation was developed to estimate the solid salt saturation in the pores based on the properties of the aqueous phase. A parameter capable of tracking the development of the dry-out zone was introduced to model the distribution of salt in the pores. A relative injectivity change index was then used to quantify injectivity impairment induced by precipitated salts. A tortuosity factor was incorporated to account for the tortuous path taken by fluids in porous media. A sensitivity study was performed to assess the effects of parameters such as brine salinity, initial permeability, injection flowrate and porosity on injectivity loss. The model can reproduce some experimental results of drying of brine-saturated sandstone cores by supercritical CO2. A sensitivity study of the parameters affecting injectivity show that; (1) salt precipitation occurs in the dry-out zone where most of the irreducible water in the trapped brine has evaporated, (2) increasing brine salinity has adverse effect on injectivity, (3) salt precipitation affects permeability more than porosity and (4) in rocks with high initial permeability, salt precipitation is minimal. These findings are important for a successful CCS project since CO2 injectivity controls essential aspects of storage which are the rate, the quantity and length of time for CO2 injection into a formation.

An assessment of methane gas production from natural gas hydrates: Challenges, technology and market outlook

“…5c and 6 show the CO 2 -CH 4 exchange procedure. The exchange of CH 4 in the NGH deposits with CO 2 is perceived as a win-win approach because of the simultaneous production of methane and storage of CO 2 (Na et al, 2016;Shaibu et al, 2018;Gharasoo et al, 2019). Koh et al (2016) explained that pure CO 2 hydrates have better formation conditions than pure methane hydrates when gaseous CO 2 is present.…”

“…Injecting CO 2 directly into hydrate bearing geologic structures below the ocean floor could cause leaks to the seabed if a poor seal exists, which may affect the chemistry of seawater. A typical effect is the reduction in pH of seawater which can lead to ocean acidification (Shaibu et al, 2018). This could…”