Sensitivity of chemical cement alteration – modeling the effect of parameter uncertainty and varying subsurface conditions

Abstract

To ensure the safety of a CO 2 storage site and containment of CO 2 in the subsurface, the integrity of wellbore materials must be maintained. Field and laboratory studies have shown CO 2 -induced reactivity of wellbore cement, but these results have to be extrapolated to the extended time span of CO 2 storage. Geochemical modeling provides a tool for the prediction of cement alteration; however, large uncertainties in input parameters exist and signifi cant variation in subsurface conditions is expected. This asks for a systematic investigation of the sensitivity of modeled cement alteration towards these factors. In this paper we report PHREEQC simulations of CO 2 diffusion into cement and subsequent chemical reactions. The sensitivity of cement alteration toward reaction rates, initial porosity, temperature/mineralogy and fl ow/no fl ow conditions were investigated. The base case model indicated that intact cement and tight interfaces between the reservoir and the cement would yield less than 1% porosity change after 300 days of diffusion. For porosity increase or degradation to occur at the cement interface, leaching/fl ow along the wellbore was required. The sensitivity scenarios yield CO 2 penetration depths between 0.3 cm and 1.4 cm after 300 days of diffusion. The maximum was reached for the high porosity (fast diffusion) scenario that facilitates CO 2 transport through the cement matrix. The minimum CO 2 penetration was for enhanced calcium silicate hydrate (C-S-H) decalcifi cation, which increases calcite precipitation, CO 2 consumption, and hence decelerates CO 2 penetration. This is related to high temperatures (and more crystalline C-S-H) or to higher kinetic rate constants used.

Advances and Prospects of Supercritical CO2 for Shale Gas Extraction and Geological Sequestration in Gas Shale Reservoirs

“…CO 2 primarily reacts with Ca­(OH) 2 and CSH in cement, and this reaction is accompanied by solute transport. The corrosion reaction rate is positively correlated with the porosity, permeability, and CO 2 –brine leaching time of the cement sheath, while it is negatively correlated with the pore tortuosity of the cement sheath. − Wasch et al conducted coupled numerical simulations of CO 2 storage and divided the reaction between diffusing CO 2 and the cement sheath into four regions, as shown in Figure . Region I represents the nonpenetrated area of CO 2 where no corrosion reaction, porosity change, or permeability change occurs.…”

Injection of a CO2-Reactive Solution for Wellbore Annulus Leakage Remediation

“…However, cement reactivity will most-likely only lead to cement degradation under leaching/flow conditions when reaction products are quickly removed from the reaction site. At no/low flow conditions, calcite precipitation is the dominant process rather than (re-)dissolution [4,15,16]. Depending on the initial flow and chemical conditions, continuous cement leaching occurs, or cement reactivity may actually support natural sealing of the micro annulus [17][18][19].…”