Chemical and Mechanical Properties of Wellbore Cement Altered by CO₂-Rich Brine Using a Multianalytical Approach

Abstract

Defining chemical and mechanical alteration of wellbore cement by CO(2)-rich brines is important for predicting the long-term integrity of wellbores in geologic CO(2) environments. We reacted CO(2)-rich brines along a cement-caprock boundary at 60 °C and pCO(2) = 3 MPa using flow-through experiments. The results show that distinct reaction zones form in response to reactions with the brine over the 8-day experiment. Detailed characterization of the crystalline and amorphous phases, and the solution chemistry show that the zones can be modeled as preferential portlandite dissolution in the depleted layer, concurrent calcium silicate hydrate (CSH) alteration to an amorphous zeolite and Ca-carbonate precipitation in the carbonate layer, and carbonate dissolution in the amorphous layer. Chemical reaction altered the mechanical properties of the core lowering the average Young's moduli in the depleted, carbonate, and amorphous layers to approximately 75, 64, and 34% of the unaltered cement, respectively. The decreased elastic modulus of the altered cement reflects an increase in pore space through mineral dissolution and different moduli of the reaction products.

Self‐healing of cement fractures under dynamic flow of CO2‐rich brine

“…As discussed in other studies [Luquot et al, 2013;Mason et al, 2013], the residual silica gel produced from the C-S-H dissolution can potentially swell and therefore reduce the permeability. These processes can potentially lead to higher likelihood of self-sealing than what we present here.…”

“…Zones 3 and 4 are statistically very close if we consider the measurement error, resolution, and cement heterogeneity; so the choice of these zones is somewhat arbitrary and is based on prior knowledge from other studies with similar observations under either static conditions or dynamic flow conditions [Brunet et al, 2013;Luquot et al, 2013;Mason et al, 2013;Walsh et al, 2012]. The observed zonation was for after 8 days of core-flooding experiment.…”

“…When the hydrated cement was in direct contact with CO 2 -brine, both portlandite and C-S-H dissolved and released calcium ions. The dissolution also converted C-S-H to amorphous silica gel, which is a highly porous material [Mason et al, 2013]. The leached Ca(II) diffused into the inner part of the cement where pH was also higher, leading to the precipitation of calcite and the formation of zone 2 with a thickness of around 200 mm.…”

“…Portlandite (Ca(OH) 2 ) and Calcium Silicate Hydrates (C-S-H) are the two primary mineral phases formed upon hydration [Taylor, 1997]. Numerous studies in recent years have addressed the interactions between cement and supercritical CO 2 or CO 2 -saturated formation water under conditions relevant to carbon sequestration [Bachu and Bennion, 2009;Barlet-Gouedard et al, 2006;Barlet-Gou edard et al, 2009;Brandvoll et al, 2009;Duguid and Scherer, 2010;Duguid et al, 2006;Kutchko et al, 2007Kutchko et al, , 2009Liteanu et al, 2009;Mason et al, Water Resources Research PUBLICATIONS 2013; Scherer et al, 2005;Condor and Asghari, 2009]. Many studies have focused on the reactive transport of CO 2 -rich fluid through cement-cement interface and the associated property evolution of cement fractures [Cao et al, 2013;Huerta et al, 2011;Huerta et al, 2013aHuerta et al, , 2013bLiteanu and Spiers, 2011;Luquot et al, 2013;Ozyurtkan and Radonjic, 2014;Walsh et al, 2012;Wenning et al, 2013;Yalcinkaya et al, 2011].…”

Can a fractured caprock self-heal?

“…Predicting the potential for fractures to provide leakage pathways is further complicated by the possibility for fracture permeability to change with time due to injectioninduced perturbations in stress and fluid chemistry. Stress perturbations lead to mechanical deformation and fracture propagation that can increase or decrease formation permeability [Bandis et al, 1983;Liu, 2005;Elkhoury et al, 2006Elkhoury et al, , 2011Candela et al, 2011;Renard et al, 2012;Mason et al, 2013]. Chemical disequilibrium between fluids and resident minerals leads to dissolution or precipitation that further alter fracture porosity and permeability [Lowell et al, 1993;Durham et al, 2001;Berkowitz, 2002;Chaudhuri et al, 2008;Wigand et al, 2009;Smith et al, 2013;Mason et al, 2013;Noiriel et al, 2013;Elkhoury et al, 2013].…”