Effective Permeability Change in Wellbore Cement with Carbon Dioxide Reaction

Abstract

SummaryPortland cement, a common sealing material used in wellbores for geological carbon sequestration, was reacted with carbon dioxide (CO2) in supercritical, gaseous, and aqueous phases at various pressure and temperature conditions to simulate cement-CO 2 reaction along the wellbore from carbon injection depth to the near surface. Hydrated Portland cement columns (14 mm diameter × 90 mm long; water-tocement ratio = 0.33), including additives such as steel coupons and Wallula basalt fragments, were reacted with CO2 in the wet supercritical (the top half) and dissolved (the bottom half) phases under carbon sequestration conditions with high pressure (10 MPa) and temperature (50°C) for 5 months. In parallel, small-sized hydrated Portland cement columns (7 mm diameter × 20 mm long; water-to-cement ratio = 0.38) were reacted with CO 2 in a dissolved phase at high pressure (10 MPa) and temperature (50°C) for 1 month or with wet CO2 in gaseous phase at low pressure (0.1 MPa) and temperature (20°C) for 3 months. X-ray microtomography images reveal the cement that reacted with CO 2 saturated groundwater had degradation depth of~1 mm for 1 month and~3.5 mm for 5 months, whereas the degradation was minor with cement exposure to supercritical CO 2 . Scanning electron microscopy-energy dispersive spectroscopy analysis showed the carbonated cement was comprised of three distinct zones: the innermost less degraded zone with Ca atom % > C atom %, the inner degraded zone with Ca atom % ≈C atom % due to precipitation of calcite, the outer degraded zone with C atom % > Ca atom % due to dissolution of calcite and C-S-H, as well as adsorption of carbon to cement matrix. The outer degraded zone of carbonated cement was porous and fractured because of dissolution-dominated reaction by carbonic acid exposure, which resulted in the increase in BJH (Barrett-Joyner-Halenda) pore volume and BET (Brunauer-Emmett-Teller) surface area. In contrast, cement-wet CO 2 (g) reaction at low P (0.1 MPa)-T (20°C) conditions for 1 to 3 months was dominated by precipitation of micron-sized calcite on the outside surface of cement, which resulted in the decrease in BJH pore volume and BET surface area. Cement carbonation and pore structure change are significantly dependent on pressure and temperature conditions, as well as the phase of CO 2 , which controls the balance between precipitation and dissolution in cement matrix. Geochemical modeling result suggests that ratio of solid (cement)-to-solution (carbonated water) has a significant effect on cement carbonation; thus, the cement-CO2 reaction experiment needs to be conducted under realistic conditions representing the in-situ wellbore environment of a carbon sequestration field site.Total porosity and air permeability for a duplicate cement column with water-to-cement ratio of 0.38 measured after oven drying by Core Laboratories using Boyle's Law technique and steady-state method were 31% and 0.576 mD. A novel method to measure the effective liquid permeability of a cement column using X-ray micr...

Concept of complete CO2 capture from natural gas inside exploration wells and its storage in rock reservoirs

“…The air permeability of cement samples was predicted to increase, according to Ghabezloo et al (2009) porosity-dependent equation, from 0.58 to 34.74 mD (34.74×10 -15 m 2 ) after 1 month reaction with CO 2 saturated water at high P-T, as a result of porosity increment from 31 to 45%. The results obtained by Um et al (2011) revealed that the degradation effect of CO 2 saturated groundwater was higher than the effect of cement exposure to supercritical CO 2 , according to X-ray microtomography images carried out on deteriorated specimens. Gasda et al (2004) also referred the potential leakage of CO 2 occurrence on the interface between host rock and cement, cement and casing, cement plug and casing, or through the cement pore space and fracture.…”

“…The porosity and permeability data of the cement class G are herein analyzed under degradation effect of carbon dioxide saturated water and supercritical carbon dioxide, based on an experimental simulation case of a completion inside a gas well. Um et al (2011) conducted an experiment on 14 mm diameter × 90 mm long samples of a class G cement with w/c = 0.33 (water/cement ratio). These specimens were tested under the temperature of 50°C and a pressure of 10 MPa in order to represent the CO 2 injection's temperature and pressure conditions at 1 km of depth, a geothermal gradient of 30°C/km and a pressure gradient of 10.5 MPa/km.…”

The role of host rock properties in determining potential CO2 migration pathways

“…This is because sandstone is primarily composed of silica quartz, which reacts at rates that are orders of magnitude lower than cement. Due to the more than 4 orders of magnitude in permeability contrast between the sandstone (100 mD, reported by the provider) and cement zone (4-8 µD, Um et al, 2011), CO 2 -brine primarily flowed through the more permeable sandstone zone. As a result, the acidic brine degraded the cement at the interface of sandstone and cement zone.…”

“…The effective porosity of the sandstone-cement core and limestone-cement core was measured to be 15.4% and 13.9%, respectively. According to literature, an unreacted cement column with water-to-cement ratio of 0.38 has a total porosity of 31% and an effective permeability of 4~8 µD (Um et al, 2011). These core plugs were then dried overnight in an oven before the core flooding experiments.…”

“…Both limestone and cement are highly reactive under acidic conditions. Because limestone has much higher permeability (1.5 md as estimated from initial measurement) than that of cement (4~8 µD, Um et al, 2011), the CO 2 -rich brine propagated into the more permeable limestone and developed highly conductive channels. 3D spatial view of wormholes (shown in blue) developed after the experiment.…”