Geochemical narrowing of cement fracture aperture during multiphase flow of supercritical CO2 and brine (original) (raw)
2020, International Journal of Greenhouse Gas Control
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International Journal of Greenhouse Gas Control, 2016
We investigate experimentally the alteration of fractured class-G cement flowed by CO 2-rich brine. The experiment mimics a mechanically damaged rough-walled fractured cement annulus at temperature 60 • C and pressure 10 MPa. The experiment consists of flowing a reservoir-equilibrated brine mixed with CO 2 (partial pressure of 2.3 MPa) through the fracture of average aperture 14 m at constant flow rate (100 L min −1). This flow rate corresponds to pressure gradient representative of an average in situ hydrodynamic condition. Results indicate an intense alteration of the cement with a large removal of mass at the scale of the sample. However, the fracture alteration patterns are triggered by the initial heterogeneity of the fracture aperture; the aperture of the low aperture zones tends to decrease due to calcite precipitation whereas preferential paths develop in the zones of higher aperture associated. Nevertheless, the expected large permeability increase triggered by the mass removal is mitigated by the precipitation of a low density Si-rich amorphous material. The alteration rate will decrease with time because of the increasing distance of diffusion between the fracture where the reactants are actively renewed by advection and the portlandite and C-S-H dissolution fronts. The different zones of reaction can be adequately modeled by a simple 1D diffusion-reaction model using published kinetics coefficients and extrapolation to larger times than the experiment time can be drawn. Altogether, and in addition to the previous studies of the alteration of fractured well cement annulus, this study shows that the leakage potential is strongly controlled by the initial distribution of the aperture along the fracture: low aperture zones will tend to self-heal while localized flow in connected high aperture paths will be perennial.
Experimental Study on a Single Cement-Fracture Using CO[subscript 2] Rich Brine
Energy Procedia, 2011
The efficiency of Carbon Capture and Storage (CCS) projects is directly related to the long term sealing efficiency of barrier systems and of wellbore cement in wellbores penetrating storage reservoirs. The microfractures inside the wellbore cement provide possible pathways for CO 2 leakage to the surface and/or fresh water aquifers, impairing the long-term containment of CO 2 in the subsurface. The purpose of this experimental study is to understand the dynamic alteration process in the cement caused by the acidic brine. The first experiment, at ambient temperature and pressure, was conducted by flowing CO 2 -rich brine through 1 in. by 2 in. (25.4 mm by 50.8 mm) cement cores for 4 and 8 weeks durations. The second experiment was a 4 weeks long flow-through experiment conducted at ambient conditions using a 1 in by 12 in.(25.4 mm by 304.8 mm) cement core and CO 2 -rich brine with a core flooding system under 600 psi (4.13 MPa) confining stress. Post-experiment material analysis from both experiments confirmed leaching of Ca 2+ from reacted cement, as reported in literature. However for the first time, porosity of the reacted regions was semi-quantified applying micro-CT images.
Experimental study on a single cement-fracture using CO 2 rich brine
Energy Procedia, 2011
The efficiency of Carbon Capture and Storage (CCS) projects is directly related to the long term sealing efficiency of barrier systems and of wellbore cement in wellbores penetrating storage reservoirs. The microfractures inside the wellbore cement provide possible pathways for CO2 leakage to the surface and/or fresh water aquifers, impairing the long-term containment of CO2 in the subsurface. The purpose of this experimental study is to understand the dynamic alteration process in the cement caused by the acidic brine. The first experiment, at ambient temperature and pressure, was conducted by flowing CO2-rich brine through 1 in. by 2 in. (25.4 mm by 50.8 mm) cement cores for 4 and 8 weeks durations. The second experiment was a 4 weeks long flow-through experiment conducted at ambient conditions using a 1 in. by 12 in.(25.4 mm by 304.8 mm) cement core and CO2-rich brine with a core flooding system under 600 psi (4.13 MPa) confining stress. Post-experiment material analysis from both experiments confirmed leaching of Ca2+ from reacted cement, as reported in literature. However for the first time, porosity of the reacted regions was semi-quantified applying micro-CT images.
Chemical Geology, 2009
The potential impact to the integrity of wellbore cements as a result of exposure to supercritical carbon dioxide (SCCO 2) has been raised as an area of some concern with respect to long-term effectiveness of CO 2 storage in geological formations. In flow-through experiments we simulated diffusion of brine and SCCO 2 from the interface between wellbore cement and caprock into a fracture-bearing Portland cement. The experiments were performed at in-situ reservoir pressure (pore pressure: 19.9 MPa) and temperature (54°C) conditions for 113 days. For this purpose we saturated illite-rich shale and the Portland cement core (2.02 cm × 5.35 cm) with 1.65 M brine for 14 days. After this period of time we injected SCCO 2 into the system for 99 days and simulated a diffusion process by using a pressure gradient of 0.7 MPa. Calcite precipitation occurred within the fracture and the induced pressure of crystal growth may explain an increase in the relative permeability along the fracture with time. SCCO 2-induced reactions extended~5 mm into the Portland cement core from the fracture and formed an orange-colored zone. The orange-colored zone is nearly completely carbonated with crystalline phases consisting mainly of calcite, aragonite, and vaterite. The only crystalline cement component that persisted in the orange-colored zone was brownmillerite. Interior portions of the hydrated cement were partially carbonated, modified in texture and contained newly formed calcite, hydrogarnet and hydrocalumite (Friedel's salt). Cement porosity decreased from 37.8% to 23.8% during carbonation and was associated with a 19.6% increase in mass.
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