scCO2 Injection Research Articles

Microbial CaCO3 mineral formation and stability in an experimentally simulated high pressure saline aquifer with supercritical CO2

The use of microbiologically induced mineralization to plug pore spaces is a novel biotechnology to mitigate the potential leakage of geologically sequestered carbon dioxide from preferential leakage pathways. The bacterial hydrolysis of urea (ureolysis) which can induce calcium carbonate precipitation, via a pH increase and the production of carbonate ions, was investigated under conditions that approximate subsurface storage environments, using a unique high pressure (∼7.5MPa) moderate temperature (32°C) flow reactor housing a synthetic porous media core. The synthetic core was inoculated with the ureolytic organism Sporosarcina pasteurii and pulse-flow of a urea inclusive saline growth medium was established through the core. The system was gradually pressurized to 7.5MPa over the first 29 days. Concentrations of NH4+, a by-product of urea hydrolysis, increased in the flow reactor effluent over the first 20 days, and then stabilized at a maximum concentration consistent with the hydrolysis of all the available urea. pH increased over the first 6 days from 7 to 9.1, consistent with buffering by NH4+⇔NH3+H+. Ureolytic colony forming units were consistently detected in the reactor effluent, indicating a biofilm developed in the high pressure system and maintained viability at pressures up to 7.5MPa. All available calcium was precipitated as calcite. Calcite precipitates were exposed to dry supercritical CO2 (scCO2), water-saturated scCO2, scCO2-saturated brine, and atmospheric pressure brine. Calcite precipitates were resilient to dry scCO2, but suffered some mass loss in water-saturated scCO2 (mass loss 17±3.6% after 48h, 36±7.5% after 2h). Observations in the presence of scCO2 saturated brine were ambiguous due to an artifact associated with the depressurization of the scCO2 saturated brine before sampling. The degassing of pressurized brine resulted in significant abrasion of calcite crystals and resulted in a mass loss of approximately 92±50% after 48h. However dissolution of calcite crystals in brine at atmospheric pressure, but at the pH of the scCO2 saturated brine, accounted for only approximately 7.8±2.2% of the mass loss over the 48h period. These data suggest that microbially induced mineralization, with the purpose of reducing the permeability of preferential leakage pathways during the operation of GCS, can occur under high pressure scCO2 injection conditions.

Low-frequency laboratory measurements of the elastic properties of sandstone flooded with supercritical CO2

This extended abstract presents the results of the first low-frequency experiments conducted on a sandstone sample (Donnybrook, WA) flooded with supercritical CO2 (scCO2). The experiments investigated the effects of scCO2 injection on the elastic and anelastic properties of the rock. The sandstone sample (porosity—11.4%, permeability—0.28 mD) was cut in the direction orthogonal to a formation-bedding plane and tested in a Hoek's triaxial pressure cell equipped with the means for independent control of pore and confining pressures. The pore and confining pressures were set up at 10 and 31 MPa correspondingly. The low-frequency system and the pump comprising of scCO2 were held at a temperature of 42°C. Supercritical CO2 was injected into the sample preliminary saturated with distilled water. The amount of the residual water in the sample after the scCO2 injection was about 40% of pore volume. The elastic parameters obtained for the sample with scCO2 at frequencies from 0.1–100 Hz are very close to those for the dry sample. Some discrepancy in calculated acoustic velocities are caused by the difference in water and scCO2 densities. The measured extensional attenuation is larger when the sample is saturated with scCO2. The applicability of Gassmann's fluid substitution theory for the interpretation of obtained results was also tested during the experiments.

Mobility ratio, relative permeability and sweep efficiency of supercritical CO2 and methane injection to enhance natural gas and condensate recovery: Coreflooding experimentation

Enhanced natural gas and condensate recovery has more recently stimulated an immense popular interest in oil exploration and production. While numerous laboratory and computational studies of carbon dioxide (CO2) injection into conventional oil reservoirs have been reported in the open literature, scarce work is being disclosed on CO2 displacement characteristics with both natural gas and liquid condensate where the displacement mechanisms are well-known to be significantly different to those in conventional gas/oil systems.This paper quantitatively investigates the recovery efficiency, pattern behavior and relative permeability of: (1) condensate following supercritical carbon dioxide (SCCO2) injection, methane injection and the injection of their mixtures; and (2) natural gas of various compositions following pure SCCO2 injection. This investigation includes two sets of coreflooding experiments: the first is to observe the microscale displacement efficiency and stability of natural gas following pure SCCO2 injection while the second was conducted to study the percentage of condensate recovery following the injection of different SCCO2-methane concentrations. This work is part of an integrated enhanced natural gas and condensate recovery project conducted for a local reservoir in Western Australia. This data will help the operators develop operational and design strategies for their current and future EOR projects, as well as provide parameters for full-field simulation practices.

The effects of initial acetate concentration on CO2–brine-anorthite interactions under geologic CO2 sequestration conditions

Acetate is one of the most abundant organic compounds in many formation waters and is likely to be present in deep saline aquifers suitable for geologic CO2 sequestration (GCS). This work studied the effect of initially present acetate on the dissolution of anorthite (CaAl2Si2O8) and on subsequent secondary mineral precipitation under GCS conditions (35 °C and 74.8 atm). Anorthite was chosen as a model mineral because of the abundance of feldspar in clayey sandstones and the possibility of metal carbonation. In this study, acetate was found to decrease the cumulative aqueous concentrations of Al, Si, and Ca upon CO2 injection by inhibiting anorthite dissolution and increasing the amount of secondary mineral precipitates. The extent of the effect of acetate on metal concentration changes was element-specific (Al > Si > Ca), and the effect was found to be more significant in systems with lower salinity and lower pH. For anorthite dissolution, acetic acid inhibited the proton-mediated decomposition of the Al/Si-containing feldspar framework, while acetate anions may have facilitated the ion-exchange between interstitial Ca and aqueous cations. For secondary mineral precipitation, stoichiometry analysis of aqueous metal concentrations suggested the formation of Al-containing mineral(s). The presence of kaolinite as a secondary mineral was confirmed using high resolution transmission electron microscopy's electron diffraction data. An increase in the relative amount of precipitation due to the initial presence of acetate was suggested by mass balancing and verified on the cleaved anorthite surfaces by atomic force microscopy analysis. These results provide new insights for understanding and predicting GCS system evolution upon scCO2 injection in the initial presence of acetate.

Phase Behaviour, Fluid Properties and Recovery Efficiency of Immiscible and Miscible Condensate Displacements by SCCO2 Injection: Experimental Investigation

This paper presents a quantitative investigation of the interfacial tension dependent relative permeability (IFT-DRP) and displacement efficiency of supercritical CO2 injection into gas-condensate reservoirs. A high-pressure high-temperature experimental laboratory was established to simulate reservoir conditions and to perform relative permeability measurements on sandstone cores at a constant reservoir temperature of 95°C and displacement velocity of 10 cm/h. This investigation covers immiscible displacements (1100 and 2100 psi), near-miscible displacement (3000 psi) and miscible displacements (4500 and 5900 psi). The coreflooding results demonstrated that displacement pressure is a key factor governing the attainment of optimum sweep efficiency. The ultimate condensate recovery increased by almost threefold when CO2 was injected at near-miscible conditions (i.e., 23.40% ultimate recovery at 1100 psi compared to 69.70% at 3000 psi). Miscible flooding was found to give the optimum condensate recovery (9% extra ultimate recovery compared to near-miscible injection). Besides improving the ultimate recovery, miscible floods provided better mobility ratios and delayed gas breakthrough (0.62 PV BT at 5900 psi compared to 0.21 PV BT at 1100 psi). In addition to the elimination of IFT forces in miscible displacements, favourable ratios of fluid properties and phase behaviour relationships between the SCCO2 and condensate were believed to be the driving force for the improved recovery as they provided a stabilising effect on the displacement front and stimulated swelling of the condensate volume. This paper incorporates the theoretical aspects of phase behaviour and fluid properties that largely affect the microscopic displacement efficiency and serves as a practical guideline for operators to aid their project designs and enhance their recovery capabilities.

Rheology and Expansion of Starch-Water-CO2 Mixtures with Controlled Gelatinization by Supercritical Fluid Extrusion

A slit die rheometer fitted to a twin-screw extruder was used to measure the viscosity and expansion characteristics of starch-based melts plasticized with water and supercritical CO2. Experiments were conducted for four intermediate moisture starch-water mixtures with varying degree of starch gelatinization (DG), achieved by blends of pregelatinized and native common corn starch. SC-CO2 was shown to be an effective plasticizer for starch-water mixture at 0.45 g SC-CO2/100 g sample, lowering the viscosity of the melt by an average of 14%. Apparent viscosity was measured for shear rate ranging from 100–200 s−1. The viscosity reduction factors based on DG and SC-CO2 indicated that the free volume added to starch-water mixtures with SC-CO2 is an effective mechanism for viscosity reduction. In addition, the higher water affinity of pregelatinized starch increased the water induced plasticization effect in the mixtures. SC-CO2 was a good blowing agent producing distinct expanded microcellular morphology for the starch-water mixtures with DG at or above 80%. The expansion and cellular characterization of these starch-based extrudates produced by SC-CO2 injection may be governed by the viscosity-dependent parameters including gas retention capability, CO2 diffusivity and the pressure drop rate.