Geochemical modelling of formation damage risk during CO2 injection in saline aquifers (original) (raw)
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Journal of Natural Gas Science and Engineering, 2016
A systematic and careful analysis of changes in the magnitude of geomechanical parameters is essential to mitigate the risk of leakage from CO2 storage sites. However, depending on rocks and storage sites, these changes might be different due to chemical reactions taking place, especially when it comes to saline aquifers. There have only been few studies carried out in the past to evaluate the maximum sustained pressure of rocks being exposed to these chemical interactions. However, more studies are still required to evaluate the strength of the storage medium or seals when different kinds of rocks and fluids (fresh water or brine) are included in the hostile environment of a storage site. In this paper, attempts were made to evaluate changes in the variation of geomechanical parameters of the Berea sandstone during and after the injection of supercritical CO2 in a short period of time. The results obtained indicated that the presence of brine in the pore space during injection enhances the severity of geochemical reactions, causing reductions in the magnitudes of elastic parameters including shear modulus. Having a good look into the SEM images of the sample before and after exposure to scCO2 indicated that these changes can be attributed to the dissolution/fracturing of calcite and clays in the matrix of the sample. Although findings were provided based on the pulse measurements tests, more studies are required to have a deeper understanding as to how geochemical reactions may cause difficulties during and after injection into a storage site.
Geochemical Modeling of Changes in Storage Rock Environments at CO2 Injection Sites
Minerals
Geochemical modeling in TOUGHREACT code was used to simulate chemical processes in CO2–rock–brackish water systems in a pilot research environment of CO2 storage in the Brodske area (Czech Republic). Models studied mineralogical changes in rock samples resulting from acidification of the aqueous phase caused by the dissolution of pressurized supercritical CO2. Rock samples of the reservoir horizon and cement from the grouting of an injection borehole were considered, and the water phase represented the mineralized groundwater. The aim of the study was to characterize the influence of CO2 in the geological structure on mineralogical rock changes and to predict gas distribution through the rocks bearing brackish water. The most important chemical processes are dissolution of carbonates and clay minerals during the injection of CO2 into the structure, as the increase in porosity in the structure affects the sequestration capacity of the reservoir rock. In the CO2–cement–brackish water ...
CO 2 injection into saline carbonate aquifer formations I: laboratory investigation
Transport in Porous Media, 2008
Although there are a number of mathematical modeling studies for carbon dioxide (CO2) injection into aquifer formations, experimental studies are limited and most studies focus on injection into sandstone reservoirs as opposed to carbonate ones. This study presents the results of computerized tomography (CT) monitored laboratory experiments to analyze permeability and porosity changes as well as to characterize relevant chemical reactions associated with injection and storage of CO2 in carbonate formations. CT monitored experiments are designed to model fast near well bore flow and slow reservoir flows. Highly heterogeneous cores drilled from a carbonate aquifer formation located in South East Turkey were used during the experiments. Porosity changes along the core plugs and the corresponding permeability changes are reported for different CO2 injection rates and different salt concentrations of formation water. It was observed that either a permeability increase or a permeability reduction can be obtained. The trend of change in rock properties is very case dependent because it is related to distribution of pores, brine composition and thermodynamic conditions. As the salt concentration decreases, porosity and the permeability decreases are less pronounced. Calcite deposition is mainly influenced by orientation, with horizontal flow resulting in larger calcite deposition compared to vertical flow.
Numerical simulations performed with the TOUGHREACT code focus on the chemical reactivity of deep reservoir rock impacted by an injection of CO 2 and associated reactive impurities (mainly SO 2 and O 2). A simplified two-dimensional radial geo-model representing the near wellbore domain of a saline reservoir enabled us to capture the global geochemical behaviour of this underground zone. Two ratios CO 2 /SO 2 are investigated. The results of the numerical simulations highlight the high reactivity of the near-well zone in the case where ancillary gases (SO 2 and O 2) are injected with CO 2 with dissolution of carbonates and precipitation of sulfate minerals. Major reactions occur in the reservoir formation, whereas clays of the caprock are only slightly affected by the injection of CO 2 and associated reactive impurities.
Energy Procedia, 2011
Over the past few years several geochemical evaluations of CO 2 storage in Dutch potential reservoirs are carried out, including predictions of the short-and long-term impact of CO 2 on the reservoir using geochemical modelling. The initial mineralogy of the reservoir is frequently obtained from core analysis and is then used to compute the formation water composition. In this paper geochemical modelling with TOUGHREACT is used to predict and compare the short-and long-term geochemical impact of CO 2 injection into three reservoirs. The mineralogical composition of these reservoirs is an assemblage based on commonly observed minerals from the Buntsandstein and Rotliegend formations. These formations contain potential onshore and offshore CO 2 storage locations in the Netherlands. The results predict drying out and salt precipitation in the near-well area, due to water evaporation by the injected dry CO 2 . Several mineral transformations are predicted, dominated by the transformation of albite into dawsonite, thereby fixing CO 2 . Due to the relatively low density of dawsonite, the porosity significantly decreases, which can lead to a pore pressure increase. Disabling of dawsonite precipitation in the simulations, thereby taking into account the ongoing debate on dawsonite stability, only shows a small increase of the porosity. Future (experimental) work should be focused on dawsonite occurrence for accurate predictions of the long-term reservoir integrity.
Heliyon, 2020
Carbon capture and storage (CCS) is expected to play a key role in meeting greenhouse gas emissions reduction targets. In the UK Southern North Sea, the Bunter Sandstone formation (BSF) has been identified as a potential reservoir which can store very large amounts of CO 2 . The formation has fairly good porosity and permeability and is sealed with both effective caprock and base rock, making CO 2 storage feasible at industrial scale. However, when CO 2 is captured, it typically contains impurities, which may shift the boundaries of the CO 2 phase diagram, implying that higher costs will be needed for storage operations. In this study, we modelled the effect of CO 2 and impurities (NO 2 , SO 2 , H 2 S) on the reservoir performance of the BSF. The injection of CO 2 at constant rate and pressure using a single horizontal well injection strategy was simulated for up to 30 years, as well as an additional 30 years of monitoring. The results suggest that impurities in the CO 2 stream affect injectivity differently, but the effects are usually encountered during early stages of injection into the BSF and may not necessarily affect cumulative injection over an extended period. It was also found that porosity of the storage site is the most important factor controlling the limits on injection. The simulations also suggest that CO 2 remains secured within the reservoir for 30 years after injection is completed, indicating that no post-injection leakage is anticipated.
Greenhouse Gases: Science and Technology, 2019
CO 2 storage in different geological formations has been recognized as one of the promising mitigation approaches to reduce the emission of CO 2 into the atmosphere. There are many complex hydro-chemo-mechanical interactions (effective stress changes, water acidification, and mineral dissolution) that may take place in a storage site during or after injection, reducing the integrity of formations in the short or long term. Although there have been several studies carried out in the past to assess the feasibility of sandstones and limestone formations as a safe CO 2 storage site, the effect of hydrological, mechanical, and chemical processes on the storage site integrity has not been deeply addressed. The aim of this study is to couple thermo-hydro-chemo-mechanical processes upon CO 2 injection and assess their impact on the key storage aspects of quartz-rich sandstone and calcite-rich limestone. A numerical model was built to simulate CO 2 flooding into a saline aquifer with sandstone and limestone composition for 500 years. The results obtained indicated that geochemical activity and CO 2 dissolution are significantly higher in limestone and may increase the porosity by ß16%. During injection, a decrease in the reservoir strength was observed in both rock types upon exposure to CO 2. A remarkable variation in the geomechanical characteristics was also revealed in the sandstone after injection. However, ground displacements (subsidence) of 0.0017 and 0.033 m were, respectively, observed in sandstone and limestone aquifers, at the end of 500 years. It is recommended to consider a high-strength reservoir for carbon capture and storage (CCS) projects in order to reduce the likelihood of compaction. It was also found that both rock types have a good storage capacity,
Injection of CO 2 -saturated brine in geological reservoir: A way to enhanced storage safety
Injection of free-phase supercritical CO 2 into deep geological reservoirs is associated with risk of considerable return flows towards the land surface due to the buoyancy of CO 2 , which is lighter than the resident brine in the reservoir. Such upward movements can be avoided if CO 2 is injected in the dissolved phase (CO 2aq). In this work, injection of CO 2-saturated brine in a subsurface carbonate reservoir was modelled. Physical and geochemical interactions of injected low-pH CO 2-saturated brine with the carbonate minerals (calcite, dolomite and siderite) were investigated in the reactive transport modelling. CO 2-saturated brine, being low in pH, showed high reactivity with the reservoir minerals, resulting in a significant mineral dissolution and CO 2 conversion in reactions. Over the injection period of 10 yr, up to 16% of the injected CO 2 was found consumed in geochemical reactions. Sorption included in the transport analysis resulted in additional quantities of CO 2 mass stored. However, for the considered carbonate minerals, the consumption of injected CO 2aq was found mainly in the form of ionic trapping.
Energy, 2017
Although CO 2 storage in deep saline aquifers is now accepted as a potential option for atmospheric CO 2 mitigation, the chemico-mineralogical property alterations in the aquifer formation associated with CO 2 / brine/rock mineral interactions, the corresponding influence on formation hydro-mechanical properties and the effect of rock mineral structure, are not yet fully understood. This study was therefore conducted to obtain a comprehensive understanding of the effect of long-term CO 2 exposure on the chemicomineralogical structure and corresponding strength characteristics of saline aquifer rock formations using silicate cement (SS) and carbonate cement (CS) Hawkesbury sandstone samples collected from the Sydney basin. Sandstone samples were first reacted with brineþCO 2 under different injection pressures (both sub-critical (4, 6 MPa) and super-critical (8, 10 MPa)) under a constant temperature of 35 C. A comprehensive chemico-mineralogical analysis (ICP-AES and XRD) was first conducted on both the rock mass pore fluid and the rock matrix over the saturation period of one year, giving special attention to the alteration of dominant rock minerals (quartz, calcite and kaolinite). The overall influence after 12 months of saturation with brine and CO 2 on the strength characteristics of the two types of sandstones (SS and CS) was then investigated and correlated with the chemico-mineralogical reaction, in order to understand the coupled process. According to the test results, compared to the silicate cement-dominant mineral structure (SS), the presence of a carbonate cement-dominant mineral structure (CS) in the aquifer rock formation creates more significant alterations in the formation's chemico-mineralogical structure upon CO 2 injection. This is because calcite mineral reactions occur at much greater rates compared to quartz mineral reactions in CO 2exposed environments. In addition, although some minor precipitation of kaolinite minerals may also occur upon CO 2 injection, the effect may not be significant. Overall, rock mineral changes in deep saline aquifers upon CO 2 injection have a significant influence on the strength characteristics of the reservoir rock mass, depending on the aquifer mineral structure, and CS formations are subject to much greater strength property changes upon exposure to CO 2 than SS formations. Interestingly, CO 2 injection causes a strength gain in SS sandstone and a strength reduction in CS sandstone. These mechanical property alterations in aquifer rock formations are also dependent on the CO 2 injection pressure and phase, and increasing the injecting CO 2 pressure significantly enhances the changes, due to the highly acidic environment created by the enhanced CO 2 solubility process. Changing the CO 2 phase from sub-to super-critical condition also accelerates the reaction mechanisms, due to the greater chemical potential of super-critical CO 2. However, overall SS sandstone exhibits more stable chemical-mineralogical and mechanical characteristics upon CO 2 injection than CS sandstone, and exhibits more suitable characteristics for CO 2 sequestration.