Geologic Sequestration Conditions Research Articles

Thermodynamic insights into the degradation of oil well cement by CO2 under geologic sequestration conditions

Geological carbon storage (GCS) is an effective way to reduce CO2 emissions into the atmosphere. The degradation of oil well cement by CO2 poses a risk to the feasibility of GCS. It is critical to understand how the oil well cement degrades. The previous research is mainly experimental. The objective of this paper is to investigate the degradation of the oil well cement by thermodynamic theory in terms of the chemical reaction of individual phase and the phase evolution of the cement-CO2-water system. The results show that hydration products have different degradation resistance. The order of degradation resistance from best to worst is revealed. The thermodynamic equilibrium of the chemical reactions of degradation is affected by temperature and pressure. The higher the temperature and pressure, the less likely a chemical reaction will occur. Temperature tends to affect more than pressure does. The hydration product of the oil well cement is determined by thermodynamic modeling. The hydration products consist of calcium silicate hydrate solid solution (CSHQ), Si-hydrogarnet solid solution (Si-HG), ettringite solid solution (Ettri), portlandite (CH), and OH-hydrotalcite (OH-HT). The hydration products begin to degrade in the following order: CH, CSHQ, Si-HG, Ettri, and OH-HT. The results can be used to improve the degradation resistance of the oil well cement and research new type of degradation resistant cement. The thermodynamic theory is an effective way to investigate the degradation of the oil well cement by CO2 under geologic sequestration conditions.

Permeability evolution of defective wellbore cement under geologic carbon sequestration conditions by means of varying-radius pipeline modeling

X-ray imaging in combination with image registration was employed to unveil the microstructure alteration of defective wellbore cement cores when exposed to stagnant or flowing CO2-saturated brine under geologic carbon sequestration conditions. A varying-radius pipeline (VRP) modeling approach is proposed for estimating the permeability alteration from computed tomography (CT) images of artificial channels in the cement cores. The VRP model simplifies the three-dimensional channels into varying-radius pipelines, solves the problem of flow with one-dimensional Navier‒Stokes equations, and can readily be coupled with the Cahn–Hilliard equation to address multiphase flow problems. Furthermore, the accuracy of VRP modeling was verified by permeability testing and direct pore-scale modeling. The channel after CO2 exposure in the reactive-diffusion process was covered by substantial precipitation of calcite, and the measured channel permeability decreased by 28.67% from the original value 4.15 × 10−8 m2. In contrast, the channel after CO2 exposure in the reactive-flow process underwent significant dissolution, substantial tensile microfractures occurred at channel surface, and the measured channel permeability increased by 8.18% from the original 3.91 × 10−8 m2. The CT image–based microstructure investigation implied that when exposed to immobile CO2-saturated brine, even large fluid channels in wellbore cement may be shielded from further degradation; however, when encountering flowing CO2-saturated brine, cement with large fluid channels may fail. The proposed VRP model has the potential to assess field-scale CO2 leakage in wells.

Structural evolution in micro-calcite bearing Ca-montmorillonite reinforced oilwell cement during CO2 invasion

High concentration CO2 invades and forms carbonate layers in oilwell cement under geological CO2 sequestration conditions. Long-term invasion of CO2 makes the carbonation structure unstable and prone to damage. For the reinforcement of oilwell cement, Ca-montmorillonite (Ca-MMT) was modified using supercritical CO2 (ScCO2) as the solvent and intercalator. The micro-calcite bearing Ca-montmorillonite (MC Ca-MMT) was added to the cement slurry to reinforce the oilwell cement after the modification. Microcrystal calcite was identified in the MC Ca-MMT through transmission electron microscopy(TEM) and selected-area electron diffraction(SAED) analyses. The mechanical properties and microstructural evolution of the MC Ca-MMT reinforced oilwell cement were investigated, revealing that the carbonation was inhibited by MC Ca-MMT. Through the analysis of microcrystal formation and densified carbonation area, the CO2-resisting mechanisms of MC Ca-MMT reinforced oilwell cement were revealed in this study.

Structural evolution in Nanoclay reinforced oilwell cement during Supercritical CO2 (ScCO2) invasion

Supercritical CO2 (ScCO2) invades oilwell cement and forms carbonate layers in the cement under geological CO2 sequestration conditions. Long-term invasion of ScCO2 makes the carbonation structure unstable and prone to damage. Nanoclay was modified with ScCO2 as the solvent and intercalator for the reinforcement of oilwell cement, forming the microcrystalline Nanoclay (MC Nanoclay). MC Nanoclay is identified and added into the cement slurry to reinforce oilwell cement after the above modification. Microcrystal calcite is found in the MC Nanoclay with transmission electron microscopy (TEM) and selected area electron diffraction (SAED) analyses. Both mechanical properties and microstructural evolution of MC Nanoclay reinforced oilwell cement are investigated, showing that the carbonation was inhibited with MC Nanoclay. With generalized analysis from microcrystal formation and densified carbonation area, the reinforce mechanisms of MC Nanoclay were revealed in this study.

Analysis of shale property changes after geochemical interaction under CO2 sequestration conditions

This study implements a supercritical CO2 (scCO2) sequestration environment in a laboratory and investigates the geochemical effects of scCO2 on the properties of rock specimens. Shale specimens constituting caprock were kept in a laboratory reactor chamber with scCO2 for 63 days. Chemical interaction between rock surface and the scCO2 was then induced, and the changes in the properties were inspected before and after the reaction through various tests. The non-destructive tests comprised measurement of elastic wave velocity, shore hardness followed by investigation using the inductively coupled plasma mass spectrometer, and scanning probe microscope. The destructive tests include uniaxial compressive strength, Brazilian tensile strength, and X-ray fluorescence tests. Results show that mechanical properties are significantly weakened when shale specimens are exposed to both scCO2 and brine. The specimens reacting with only scCO2 induced a self-healing effect by precipitation of secondary sediments, becoming a more intact rock with increased strength and elastic modulus. The results denote that the geochemical alteration of shale occurs in a short time and are highly dependent on the reaction conditions. These results provide fundamental information for the stability of CO2 storage sites regarding the physical and chemical reactions between rocks under geological sequestration conditions.

Molecular simulation of equal density temperature in CCS under geological sequestration conditions

AbstractStoring carbon dioxide (CO2) in geological reservoirs, principally saline aquifers, is one of the main methods proposed to address the issue of anthropogenic CO2 emissions. With the aim of ensuring long‐term CO2 storage in geological reservoirs, the density of the CO2–brine solution is an important property that controls brine buoyancy. In this study, molecular dynamics simulations were performed to investigate the density of CO2–water solutions at temperatures in the range 60–240°C, pressures in the range 10–100 MPa, varying CO2 mass fractions (1%, 2%, and 3%), and varying CO2–NaCl–water solution salinities (2 and 4 mol/kg), all of which are crucial parameters for CO2 geological sequestration. The optimal combination model of CO2(TraPPE)–NaCl(OPLS)–water(TIP4P/2005) was determined by comparing experimental values with simulate density under geological conditions. The simulation results reproduced the trends of the experimental values. The equal density temperature (Te) indicated that solution density decreases upon CO2 dissolution in water when the temperature increases to a certain point. According to the simulation results, Te increases with increasing pressure and decreases with increasing salinity. Further, the results of analysis of the structural properties of the solution to determine the causes of Te showed that, with increasing temperature, the distance between CO2 molecules and adjacent atoms increases significantly, which reduces the local density around the CO2 molecules. © 2019 Society of Chemical Industry and John Wiley & Sons, Ltd.

Determination of CO2 Solubility in Water and NaCl Solutions under Geological Sequestration Conditions Using a Fused Silica Capillary Cell with in Situ Raman Spectroscopy

To investigate the solubility of carbon dioxide (CO2) in geological fluids at different temperatures and pressures, we developed a method for measuring solubility using an optically transparent fus...

Clay Swelling in Dry Supercritical Carbon Dioxide: Effects of Interlayer Cations on the Structure, Dynamics, and Energetics of CO2 Intercalation Probed by XRD, NMR, and GCMD Simulations

In situ X-ray diffraction (XRD) and nuclear magnetic resonance (NMR) experiments combined with molecular dynamics simulations using the grand canonical ensemble [grand canonical molecular dynamics (GCMD)] show that the cation size, charge, and solvation energy play critical roles in determining the interlayer expansion of smectite clay minerals when exposed to dry supercritical scCO2 (scCO2) under conditions relevant to petroleum reservoirs and geological CO2 sequestration conditions. The GCMD results show that the smectite mineral, hectorite, containing interlayer alkali and alkaline earth cations with small ionic radii and high solvation energies (e.g., Na+ and Ca2+) does not intercalate CO2 and that the fully collapsed interlayer structure is the most energetically stable configuration. With Cs+ and Ba2+, the monolayer structure is the stable configuration, and CO2 should spontaneously enter the interlayer. With Cs+, there is not even an energy barrier for CO2 intercalation, in agreement with the XRD a...

Molecular Dynamics Study of CO2 and H2O Intercalation in Smectite Clays: Effect of Temperature and Pressure on Interlayer Structure and Dynamics in Hectorite

Grand Canonical Molecular Dynamics (GCMD) simulations were performed to investigate the intercalation of CO2 and H2O molecules in the interlayers of the smectite clay, Na-hectorite, at temperatures and pressures relevant to petroleum reservoir and geological carbon sequestration conditions and in equilibrium with H2O-saturated CO2. The computed adsorption isotherms indicate that CO2 molecules enter the interlayer space of Na-hectorite only when it is hydrated with approximately three H2O molecules per unit cell. The computed immersion energies show that the bilayer hydrate structure (2WL) contains less CO2 than the monolayer structure (1WL) but that the 2WL hydrate is the most thermodynamically stable state, consistent with experimental results for a similar Na-montmorillonite smectite. Under all T and P conditions examined (323–368 K and 90–150 bar), the CO2 molecules are adsorbed at the midplane of clay interlayers for the 1WL structure and closer to one of the basal surfaces for the 2WL structure. Inte...

Dissolution and surface roughening of Columbia River flood basalt at geologic carbon sequestration conditions

Carbon storage in basalt reservoirs can mitigate CO2 emissions to the atmosphere that contribute to climate change. For basalt reservoirs, CO2 injection leads to Ca2+, Fe2+, and Mg2+-rich solutions that may result in carbonate precipitation for long-term stable carbon sequestration. Examination of basalt surfaces as dissolution progresses can offer important information about which minerals are dissolving, the timing and sequence of dissolution, and the effects these processes have on surface roughness and morphology. We carried out two series of experiments using two polished Columbia River flood basalt samples in CO2-rich water at 150°C and 100bar to observe the physical and geochemical changes during dissolution. One series reacted a sample over short time increments, while the other series examined a separate sample over longer time increments. Scanning electron microscopy, 2D profilometer analysis, and 3D laser confocal microscopy were combined with ICP-MS to characterize dissolution. Dissolution resulted in pitting, dissolution along fractures and grain boundaries, and an increase in species concentrations in the bulk solution over incremented reaction times. Based on these observations, early dissolution of olivine grains contribute Mg2+ and Fe2+ to aqueous solution in initial stages (<1week at a pH<4), while slower continuous dissolution of Ca-rich pyroxene contributes Mg2+, Fe2+, and Ca2+ to the bulk solution over a longer period of time. The complete dissolution of olivine grains resulted in pits up to 200μm deep. Dissolution of plagioclase and matrix was slower and resulted in the formation of micro-sized textures (<10μm). Following 1–2months of reaction, the surface roughness parameters (mean and root mean squared) increased by factors of 42 and 28, respectively, while surface area of the flood basalt increased 20% relative to the starting polished surface. The results of this study indicate 1) pyroxene is the sustaining contributor of divalent metal cations during dissolution of basalt and 2) the limited connectivity limits of olivine and pyroxene grains the exposure of new reactive surface areas.

Effect of Layer Charge on CO2 and H2O Intercalations in Swelling Clays.

The effect of layer charge on the intercalation of supercritical carbon dioxide (scCO2)-H2O mixture in Na-montmorillonite clay interlayers under T = 323 K and P = 90 bar geologic sequestration conditions has been further investigated. This effect includes the charge amount and its location (within either octahedral or tetrahedral layers due to isomorphic substitutions). Two clay models with different layer charges are used in this study. Simulation results show that the increase of charge amount shifts the monolayer-to-bilayer (1W-to-2W) hydration transition toward the lower relative humidity (RH), increasing water sorption at the expense of reducing the overall sorption amount of CO2 in the clay interlayer. However, the combination of the influence of charge amount and charge location leads to insignificant changes in equilibrium basal spacings of the high- and low-charge clays. Molecular dynamics simulations show that the CO2 dimers, which are frequently seen in low-charge clay interlayers, vanish in high-charge clay interlayers even at low RH of 30%.

Evidence from 29Si Solid-State Nuclear Magnetic Resonance of Dissolution Reactions of Forsterite

We have used solid-state nuclear magnetic resonance (NMR) of 29Si to monitor the reaction of forsterite (Mg2SiO4) with isotopically enriched 13CO2. Fate of silicon that comes from dissolution of forsterite in the presence of water or NaCl brine was monitored as a function of depth in a packed bed reactor, which used elevated-temperature and -pressure conditions to mimic underground geological sequestration conditions. Silicon provides an important window into the reaction since the precipitation of amorphous silica can affect forsterite dissolution, and solid-state magic-angle spinning NMR can readily distinguish between 29Si in forsterite and amorphous silica. Furthermore, differences between Q3 and Q4 species of amorphous silica were observed as a function of depth. Results differed between water- and brine-based reactions, with enhanced dissolution of forsterite observed in the brine.

Hydrogen bonds at silica–CO2 saturated water interface under geologic sequestration conditions

ABSTRACTTo investigate the effects of sequestration condition on hydrogen bonds between mineral and water, molecular dynamics simulations have been performed. The simulations were conducted at conditions related with geologic sequestration sites: pressure (3.1–32.6 MPa), temperature (318 and 383 K), salinity (0–3 M), salt (NaCl and CaCl2) and silica surface models Q2 (geminal), Q3 (isolated) and amorphous Q3. The hydrogen bonds were classified into four types: silica–silica, silica–dissolved CO2, silica–water as donors and silica–water as acceptors. The mean numbers of hydrogen bonds for each type were analysed. The results show that: (1) silica surface silanol groups do not form H-bonds with dissolved CO2 molecules in water (brine); (2) The mean number of hydrogen bonds between silanol groups follows the order: Q2 > amorphous Q3 > Q3; (3) The mean number of hydrogen bonds between silanol and water molecules follows the order: Q3 > amorphous Q3 > Q2.

Molecular Understanding of CO2 and H2O in a Montmorillonite Clay Interlayer under CO2 Geological Sequestration Conditions

Grand canonical Monte Carlo (GCMC) simulations are carried out to investigate a supercritical carbon dioxide (scCO2)-water mixture in the Na-montmorillonite clay interlayer under typical CO2 geological sequestration conditions (T = 323 K, P = 90 bar and T = 348 K, P = 130 bar). The stable clay interlayer distances at different relative humidity (RH) are determined based on the normal pressure and free energy curves of the CO2–H2O–Na+ complex in the montmorillonite clay interlayer. Simulation results show that stable monolayer hydrates (1W) with a basal spacing around 12 A are formed at RH = 30–60%. As RH is increased to 70% and above, bilayer CO2–H2O mixtures with a basal spacing around 15–16 A (2W) are more stable. In general, the CO2 intercalation process is strongly influenced by RH. While a high relative humidity facilitates water molecules entering the clay interlayer, it nonetheless decreases CO2 intercalations. The sorbed H2O concentrations from our simulations compare remarkably well with the in s...

Water contact angles on quartz surfaces under supercritical CO2 sequestration conditions: Experimental and molecular dynamics simulation studies

The ambiguity of contact angle experimental measurements due to surface chemistry changes resulted from sample contamination and/or the degrees of reaction with supercritical CO2 has resulted in great difficulties to precisely understand the wetting behavior of CO2 under the geological carbon sequestration (GCS) conditions. In this study, water contact angles on quartz surface under GCS conditions were investigated through the combined experimental and molecular dynamics simulation (MDS) methods. The experimental results show that water contact angles increases as ionic strength increases. The effects of pressure and temperature are very weak. The dependence of ionic strength, pressure and temperature is same for monovalent and divalent ions solutions. In the MDS, a hydroxylated quartz surface was used as the base point. A good agreement between the MDS and experimental results were obtained. Using the MDS method, a clean mineral surface with a desired surface chemistry can be constructed, which is difficult in experiments. So by comparing MDS and experimental results, the mechanisms of the reservoir wettability can be better understood. Further investigation can be made on quartz surface with different functional groups to better understand wettability alteration caused by contamination and/or CO2 reaction.

Application of Ca-doped mesoporous silica to well-grouting cement for enhancement of self-healing capacity

Carbonation has been considered as an alternative to prevent CO2 leakage. In this study, calcium-doped mesoporous silica (CDMS) was introduced into Portland cement as a promoter of carbonation. An admixture of CDMS and American Petroleum Institute (API) Class G Portland cement exposed to CO2-saturated water was analyzed under geologic sequestration conditions (40°C and 80MPa) to assess the carbonation properties and self-healing effect of CDMS for CO2 storage. The capacity of CDMS to synthesize CaCO3 from CO2via carbonation was identified in an in vitro crystallization test. Analysis of the cut surface of a cement core showed the rapid synthesis of CaCO3 including calcite and aragonite. Rietveld analysis was employed for quantitative phase analysis. The quantitative analysis of the cement carbonation showed that tricalcium silicate (C3S) and dicalcium silicate (C2S) play important roles in cement carbonation. Several crystal phases of CaCO3 were identified in this study including calcite, aragonite and amorphous CaCO3. X-ray diffractometry (XRD), a field emission-scanning electron microscope (FE-SEM) equipped with an energy dispersive X-ray spectrometer (EDS), 29Si MAS-NMR (magic angle spinning–nuclear magnetic resonance) spectrometry, thermogravimetry-differential thermal analysis (TG-DTA) and FT-IR (Fourier transform infrared spectroscopy) were applied to characterize the admixture.

Numerical simulation of porosity and permeability evolution of Mount Simon sandstone under geological carbon sequestration conditions

A numerical model was developed with the use of reactive transport code CrunchFlow to estimate porosity, permeability and mineral composition changes of Mount Simon sandstone under typical geological carbon sequestration conditions (P=23.8MPa and T=85°C). The model predicted a permeability decrease from 1.60mD to 1.02mD for the Mount Simon sandstone sample in a static batch reactor after 180days of exposure to CO2-saturated brine, which is consistent with measured permeability results. Model-predicted solution chemistry results were also consistent with laboratory-measured solution chemistry data. SiO2 (am) was the primary mineral that causes permeability decrease, followed by kaolinite. Both SiO2 (am) formation and kaolinite formation were attributed to the dissolution of quartz and feldspar. This study shows that the formation of SiO2 (am) and kaolinite in the pore space of host rock is possible under typical CO2 sequestration conditions. SiO2 (am) and kaolinite precipitation at the CO2 plume extent could reduce the permeability of host rock and improve lateral containment of free-phase CO2, contributing to overall security of CO2 storage.

Modeling and measurement of CO2 solubility in salty aqueous solutions and application in the Erdos Basin

Geological carbon storage (GCS) is recognized as an effective method for mitigating the greenhouse effect. Deep saline aquifers hold the highest potential capacity for CO2 storage. CO2 solubility in salty aqueous solutions under geological sequestration conditions plays a key role in GCS. However, most CO2 solubility studies focus mainly on single-salt solutions (NaCl and CaCl2), and extrapolation of these studies to aqueous solutions with mixed ions is unavailable. To fill the research gap, based on the collection of CO2 solubility data, a semi-empirical thermodynamic model is proposed in this paper to calculate CO2 solubility in aqueous solutions containing K+, Na+, Ca2+ and Mg2+ in the temperature and pressure ranges from 313K to 378K and from 50bar to 220bar. To describe the CO2–liquid phase equilibrium, the Peng–Robinson equation of state (PR EoS) and the Setschenov equation are applied. The former has been modified to improve its performance in the studied T–P range, and the latter shows excellent accuracy with only three optimized parameters. Before modeling was done, experimental studies were conducted. Brine sampling from five reservoirs potentially chosen for CO2 sequestration in the Erdos Basin was carried out using a monitoring well in the support of the Shenhua Group carbon capture and storage (CCS) site project. The chemical composition of the samples was determined, and experiments measuring CO2 solubility were carried out in synthetic brine with 64 valid data points reported. An analytical method with a simplified sampling technique was chosen. In the range studied, the average absolute deviation of CO2 solubility between the model and experimental results was 2.01%, and the maximum absolute deviation in this study was less than 4.79%. The proposed model and experimental data therefore possess broad adaptability to GCS with satisfactory accuracy.

Experimental dissolution of dolomite by CO2-charged brine at 100 °C and 150 bar: Evolution of porosity, permeability, and reactive surface area

Hydrothermal flow experiments of single-pass injection of CO2-charged brine were conducted on nine dolomite cores to examine fluid–rock reactions in dolomite reservoirs under geologic carbon sequestration conditions. Post-experimental X-ray computed tomography (XRCT) analysis illustrates a range of dissolution patterns, and significant increases in core bulk permeability were measured as the dolomite dissolved. Outflow fluids were below dolomite saturation, and cation concentrations decreased with time due to reductions in reactive surface area with reaction progress. To determine changes in reactive surface area, we employ a power-law relationship between reactive surface area and porosity (Luquot and Gouze, 2009). The exponent in this relationship is interpreted to be a geometrical parameter that controls the degree of surface area change per change in core porosity. Combined with XRCT reconstructions of dissolution patterns, we demonstrate that this exponent is inversely related to both the flow path diameter and tortuosity of the dissolution channel. Even though XRCT reconstructions illustrate dissolution at selected regions within each core, relatively high Ba and Mn recoveries in fluid samples suggest that dissolution occurred along the core's entire length and width. Analysis of porosity–permeability data indicates an increase in the rate of permeability enhancement per increase in porosity with reaction progress as dissolution channels lengthen along the core. Finally, we incorporate the surface area–porosity model of Luquot and Gouze (2009) with our experimentally fit parameters into TOUGHREACT to simulate experimental observations.

Rate of H2S and CO2 attack on pozzolan-amended Class H well cement under geologic sequestration conditions

Experiments were conducted to investigate the rates of H2S and CO2 alteration of pozzolan-amended wellbore cement (35vol% pozzolan–65vol% cement), so as to evaluate the potential impact of H2S and CO2 induced degradation of existing cemented wells present at acid gas co-sequestration sites. In the exposure experiments, pozzolan-amended cement samples were mixed, cured and exposed to mixtures of H2S and CO2 under lab-simulated geologic sequestration conditions (50°C and 15.2MPa) for 2.5, 9, 28 and 90 days. Measurement of the carbon alteration front was used to calculate the rate of CO2 alteration of pozzolan-amended cement exposed to a mixture of 79mol% CO2 and 21mol% H2S under geologic sequestration conditions in exposure periods of 0–90 days. Average CO2 alteration rates (rate of movement of CaCO3 precipitation front) were 3.3×10−3mm/day and 3.2×10−3mm/day for cement samples exposed to a 1% NaCl solution saturated with CO2 and H2S, and those in contact with a supercritical mixture of CO2 and H2S, respectively. Two scenarios were considered for measuring and quantifying alteration caused by H2S over the exposure periods of 0–90 days: sulfur-rich zone thickness, and sulfur alteration index. The average rate of H2S alteration determined by sulfur-rich zone thickness divided by exposure duration was 4.3×10−3mm/day for cement exposed to 1% NaCl solution saturated with CO2 and H2S, and the average rate of H2S alteration determined by sulfur alteration index divided by exposure duration was 8.2×10−3day−1. Cement exposed to a supercritical mixture of CO2 and H2S result in H2S alteration rates determined by sulfur-rich zone thickness divided by exposure duration of 3.1×10−3mm/day, and average rates of H2S alteration determined by sulfur alteration index divided by exposure duration of 6.3×10−3day−1. Sulfur alteration index results also show that H2S was able to penetrate to the core of pozzolan-amended wellbore cement after 2.5 days of exposure, though this was not readily apparent in the sulfur-rich zone thickness results. Sulfur-rich zone thickness is best used to describe high-level sulfur alteration in the rim of samples. The results indicate that (1) an aqueous environment is more favorable for H2S attack on pozzolan-amended cement than a supercritical CO2 and H2S environment; (2) for 90 days of exposure significant alteration induced by H2S and CO2 occurs at regions very close to the fluid/cement interface; (3) H2S penetrates pozzolan-amended cement more rapidly than CO2 in aqueous contact environments. In contrast, under supercritical liquid environment, H2S and CO2 have similar penetration rates in pozzolan-amended cement.