Effect Of Mineral Dissolution Research Articles

Effect of mineral dissolution on fault slip behavior during geological carbon storage

Geological carbon dioxide storage is one of the most effective technologies to reduce greenhouse gas emissions to the atmosphere. The mineral dissolution is inevitable during the long-term storage process, while the chemical effect on fault slip behavior remains poorly understood. In this paper, we present a hydro-chemical–mechanical coupled fault reactivation study using the unified pipe-interface element method (UP-IEM). The impact of chemical dissolution on stress redistribution is considered. The accuracy of the numerical method to simulate reactive solute transport and fault frictional slip are confirmed by analytical solution and numerical verification. Two different fault tectonic scenarios, of which fault locating in the caprock and fault crosscutting the reservoir and caprock, are designed to investigate the fault slip behavior induced by mineral dissolution. The effect of dissolved CO2 solute concentration, fault aperture, reservoir permeability and chemical reaction rate are discussed. Results show that fault locating in the caprock is easier to be activated. The chemical reaction has a more significant effect on fault slip behavior than fluid pressure during the long-term low-velocity CO2 leakage. The increase of CO2 solute concentration and reservoir reaction rate cause an obvious growth on fault slip displacement. The decrease of fault initial aperture results in the fault slip velocity slower and the slipping area smaller. The high-permeability reservoir keeps the fault more stable than low-permeability reservoir under the influence of mineral dissolution.

Chemo-Mechanical Couplings at Granular Contact: The Effect of Mineral Dissolution and Precipitation across the Scales

Strong interactions between mechanical deformation and chemical reactions may play a critical role in the response of geomaterials or geological systems to evolving environmental circumstances that may occur in both natural and engineered processes. The present study focuses on mineral dissolution and precipitation at the intergranular contact whose consequences are often manifested at the macro-scale where the mechanical and transport properties of the geomaterial may be altered. Discrete element modeling is employed to explore two applications involving such mineral transformations. The first example is primarily focused on the chemo-mechanical coupling mechanisms of intergranular contact in the natural process of pressure solution and secondary compression. The effect of the mineral dissolution on the mechanical response at the grain contact is incorporated into the contact model. Discrete element simulations are performed to examine the overall mechanical response of particle assembles subject to mineral dissolution and the results demonstrate the important role of the kinetic rate characteristics of the dissolution process. The second part of the present study revolves around the effect of mineral precipitation in an engineered process known as microbially induced calcite precipitation for potential soil improvement. The kinetics of involved bio-chemical process is incorporated into on the contact model and the simulation results indicate considerable strengthening effect. Overall, the present study demonstrates the feasibility of discrete element approach as a numerical tool to model coupled chemo-mechanical phenomena across the scales.

Mathematical Modeling and Numerical Simulation of Water‐Rock Interaction in Shale Under Fracturing‐Fluid Flowback Conditions

AbstractWater‐rock interaction cannot be ignored for shale reservoirs with high‐salinity formation brine and complex rock composition, and stimulated by massive slick‐water fracturing treatment. However, there have been few studies on the flowback model fully coupled with different effects of water‐rock interaction. This paper presents the development of a coupled hydro‐chemical‐mechanical model for modeling water‐rock interaction in fractured shale during the post‐fracturing flowback period. The model considers distinguishing water‐rock interaction phenomena, that is, mineral dissolution, clay swelling and chemical osmosis, and accounts for multi‐phase flow in a fractured shale reservoir. The coupling and solution method and a numerical simulator were developed. Numerical simulation indicates that the swelling volume of clay minerals occupies the pores and leads to a decline in matrix porosity, while mineral dissolution increases both the matrix porosity and the solute concentration in the aqueous phase in matrix pores. Clay swelling mainly affects the shape of the porosity ratio profiles. The effect of mineral dissolution becomes increasingly stronger as flowback progresses. Mineral dissolution mainly affects the relative positions of the porosity ratio curves with the progress of flowback. The water‐rock interaction coupled flowback modeling and the numerical simulation results in this study quantify the effects of chemical osmosis, clay swelling and mineral dissolution. Results from this study provide new insights into the mechanisms of fracturing‐fluid flowback and value to flowback transient analysis.

Role of Monovalent and Divalent Ions in Low-Salinity Water Flood in Carbonate Reservoirs: An Integrated Analysis through Zeta Potentiometric and Simulation Studies

The presence of principal ions in the water injected is essential for enhanced oil recovery by formation of water-wet state in carbonates. This study reaffirms this and presents an evaluation of the positive influence of both divalent as wells as monovalent ions on wettability alteration mechanisms during low salinity waterflooding using brines of varying ionic composition, referred to as “smart brines”. Zeta potentiometric analysis and reservoir simulation studies were conducted with diluted and smart brines that were prepared by varying the composition of principal ions. Surface charge of oil-saturated whole core samples of rock in the presence of various diluted and smart brines was estimated by zeta potential measurements. A comprehensive analysis of zeta potentiometric and reservoir simulation studies was done to establish and investigate the linkage between the recovery mechanism and the incremental recovery achieved. It is noted that zeta potential increases with the increasing level of dilution and it can be attributed to electric double-layer mechanism. On the contrary, simulation studies implied a different mechanism where an increase in effluent’s pH and Ca2+ mole fraction along with decrease in moles of minerals and saturation index implied rock dissolution was dominant mechanism. Moreover, the effect of mineral dissolution beyond the injection block is highly doubtful. This study demonstrates that an integrated approach from both zeta potentiometric and simulation studies can be used to provide insights into the underlying science of interactions at pore scale during a low salinity waterflood using smart brines. With the aid of an adequately designed upscaling procedure and protocol, the laboratory results can be further used towards developing field-scale models to obtain with realistic recovery factors with optimized brine composition and salinity.

Fracture Propagation in Heterogeneous Porous Media: Pore-Scale Implications of Mineral Dissolution

Open-mode fractures in sediments and rock occur both in natural processes and in engineering practice. In contrast to long planar fractures predicted by solutions in homogeneous media, laboratory and field observations often evidence complex and non-planar open-mode fracture networks in geological media. One cause of fracture complexity is the heterogeneity of material mechanical properties. This study focuses on the effects of mineral dissolution on pore structure modification in heterogeneous porous media and ensuing changes on fracture propagation characteristics. We performed semicircular bending experiments on limestone samples pre- and post-acidizing, mapped 3-D pore structure with X-ray microtomography, and used a finite element formulation based on the phase-field approach and linear elastic fracture mechanics to model initiation and propagation of open-mode fractures. Semicircular bending experiments on acidized carbonate rock samples show that non-planar fractures follow high porosity regions and large pores, and that fracture toughness correlates well with local porosity. Numerical modeling shows that a direct relationship between fracture toughness and porosity permits replicating fracture stress intensity at initiation and non-planar fracture propagation patterns observed in experiments. The results of this study indicate that mineral dissolution can affect fracture propagation patterns and that a coupling of mechanical and reactive processes in porous media formulations can be achieved through porosity and toughness. The understanding of fracture propagation patterns and geometry manipulation is critical for safe and effective use of reactive fluids in the subsurface, such as in hydraulic fracturing and carbon geological sequestration applications.

Permeability Damage Due to Fines Migration During CO2 Sequestration

Fines migration has not been widely considered during CO2 injection into water-saturated rocks. Mineral dissolution effects are only considered in long-term experiments (weeks to months scale). This study conducts a series of short (few hours) dynamic experiments to study the effect of dissolution and fines migration on CO2 injectivity in cores. Three coreflooding experiments were performed using Berea sandstone at difference salinity brine (0, 10, 30 and 60 g/L NaCl). First, the core plugs were subjected to brine injection. Then, CO2-saturated brine was injected to displace unsaturated brine from the core. Afterward, brine saturated supercritical CO2 (scCO2) was injected into the core. The Pressure drop across the core was monitored and produced water samples were collected continuously during the experiments. To characterize the core sample, X-Ray Powder Diffraction (XRD), X-Ray Fluorescence (XRF), and Scanning Electron Microscopy (SEM) analyses were performed. After the experiment, SEM-EDS analysis was run and registered with the pre-injection images to visualize fines migration. Fines concentration was measured, and ionic chromatography analysis was performed to characterize produced water samples. Numerical simulations were performed to model the experiment geochemical reactions. The permeability of the core sample is significantly reduced after the experiment due to pore blockage. SEM-EDS analysis of the blocked pores and produced fines show blockage is mostly caused by clay, quartz and cement. Numerical simulations showed that the reaction rate; hence, cement dissolution is faster at higher salinity.

The Coupled Effect of Fines Mobilization and Salt Precipitation on CO2 Injectivity

In terms of storage capacity and containment efficiency, deep saline aquifers are among the best candidates for CO2 storage. However, salt precipitation in the wellbore vicinity and fines mobilization ensued from in situ mineral dissolution could impair CO2 injectivity and reduce the quality and capacity of deep saline reservoirs for CO2 storage. The mechanisms of salt precipitation and its impact on CO2 injectivity have been studied, but the effects of fines mobilization have not been properly investigated. We conducted core-flood experiments and theoretical studies to investigate the impact of fines mobilization on CO2 injectivity, the relative contribution of fines mobilization and salt precipitation to injectivity impairment, and the coupled effect of salt precipitation and fines mobilization. We found that, mineral dissolution and transport effects could induce up to about 26% injectivity impairment. The findings also suggest that about 0.3 wt % particle concentration in the pore fluid could induce over twofold injectivity impairment compared to about 10 wt % of total dissolved salt in the formation water. Salt precipitation was also found to compound injectivity impairment induced by fines mobilization. The present study provides important insight, and could serve as a foundation to inspire further experimental and theoretical investigation into the effects of mineral dissolution and fines mobilization in the context of CO2 injectivity.

Tests Investigate Recovery Mechanisms of Steam Injection in Carbonate Reservoir

This article, written by Editorial Manager Adam Wilson, contains highlights of paper SPE 153812, ’Investigation of Recovery Mechanism of Steam Injection in Heavy-Oil Carbonate Reservoir and Mineral Dissolution,’ by Guo-Qing Tang, SPE, Art Inouye, Vincent Lee, SPE, Dustin Lowry, and Wei Wei, Chevron, prepared for the 2012 SPE Western Regional Meeting, Bakersfield, California, 19-23 March. The paper has not been peer reviewed. Steam injection in carbonate heavy-oil reservoirs is a complex process. The main challenge is that the injected steam breaks through from a fracture network, resulting in poor sweep efficiency. A large amount of oil remains behind the steam front. In addition, severe mineral dissolution (or precipitation) because of steam/brine/rock interaction at high temperatures has a significant effect on steam injectivity and recovery mechanisms. An extensive laboratory study focused on understanding the recovery mechanism and relevant mineral dissolution. Introduction Ten reservoir cores and 14°API crude oil were used for this study. Imbibition, steamflooding, and pressure blowdown tests were conducted. The results show that the recovery mechanism of steam injection in the target carbonate reservoir is composed of imbibition, viscosity reduction, in-situ steam generation induced by pressure blowdown, and oil expansion mechanisms. As the rock is heated to near 400°F, imbibition becomes the dominant recovery mechanism. The increased imbibition recovery is strongly dependent on mineral dissolution at a high temperature, which results in wettability alteration to-ward strong water-wetness. Because of microfractures, steamdrive is less efficient compared with imbibition. In-situ steam generation still can increase oil recovery by an additional 17–32% of original oil in place (OOIP) following steamflood displacement at residual oil saturation. Significant mineral dissolution is observed with high-resolution computed tomography (CT) scanning and effluent geochemical analysis. CT-image analysis shows that the size of vugs is increased 2 to 5 times by mineral dissolution. Mineral dissolution does not increase the effective permeability because these vugs are mainly connected by microfractures, where mineral dissolution effects are negligible. In fact, permeability is reduced by fines migration resulting from mineral dissolution. Experiments Carbonate reservoir rock samples with permeability ranging from 121 to 317 md and porosity ranging from 40.1 to 50.9% were selected for this study. CT scans showed that the selected rock samples have many vugs, with a size ranging from 0.11 to 3 mm. These vugs are connected with very tiny pores and microfractures with sizes of approximately 20 µm. An in-house high-temperature (up to 400°F) and -pressure (up to 1,000 psi) experimental system that is capable of running either free imbibition (counter-current) or forced imbibition (cocurrent) was used for all experiments. Different experiments, such as free imbibition, forced imbibition, thermal expansion, steamflooding, and pressure blowdown, were performed. Fig. 1 shows the experimental design.

Mineral dissolution effects on mechanical strength

The fabric of soil media may change due to certain factors such as the dissolution of soluble mineral particles, desiccation, and cementation. The fabric changes lead to mechanical behaviour changes. The purpose of this study is to investigate the effects of mineral dissolution on mechanical strength. Experimental studies and numerical simulations are performed by using conventional direct shear and discrete element methods. The dissolution specimens are prepared with different volumetric soluble particle fractions in sandy soils. The dissolution of the specimens is implemented by saturating the salt–sand mixtures at the different confining stresses in the experimental study and reducing the sizes of soluble particles in the numerical simulations. Experimental results show that after the particle dissolution as the soluble particle fraction increases, the peak shear strength decreases, the void ratio increases, and the vertical displacement behaviour during shearing changes from dilative to contractive behaviour. The numerical simulations exhibit that the macro-behaviours match well with the experimental results. In addition, the micro-scale observation shows that the reduction in the shear strength of the soluble particle mixtures after the particle dissolution results from the reductions of the coordination number, the stability of the fabric, the ability to develop the anisotropy of the fabric, and the increases in the local voids and anisotropy. This study reveals that the particle dissolution has a significant effect on the shear strength, deformation, and fabric change.

Physical and chemical steady-state compaction in deep-sea sediments: Role of mineral reactions

Marine sediments typically exhibit steep porosity gradients in their uppermost centimeters. Although the decrease in porosity with depth below the sediment–water interface is primarily due to compression arising from the accumulation of overlying sediment, early diagenetic mineral dissolution and precipitation reactions may potentially also affect the porosity gradient. Here, we present a steady state compaction model, based on the mass and momentum conservation of total fluid and solid phases, in order to quantify the relative contributions of mineral reactions and physical compaction on porosity changes. The compaction model is applied to estimate hydraulic conductivity and compressive response coefficients of deep-sea sediments from measured porosity depth profiles. The results suggest an inverse relation between the compressive response coefficient and the lithogenic content of marine sediments. For deep-sea sediments exhibiting high rates of dissolution of siliceous shell fragments, the compaction model ignoring mineral reactions overestimates the hydraulic conductivity and compressive response coefficients. In contrast to non-compacting porous media, mineral dissolution in surficial sediments can lead to lower porosity. However, as illustrated for a deep-sea sediment in the equatorial Atlantic characterized by extensive dissolution of calcareous shell fragments, the effect of mineral dissolution and precipitation reactions on porosity gradients is, in most cases, negligible.

Effect of mineral dissolution from bone specimens on the viscoelastic properties of cortical bone

Although physiological saline (0.15 M NaCl aqueous solution) has been used as a storage solution to prevent bone specimens from drying, there have been reports that Ca 2+ ions dissolve from bone specimens during the storage in saline. In order to determine whether such storage has a marked effect on mechanical properties, the relaxation modulus of bovine cortical bone stored in physiological saline was compared with that stored in a buffer solution containing a sufficient amount of Ca 2+ ions. After storage in saline, the modulus value of specimens was significantly reduced from that before storage. On the other hand, the modulus value of specimens soaked in the solution containing sufficient Ca 2+ ions did not change after storage. The relaxation rate of a bone specimen stored in physiological saline was larger than that of a specimen stored in Ca 2+-buffered saline solution and that of the control specimens. The results suggest that by the dissolution of Ca 2+ ions from a bone specimen during storage in physiological saline, percolated paths of mineral phase and of reinforced matrix phase are disjoined, resulting in reduction in the elastic modulus and change in the viscoelastic properties of bone.

Reactive transport modeling of the interaction between a high-pH plume and a fractured marl: the case of Wellenberg

In the context of the proposed low- and intermediate-level radioactive waste repository at Wellenberg (Switzerland), calculations simulating the interaction between hyperalkaline solutions and a fractured marl, at 25 °C, have been performed. The aim of these calculations is to evaluate the possible effects of mineral dissolution and precipitation on porosity and permeability changes in such a fractured marl, and their impact on repository performance. Solute transport and chemical reaction are considered in both a high-permeability zone (fracture), where advection is important, and the wall rock, where diffusion is the dominant transport mechanism. The mineral reactions are promoted by the interaction between hyperalkaline solutions derived from the degradation of cement (a major component of the engineered barrier system in the repository) and the host rock. Both diffusive/dispersive and advective solute transport are taken into account in the calculations. Mineral reactions are described by kinetic rate laws. The fluid flow system under consideration is a two-dimensional porous medium (marl, 1% porosity), with a high-permeability zone simulating a fracture (10% porosity) crossing the domain. The dimensions of the domain are 6 m per 1 m, and the fracture width is 10 cm. The fluid flow field is updated during the course of the simulations. Permeabilities are updated according to Kozeny's equation. The composition of the solutions entering the domain is derived from modeling studies of the degradation of cement under the conditions at the proposed underground repository at Wellenberg. Two different cases have been considered in the calculations. These 2 cases are representative of 2 different stages in the process of degradation of cement (pH 13.5 and pH 12.5). In both cases, the flow velocity in the fracture diminishes with time, due to a decrease in porosity. This decrease in porosity is caused by the precipitation of calcite (replacement of dolomite by calcite) and other secondary minerals (brucite, sepiolite, analcime, natrolite, tobermorite). However, the decrease in porosity and flow velocity is much more pronounced in the lower pH case. The extent of the zone of mineral alteration along the fracture is also much more limited in the lower pH case. The reduction of porosity in the fractures would be highly beneficial for repository performance, since it would mean that the solutions coming from the repository and potentially carrying radionuclides in solution would have to flow through low-conductive rock before they would be able to get to higher-conductive features. The biggest uncertainty in the reaction rates used in the calculations arises from the surface areas of the primary minerals. Additional calculations making use of smaller surface areas have also been performed. The results show that the smaller surface areas (and therefore smaller reaction rates) result in a smaller reactivity of the system and smaller porosity changes.

Reactive Transport Modelling of the Interaction Between a High pH Plume and a Fractured Marl

In the context of the proposed low and intermediate level radioactive waste repository at Wellenberg (Switzerland), calculations simulating the interaction between hyperalkaline solutions and a fractured marl, at 25~ have been performed. The aim of these calculations is to evaluate the possible effects of mineral dissolution and precipitation on porosity and permeability changes in such a fractured marl, and their impact on repository performance. Solute transport and chemical reaction are considered in both a high permeability zone (fracture), where advection is important, and the wall rock, where diffusion is the dominant transport mechanism. The mineral reactions are promoted by the interaction between hyperalkaline solutions derived from the degradation of cement (a major component of the engineered barrier system in the repository) and the host rock.

Rock-water interactions in the Fenton Hill, New Mexico, hot dry rock geothermal systems. II. Modeling geochemical behavior

A transient mass balance model is developed to account for the dynamic behavior of an artificially stimulated hot dry rock (HDR) geothermal reservoir system in fractured granitic rock. Fluid mixing between fractured zones, hydrodynamic dispersion within zones, pore fluid displacement, and mineral dissolution effects are incorporated into the model. A two-zone system is sufficient to account for the major observed results from field testing of the Fenton Hill HDR system.