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Abstract Reservoir heterogeneities and reactive processes strongly affect the fluid flow in porous media. The mechanism of transport and reaction of the fluid varies from pore-to core-scales, leading to the discrepancies between theoretical predictions and experimental observations, which are caused by the anomalous diffusion. Also, the reactive processes in porous media may alter reservoir properties in different spatial and temporal scale, varying subsequent transport and reaction behaviors. In this article, the coupled transport and reaction process in heterogeneous porous media is studied. The Continuous Time Random Walk (CTRW) framework incorporating particle tracking (PT) method is proposed to simulate the transport and reaction processes at pore-scale and show macroscopic behavior at core-scale. Utilizing the CTRW-PT approach, the motion of solute particles is described as a combination of random independent spatial and temporal increments in each walk step. The particle transition distance and time are chosen from a joint space-time probability density function by a stochastic process. The modeling of reaction is followed by the modeling of transport and updates the change of porous media with its effect on following transport and reaction. Simulations of non-reactive tracer and reactive nanofluid flow under different heterogeneity, injection flow rate and rate of reaction were performed. By adjusting the ensemble parameter β and t 2 the effects of the above factors on flow behavior are accounted. The concentration profiles with time are displayed to show the effect of heterogeneity, flow rate and rate of reaction on anomalous behavior. Higher level of heterogeneity, higher flow rate and rate of reaction are captured by smaller β and larger t 2 quantitatively, representing more anomalous flow behavior. The breakthrough curves from CTRW-PT simulation well match the experimental as well as Advection-Diffusion-Reaction Equation (ADRE) modeling results in most cases. The CTRW results also better match the experimental results than the ADRE as the anomalous behavior becomes significant. It is also found that CTRW-PT simulation as a statistical approach is more computationally efficient than solving the ADRE. Highlights • Utilizing Continuous Time Random Walk to simulate nanoparticle transport. • Incorporating novel Particle Tracking algorithm to monitor concentration profile. • Capturing the anomalous behaviors of highly reactive flow in heterogeneous media. • Results are more accurate than solving Advection-Diffusion-Reaction Equation. • Using the statistical model improves efficiency over conventional numerical method. [ABSTRACT FROM AUTHOR]

Abstract Injectivity decline due to mineral scale deposition in near wellbore region of water injection wells is one of the main challenging issues and have been widely reported in the literature. One of the main mechanisms of injectivity loss is incompatibility between injected and formation waters that may result in inorganic scale precipitation and subsequent deposition in porous media. Reliable reactive flow models to predict type and amount of scale along with permeability decline estimation allow planning and risk management of water flood projects. In this paper, we present a coupled geochemical and hydrodynamic model to simulate the scale precipitation and deposition of mineral scales in multicomponent aqueous systems which is able to predict type of scale and permeability decline in porous medium. Geochemical software was used to simulate reactions between injected and formation brine suspicions to risk of composite scale formation and hydrodynamic flow model was applied to predict subsequent permeability decline during water injection. High quality match of permeability decline in following of robust static modeling of mineral scale formation in multicomponent aqueous systems was achieved. Highlights • A geochemical package was used to identify type and amount of composite scale formation during water injection. • Coupling geochemical and hydrodynamic models allowed prediction of permeability decline. • Laboratory data was matched successfully with proposed model. [ABSTRACT FROM AUTHOR]

Acidizing is a commonly used stimulation treatment for carbonate reservoirs, performed by injecting acid into the near-wellbore rocks to remedy drilling damage, or to create, by mineral dissolution, deeply-penetrating, narrow, high-permeability channels, termed wormholes. Wormhole formation in un-fractured matrix has been widely studied by numerical modeling, but little work has been done for fractured cases, which may cause wormholes to propagate quite differently. In this study, a continuum model with explicit fractures is developed, where the governing equations are discretized by the finite-volume method. This model produces the correct dissolution patterns on a 2-D un-fractured domain discretized by Delaunay triangulation. Then it is used to examine wormhole formation in cases with single and multiple fractures, including consideration of characteristics such as fracture orientation, pattern and aperture. Fractures oriented along the flow direction can dominate the wormhole propagation, while fractures perpendicular to the flow not only change the number of branches, but also the orientation of the wormhole. Because of the positive feedback associated with fractures, the flow+dissolution process typically uses only some of the available fracture pathways. Perhaps the most significant result is that the optimum injection rate is almost unchanged from that of the same un-fractured medium. [ABSTRACT FROM AUTHOR]

Significant natural fractures develop in deep sandstone reservoirs. However, the previous numerical simulation for matrix acidizing in sandstone rocks always focused on the reactive flow in porous media. A series of responses between multiple types of acids and minerals in fracture and matrix pores have been a significant setback for seeking the mechanism of acid flow in fractured sandstone rocks. This paper, established a multistage reactive-transport model for fractured sandstone rocks based on the two-scale continuum model to explore the effects of fractures on the reactive flow. The weak forms of fluid flow and solute transport equations are derived using the Galerkin method to couple the matrix and fracture domains, and the extended finite element method was used to solve the discretization model. Additionally, we presented numerical simulations under 2D linear flow conditions with specific and sensitive analyses about fracture and matrix properties. Numerical cases showed that the wormhole-shaped structure generated by acid dissolution is hard to develop even in highly heterogeneous fractured sandstone rocks due to the low reaction rate between mud acid and minerals. However, fractures that are not parallel to the flow direction can accelerated acid flow in the formation and reduced Si(OH) 4 precipitation. Increasing the injection rate can not change the dissolution patterns of sandstone, but expanded the acid diffusion range and decreased Si(OH) 4 precipitation in fractured sandstone. • A multistage reactive-transport model of fractured sandstone was developed based on the two-scale continuum model. • The mechanism of acid flow in fractured sandstone rocks was explored. • The effects of the characteristic parameters of fracture and matrix on the acid transport were investigated. • The potential for generating wormhole-like structures in fractured sandstone rocks was analyzed. [ABSTRACT FROM AUTHOR]

Significant natural fractures develop in deep sandstone reservoirs. However, the previous numerical simulation for matrix acidizing in sandstone rocks always focused on the reactive flow in porous media. A series of responses between multiple types of acids and minerals in fracture and matrix pores have been a significant setback for seeking the mechanism of acid flow in fractured sandstone rocks. This paper, established a multistage reactive-transport model for fractured sandstone rocks based on the two-scale continuum model to explore the effects of fractures on the reactive flow. The weak forms of fluid flow and solute transport equations are derived using the Galerkin method to couple the matrix and fracture domains, and the extended finite element method was used to solve the discretization model. Additionally, we presented numerical simulations under 2D linear flow conditions with specific and sensitive analyses about fracture and matrix properties. Numerical cases showed that the wormhole-shaped structure generated by acid dissolution is hard to develop even in highly heterogeneous fractured sandstone rocks due to the low reaction rate between mud acid and minerals. However, fractures that are not parallel to the flow direction can accelerated acid flow in the formation and reduced Si(OH) 4 precipitation. Increasing the injection rate can not change the dissolution patterns of sandstone, but expanded the acid diffusion range and decreased Si(OH) 4 precipitation in fractured sandstone. • A multistage reactive-transport model of fractured sandstone was developed based on the two-scale continuum model. • The mechanism of acid flow in fractured sandstone rocks was explored. • The effects of the characteristic parameters of fracture and matrix on the acid transport were investigated. • The potential for generating wormhole-like structures in fractured sandstone rocks was analyzed. [ABSTRACT FROM AUTHOR]

Acidizing is a well-stimulation operation that consists of injecting a reactive fluid into the rock formation. When in carbonate rocks, the dissolutions create conductivity channels called wormholes. The pattern formed depends on the flow rate, thermodynamic conditions, and several rock-fluid interaction parameters. Despite acidizing operations being well-known, several factors or conditions affecting wormhole formation are not thoroughly tested in the laboratory. We observe a difficulty in the literature to summarize the main aspects involved in wormhole formation. At the same time, understanding how each parameter could affect the wormholing process can help to optimize the acidizing design, maximizing the financial return. Therefore, this review article discusses the main studies about the parameters affecting the wormhole's formation: acid concentration, reaction rate, flow rate, temperature, core sample dimension, and heterogeneity. The main idea here is to provide a resume of the most relevant works founds in our literature review and a reference base for researchers interested in carbonate acidizing. The pore-volume-to-break-thought (PVbt) plotted as a function of the flow rate is the most common approach to evaluate the dissolution pattern observed for each reactive fluid-rock combination. However, PVbt should be seen more comprehensively as a consequence of advection-diffusion-reaction balance. Other essential aspects that need to be considered to obtain a significant representation of the PVbt plots are sample geometry and the initial rock saturation. • We present a review of reactive flow applied to acidizing experiments. • We discuss how are experimentally obtained the PVbt plots. • Several factors that affect PVbt are discussed. • We still observe a limited number of experiments on reactive flow. • Most experiments on acidizing, reported in the literature, are not wholly comparable. [ABSTRACT FROM AUTHOR]

Microorganisms have different benefits including bioremediation of aquifers contaminated with the non-aqueous liquid phase, microbial EOR, and bacterial degradation of asphaltenes. Despite these profits, a special kind of bacteria named Sulfate Reducing Bacteria (SRB) causes H 2 S generation which is toxic and also results in equipment erosion and corrosion. The injected water approaches the production well in a radial form geometry. However, less is known about the H 2 S generation and movement in the radial coordinate. In this study, we investigated SRB souring in aquifers and oil reservoirs using a reactive numerical simulation of multicomponent and multiphase radial flow. The operator-splitting method was utilized to model this dispersion-dependent phenomenon. Furthermore, a higher-order finite difference approach was adopted to more accurately model SRB souring by avoiding the numerical dispersion. The results of the proposed approach were verified with the existing analytical radial solution by applying the simplifying assumption of the analytical radial solution. Also, the effect of numerical and physical dispersions was evaluated and it was highlighted that under certain conditions numerical dispersion can be confused with the physical one. Moreover, a comparison of the H 2 S profile in the radial coordinate with linear geometry showed significant differences which should be considered in SRB souring studies. This difference highlights the necessity of radial grid refinement around the wells in full-field reservoir simulation to attain more accuracy. The study of SRB souring during water injection in an oil reservoir also illustrates the same pattern as souring in aquifer but the oil presence delays mixing between sea and formation water and postpones H 2 S generation. The findings of this work provide a better understanding of near-wellbore SRB souring during water injection in porous media. • Using a higher-order finite difference approach to model SRB souring in porous media. • Evaluating of numerical and physical dispersion in radial geometry. • Comparison of generated H 2 S profile in the radial and linear geometries. • Studying near-wellbore SRB souring during water injection in oil reservoirs. [ABSTRACT FROM AUTHOR]

Enhancing the oil recovery of carbonate reservoirs with acidic oil depends on injected brine composition and salinity throughout the low salinity water flooding. The typical description of this phenomenon on oil and water relative permeability curves is being put forward by the process-dependent interpolation function, which barely addresses the underlying fundamentals governing the direct impact of wettability alteration and geochemical reactions on flow saturation functions. The main objective of this work is to perform an integrated investigation of the effect of salinity on oil and water relative permeability curves by dynamic coupling of the Derjaguin, Landau, Verwey, and Overbeek (DVLO) theory and geochemical reactions. We studied both the single and two-phase systems using the basis of the geochemical reactions to track the variations of the wetting and non-wetting phase relative permeability curves. In the single-phase scenario, the results show the superiority of the reactive flow modeling technique with kinetic-controlled reactions, in the range between [2–4] of the Damkohler number, to yield a better result for the experimental effluent ions' concentrations than the equilibrium approach. In addition, the single-phase results under dynamic conditions propose Civan correlation as the best predictor of residual resistance factor (RRF) by numerically adjusting the correlation of coefficients based on the physical variables - salinity, dimensionless consumed ion concentration, and Peclet number. Accordingly, the results indicate a novel linkage between the single-phase and two-phase results in the sense that RRF under single-phase mode can be used to estimate the change in the wetting phase relative permeability under the two-phase mode. The single-phase methodology provides the capability for an improvement – up to 15% - in the prediction of the pressure drop curve. For two-phase cases, our procedure involved coupling the characterized geochemical reactions and the DLVO theory to consider the effect of injected water composition on contact angle as the static two-phase parameter. The phase-field method is coupled with DLVO theory to calculate the relative permeability curves for the non-wetting phase, which corresponds to the contact angle at each simulation time step. The two-phase results indicate an improvement – up to 30% - in the prediction of the recovery factor curve, on a history-matching basis, using the DLVO theory with contact angle-dependent correlation of non-wetting phase relative permeability curve. The main novelties of this study are using the single-phase dynamic permeability impairment results in calculating the variation of the wetting-phase relative permeability curve. Moreover, dynamic coupling of DLVO and non-linear contact angle-dependent correlation is used to calculate the non-wetting phase relative permeability curve. According to these novelties, more accurate prediction of the laboratory production profiles can be obtained. [Display omitted] • Tuning the reaction properties in reactive modeling for specific Damkohler numbers. • Discussing the major mechanisms of low-saline flooding in dolomitized limestones. • Involving the effect of Residual Resistance Factor on the shift of K rw curve. • 30% better prediction of recovery profiles via a new K ro coupling method [ABSTRACT FROM AUTHOR]

Molecular diffusion of acid into a porous carbonate medium is usually referred to as acid imbibition. Accurate prediction of acid penetration into a formation and reaction with rock is not possible without a comprehensive understanding of the acid diffusion process and associated parameters. This work aimed to derive an analytical solution for mineral-dissolution reactive diffusion when acid imbibes into a rock surface and where there is no flow condition under laboratory conditions. For the experimental part of the study, different disk samples of Eagle Ford shale were selected, and the effect of acid diffusion on the rock surface was fully investigated. Digital microscopic images confirm that with differing concentrations of consumed acid and saturation front movement, varying degrees of reactivity are conceivable, including surface reaction, surface dissolution, matrix acidizing, and induced fracturing. For the mathematical modeling section, a continuity equation without an advection term and only a diffusion term was considered. An analytical solution was found for the dissolution of minerals as a result of reactive imbibition in a porous medium with porosity variations. The final form of the equation and the analytical solution is proposed here for the first time. Additional experiments were performed on Indiana limestone samples as control tests, with all experimental results matching perfectly with the developed analytical solution. Data from the literature relating to different temperatures also matched appropriately with the mathematical solution, effectively affirming the validity of the suggested solution. The proposed approach can be used as a predictive tool to verify the reactive models leading to porosity creation in the field scale. • Mathematical modeling and analytical solution for acid diffusion into the carbonaceous formations. • Experimental setup preparation and validation of mathematical model with experimental data. • Sensitivity analysis on the effective parameters of acid diffusion and investigating the extent of each parameter. [ABSTRACT FROM AUTHOR]

The implication of entropy analysis is noticed in various processes like cooling system, heat exchangers, thermal systems, thermal power plants, combustion, porous media, turbine systems and nuclear reactions etc. In view of such thermal applications, the theme of this paper is to analyze the entropy optimization in chemical reactive flow of Darcy-Forchheimer viscous liquid with Lorentz force by a stretched bended sheet. Energy equation is developed through thermodynamics first law with radiation, magnetic field, heat generation and dissipation. Entropy is calculated through second law of thermodynamics. Furthermore, chemical reaction is addressed. Here heat transport phenomena for both prescribed surface temperature (PHF) and prescribed heat flux (PST) types are discussed. The proposed systems are modeled in a curvilinear coordinate. Nonlinear dimensionless systems are obtained through implementation of suitable variables. The proposed systems are solved for convergent solution through numerical approach (ND-solve method). Significant effect of entropy generation, fluid flow, concentration, thermal filed and Bejan number against influential variables are studied. Computational analysis of skin friction and thermal transport rate via flow variables are discussed. Here heat transport rate for both (PHF) and (PST) cases are studied. A reverse scenario is seen for fluid flow and thermal field through Hartman number. A decrement in fluid flow is noticed for porosity variable. A similar impact holds for entropy rate and thermal field through radiation effect. An intensification in curvature variable improves both fluid flow and concentration. A reverse trend for Bejan number and thermal field is seen through Brinkman number. Reduction occurs in concentration with higher Schmidt number. An amplification in drag force is observed for Hartman number, while reverse effect holds for curvature variable. An intensification in porosity variable rises both entropy and Bejan numbers. Higher approximation of curvature parameter reduces thermal transport rate for prescribed surface temperature (PHF) while reverse trend holds for prescribed heat flux (PST). • Darcy-Forchheimer viscous liquid flow by a curved stretching surface is scrutinized. • Heat source/sink, Joule heating and dissipation effect are discussed in energy equation. • Physical feature of irreversibility exploration is addressed. [ABSTRACT FROM AUTHOR]

Matrix acidizing is a common practice in well stimulation to increase the permeability of carbonate formations and then facilitate the oil flow to the wellbore. The acidizing operation is accomplished by injecting reactive fluids to dissolve and disperse the rock while creating highly conductive wormholes. Modeling and numerical simulations of carbonate acidizing present an effective tool to determine dynamic behavior trends and when supported by experimental studies may provide useful guidance to design successful matrix treatment. In this work, we develop and validate a 3D core scale predictive model for carbonate acidizing, benchmarked by linear core flooding experiments. The model employs the two-scale continuum approach to simulate reactive fluid flows and wormhole propagation in carbonate rocks. It takes CT porosity scans along with detailed knowledge of measured reaction kinetics to describe the reactive transport of acid species at Darcy scale and accounts for the underlying physics at the pore-scale through structure–property relationships which couple the local permeability, porosity, pore radius, and solid–fluid interfacial area. The present model shows a good capability to qualitatively capture the experimentally observed wormhole morphology and quantitatively predict the pore volume to breakthrough. Furthermore, we employ the two- and three-dimensional versions of the cluster multiple labeling technique to characterize the wormhole formation and penetration for varying operating conditions. Distinctive and informative features in terms of wormhole distribution and size are obtained. The three-dimensional clustering technique show the generation of more wormholes with higher ability to sustain during the acidizing process when injecting the acid at the optimal rate. The two-dimensional analysis enables to track the growth and death of transverse wormholes. It is used to show the effect of rock heterogeneity in creating highly branched wormholes, useful in providing more low-resistance paths for the oil to flow from the reservoir to the wellbore. Finally, we introduce a novel concept for real-time monitoring and control of matrix acidizing. This concept is based on performing resistivity measurements while injecting acid to track wormhole penetration. These measurements are observed to be informative of the acidizing regime. The objective is to show the potential use of resistivity logging tools in the field to achieve successful matrix treatment. [ABSTRACT FROM AUTHOR]

In this work, we present a new formulation to study the flow of a reactive non-Newtonian fluid in porous media. The mathematical model consists of a two-scale continuum model that couples information from the pore scale to Darcy one. In the place of the traditional Darcy Law, we consider a complete linear momentum equation, based on the Continuum Theory of Mixtures. The upscaling is made by an interaction source term that corresponds to the flow resistance caused by the matrix inside the pores, which considers the non-newtonian nature of the fluid. Motivated by the often applied self diverting acids we analyze the rheological dependence on the local level of p H. Simulations are performed using the finite volume method with the OpenFOAM software. We investigate the influence of the Damköhler number and the power-law index over dissolution patterns and Pore Volume to Breakthrough (PVbt) curves. The results are compared with the corresponding Newtonian cases. The effect of both shear rate and p H on viscosity are also studied. We verify a significant dependency of the dissolution patterns and also in the optimum injection rate on the rheology of the fluid. More shear-thinning fluids lead to lower values of PVbt. Although the divergent acids were really able to find different paths for the breakthrough, higher times were needed for this achievement. • The acidizing process in carbonate reservoir are numerically simulated. • A general approach is employed to take into account non-Newtonian effects. • A large range of the Damköhler number is explored. • Dissolution patterns and PVBT are obtained in a variety of scenarios. • The pH and the power-law index have a significant influence on the results. [ABSTRACT FROM AUTHOR]

Abstract: Sulphate scaling can have a disastrous impact on oil production in waterflood projects with incompatible injected and formation waters. This is due to precipitation of barium/strontium sulphate from the mixture of both waters and the consequent permeability reduction resulting in loss of well productivity. The system where sulphate scaling damage occurs is determined by two governing parameters: the kinetics coefficient characterising the velocity of chemical reaction and the formation damage coefficient reflecting permeability decrease due to salt precipitation. Previous work has derived an analytical model-based method for determination of two coefficients from laboratory corefloods during quasi-steady state commingled flow of injected and formation waters. The current study extends the method for determination of kinetics and formation damage coefficients from production well data consisting of barium concentrations in the produced water and of well productivity decline. We analyse production data for five wells from giant offshore field A, submitted to seawater flooding (Campos Basin, Brazil), and obtain values of the two sulphate scaling damage parameters. The two coefficient values were used for prediction of productivity decline for these wells. The values of kinetics and formation damage coefficients as obtained from either laboratory or field data vary in the same range intervals. These results validate the proposed mathematical model for sulphate scaling damage and the analytical model-based method “from lab and wells to wells”. [Copyright &y& Elsevier]

Abstract: Commingled injection of seawater with produced water is an option for offshore fields submitted to waterflooding. It resolves the problems of produced water disposal and of the reservoir pressure maintenance. The presence of barium (strontium) in the formation water and consequent sulphate scaling with seawater flooding is a wide spread phenomenon. In this case, the produced water also contains some barium, which results in sulphate scaling in injection well during commingled injection with seawater. One of the ways around to avoid injectivity damage during the commingled injection of incompatible waters is using a sulphate reduction plant. Being mounted on sea platform, the plant significantly reduces sulphate concentration in seawater and allows using it for commingled produced water re-injection (PWRI). Low sulphate seawater injection together with PWRI causes low injectivity decline and makes it feasible to apply in offshore waterflood projects. Planning and design of commingled PWRI with low sulphate seawater injection includes choice of the ratio “produced water:seawater”, determination of maximum allowed sulphate concentration in seawater after treatment, and injectivity decline prediction. The reliable design and plan is based on mathematical modelling with well-known model coefficients. In the current paper we derive an analytical model for the co-injection of low sulphate seawater with barium-containing produced water. Reagent and deposit concentrations along with the injectivity index are expressed by explicit formulae. It was found out that bulk sulphate deposition occurs in the 10–20 well radius neighbourhood. The injectivity decline is one order of magnitude higher than the productivity decline under similar reservoir conditions. Calculations for sulphate reduction plant have been performed for six fields of Campos Basin (Brazil). [Copyright &y& Elsevier]

The reactive transport process in oil gas reservoirs is complicated due to the coupling between dissolution and precipitation. In the present study, based on lattice Boltzmann method, the coupled dissolution and precipitation process in randomly generated porous media by quartet structure generation is investigated at the scale of geological pores. The fluid velocity, temperature and concentration in porous media are solved by multicomponent flow lattice Boltzmann model, multicomponent thermal lattice Boltzmann model and mass transport lattice Boltzmann model, respectively. The solid phase is updated by volume of pixel method. The results show that the dissolution reaction rate has a positive impact on the consumption of reactants. For different precipitation reaction rates, there exists an optimal value resulting in abundant precipitate and sparse solid distribution. Reaction equilibrium constant affects reaction rates slightly but influence the solid morphology heavily. The coupled dissolution and precipitation process accelerates with the increase of Peclet number, but the precipitate produced increases with the decrease of Peclet number. • The coupled dissolution and precipitation process in porous media is investigated by LBM. • The coupled process happens seriously firstly and then slows down with increasing reaction time. • Porous media morphology difference increases with increasing reaction time. • The final produced precipitate increases with decreasing Pelect number. [ABSTRACT FROM AUTHOR]

Complex geochemical reactions can occur during the water and CO 2 flooding for improved oil recovery, influencing the reservoir porosity and permeability, especially for low-permeability reservoirs. Core flooding experiments can be adopted to assess this effect, but it usually takes months or even years to accomplish. In this study, scaling and geochemical reaction experiments were firstly conducted to investigate the precipitation and dissolution of the main minerals induced by water and CO 2 injection, based on a typical low-permeability oil reservoir in Xinjiang Oilfield China. Secondly, reactive flow simulation models were then established, based on the experimental data, to evaluate the influence of the geochemical reactions on the porosity and permeability in the reservoir. The experimental results show that the injection water can result in severe mineral precipitation after it mixes with the original formation water, while the injected CO 2 can acidize the formation water and result in the dissolution of some minerals (e.g. calcite and silicate) and precipitation of dolomite, which can change the composition of the formation water. The simulation results show that severe carbonate precipitation can occur near the injection well, resulting in a decrease in porosity and permeability after 10 years of water injection. However, the change of rock minerals induced by CO 2 injection can cause a slight increase in porosity and permeability near the injector, which benefits the injection of ultra-low permeability reservoirs. Therefore, CO 2 flooding is recommended for improved oil recovery. • Geochemical reactions during water and CO 2 flooding were contrastively analyzed. • Water compatibility experiments show serious scaling occurs after water injection. • CO 2 geochemical reaction experiments indicate mineral dissolution is not strong. • Calcite precipitation reduces the permeability by 10% during the water flooding. • CO 2 geochemical reactions slightly increase the permeability during CO 2 flooding. [ABSTRACT FROM AUTHOR]

Acid stimulation has been used worldwide as a stimulation technique either by matrix acidizing to remove the near-wellbore permeability impairment which is referred to as formation damage or acid fracturing to enhance the connectivity between wells and reservoirs. Carbonate acid stimulation improves the near-wellbore permeability through the creation of deeply penetrating fluid pathways referred to as wormholes. The stimulation success depends on the length and width of these wormholes. Here, we test the results of a theoretical study which suggests that the effect of acid flow in a reactive porous medium can be fully defined by just two significant dimensionless numbers, the non-dimensional Damköhler and Péclet numbers. The approach was validated in an idealized numerical study and is here tested in a systematically controlled laboratory experiment for real carbonate rocks. In order to obtain statistically meaningful results, we pushed the envelope by testing the prediction of the critical point for the wormholing phenomenon in a difficult domain, where sufficient randomly distributed pathways exist such that the wormholing domain is rarely achieved. The result confirmed that for a randomly-structured highly porous media, the critical point for dissolution pattern formation including the wormholing phenomenon can be fully captured by a domain diagram of inverse Damköhler versus Péclet number as predicted by the theoretical model. The model also holds for moderately tight formations, however, breaks down when the natural permeability drops well below 100 mDarcy. We conclude that the result of this research can be applied to reliably predict the wormholes initiation and various dissolution structures under various injection rate and HCl-concentration. • The effect of HCl-concentrations at different injection rates on highly porous carbonate samples. • The dimensionless numbers Damkhöler and Péclet govern the flow of stimulation fluids throughout matrix stimulation. • Comparison and validation of laboratory core flooding results against numerically constructed phase dissolution plot. • Gaseous C O 2 phase increases resistance to flow and hence affect the pressure drop. • Wormhole prediction using phase dissolution plot based on dimensionless numbers. [ABSTRACT FROM AUTHOR]

Characterizing the process of dissolution in porous media by thermally energized reactants is of great importance to different aspects of the geothermal science and petroleum industry. Notably for the petroleum industry, understanding the porosity-permeability relationship in different dissolution regimes significantly helps the optimal design of wellbore acidizing processes. Thus, in this paper, reactive flow of a non-isothermal solvent in a complex porous medium is studied at pore scale and the evolution of permeability values with dissolution advancement are thoroughly investigated. Dimensional analysis of the governing transport equations is also performed and it is shown that generally 10 dimensionless numbers characterize such processes. The effects of Arrhenius number (A r), temperature ratio (ψ), Peclet (P e) and Damkohler (D a) on morphology is investigated in a wide range and the corresponding porosity-permeability diagrams are presented for each regime. It is also found that at high P e and D a where initially wormhole pattern would be dominant, decrease of ψ below 1 (injection of cooler reactant), delays face dissolution and shifts the dissolution shape toward a more uniform pattern. In contrast, by letting ψ > 1 (injection of warmer reactant), the pattern shifts toward a more facial dissolution whose intensity is characterized by A r. At low P e and high D a , it is found that face dissolution pattern would be dominant and letting ψ > 1 does not considerably affect the pattern. However, if ψ is lowered below 1, the local reaction rates are decreased and dissolution pattern slightly shifts toward a more uniform dissolution. Finally, when both P e and D a are low, a competition between face dissolution and uniform dissolution is established. In this case, letting ψ < 1 reduces the local D a and leads to a more uniform dissolution and if ψ > 1 , the pattern shifts to a more facial one. The role of A r is also discussed and shown to act as an amplifier for ψ effects. • Dissolution of porous media is studied at pore scale by lattice Boltzmann method. • Reaction coefficient is assumed as a temperature-dependent parameter. • Dimensional analysis of the coupled heat and mass transfer problem is presented. • Temperature ratio of the medium shows degree of deviation from initial Damkohler. • Arrhenius number is found to have amplification effects on temperature ratio. [ABSTRACT FROM AUTHOR]

Matrix acidizing is a stimulation technique to improve oil recovery in carbonate reservoirs. In this work, a new two-scale continuum model is used to study acidizing process in radial flow. Naiver-Stokes_Darcy equation is adapted to quantity fluid velocity instead of Darcy's law. Furthermore, the continuity equation of fluid phase is redeveloped to consider mass exchange between fluid and solid phases. Based on this model, several numerical case studies are conducted to ascertain effect of acid and rock physical parameters. Results show that acidizing process is obviously affected by acid injection velocity and acid surface reaction rate. Ignoring the mass exchange term between fluid and solid phases results in an overestimation of pore volume to breakthrough. Darcy's law is not applicable when acid is injected into core sample at low velocity. Pore volume to breakthrough calculated by original two-scale continuum model based on the Darcy equation is much lower than that calculated by updated two-scale continuum model based on Naiver-Stokes_Darcy equation with low acid injection velocity. The simulation results are compared with available experimental data and are found to keep a consistent pattern. • A new two-scale continuum model is used to study acidizing process in radical flow. • Naiver-Stokes-Darcy equation is adapted to quantity fluid velocity instead of Darcy's law. • Mass conservation equation of fluid phase is modified to consider mass exchange between fluid and solid phases. • Several numerical case studies are conducted to ascertain effect of acid and rock physical parameters on acidizing results. [ABSTRACT FROM AUTHOR]

Oil and gas wells across different offshore fields are currently experiencing plugging and abandonment. With this comes the risk associated with leakage of fluids from wellbores. One area of the long-term integrity of oil and gas wells that has received less attention is the geochemical assessments of cement and cement-rock integrity. This study investigates rock-fluid-cement interactions over long time scales using numerical models of coupled heat and fluid flow and reactive solute transport. Four different kinds of brine compositions from the Gulf of Mexico formations are used to simulate chemical interactions in wellbore plug, cement, and adjacent rock. Porosity changes are used as indicators of the geochemical integrity of the plugging and cement materials. Results demonstrate the impact of temperature, pH, and depth of cement placement in integrity predictions. At greater depths, higher temperatures and pressure will be encountered leading to the precipitation of gypsum and the dissolution of ettringite, calcite, and portlandite which adversely affects the integrity of the wells. The cement-rock interface is a zone of vulnerability and subject to greater loss of integrity. Other modeling parameters from our study which influenced integrity include reactive areas, diffusion coefficients, flux rates, boundary conditions, and the presence of mechanical damage. This study highlights the importance of brine specific geochemical assessments as well as the importance of thermodynamic properties when investigating geochemical wellbore integrity, and the approach used can be applied by practitioners for predictive analysis of geochemical longevity of cement and plugs in subsurface conditions. [Display omitted] • Fluid-rock-cement interactions impact geochemical integrity of cement. • Portlandite, calcite, ettringite, and friedel salt are cement mineralogic constraints. • Temperature, pH, fluid composition and flux rates are major factors. • Cement-rock interfaces are zones of increased reactions that affect integrity. • Pre-existing mechanical damages in cement are also zones of increased reactions. [ABSTRACT FROM AUTHOR]

Matrix acidizing is one of the most effective stimulation techniques to achieve industrial development of carbonate reservoirs. In this work, a two-scale continuum model is modified to consider mass conversion between liquid and solid phases. The results show that the mass conversion between liquid and solid phases is very important and nonnegligible. Compared to modified model, original model overestimates amount of acid required for core breakthrough. A series of numerical cases based on modified model are presented for sensitivity studies on acid injection conditions, core geometries, acid, and rock properties. The modified model can well capture optimum acid injection velocity and typical dissolution patterns observed in experimental studies. Pore volume to breakthrough (PVBT) is very sensitive to acid injection concentration and acid surface reaction rate. Increasing injected acid concentration substantially reduces the amount of solute required but acid injection mass does not change significantly. Strong acid can effectively reduce least pore volume to breakthrough (PVBT) but meanwhile optimum acid injection velocity obviously increases. The simulation results are compared with available experimental and numerical data and found to attain a consistent match. In this work, a two-scale continuum model is modified to consider mass conversion between liquid and solid phases. The results show that compared to modified model, original model overestimates amount of acid required for core breakthrough and the difference is mainly reflected at intermediate acid injection velocity. Image 1 • Continuity equation in two-scale continuum model is modified to consider mass conversion between fluid and solid phases based on mass conservation of each component in both fluid and solid phases. • A very comprehensive sensitivity discussions on acid injection conditions, core geometries, acid and rock properties are presented. • Acid injection mass required to breakthrough is calculated to study effect of parameters used to define pore volume to breakthrough (PVTB). [ABSTRACT FROM AUTHOR]

Reactive flow happens during carbonate rock acidification. In the present study, carbonate rock dissolution process is investigated by lattice Boltzmann method at pore scale. The two immiscible fluids flow, solute transport and heat transfer are solved by the Shan-Chen multiphase multicomponent lattice Boltzmann model, mass transport lattice Boltzmann model and multicomponent thermal lattice Boltzmann model, respectively. The solid phase is updated by Volume of Pixel method. The results show that the immiscible phase has negative effect on dissolution, while positive effect on acid penetration. The immiscible phase effect is influenced by the inlet velocity, porous media porosity, surface wettability and temperature. The increasing inlet velocity and temperature accelerate the dissolution rate, but decrease the degree of immiscible phase suppression on dissolution. The surface wettability impact on dissolution process is influenced by the immiscible phase distribution. The porosity affects the degree of immiscible phase suppression on dissolution process slightly. • Pore-scale reactive flow in porous media is investigated by LBM. • The immiscible phase promotes the solid dissolution before a certain time. • The solid dissolution and acid breakthrough rates increase with increasing inlet velocity. • The increasing temperature accelerates dissolution rate but reduces immiscible phase influence degree. [ABSTRACT FROM AUTHOR]

Reactive flows in porous media have complex behavior that is influenced by the properties of rocks (e.g., composition, structure) and fluids. In this study, the interaction of citric acid, as a weak acid, with a sandstone core containing ankerite cement was investigated during matrix acidizing. The model, developed in Python, implemented a global implicit numerical approach to consider acid-rock geochemical interactions. The effect of multi-step dissociation of citric acid on lowering rock pH was investigated. The sugar-lump approach was used to estimate the behavior of the ions concentration originated from the variation of the reactive surface area (RSA). The model outputs were validated against matrix sandstone acidizing experiments from the literature. By assuming ankerite as the main reactive mineral and considering several other aqueous reactions, the ions concentration changes (e.g., C a 2 + , F e 2 + , and M g 2 + ) of the acidizing experiments were correctly predicted. The effect of the uncertainty of the input parameters on the predictions of the model (i.e., ions concentration) was evaluated using the Monte Carlo method. The geochemical model explained the reaction rate evolution during citric acid injection and evaluated its capacity on dissolving carbonate cement (i.e., ankerite). During the acidizing process, the sandstone RSA increases, achieves a maximum value, and finally decreases. Moreover, the results indicate that the dissociation steps of citric acid have a direct effect on the prediction of acidizing performance. • The geochemical interactions of citric acid with sandstone cores containing ankerite were investigated. • A geochemical model was developed in Python to consider acid-rock geochemical interactions. • Sugar-lump approach was used to estimate ions concentration originated from variation of reactive surface area (RSA). • During acidizing, the sandstone RSA increases, achieves to a maximum value, and finally decreases. • The dissociation steps of citric acid have a direct effect on the prediction of acidizing performance. [ABSTRACT FROM AUTHOR]