Geochemical Modeling of Petrophysical Alteration Effect on CO2 Injectivity in Carbonate Rocks

Carbon dioxide injection into sedimentary formations has been widely used in enhanced oil recovery (EOR) and geological-storage projects. Several field cases have shown an increase in water injectivity during CO2 Water-Alternating-Gas (WAG) projects. Although there is consensus that the rock-fluid interaction is the main mechanism, modeling this process is still challenging. Our main goal is to validate a physically based model on experimental observations and use the validated model to predict CO2 injectivity alteration based on geochemical reactions in carbonate rocks. In this paper, we present a new method for CO2 reactive transport in porous media and its impact on injectivity. We hypothesize that if CO2 solubilizes in the connate water, then it induces a shift in chemical equilibrium that stimulates mineral dissolution. Consequently, porosity and permeability will increase, and cause alterations to well injectivity. We develop a predictive model to capture this phenomenon and validate the model against available data in the literature. We use UTCOMP-IPhreeqc, which is a fully coupled fluid-flow and geochemical simulator to account for rock/hydrocarbon/water interactions. In addition, we perform several experiments to test CO2/water slug sizes, mineralogy assembly, injected brine composition, and gravity segregation combined with the effect of heterogeneity. Coreflood simulations using chemical equilibrium and kinetics indicate mineral dissolution at reservoir conditions. The results suggest that the intensity of rock dissolution depends on formation mineralogy and brine composition as carbonate systems work as buffers. Additionally, we show that prolonged CO2 and brine injection induces petrophysical alteration close to the injection region. Our field-scale heterogeneous reservoir simulations show that permeability alteration calculated based on Carman-Kozeny correlation and wormhole formulation had the same results. Furthermore, we observed that water injectivity increased by almost 20% during subsequent cycles of CO2-WAG. This finding is also supported by the Pre-Salt carbonate field data available in the literature. In the case of continuous CO2 injection, the carbonate dissolution was considerably less severe in comparison with WAG cases, but injectivity increased due to unfavorable CO2 mobility. With the inclusion of gravity segregation, we report that the injectivity doubles in magnitude. The simulations show more extensive dissolution at the upper layers of the reservoir, suggesting that preferential paths are the main cause of this phenomenon. The ideas presented in this paper can be utilized to improve history-matching of production data and consequently reduce the uncertainty inherent to CO2-EOR and carbon sequestration projects.

Geochemical modeling of the leaching behavior of municipal solid waste bottom ash.

Mineral trace elements (MTE) constitute an environmental restriction on the recycling of municipal solid waste incineration-bottom ash (MSWI-BA). The study of the speciation of MTE and the factors that control their release allows to predict their behavior under different environmental conditions and, consequently, suggest different actions to expand the management of MSWI-BA.A geochemical modeling led to a better understanding of the speciation of MTE. In this study, target elements were barium, copper, lead, nickel and zinc and the factors that control their release were identified.The results show that the leaching of metals as a function of pH mainly depends on the mineralogical phases. On the other hand, the organic matter has an influence in the leaching of MTE (for Ni, Cu and Pb notably); organic matter presents adsorbent or complexation properties. Les éléments traces métalliques (ETM) constituent une restriction environnementale pour le recyclage des mâchefers d'incinération des déchets non dangereux (MIDND). L'étude de la spéciation des ETM et des facteurs qui contrôlent leur mobilité permet de prédire le comportement des MIDND dans différentes conditions environnementales et de suggérer ensuite des actions pour élargir leur gestion. Une modélisation géochimique des MIDND a permis de mieux comprendre la spéciation des ETM. Dans cette étude, les éléments ciblés étaient le baryum, le cuivre, le plomb, le nickel et le zinc et les facteurs qui régissent leur mobilité ont été définis. Les résultats montrent que la lixiviation des métaux en fonction du pH dépend principalement des phases minéralogiques ; la matière organique joue également un rôle en tant qu'adsorbant ou complexant dans la lixiviation de certains éléments (Ni, Cu et Pb, notamment). Mots-clés Mâchefers d'incinération des déchets non dangereux (MIDND), éléments traces métalliques, capacité de neutralisation acide, modélisation géochimique, PhreeqCI.

Incorporating Kinetic Modeling in the Development Stages of Hard Rock Mine Projects

Weathering cell test, designed specifically to overcome material-limited constraints, yields prompt and efficient experimental assessment during the development stages of mining projects. However, it has barely benefited from geochemical modeling tools despite their ease of use. Accordingly, this paper aims to strengthen the upstream geochemical assessment via parametric analysis that simulates the effect of various mineral assemblages on leachate quality recovered from weathering cells. The main objective is to simulate the pH in presence of silicate neutralizing minerals and Mn release from carbonates based upon minimal characterization data. The public domain code PHREEQC was used for geochemical kinetic modeling of four weathering cells. The kinetic model utilized a water film concept to simulate diffusion of chemical elements from mineral surfaces to the pore water. The obtained results suggest that the presence of the silicate neutralizing minerals slightly affects the Mn release from carbonates. Furthermore, plagioclases could supply a significant neutralization potential when they predominate the mineral assemblage. Finally, coupling weathering cell test and parametric analyses illuminate the pH evolution for various mineral proportion scenarios.

Hadean zircon formed due to hydrated ultramafic protocrust melting

Hadean zircons, from the Jack Hills (Western Australia) and other localities, are currently the only window into the earliest terrestrial felsic crust, the formation of which remains enigmatic. Based upon new experimental results, generation of such early crust has been hypothesized to involve the partial melting of hydrated peridotite interacting with basaltic melt at low pressure (<10 km), but it has yet to be demonstrated that such liquids can indeed crystallize zircons comparable to Jack Hills zircon. We used thermodynamic and geochemical modeling to test this hypothesis. The predicted zircon saturation temperatures of <750 °C, together with the model zircon Th, U, Nb, Hf, Y, and rare earth element (REE) contents at 700 °C, δ18OVSMOW (Vienna standard mean ocean water) signatures, and co-crystallizing mineral assemblage were compared to those of the Jack Hills zircon. This comparison was favorable with respect to crystallization temperature, most trace-element contents, and mineral inclusions in zircon. The discrepancy in δ18OVSMOW signatures may be explained by hotter conditions of Hadean protocrust hydration. Our work supports the idea that felsic magma generation at shallow depths involving a primordial weathered ultramafic protocrust and local basaltic intrusions is indeed a viable mechanism for the formation of felsic crust on early Earth.

Hydrochemical modeling of migration of dissolved oil products in groundwater

Изложена методика прогнозирования распространения нефтепродуктов группы BTEX (бензол, толуол, этилбензол, ксилолы) в подземных водах на основе гидрохимического моделирования с учетом изменения окислительно-восстановительных и кислотно-щелочных свойств раствора в процессе биодеградации нефтепродуктов. Представлена геохимическая модель биологического разложения нефтепродуктов комплекса BTEX на основе модифицированной кинетики Моно с учетом реакций между акцепторами, продуктами реакции биодеградации и неорганическими компонентами раствора. Приведены примеры геохимического моделирования, демонстрирующие важность учета процессов, связанных с изменением гидрогеохимической обстановки в подземных водах при разложении углеводородов. Разработанная модель может быть использована для выполнения геохимических прогнозов распространения легких нефтепродуктов в подземных водах, проведения работ в рамках оценки воздействия на природную среду, разработки систем инженерной защиты подземных вод от загрязнения нефтепродуктами. A method for predicting the spread of BTEX group oil products (benzene, toluene, ethylbenzene, xylenes) in groundwater based on hydrochemical modeling with account of changes in the redox, acidity or alkalinity of the solution during the biodegradation of oil products is stated. A geochemical model of the biological decomposition of oil products of BTEX group based on modified Mono kinetics with account of the reactions between acceptors, biodegradation products and inorganic components of the solution is presented. Examples of geochemical modeling are given that demonstrate the importance of taking into account the processes associated with the changes in the hydrogeochemical environment in groundwater during the decomposition of hydrocarbons. The developed model can be used to carry out geochemical predictions of the spread of light-end oil products in groundwater, to carry out works within the framework of estimating the environmental impact, and to develop systems for engineering protection of groundwater from oil pollution.