A New Geochemical Reaction Model for Groundwater Systems

Through a survey of the literature on geology, hydrogeology and hydrogeochemistry, this paper presents a hydrogeochemical model for the groundwater system in a dross-dumping area of the Shandong Aluminium Plant. It is considered that the groundwater-bearing medium is a mineral aggregate and that the interactions between groundwater and the groundwater-bearing medium can be described as a series of geochemical reactions. On that basis, the principle of minimum energy and the equations of mass balance, electron balance and electric neutrality are applied to construct a linear programming mathematical model for the calculation of mass transfer between water and rock with the simplex method.

Assessing roles of geochemical reactions on CO_(2)plume,injectivity and residual trapping

With increasing CO_(2)concentration in the atmosphere,CO_(2)geo-aequestration has become a popular technique to counter the dangers of global warming resulting from high levels of CO_(2)in the atmosphere.This paper examins sequestration parameters such as CO_(2)plume behaviour,residual gas trapping and injectivity as a means of achieving safe and successful CO_(2)storage in saline aquifers.Mineral precipitation/dissolution rates are used to establish a relationship between these parameters and geochemical reactions in saline aquifers.To achieve this,mechanistic models(6 models with different inputs,created using CMG e GEM,2016 and WINPROP,2016)are simulated using input data from literature and studying changes in fluids and formation properties as well as mineral precipitation/dissolution rates in aquifers when subjected to different conditions in the different models.The results from the models show that high CO_(2)dissolution,which creates large CO_(2)plume,leads to high mineral dissolution/precipitation as results of increased fluid-rock interactions(geochemical reactions);whereas injectivity,although enhanced by CO_(2)-water cyclic injection,does not show much increase in bottom hole pressure when mineral trapping(thus geochemical reactions)is introduced into the model.Sensitivity study on residual gas trapping shows that high residual gas saturation leads to reduced mineral precipitation/dissolution due to the reduced amount of dissolved CO_(2)in brine.Also,rapid changes in the bottom hole pressure at high residual gas saturation means that a formation that fosters high residual gas trapping,rather than CO_(2)dissolution in brine,is more likely to experience injectivity issues during the sequestration process.

A multiphysical-geochemical coupling model for caprock sealing efficiency in CO_(2) geosequestration

Precipitation or dissolution due to geochemical reactions has been observed in the caprocks for CO_(2) geosequestration.Geochemical reactions modify the caprock sealing efficiency with self-limiting or self-enhancement.However,the effect of this modification on the caprock sealing efficiency has not been fully investigated through multiphysical-geochemical coupling analysis.In this study,a multiphysical-geochemical coupling model was proposed to analyze caprock sealing efficiency.This coupling model considered the full couplings of caprock deformation,two-phase flow,CO_(2) concentration diffusion,geochemical reaction,and CO_(2) sorption.The two-phase flow only occurs in the fracture network and the CO_(2) may partially dissolve into water and diffuse through the concentration difference.The dissolved CO_(2) has geochemical reactions with some critical minerals,thus altering flow channels.The CO_(2) in the fracture network diffuses into matrix,causing the matrix swelling.This fully coupling model was validated with a penetration experiment on a cement cube and compared with two other models for CO_(2) storage plumes.Finally,the effects of geochemical reactions on penetration depth and pore pressure were studied through parametric study.The numerical simulations reveal that the coupling of geochemical reactions and matrix diffusion significantly affect the caprock sealing efficiency.Geochemical reactions occur at a short time after the arrival of CO_(2) concentration and modify the fracture porosity.The CO_(2) diffusion into the matrix requires a much longer time and mainly induces matrix swelling.These effects may produce selfenhancement or self-limiting depending on the flow rate in the fracture network,thus significantly modifying caprock sealing efficiency.

Effect of multi-component ions exchange on low salinity EOR:Coupled geochemical simulation study

The mechanism(s)of Low salinity water flooding(LSWF)has been extensively investigated for 15 e20 years,as a cost-effective and environmentally friendly technique for improved oil recovery.However,there is still no consensus on the dominant mechanism(s)behind low salinity effect due to the complexity of interactions in the Crude oil/Brine/Rock(COBR)system.While wettability is most agreed mechanism of low salinity EOR effect.Nevertheless,the mechanism(s)behind the wettability change is debated between multi-component ion exchange(MIE)and double layer expansion(DLE)in sandstone reservoirs.This paper aims to investigate the effectiveness of MIE with a coupled geochemical-reservoir model using published experimental data reported by Nasralla and Nasr-El-Din[1].We created core-scale numerical models with parameters identical to those used in the experiments.We simulated the low salinity effect using a commercial reservoir simulator,CMG-GEM,by coupling three chemical reactions:(1)aqueous reaction,(2)multi-component ion exchange,and(3)mineral dissolution and precipitation.We modelled the adsorption of divalent cations on the surface of the clay minerals during low salinity water injection.Simulation results were compared with the experimental results.Simulation results show that the fractional adsorption of divalent cations(Ca^2+)increased almost 25%by injecting a 2000 ppm NaCl solution,compared to initial 10,000 ppm NaCl.Injecting a 2000 ppm of CaCl2 solution,however,significantly increased the adsorbed Ca^2+from 0.1 to 1,which implies the complete saturation of mineral surface with divalent cations.Moreover,injecting 50,000 ppm of CaCl2 solution also demonstrated the same effect as the 2000 ppm CaCl2 solution but with a faster rate.Upon combining the simulation and experimental results,we concluded that the multicomponent ion exchange is not the sole mechanism behind low salinity effect for two reasons.First,almost 10%additional oil recovery was observed from the experiments by injecting the 2000 ppm CaCl2 compared with 50,000 ppm CaCl2 solutions.Even though in both cases the surface is expected to be fully saturated with Ca^2+according to the geochemical modelling.Second,6%incremental oil recovery was achieved from the experiments by injecting 2000 ppm NaCl solution compared with that of 50,000 ppm NaCl.Although 25%incremental adsorption of divalent cations(Ca^2+)were presented during the flooding of the 2000 ppm NaCl solution.Therefore,it is worth noting that the electrical double layer expansion due to the ion exchange needs to be taken into account to pinpoint the mechanism(s)of low-salinity water effect.