Dense, viscous brine behavior in heterogeneous porous medium systems

The behavior of dense, viscous calcium bromide brine solutions used to remediate systems contaminated with dense nonaqueous phase liquids (DNAPLs) is considered in laboratory and field porous medium systems. The density and viscosity of brine solutions are experimentally investigated and functional forms fit over a wide range of mass fractions. A density of 1.7 times, and a corresponding viscosity of 6.3 times, that of water is obtained at a calcium bromide mass fraction of 0.53. A three-dimensional laboratory cell is used to investigate the establishment, persistence, and rate of removal of a stratified dense brine layer in a controlled system. Results from a field-scale experiment performed at the Dover National Test Site are used to investigate the ability to establish and maintain a dense brine layer as a component of a DNAPL recovery strategy, and to recover the brine at sufficiently high mass fractions to support the economical reuse of the brine. The results of both laboratory and field experiments show that a dense brine layer can be established, maintained, and recovered to a significant extent. Regions of unstable density profiles are shown to develop and persist in the field-scale experiment, which we attribute to regions of low hydraulic conductivity. The saturated-unsaturated, variable-density ground-water flow simulation code SUTRA is modified to describe the system of interest, and used to compare simulations to experimental observations and to investigate certain unobserved aspects of these complex systems. The model results show that the standard model formulation is not appropriate for capturing the behavior of sharp density gradients observed during the dense brine experiments

Buoyancy Effects on Upward Brine Displacement Caused by CO2 Injection

Upward displacement of brine from deep reservoirs driven by pressure increases resulting from CO{sub 2} injection for geologic carbon sequestration may occur through improperly sealed abandoned wells, through permeable faults, or through permeable channels between pinch-outs of shale formations. The concern about upward brine flow is that, upon intrusion into aquifers containing groundwater resources, the brine may degrade groundwater. Because both salinity and temperature increase with depth in sedimentary basins, upward displacement of brine involves lifting fluid that is saline but also warm into shallower regions that contain fresher, cooler water. We have carried out dynamic simulations using TOUGH2/EOS7 of upward displacement of warm, salty water into cooler, fresher aquifers in a highly idealized two-dimensional model consisting of a vertical conduit (representing a well or permeable fault) connecting a deep and a shallow reservoir. Our simulations show that for small pressure increases and/or high-salinity-gradient cases, brine is pushed up the conduit to a new static steady-state equilibrium. On the other hand, if the pressure rise is large enough that brine is pushed up the conduit and into the overlying upper aquifer, flow may be sustained if the dense brine is allowed to spread laterally. In this scenario, dense brine only contacts the lower-most region of the upper aquifer. In a hypothetical case in which strong cooling of the dense brine occurs in the upper reservoir, the brine becomes sufficiently dense that it flows back down into the deeper reservoir from where it came. The brine then heats again in the lower aquifer and moves back up the conduit to repeat the cycle. Parameter studies delineate steady-state (static) and oscillatory solutions and reveal the character and period of oscillatory solutions. Such oscillatory solutions are mostly a curiosity rather than an expected natural phenomenon because in nature the geothermal gradient prevents the cooling in the upper aquifer that occurs in the model. The expected effect of upward brine displacement is either establishment of a new hydrostatic equilibrium or sustained upward flux into the bottom-most region of the upper aquifer

Numerical Studies of Co2 Leakage Remediation by MICP-Based Plugging Technology

Microbially induced calcite precipitation (MICP) is a technology for sealing leakage paths to ensure the safe storage of ��! in geological formations. In this work we introduce a numerical simulator of MICP for field-scale studies. This simulator is implemented in the open porous media (OPM) framework. We compare the numerical results to simulations using an upgraded implementation of the mathematical model in the MATLABÒ reservoir simulation toolbox (MRST). Finally, we consider a 3D system consisting of two aquifers separated by caprock with a leakage path across the width of the reservoir. We study a strategy where microbial solution is injected only at the beginning of the treatment and subsequently either growth solution or cementation solution is injected for biofilm development or calcite precipitation. By applying this strategy, the numerical results show that the MICP technology could be used to seal these leakage paths.publishedVersio

PVT and Flow Behavior of Impure CO2 in Aquifers

We combine compositional modelling of a Brine-CO2 system with detailed resolution of the well interface and the near-well reservoir region. Via a small selection of case studies, we explore how impurities added to a CO2 injection stream impacts reservoir flow and well response

Numerical Studies of Co2 Leakage Remediation by MICP-Based PluggingTechnology

Microbially induced calcite precipitation (MICP) is a technology for sealing leakage paths to ensure the safe storage of ��! in geological formations. In this work we introduce a numerical simulator of MICP for field-scale studies. This simulator is implemented in the open porous media (OPM) framework. We compare the numerical results to simulations using an upgraded implementation of the mathematical model in the MATLABÒ reservoir simulation toolbox (MRST). Finally, we consider a 3D system consisting of two aquifers separated by caprock with a leakage path across the width of the reservoir. We study a strategy where microbial solution is injected only at the beginning of the treatment and subsequently either growth solution or cementation solution is injected for biofilm development or calcite precipitation. By applying this strategy, the numerical results show that the MICP technology could be used to seal these leakage paths

Vertical Equilibrium Flow Models with Fully Coupled Geomechanics for CO2 Storage Modeling, Using Precomputed Mechanical Response Functions

Vertical equilibrium (VE) models have proved to be attractive for simulation of \co storage scenarios. Their primary advantage is a substantial reduction in computational requirements compared to standard 3D simulation tools. In this work, we aim to include the effects of geomechanics on aquifer flow while preserving computational efficiency. When fluids are injected into a geological formation, changes in pore pressure leads to rock deformation, which influence the flow properties of the formation. To fully model this effect, a two way coupling between flow and mechanics equations is generally necessary, including the full under- and overburden. This leads to a computationally expensive system, thus reducing the computational advantage of using VE models. Within a linear poroelastic framework, the full effect of deformation on flow is captured through changes in volumetric strain, which can be precomputed for a given pressure basis at grid generation time and used directly in the flow equations during simulation. This allow us to model the full effect of geomechanics on aquifer flow while eliminating the need for solving the mechanics equations at simulation time. We demonstrate the approach on 2D and 3D examples, and compare with results obtained from a standard VE flow models and a model that includes the full poroelastic set of equations. Compared to the latter, we observe a significant computational benefit using our proposed approach. On the other hand, the impact of geomechanics appears to be primarily captured by a well-chosen rock compressibility coefficient, suggesting that a fully coupled model might not be required in many practical cases