High-Pressure High Temperature Coreholder for in-situ failure characterization under thermohydromechanical loading conditions using ultrasonic monitoring
Instron triaxial load frame for failure characterization
Hydraulic fracture and natural fracture interact mechanically and hydraulically. This interaction can be modeled and upscaled in order to map hydraulic fractures in a naturally fractured rock.
Seismicity induced by fluid injection and withdrawal is a matter of public concern. We use geological, geophysical, and engineering data of real fields to model various physical processes in the subsurface for assessment and mitigation of the risks of induced seismicity. The challenge here is the multiphysics and multiscale nature of the physical problem. Fluid injection and production occurs over years and decades while a triggered event may last only for minutes. Sequentially coupled solution algorithms provide the desired numerically efficiency in such multiphysics problems.
A two-dimensional model of injection-induced slip is shown below. Aquifer is pressurized due to carbon dioxide injection, which leads to volumetric expansion of the aquifer. This builds up shear traction and reduces compression on the fault. The ratio of shear to effective normal traction at the bottom intersection point of aquifer with the fault reaches the static friction coefficient, which causes nucleation of slip at that point.
Production of oil and gas from faulted reservoirs requires assessment of the risk of inducing slip on critically-stressed faults in the reservoir.
We develop new computational frameworks to model coupled multiphase flow and geomechanics of faulted and fractured reservoirs. The challenges here are related to the mathematical formulation of the coupled problem, space discretization and time integration, design of numerically stable and computationally efficient algorithms to solve the discretized problem, and computer implementation for parallel computing.
Reservoir characterization refers to the estimation of spatial distributions of rock and fluid properties in the reservoir, such as porosity, permeability, and pore compressibility. We use ensemble-based methods to assimilate multiple sources of data such as well flow rates and pressures, surface deformation measurements from InSAR and GPS satellites, and seismic measurements from geophones, into a forward prediction model based on coupled flow and geomechanics. The challenge here is to develop a consistent and robust theory of poromechanical inversion.
Joint inversion of flow and surface deformation data is used for statistical estimation of rock properties in a gas storage reservoir. The Ensemble Smoother method is used for data assimilation and inversion.
Fluid mixing in porous media
Mixing of fluids is an important phenomenon that controls many natural and industrial processes from gravity current flows to DNA testing. Mixing in porous media and low Reynolds number flows is especially difficult because of the absence of turbulence. Development and control of mixing in such flows is an active area of research.
Mixing from viscous fingering
In enhanced oil recovery techniques such as miscible gas flooding where CO2 is injected to mix with and mobilize crude oil, recovery efficiency can be increased by developing miscibility between the two fluids. We show that viscous fingering, a type of hydrodynamic instability, can be used to induce disorder in the flow and thereby enhance mixing. Tip-splitting and channeling during viscous fingering are two different mechanisms for creation of interfacial area and subsequent mixing across the interface.
We develop a two-equation model for the concentration variance and mean scalar dissipation rate to quantify the evolution of the degree of mixing in a viscously unstable displacement. Fastest mixing is achieved by optimizing the interplay between tip-splitting and channeling mechanisms.
Stokes flow in a Hele-Shaw cell serves as a simple analog for porous media flows. We study spreading and mixing of slugs of different viscosities flowing in the gap between two parallel rigid plates.
Mixing during slug injection
Mixing at low Reynolds number can be enhanced by alternating injection of slugs of the two fluids of different viscosities, for example by solvent-alternating-gas injection during enhanced oil recovery. This is also relevant for achieving fast mixing in microfluidic flows. We show that the synergetic action of alternating injection and viscous fingering leads to a dramatic increase in the mixing efficiency at optimum viscosity contrasts.
Mixing and dilution in heterogeneous formations
Heterogeneity of the porous medium is another source of disorder in the flow that causes spreading and dilution of tracers in groundwater flows. We develop reduced-order models to describe and predict mixing during simulation of such flows.