Publications

Abstract not provided.

High and low salinity water flooding are common oil recovery processes performed in the oil fields for extracting crude oil from the reservoir. These processes are often performed sequentially, naturally establishing non-uniform salinity in the porous subsurface. In this article, we investigate oil transport in porous media induced by salinity change upon flooding with high and low salinity water. As we observe a large number of impervious dead-ends from three-dimensional imaging of the actual reservoir, we identify that these areas play an important role in oil recovery where the oil transport is governed by the salinity change rather than hydrodynamics. The salinity gradients induced upon high salinity water flooding provide pathways to enhance the transport of oil drops trapped in the dead-end regions via non-equilibrium effects. However, above a critical salinity, we observe a rapid aggregation of drops that lead to the complete blockage of the pore space, thereby inhibiting oil recovery. We also find that, at an intermediate salinity where the drop aggregation is modest, the aggregation rather promotes the oil recovery. Our observations suggest that there exist optimal salinity conditions for maximizing oil recovery during chemical flooding.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Estimation of permeability in porous media is fundamental to understanding coupled multi-physics processes critical to various geoscience and environmental applications. Recent emerging machine learning methods with physics-based constraints and/or physical properties can provide a new means to improve computational efficiency while improving machine learning-based prediction by accounting for physical information during training. Here we first used three-dimensional (3D) real rock images to estimate permeability of fractured and porous media using 3D convolutional neural networks (CNNs) coupled with physics-informed pore topology characteristics (e.g., porosity, surface area, connectivity) during the training stage. Training data of permeability were generated using lattice Boltzmann simulations of segmented real rock 3D images. Our preliminary results show that neural network architecture and usage of physical properties strongly impact the accuracy of permeability predictions. In the future we can adjust our methodology to other rock types by choosing the appropriate architecture and proper physical properties, and optimizing the hyperparameters.

Anisotropy in the mechanical properties of rock is often attributed to bedding and mineral texture. Here, we use 3D printed synthetic rock to show that, in addition to bedding layers, mineral fabric orientation governs sample strength, surface roughness and fracture path under mixed mode I and II three point bending tests (3PB). Arrester (horizontal layering) and short traverse (vertical layering) samples were printed with different notch locations to compare pure mode I induced fractures to mixed mode I and II fracturing. For a given sample type, the location of the notch affected the intensity of mode II loading, and thus affected the peak failure load and fracture path. When notches were printed at the same location, crack propagation, peak failure load and fracture surface roughness were found to depend on both the layer and mineral fabric orientations. The uniqueness of the induced fracture path and roughness is a potential method for the assessment of the orientation and relative bonding strengths of minerals in a rock. With this information, we will be able to predict isotropic or anisotropic flow rates through fractures which is vital to induced fracturing, geothermal energy production and CO2 sequestration.

Coupled poroelastic stressing and pore-pressure accumulation along pre-existing faults in deep basement contribute to recent occurrence of seismic events at subsurface energy exploration sites. Our coupled fluid-flow and geomechanical model describes the physical processes inducing seismicity corresponding to the sequential stimulation operations in Pohang, South Korea. Simulation results show that prolonged accumulation of poroelastic energy and pore pressure along a fault can nucleate seismic events larger than Mw3 even after terminating well operations. In particular the possibility of large seismic events can be increased by multiple-well operations with alternate injection and extraction that can enhance the degree of pore-pressure diffusion and subsequent stress transfer through a rigid and low-permeability rock to the fault. This study demonstrates that the proper mechanistic model and optimal well operations need to be accounted for to mitigate unexpected seismic hazards in the presence of the site-specific uncertainty such as hidden/undetected faults and stress regime.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Recent observations of seismic events at the subsurface energy exploration sites show that spatial and temporal correlations sometimes do not match the spatial order of the known or detected fault location from the injection well. This study investigates the coupled flow and geomechanical control on the patterns of induced seismicity along multiple basement faults that show an unusual spatiotemporal relation with induced seismicity occurring in the far field first, followed by the near field. Two possible geological scenarios considered are (1) the presence of conductive hydraulic pathway within the basement connected to the distant fault (hydraulic connectivity) and (2) no hydraulic pathway, but the coexistence of faults with mixed polarity (favorability to slip) as observed at Azle, TX. Based on the Coulomb stability analysis and seismicity rate estimates, simulation results show that direct pore pressure diffusion through a hydraulic pathway to the distant fault can generate a larger number of seismicity than along the fault close to the injection well. Prior to pore pressure diffusion, elastic stress transfer can initiate seismic activity along the favorably oriented fault, even at the longer distance to the well, which may explain the deep 2013–2014 Azle earthquake sequences. This study emphasizes that hydrological and geomechanical features of faults will locally control poroelastic coupling mechanisms, potentially influencing the spatiotemporal pattern of injection-induced seismicity, which can be used to infer subsurface architecture of fault/fracture networks.

Abstract not provided.

Abstract not provided.