X-ray monitoring in heterogeneous and fractured porous media : experimental measurement and numerical modeling

• Main Authors: Luo, Jeffery Shipeng, 0000-0003-4163-0829
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: The University of Texas at Austin 2019
• Subjects: X-ray; Porous media; Methane hydrate
• Online Access: https://dx.doi.org/10.26153/tsw/5446; https://repositories.lib.utexas.edu/handle/2152/78359

The complexity of fluid flow in heterogeneous and fractured media has long been a focus in the energy industry. Models have been developed in an attempt to determine the effects of rock heterogeneity, including fractures and laminations, on hydrocarbon flow. These models rely on an integration of data from different scales, including but not limited to seismic, core, and pore-level. This study focuses on the integration of studies at the core and pore-level through X-ray analysis of three unique projects. The first project addresses gas mobility control through X-ray micro-focus visualization of WAG core-flood experiments and interpretation aided by numerical simulation. We use surfactant as our primary mobility control agent to stabilize the nitrogen gas dispersion during WAG injection. We quantify the improvement in sweep efficiency by utilizing an automated fluid injection system monitored by an X-ray micro-focus scanner to quantify how displacement patterns and water saturation change with time. The core-flood device is wirelessly operated through a computer. The resolution of the images permits observation of not only core scale fingering but also pore-scale displacement. Results show that saturation patterns and displacement front during WAG injection are highly influenced by bedding orientation and rock heterogeneity. Without gas mobility control during WAG injection, fingering and early breakthrough occur in those cases in which bedding orientation facilitates gas to flow through high permeability layers. In these cases, sweep efficiency is low during early time injection of nitrogen and only improves after injection is prolonged. With gas mobility control, the displacement efficiency is significantly improved. Simulation work matches experimental data well and replicates saturation patterns measured experimentally in laminated Berea sandstone samples. The second project focuses on understanding how pre-existing fractures and rock heterogeneities can aid the propagation of induced fractures by 3D mapping of fracture networks in Mancos shale core plugs using X-ray micro-CT. Analysis of both intact samples and samples with pre-existing fractures show that induced fractures tend to develop along the same orientation of lamination planes, which more often than not correspond to the same orientation of any pre-existing fractures. The nature of this work requires inspection of fine fracture networks within larger specimens, so scanning at these coarser resolutions to capture the sample in their entirety leads to a compromise on the range of fracture sizes that can be accurately visualized. Moreover, existing limitations of the technique, including blurring effects further complicate interpretation. This project reviews some of these issues and remedies to overcome these limitations. The third project uses X-ray micro-CT to monitor methane hydrate growth and dissociation experiments in sands partially saturated with KI brine under excess-gas and excess-water conditions. The experiments show coexistence of brine, gas, and hydrate at the pore-scale and their evolution towards three-phase equilibrium. Analysis reveals that hydrate first forms as a porous hydrate mixing of brine and gas and then evolves into separate phases as hydrate cages exclude ions. During this time, hydrate growth mobilizes water over long distances. This mobilization of water is critical to explaining heterogeneous hydrate distribution as a result of hydrate ripening. The novel visualization of various pore-scale phenomenon presented here provides new pore-scale experimental insight to the structure and flow behavior of various heterogeneous mediums at a resolution one order of magnitude higher than with medical X-ray CT or other core-scale visualization techniques. The findings are useful for understanding complex flow patterns and structures of heterogeneous mediums.