Visualization and Quantification of Water Spreading on Fracture Surfaces in Low Matrix Porosity Rocks ARO Research Area: 2.1 Earth Materials and Processes
Abstract
The technical objective of the proposed effort is to explore the physics of water movement on rough surfaces through investigation of the wettability and dynamics of water spreading on freshly exposed fracture surfaces in low-porosity rocks. Only one or two studies have previously investigated the wettability and dynamics of water spreading on actual rock fracture surfaces. The proposed effort seeks to achieve the stated technical objective using a four-part approach: (1) Characterize the width of the in situ damage zone and the roughness of exposed fracture surfaces. This step involves the selection of samples from a variety of low-porosity rock types. Rock cores will be oven dried and the total porosity of each core sample will be measured using a gas pycnometer and laser scanner. A simple linear fracture will be created in each core by compressive loading until failure between parallel plates following the Brazilian method. Three to four replicates will be prepared for each sample. For a subset of cores, samples will be separated along the fracture plane into two semi-cylindrical halves, each with an exposed fracture surface. (2) Quantify the wettability of exposed fracture surfaces with effective solid-liquid contact angles. Neutron tomography will be performed on the dry fractured cores to visualize variations in the width of the fracture damage zone in three-dimensions, and the resulting tomographic reconstructions will be quantitatively analyzed to determine the mean and variance of the fracture aperture width. Cores separated into two halves will be scanned to characterize the micro-topography of the exposed fracture surfaces using a non-contact optical profiling system. Fractal analyses of the fracture micro-topography data obtained using optical profilometry will be performed and used, in conjunction with solid-liquid contact angles measured on polished rock surfaces, to estimate effective solid-liquid contact angles for water on rough fracture surfaces. (3) Visualize, parameterize, and model spontaneous imbibition of water in damage zones and on fracture surfaces. Visualization and quantification of water uptake into fractured rock cores in cross-section will be performed using dynamic neutron radiography. The resulting measurements, along with estimation of parameters such as the sorptivity and dispersion coefficient, will be used to extend an existing one-dimensional model to two dimensions to quantify water uptake and spreading. (4) Identify changes in fracture hydraulic parameters due to wetting and drying. Samples will be oven-dried and reprocessed through steps (2) and (3) above to determine if the samples’ roughness elements and associated hydraulic properties change as a result of short-term weathering and erosion processes. Repeating the measurements through several wetting and drying cycles will allow identification of any weathering-induced changes over time in the wettability and/or spreading behavior of water in the fracture damage zones or on the fracture surfaces. Low matrix porosity rocks are important as natural barriers to flow and transport in the subsurface. However, fractures in these rocks can provide significant conduits for water flow. The basic research proposed here will contribute to a better understanding of the physics of water movement on rough surfaces, leading to an improved capability for predicting flow and transport in fractured rocks under variably-saturated conditions.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jan 12, 2017
- Source ID
- W911NF1610043
Entities
People
- Edmund Perfect
Organizations
- Army Contracting Command
- United States Army
- University of Tennessee