Derek Bammel

Graduation Semester and Year




Document Type


Degree Name

Master of Science in Earth and Environmental Science


Earth and Environmental Sciences

First Advisor

John Wickham


A significant area of research within the Oil and Gas industry centers around the understanding of rock brittleness and fracture mechanics related to inducing and extending hydraulic fractures. This study defines rock brittleness as the fracture density, or the fracture surface area per unit volume (m-1), at a particular strain state. The first goal of this research was to test whether or not the strain conditions of various rock layers were constant using a geomechanically derived equation, ����������24��2(1+��)=����1−2��+��, where Fd is fracture density, Kic is fracture toughness, u is the shear modulus, v is Poisson’s Ratio, and A and B are functions of the strain invariants. If the strain states were similar, the results would plot as a straight line with a positive slope. Analysis of the collected samples consisted of acoustic testing for P and S-wave velocities as well as mercury intrusion porosimetry for density and porosity. Fracture density measurements and samples were taking at three separate locations: Palo Duro Canyon, TX, Bighorn Basin, WY, and along Highway 90 in Del Rio, TX. The second goal was to compare the geomechanical definition of brittleness with a mineralogical brittleness definition commonly used in the industry. The mineralogical content of each sample was estimated using X-Ray Diffraction and then used to calculate the Brittleness Index (Wang and Gale, 2009) which was compared with the Geomechanical Brittleness. Since the geomechanical brittleness equation is based on fracture mechanics, the mineralogical brittleness should correlate with the geomechanical brittleness. If it doesn’t the mineralogical brittleness should be modified or discarded. Using the Geomechanical Brittleness equation, the data from Palo Duro, TX produced a positive correlation of 0.9701, indicating that the strain was constant through each layer. It was determined that a correlation can’t be definitively established for samples from Bighorn Basin, WY due to limited sampling. Finally, a poor correlation coefficient of 0.005 from the Highway 90 Road Cuts in Del Rio, TX indicates that the samples from were either subjected to different strain states or deformed beyond their tensile strength. The results for the geomechanical brittleness and mineralogical brittleness comparisons show that there is a strong positive correlation of 0.99 for the Palo Duro Canyon, TX samples. The results for Bighorn Basin, WY and Del Rio, TX suggest that the geomechanical brittleness does not correlate with the mineralogical brittleness, both yielding a low correlation coefficient. Because of the inconclusive correlation for two of the study locations, additional analysis is recommended for the samples from Del Rio, TX and Bighorn Basin, WY.


Geomechanics, Geomechanical, Rock brittleness, XRD, X-ray diffraction, Brittleness Index, Mineralogical Brittleness Index, Hydraulic fracturing, Fracture density, Fracture intensity, Fracture toughness, Stress, Strain, Shear modulus, Strain invariants, Geomechanical brittleness


Earth Sciences | Physical Sciences and Mathematics


Degree granted by The University of Texas at Arlington