Brittleness and Fracability Evaluation of Unconventional Reservoirs

Date
2018-05-10
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Abstract
Brittleness and fracability evaluation plays an important role in recovery of unconventional oil and gas; it directly influences the effect of hydraulic fracturing. The definition of brittleness is controversial and the existing analytical/semi-analytical models have no unified theory to support them. Brittleness and fracability evaluation is currently unreliable. Unconventional reservoirs have different confining pressure, pore pressure and temperature. Models that do not consider these influences lack accuracy in the brittleness index (BI) calculation, resulting in failure during hydraulic fracturing. This research is focused on establishing new methods for brittleness and fracability evaluation. First, analytical/semi-analytical models are proposed considering the influence of confining pressure, pore pressure and temperature, respectively. The influence of calcite on rock mechanics parameters and brittleness is compared to quartz and clay. The weight of each parameter in models based on elastic modulus and mineralogy is analyzed. Finally, a numerical method to evaluate rock brittleness in terms of energy is developed. This novel method is applied to evaluate rock brittleness and fracability in more complicated conditions by considering hydro-mechanical (HM) interaction. By defining brittleness in terms of energy, rock brittleness from different sources can be compared. The influence factors ignored by other models of brittleness evaluation: pressure, temperature and rock texture can be addressed at the same time. By combining the analytical method and the numerical method for brittleness and fracability the resulting evaluations are more applicable because they reflect a more realistic unconventional oil and gas reservoirs environment.
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Keywords
brittleness, fracability, unconventional reservoirs, Energy
Citation
Hu, Y. (2018). Brittleness and Fracability Evaluation of Unconventional Reservoirs (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca. doi:10.11575/PRISM/31917