Investigating effects of temperature and confining pressure on dynamic elastic properties and permeability—An experimental study

Unconventional reservoirs refer to hydrocarbon reservoirs that require special stimulation treatments, such as hydraulic fracturing, to economically produce hydrocarbon. These reservoirs are tight with very low permeability, less than 0.1 milli Darcy (0.1 mD). Shale oil and shale gas reservoirs are prime examples of unconventional reservoirs. Effects of temperature on unconventional reservoirs’ dynamic elastic properties and permeability are usually overlooked during laboratory measurements and reservoir simulations leading to erroneous results and unsuccessful stimulation operations. To investigate effects of temperature and confining pressure on dynamic elastic properties and permeability of unconventional core samples, two series of experiment were conducted on outcrop core samples from three prominent unconventional basins (Barnett, Wolfcamp, and Eagle Ford) in the United States. In the first set of experiments, eleven unsaturated outcrop core samples (four Barnett, four Eagle Ford, and three Wolfcamp) were used to assess effects of temperature and confining pressure on their dynamic elastic properties. In the second set of the experiments, seven core samples (two Barnett, two Eagle Ford, and three Wolfcamp) were used to study effect of temperature on their permeability at a constant confining pressure. Also, X-ray diffraction (XRD) analysis was conducted on core samples to determine the mineral compositions them. The results were then used to study effect of mineralogy on the rock samples’ dynamic elastic properties and permeability. The results of this experimental study show that increase in temperature makes the core samples more ductile and less permeable. The results also demonstrate that the degree of the effect of the temperature on the dynamic elastic properties of the samples is directly related to the presence and volume of the clay minerals.