GEOCHEMICAL CHARACTERIZATION OF HYDRAULIC FRACTURING FLUID AND UNCONVENTIONAL RESERVOIR ROCK: A STUDY OF TEMPORAL EFFECTS ON FLUID STABILITY

Technological advancements in the oil and gas industry in the past few decades has led the Marcellus Shale to be one of the most productive unconventional reservoirs in the United States. Increased production has resulted in more fundamental questions regarding how the fluids being injected interact with the reservoir. Previous research at the National Energy Technology Laboratory has characterized the geochemical and physical changes to the Marcellus Shale as a function of variable hydrofracturing fluid compositions that were based on average compositions found in the Appalachian Basin. In these studies, synthetic fracking additives were mixed up to 3 weeks prior to experimental operations and then injected into Marcellus Shale cores. This is in stark contrast to field operations where mixing of chemicals typically happens at the wellhead as fracking operations commence. Observed variations in dissolution and precipitation in these experiments is potentially due to temporal variability between mixing and injection; it is possible that the additives are degrading over time. In the current study, synthetic fracturing fluids of the same composition as the previous studies were prepared and then immediately injected into artificually fractured Marcellus Shale cores. Marcellus Shale cores were held at representative conditions of 150°F, 2,800 PSI, and 3,000 PSI for temperature, pore pressure, and confining pressure respectively. Computed Tomography and geochemistry were used to characterize the chemical and physical changes in the rock as a function of exposure time. Comparing mineral dissolution and precipitation from Computed Tomography images in conjunction with calculated mineral saturation indices, the reactivity of the fracturing fluid with the Marcellus Shale can be related to temporal differences between experiments. Results from this study will provide insight on fluid stability relative to temporal differences in preparing synthetic fracturing fluid in laboratory studies on fluid-rock interactions.