Understanding water-rock interactions occurring during hydraulic fracturing is vital to better engineer the hydraulic fracturing water. In this study, a systematic model of water-rock reactions is presented to mimic the interaction of reservoir rock with water.
To investigate the water-rock interaction Marcellus Formation was selected. The reservoir rock samples from the Marcellus Formation were first characterized for its mineral composition by an X-ray diffraction (XRD) and for its elemental composition by an X-Ray fluorescence (XRF). Based on XRD results 3 major minerals were found in Marcellus shale; quartz, calcite, and illite. Later, these minerals with high purity content were ordered from an external chemical company to prepare pseudo rock samples and single-, two-, and three- component mineral-deionized water systems were prepared. The supernatant of these solutions were analyzed for their pH, total dissolved solids (TDS) content, particle size of the colloidal system, and zeta potential of the colloidal systems.
For single-component mineral-water systems, it has been observed that pH and TDS in general give a linear relation with the mineral concentration. For two component mineral-water systems, these relations got weaker and for the three-component systems, only TDS gives good linear relation to the mineral concentration at room temperature. When the experiments repeated at 75 °C to see the effect of temperature on dissolution of minerals in a single-component system, no difference was observed in the linear relations, however, it has been observed that particle sizes of the colloidal systems for all single-component mineral-water system correlates with the TDS content of the water. It should be noted that while particle sizes measure in water gives an idea of the average size of the suspended particles in water, TDS provides information on the dissolved molecules or ionized particles in water. Moreover, we observed that for all experimental data regardless the temperature that we collected them, the TDS concentration decreases with the increase in pH.
Our results for the first time link dissolved matter concentration in water (TDS) with the colloidal system parameter (particle size) and provide an insight on how the colloidal system (suspended solids in water) can affect TDS concentration.