Summary Knowledge of water/rock interactions on the surface of fractures is important to develop an understanding of the geological structures and changes within the formation, and to determine hydraulic-fracturing (HF) performance. To obtain this knowledge, this study investigates water/shale interactions in carbonate-rich (Eagle Ford), organic-rich (Green River), clay-rich (Barnett), and other-minerals-rich (Marcellus) shale samples. Crushed shale samples were exposed to water for 3 weeks at reservoir conditions. The water and rock samples before and after each static experiment were subjected to several analyses. The change in the rock mineralogy was defined by X-ray diffraction (XRD), the elemental composition of rock was determined by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy energy dispersive spectroscopy (SEM-EDS), and the organic content of rock samples was estimated by thermogravimetric analysis (TGA). The water was analyzed for its anions and cations, total dissolved solids (TDS), conductivity, pH, total organic carbon (TOC), and average particle sizes of colloids. The stability of the colloids was characterized by zeta-potential. We show that Barnett rock is high in illite content, and the greatest calcite concentration is determined for Eagle Ford. The sulfate content of water correlates with the atomic percent of the sulfur and oxygen elements determined through XPS analyses. The magnesium content of water correlates mainly with the illite amount in the rock, and calcium concentration associates with the calcite and gypsum content of the rock samples. The greatest dissolution rate belongs to the minerals that yield sulfate in the water; then, gypsum and calcite that yield calcium cation in the water come second; and the lowest dissolution rates are obtained from the magnesium-containing minerals (mainly, dolomite). TDS of the water samples shows that Green River has the least tendency to interact with water, and Barnett has the greatest tendency. Zeta-potential values indicate that particles in the water that interacted with Eagle Ford have the highest tendency for precipitation. The results of this study are used to make suggestions on the engineering of hydraulic-fracturing fluids (HFFs) in the context of water/rock interactions by considering the type and the concentration of ions along with colloidal stability determined through zeta-potential measurements.

The rapid rise of oil production from unconventional resources due to the increase in oil demand brings several potential risks to the environment. Governments strictly regulate the oil field water use, treatment, and disposal to reduce both the environmental and the public health effects. Hence, exploration and production companies face several challenges mainly for the management of produced water originated from any water injection processes. On a global scale, the average water cut has increased to nearly 75%. And in the U.S., the water cut is even higher (i.e., 91%) which results in a severe reduction in revenue. The average cost for handling and disposing water can range from $0.50 to $16.80 per barrel of water. In fact, the oil and gas industry in the U.S. spends $5-10 billion per year for the handling of the produced water. Furthermore, this cost does not take into account the loss of hydrocarbons due to the excess production of water. Therefore, it is necessary to develop new technologies for oil and gas production which will reduce (i) the water use for the sustainability of the water resources, (ii) the environmental and health effects of the produced water and (iii) the enormous costs of the produced water management. This paper evaluates both the current strategies and future trends that are followed in the U.S. to manage the produced waters originated from hydraulic fracturing, water flooding, and steam-assisted gravity drainage (SAGD). The paper first summarizes the water injection projects in the U.S. Then, the quantitative impact of each process to the human health and environment along with the differences in the quality of the produced water due to the rock-fluid interactions and the additives used in the processes are discussed. Finally, the industrial attempts on the produced water management for the reduction in water use, reuse of the produced water, and the water treatment are examined. This paper provides a critical review on current and future trends of the produced water management. The short and long term effects to the environment due to the rapid changes in the quality of the water resources are criticized.

Knowledge of water-rock interactions on the surface of fractures is important to develop an understanding of the geological structures and changes within the formation, to determine the water pollutants in produced water during hydraulic fracturing, and to manage effectively the produced waters. To obtain this knowledge, the water-shale interaction is investigated on carbonate-rich (Eagle Ford), organic-rich (Green River), clay-rich (Barnett), and other minerals rich (Marcellus) shale samples.Crushed shale samples were exposed to water for three weeks at reservoir conditions. The water and rock samples before and after each static experiment subjected to several analyses. The change in the rock mineralogy was defined with XRD, the elemental composition of rock was determined with XPS and SEM-EDS. The water was analyzed for its anions and cations, total dissolved solids (TDS), conductivity, pH, total organic carbon (TOC), and average particle sizes of colloids. The stability of the colloids are characterized with Zeta potential.It has been observed that Barnett rock is high in illite content, the greatest calcite concentration is determined for Eagle Ford rock. The sulfate source of water correlates with the atomic percent of the sulfur and oxygen elements determined through XPS analyses. The magnesium content of water correlates mainly with illite amount in the rock and calcium concentration associates with the calcite and gypsum content of the rock samples. The greatest dissolution rate belongs to the minerals which yields sulfate in the water, then, gypsum and calcite which yield calcium cation in the water come second, and the lowest dissolution rates obtained from the magnesium containing minerals mainly dolomite. TDS of the water samples shows that Green River has the least tendency to interact with water and Barnett has the greatest tendency. Zeta potential values indicate that the particles in the water interacted with Eagle Ford have the highest tendency for precipitation, since it has the lowest zeta potential value.This study provides correlations on water-rock interaction for four different shale samples. These correlations can be used to understand the water-rock interactions for different rocks by conducting simple XRD and XPS measurements only on rock samples.