A Critical Review of the Physicochemical Impacts of Water Chemistry on Shale in Hydraulic Fracturing Systems

Abstract

Hydraulic fracturing of unconventional hydrocarbon resources involves the sequential injection of a high-pressure, particle-laden fluid with varying pH’s to make commercial production viable in low permeability rocks. This process both requires and produces extraordinary volumes of water. The water used for hydraulic fracturing is typically fresh, whereas “flowback” water is typically saline with a variety of additives which complicate safe disposal. As production operations continue to expand, there is an increasing interest in treating and reusing this high-salinity produced water for further fracturing. Here we review the relevant transport and geochemical properties of shales, and critically analyze the impact of water chemistry (including produced water) on these properties. We discuss five major geochemical mechanisms that are prominently involved in the temporal and spatial evolution of fractures during the stimulation and production phase: shale softening, mineral dissolution, mineral precipitation, fines migration, and wettability alteration. A higher salinity fluid creates both benefits and complications in controlling these mechanisms. For example, higher salinity fluid inhibits clay dispersion, but simultaneously requires more additives to achieve appropriate viscosity for proppant emplacement. In total this review highlights the nuances of enhanced hydrogeochemical shale stimulation in relation to the choice of fracturing fluid chemistry.

Impact of Concurrent Solubilization and Fines Migration on Fracture Aperture Growth in Shales during Acidized Brine Injection

“…Flow is initiated by injecting neutral brine (pump E) at a flow rate of 0.01 mL/min at ambient pressure and temperature with no confining pressure applied on the core. The flow rate was chosen to ensure laminar flow ( Re = 1.02) with high Péclet number ( Pe = 845; fracture width (L frac width ) = 650 μm; self-diffusion coefficient of water ( D water–water ) = 2.3 × 10 –9 m 2 /s, A frac = 6 × 10 –8 m 2 ), which is consistent with the flow characteristics at the fracture/matrix interface during hydraulic fracturing operations. , After the fracture and near fracture pore space is saturated, the three-way valve is flipped and pump R is activated, thereby initiating reactive brine injection.…”

Genomic evidence for a chemical link between redox conditions and microbial community composition

“…The injected fluid mixes and reacts with natural formation waters and the fractured rock surfaces. Water that returns to the surface is initially referred to as flowback and later as produced water during the hydrocarbon production stage of the well (34). Depending on the operator, chemical oxidants may be added to the injected fracturing fluid; these enhance mineral dissolution and can also have antibacterial effects.…”

Chemically Induced Evolution of Morphological and Connectivity Characteristics of Pore Space of Complex Carbonate Rock via Digital Core Analysis

“…They argued that the significantly lower reactions rate compared to the lab‐measured batch reaction rate was caused by diffusion‐limited transport of reactants to and away from the surface in relatively stagnant regions of the pore space. Comprehensive reviews regarding the evolution of pore‐scale structure and permeability during geochemical processes are provided in (Noiriel, 2015) and (Khan et al., 2021).…”