DEVELOPING A MOLECULAR-LEVEL UNDERSTANDING OF THE EFFECT OF OXIDATIVE BREAKERS IN SHALE-FRACTURING FLUID INTERACTIONS: IMPLICATIONS ON HYDROCARBON RECOVERY AND CRITICAL METAL (CM) RELEASE

Unconventional shale reservoirs are essential resources for hydrocarbon (HC) extraction and potentially for critical metal mining. The technological advancements have led to improved utilization of organic-rich shales for energy extraction; however, low HC recovery and the declining oil and gas prices has pushed industry operators to use new chemical additives in an attempt to increase HC production and develop additional benefits from hydraulic fracturing (HF) such as CM recovery. Strong oxidizers known as breakers are added to fracturing fluids for increasing well productivity by improving the viscosity of gel-based fluids. These oxidizers can potentially degrade shale organic matter (OM), improve shale permeability, and release critical metals present in shale. However, OM degradation reactions and the type/amount of CMs released from such interactions are still not understood.

The goal of this study was to develop a molecular-level understanding of the fluid-rock interactions between Marcellus Shale OM and oxidizing HF fluid (HFF) at the formation temperature. Three synthetic HFF solutions containing oxidative breakers, sodium hypochlorite, sodium bromate, and ammonium persulfate, were reacted with shale OM for a 14-day period to mimic the shut-in period. The molecular structural parameters of shale OM (i.e., kerogen) were characterized before and after the reaction using ¹³C solid-state NMR analysis. In addition, the reacted fluids were characterized using ICP-MS analysis to determine the amount of CMs released. Our preliminary results indicate sodium hypochlorite, sodium bromate based HFF can significantly degrade kerogen by 46% and 60%, respectively. Interestingly, it was determined that oxidative breakers mainly degrade the protonated aromatic fraction of the kerogen and release several CMs such as V, Co, Mg, Mn, Al, Ti, and Cu. Our results demonstrate the oxidative breakers could play a key role in improving the recovery of HCs and designing strategies for CM extraction from HF operation.