Oxidizers are common hydraulic fracturing fluid components used to break viscous gels and have the potential to interact directly with the rock formation.  Commonly used oxidizers in the oilfield include persulfate, chlorite, bromate, perborate, among many others.  The chemical, physical, and mechanical effects of oxidizer-bearing hydraulic fracturing fluids upon the more reducing environment of the shale rock formation have been studied to some extent.  Recent studies have described the treatment of unconventional shales using higher concentrations of oxidizers for their potential beneficial effects upon hydrocarbon production.  The shale organic matter is susceptible to oxidation and its porosity and permeability may be enhanced upon exposure to oxidative conditions.  Fe(II) bearing minerals are also susceptible to the oxidative power of the fracturing fluid.  Fe(II) is readily leached under acidic conditions, and to a lesser degree at higher pH’s, and oxidized to Fe(III). Although it is well-established that Fe(II) is leached and oxidized under acidic oxidizing conditions, less is known about the morphologies and specific phase identities of secondary precipitates at different pH’s or oxidizer concentrations.<br/>     Here we present a systematic study of four different shales and their responses to two common oilfield oxidizers under various pH, temperature, and additive conditions.  Using a combination of electron microscopy and diffraction techniques, the current study seeks to shed light on specific phases that form under hydrothermal reservoir conditions.  Here we isolate the effects of these oxidizers upon the rock formation and determine the specific conditions under which precipitation can occur as well as the identity and morphology of the structures formed.  This work highlights the possibility of reducing shale conductivity using strong oxidizers, and the need to better understand Fe leaching and secondary precipitation.

Insights on shale iron leaching and secondary mineral crystallization through phase and morphology analysis

ACS Spring Meeting 2021

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.