Review of Geochemical and Geo-Mechanical Impact of Clay-Fluid Interactions Relevant to Hydraulic Fracturing

Abstract

Shale rocks are an integral part of petroleum systems. Though, originally viewed primarily as source and seal rocks, introduction of horizontal drilling and hydraulic fracturing technologies have essentially redefined the role of shale rocks in unconventional reservoirs. In the geological setting, the deposition, formation and transformation of sedimentary rocks are characterised by interactions between their clay components and formation fluids at subsurface elevated temperatures and pressures. The main driving forces in evolution of any sedimentary rock formation are geochemistry (chemistry of solids and fluids) and geomechanics (earth stresses). During oil and gas production, clay minerals are exposed to engineered fluids, which initiate further reactions with significant implications. Application of hydraulic fracturing in shale formations also means exposure and reaction between shale clay minerals and hydraulic fracturing fluids. This chapter presents an overview of currently available published literature on interactions between formation clay minerals and fluids in the subsurface. The overview is particularly focused on the geochemical and geomechanical impacts of interactions between formation clays and hydraulic fracturing fluids, with the goal to identify knowledge gaps and new research questions on the subject.

Integrated Experimental and Modeling Study of Geochemical Reactions of Simple Fracturing Fluids with Caney Shale

“…The Caney Shale is a largely unexploited but potentially economically viable unconventional petroleum formation found within the South-Central Oklahoma Oil Province (SCOOP). − This formation was regarded a source and seal formation, accounting for its present relatively unexploited status. ,,, The target for drilling in the area in the past has been the Woodford Shale, which directly underlies the Caney Shale. Though the Caney Shale is replete with recoverable hydrocarbon resources, research and exploration activity undertaken on this formation is limited.…”

Comparative Laboratory Study of the Geochemical Reactivity of the Marcellus Shale: Rock–Fluid Interaction of Drilled Core Samples vs. Outcrop Specimens

“…The dissolution of Mn can lead to the formation of amorphous hydrous silica and alumina, which can potentially clog pores within the matrix and fractures, leading to a reduction in permeability [37]. The safe limit for Mn in drinking water is 0.05 ppm, which is exceeded in all samples (average DI water: 4.10 ppm, FF: 4.85 ppm) [36,38]. The presence of high levels of Mn in the effluents could potentially have adverse effects on human health and the environment.…”

“…Cobalt can occur in shale formations as a component of clay minerals such as illite and smectite. The dissolution of Co could lead to the formation of amorphous hydrous silica and alumina, which could potentially clog pores within the matrix and fractures, leading to a reduction in permeability [38]. Cobalt is not considered to be a major environmental or health concern, and there is no established safe limit for Co in drinking water [39].…”