PHYSICOCHEMICAL EFFECTS OF SYNTHETIC HYDRAULIC FRACTURING FLUID ON CORE SAMPLES OF THE MIDDLE DEVONIAN MARCELLUS SHALE AND UNDERLYING HUNTERSVILLE CHERT, GREENE COUNTY, PENNSYLVANIA, USA

摘要

Hydraulic fracturing from directional drilling involves the injection of large quantities of fluid into the target formation, and creates a significant volume of rock with a high surface area in contact with injection fluid and associated brines. Over time, fluid-rock interactions between the saline injection fluids, formation waters released by fracturing, and the fractured rock results in physical and chemical alteration that can lead to changes in rock strength and fracture connectivity. Factors affecting alteration processes include temperature, rock mineralogy, and the composition and ionic strength of the fluids. Experiments conducted at surface (23°C) and borehole temperatures (70°C) assessed the effect of high ionic strength fluids on the mineralogical, textural and chemical characteristics of high surface area core samples of organic rich Marcellus Shale and underlying Huntersville Chert. Comparison of pre- and post-experiment fluid composition and rock mineralogy, surface area, and textures indicate that some reactions were temperature- and/or lithology-dependent. The results also suggest that fluid-rock interaction, including cation exchange reactions, sorption, mineral alteration, and dissolution and mobilization of some trace metals (e.g., nickel, boron, manganese and lithium) can be observed over short (days) time scales.