MR41C-2647
Coupled Mineral Dissolution and Precipitation Reactions in Shale-Hydraulic Fracturing Fluid Systems
Thursday, 17 December 2015
Poster Hall (Moscone South)
Claresta M Joe-Wong1, Anna L Harrison2, Dana Thomas3, Megan Kathleen Dustin4, Adam D Jew4, Gordon E Brown4, Katharine Maher4 and John Bargar5, (1)Stanford University, Department of Geological Sciences, Stanford, CA, United States, (2)Stanford University, Geological Sciences, Stanford, CA, United States, (3)Stanford Earth Sciences, Stanford, CA, United States, (4)Stanford University, Stanford, CA, United States, (5)Stanford University, Los Altos Hills, CA, United States
Abstract:
Hydraulic fracturing of low-permeability, hydrocarbon-rich shales has recently become an important energy source in the United States. However, hydrocarbon recovery rates are low and drop rapidly after a few months. Hydraulic fracture fluids, which contain dissolved oxygen and numerous organic additives, induce dissolution and precipitation reactions that change the porosity and permeability of the shale. To investigate these reactions, we studied the interactions of four shales (Eagle Ford, Barnett, Marcellus, and Green River) with a simulated hydraulic fracture fluid in batch reactors at 80 °C. The shales were chosen for both economic viability and chemical variety, allowing us to explore the reactivities of different components. The Eagle Ford shale is carbonate rich, and the Green River shale contains significant siderite and kerogen. The Barnett shale also has a high organic content, while the Marcellus shale has the highest fractions of clay and pyrite. Our experiments show that hydrochloric acid in the fluid promotes carbonate mineral dissolution, rapidly raising the pH from acidic to circumneutral levels for the Eagle Ford and Green River shales. Dissolution textures in the Green River shale and large cavities in the Barnett shale indicate significant mineralogical and physical changes in the reacted rock. Morphological changes are not readily apparent in the Eagle Ford and Marcellus shales. For all shales, ongoing changes to the solution Al: Si ratio suggest incongruent aluminosilicate dissolution. Siderite or pyrite dissolution occurs within days and is followed by the formation of secondary Fe precipitates in suspension and coating the walls of the reactor. However, little evidence of any coatings on shale surfaces was found. The net effect of these reactions on porosity and permeability and their influence on the long-term efficacy of oil and gas recovery after hydraulic fracturing are critical to the energy landscape of the United States.
