FY 2017-2018, Final Report Project name: Understanding Water Controls on Shale Gas/Oil Mobilization into Fractures Contract: ESD14085 Tetsu Tokunaga, Jiamin Wan, Abdullah Cihan, Yingqi Zhang, Stefan Finsterle, Ken Tokunaga Reporting period: October 1, 2016 to September 30, 2018 Executive Summary: The overall objective of this research is to understand and predict the dynamics of hydraulic fracturing fluid interactions within unconventional shale reservoirs, focusing on the controlling roles of water at and around zones of fractures and adjacent shale matrix. To address this objective, we have conducted laboratory tests and modeling studies on water interactions with shales. Understanding gained from these activities is intended to strengthen the scientific basis for designing more effective hydraulic fracturing strategies that may ultimately maximize gas production while utilizing significantly less water [Gupta, 2009; Montgomery, 2013]. This Final Report summarizes work directed toward two general objectives. The first is to understand the coupling between water (or alternative fracturing fluids) uptake and gas counter flow (counter-current imbibition) in shales in order to help identify approaches to improving production. Under this first objective, we examined consequences of immiscible fluid displacement at fracture-shale matrix interfaces, within shale matrix blocks, and at larger scales of matrix blocks transected by fracture networks where influences of gravity drainage are potentially important (Figure 1). Understanding of the energetics of water interactions with shales and rates of water imbibition/drainage from shales is essential developing more mechanistic foundations for improving water use in hydraulic fracturing. The second general objective is to understand the influence of non-water fracturing fluids on shale gas/oil mobilization, and to identify the optimal formulas of fracturing fluids for specific oil types and reservoir wettability. In order to achieve these objectives, new experimental and modeling approaches were initiated. Activities completed though this study include (1) A set of physicochemical analyses of Woodford and Mahantango/Marcellus Shales were completed. These consisted of elemental and mineralogical analyses, and measurements bulk density, grain density, and porosity. (2) Water absorption-imbibition and drainage-desorption relations were measured in shales over wide ranges in capillary pressure and relative humidity [Tokunaga et al., 2017]. (3) Experiments that measured rates of vapor diffusion in Mahantango and Marcellus Shale sidewall cores were conducted under a relative humidity (rh) of 0.31 and 0.81 (50 ˚C). At the rh of 0.31, measurements were obtained for diffusion parallel and perpendicular to bedding planes. (4) Experiments and modeling of the influence of adsorbed water on methane adsorption in shales from the Qaidam Basin were performed in our LBNL laboratory in collaboration with the China University of Geosciences (Beijing). Much of that work was summarized in a recent publication [Wang et al., 2018]
