In this study, we conduct spontaneous imbibition tests and measure air-oil and air-brine contact angles of nine twin core plugs from five wells drilled in the Duvernay Formation, which is a source rock located in the Western Canadian Sedimentary Basin (WCSB). We investigate the wettability of Duvernay samples with a wide range of porosity (2.0–6.2 %B. V), TOC (2.2–6.6 wt%), kerogen type (III and IV), and kerogen maturity (wet-gas, dry-gas, and over-mature). We characterize the samples by measuring the porosity, permeability, bulk density, matrix density, mineralogy, and rock-eval pyrolysis tests.
We observe a positive correlation between porosity/permeability and the total organic carbon (TOC) content of the samples. The bulk density of the core samples decreases with increasing the TOC content. The relationships of porosity, permeability, and bulk density with TOC indicate that the majority of pores exist in the organic matter of the samples. We define oil wettability index (WIo) based on the equilibrium imbibed volume of oil and brine. The results of spontaneous imbibition experiments show that the samples with higher TOC content and porosity have higher WIo. In addition, we observe negative correlation of WIo with bulk density. We also investigate the correlations of oil wettability index with natural gamma ray (GR) radiation, uranium concentration, and density porosity (φD). The results show that the samples with higher gamma ray, uranium concentration, and density porosity have higher TOC and porosity, and thus higher affinity to oil compared with brine.
Organic-rich shales have been considered as potential reserves across the world (Gonzalez, 2013). Extraction of hydrocarbon from shale rocks in the United States is considered as one of the landmark events in this century (Wang et al., 2014). These unconventional resources with ultra-low permeability can produce hydrocarbon at economic rates from hydraulically fractured horizontal wells. However, successful recovery from such reservoirs requires correct characterization of rock/fluid properties. Wettability affects the electrical properties of rock, capillary pressure, water flood behavior, relative permeability, dispersion, and simulated EOR (Anderson, 1986). Evaluation of shale wettability is significant for
mitigating low fracturing fluid recovery after fracturing operations (Cheng, 2012; Ghanbari and Dehghanpour, 2015 and 2016),
investigating water blockage in matrix followed by rapid decline in production rate (Bertoncello et al., 2014),
selecting the type of fracturing fluid (water-based or oil-based) and its additives (Montgomery, 2013), and
investigating the consequences of condensate dropout below dew point pressure (Sheng, 2016; Sheng and Li, 2016; Meng and Sheng, 2016).