2014 Rocky Mountain Section AAPG Annual Meeting

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Characterization of Wettability using NMR and Dielectric Logging, and Pore-scale Imaging Techniques


Characterization of the wettability within a sandstone reservoir is critical for understanding the type and volumes of fluids that will be produced during both primary completion (Anderson, 1986) and secondary waterflood recovery (Morrow, 1990). The oil reservoirs within the Green River Formation of the Uinta Basin (Utah) in the Greater Monument Butte Unit (GMBU) have variable wettability validated through traditional core methods such as USBM wettability and relative permeability measurements. There are over twenty defined producing sandstone reservoir intervals within the Green River Formation with variable depositional environments, mineralogy and rock quality. Due to the reservoir variability, characterization of wettability through traditional core analysis techniques is cost prohibitive and time-consuming. A log based technique was developed because GMBU is currently under conversion to a waterflood unit, and a cost-effective method for characterizing reservoir wettability would be beneficial for sweep efficiency and increasing ultimate recovery. The wettability of a reservoir depends on the mineralogy of the open pore space and the type of oil in the reservoir. Oils with a higher asphalteine and resin content tend induce more oil-wetness due to the polar nature of these hydrocarbon compounds. Similarly, carbonates tend to be more oil-wet due to the polar electrical charge on the mineral surfaces. The types and volumes of either oil or water that are produced from a reservoir depend on the scale and wettability of the pores where the fluids reside. Consequently, mapping of the pore-scale distribution of fluids and wettability is important for predicting produced fluids. Chen et. al. (2013) proposed the use of NMR logging to map the presence of oil-wet pores. In this paper micro-CT imaging in preserved state samples is used to identify occupancy of oil at the pore scale in 3D and BSEM pore-scale imaging techniques to detect the presence of deposited asphalteines within pores allowing for an effective mapping of wettability within a rock at micro- and macro-pore scales (Knackstedt et. al., 2011). This information provides the foundation for integrating pore-scale wettability with the petrophysical response. Results are presented that validate and extend the work of Chen et. al. (2013) using pore-scale imaging of wettability and open-hole dielectric data integrated with NMR open-hole logging data. We use this integrated technique to characterize the variable wettability of GMBU reservoirs.