| dc.description.abstract | Due to their ultra-low permeability and extremely heterogeneous formations, unconventional liquids-rich reservoirs (ULR) need a support of an effective hydraulic fracturing for economic and commercial oil production. In recent years, the addition of surfactants to the fracturing fluids has been proven to be one of the effective improved oil recovery (IOR) methods in ULR. Meanwhile, rising hydraulic fracturing activities has ignited industrial and environmental concerns for increasing water demand and large volumes of high salinity flowback and produced water. This investigation studies the potential of surfactant and salt mixed aqueous phase solutions for performance improvement of completion fluids, and their interactions with different rock types. This study also provides guidance for the most favorable salt concentration for surfactant-added completion fluids which can potentially lead to economic and environmental benefits.
This study focuses on an ULR in West Texas. Five surfactants were selected and mixed at a constant concentration with brines. Brines with nine salinity variations were tested to accurately represent the fluids used or produced in the field, and to determine the most favorable salinity level. All fluids were tested with two different rock types, quartz rich and carbonate rich. Zeta potential, interfacial tension, and contact angle experiments were performed to measure the stability of the liquid film of rock particles, to analyze the impact of surfactant and salt on reducing interfacial tension, and to identify the initial wettability and wettability alteration ability of each fluid, respectively. Then, spontaneous imbibition with timely computer tomography (CT) scans were conducted to visually observe the imbibition performance of completion fluids and to validate correlations between oil recovery and other experimented parameters.
Overall, the magnitude of zeta potential, and interfacial tension reduced strongly with increasing salinity, regardless of the presence of surfactant. Also, surfactants mixed with lower salinity brines showed the most effective wettability alteration, and the highest oil recovery factor compared to no or high salinity brines. Similar behaviors and results occurred for all aqueous phase solutions and in both rock types. Among all, wettability of the rock surface was determined to be the most influential factor for oil recovery. | en |
