| dc.description.abstract | This study investigates how the structure of surfactant molecules interacts with the crude oil/rock/brine system characteristic of unconventional liquid reservoirs. In most cases, the interaction results in the improvement of oil recovery. There also exists cases where it negatively influences oil recovery. Recovery improvement by surfactant could be applied to the field, especially on unconventional oil wells that are depleted and in terminal decline. As reported in Enverus (Accessed September 3rd, 2021) in June of 2020, the number of these prospective oil wells is more than 150,000 located in the lower 48., thus making the application of Surfactant-Assisted Spontaneous Imbibition (SASI) even more attractive. However, due to the fact that improperly chosen surfactants can negatively affect recovery, a robust understanding of how different surfactant molecules behaves in the shale system is crucial.
The utilization of unconventional reservoirs is relatively recent when compared to conventional reservoirs. While interfacial studies can be commonly found in conventional reservoirs, the same cannot be said for unconventional reservoirs. In the first part of this study, the heterogeneity of crude oil composition, brine characteristics, and rock mineralogy of the Lower 48 shale is presented. Fifteen crude oil samples, five rock samples, and four brines are incorporated in this study. Characterization method such as gas chromatography (GC), Saturates, Aromatics, Resins, and Asphaltenes (SARA) analysis, X-Ray Diffraction (XRD), density, etc., are incorporated. The aim is to provide a detailed description of the shale heterogeneity. It is found that shale is highly heterogenous from one reservoir to another.
The next step is to investigate the interaction between the three phases, oil, brine, and rock. Oil and brine interaction is analyzed by studying the trend of interfacial tension value with varying oil and brine composition that can be found in unconventional reservoirs. Then, the rock-phase is added to investigate the wettability of a crude oil/brine/rock system with varying composition and mineralogy. And finally, spontaneous imbibition experiments for base case conditions are performed on multiple combination of crude oil, rock mineralogy, and brine salinity. Interfacial tension and wettability provide the greatest insight of interfacial phenomena in shale reservoir systems. Spontaneous imbibition is important as it provides context, it captures how the effects of crude oil/brine/rock properties to the interfacial tension and wettability are translated to the fluid flow in a porous media setting. Spontaneous imbibition is the ultimate experiment for understanding surfactant additives as it encapsules all aspects that are relevant in producing an oil reservoir.
Once the base scenario is determined, the next step is to incorporate surfactant. Twelve surfactants are systematically investigated the effect of tailgroup and headgroup structure. The same methodology previously described is performed. First, the effect of surfactant to an oil/brine system is investigated with IFT. Then, the effect of surfactant to an oil/brine/rock system is investigated with wettability. Finally, oil recovery as a function of surfactant structure is analyzed through imbibition experiments. | |
