The Role of Mineral Composition, Rock Permeability, and Connate-Water Composition on the Performance of Low-Salinity Waterflooding in Sandstone Reservoirs

Extensive experimental work has indicated that low-salinity waterflooding is an enhanced oil recovery technique that improves oil recovery by lowering and optimizing the salinity of the injected water. Recent field applications and laboratory studies have recognized that low-salinity waterflooding is a potentially effective technique to achieve sufficient recovery in sandstone reservoirs. It was noted that the impact of clay content, rock permeability, rock quality, and the salinity of the reservoir connate water on the performance of low-salinity waterflooding are still questionable. The main objectives of this work were to: (1) examine the performance of lowsalinity waterflooding using four outcrop sandstone rocks, (2) investigate the role of clay content, rock permeability, and average pore throat radius on the performance of lowsalinity waterflooding, (3) evaluate the effects of mineral type, brine salinity, cation type, and pH on the zeta-potential measurements, (4) investigate the role of the salinity and composition (Na^+ , Ca^2+, and Mg^2+) of the reservoir connate water on the performance of low-salinity waterflooding, and (5) study the effect of the initial water saturation on the performance of low-salinity waterflooding. Four sandstone types (Buff Berea, Grey Berea, Bandera, and Parker) with different mineralogy compositions were used. The mineralogy of the rock samples was assessed by X-ray powder diffraction, scanning electron microscopy, and X-ray fluorescence. Nuclear magnetic resonance, high pressure mercury injection, and Winland’s empirical equation were used in order to characterize the pore geometry and provide capillary pressure curves. Zeta-potential measurements were conducted for rock/brine and crude oil/brine interfaces to determine the suitable injection brine for the sandstone rocks used. In addition, several minerals such as quartz, carbonate (calcite and dolomite), clays (kaolinite, chlorite, and montmorillonite), micas (muscovite, biotite, and illite), feldspars (microcline and anorthoclase), and ilmenite were selected to perform this work. Various brines were tested including: seawater, 20% diluted-seawater, 0.5 wt% NaCl, 0.5 wt% MgCl2, and 0.5 wt% CaCl2. Next, a set of comprehensive coreflood tests were conducted using Bandera, Parker, Grey Berea, and Buff Berea outcrop sandstone cores. The coreflood experiments were conducted using 6 and 20 in. lengths and 1.5 in. diameter outcrop cores at 185°F. The oil recovery, pressure drop across the core, pore volume injected, and core effluent samples were analyzed for each coreflood experiment. In addition, experimental studies of the spontaneous imbibition of oil by low-salinity and high-salinity brines used 20-in-long outcrop samples. The volume of produced oil was monitored and recorded against time on a daily basis. Imbibition brine samples were analyzed at the end of each experiment