In this work, coreflood studies were carried out to determine the recovery benefits of low salinity waterflood compared to high salinity waterflood and the role of wettability in any observed recovery benefit. Two sets of coreflood experiments were conducted; the first set examined the EOR potential of low salinity floods in tertiary oil recovery processes, while the second set of experiments examined the secondary oil recovery potential of low salinity floods. Changes in residual oil saturation with variation in wettability, brine salinity and temperature were monitored. All the coreflood tests gave consistent increase in produced oil, corresponding to reduction in residual oil saturation and increase in water-wetness (for the second set of experiments) with decrease in brine salinity and increase in brine temperature.

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Numerous early reports on experimental works relating to the role of wettability in various aspects of oil recovery have been published. Early examples of laboratory waterfloods show oil recovery increasing with increasing water-wetness. This result is consistent with the intuitive notion that strong wetting preference of the rock for water and associated strong capillary imbibition forces give the most efficient oil displacement. However, an increasing number of examples of improved waterflood recovery with shift from strongly water-wet conditions to intermediate, weakly water-wet and oil-wet conditions have also been reported. All the early and more recently observed experimental outcomes, on wettability effects on waterflood oil recovery, point to the divergence of conclusions regarding the optimum wetting condition for maximum waterflood oil recovery. The impact of the in-situ reservoir wetting state on miscible and /or immiscible gas flood oil recovery, though not as pronounced as that observed in waterflooding processes, is still nonetheless quite significant. It has been shown that wettability does indeed determine the gasflood oil recovery efficiency and changes in wetting states have resulted in observed improved gasflood recoveries. This paper examines the effect of wettability on waterflooding and gasflooding processes respectively. Waterflood oil recoveries were examined for the dual cases of uniform and non-uniform wetting conditions. The uniformly wetted systems examined in this work are considered to be those systems in which the observed wetting state is uniformly distributed and covers the range from strongly water-wet through the intermediate-wet to strongly oil-wet conditions. The non-uniformly wetted systems examined include the mixed-wet and the fractionally-wetted systems. The effects of wettability on miscible and immiscible gas recovery processes (including WAG) are also examined. Other factors such as the spreading coefficient, mobility ratio, crossflows, etc. were also reported to affect gasflood oil recoveries. Most experiments on wettability studies are performed on core samples and depending on the process of core sample recovery / retrieval, transportation and storage, the wetting state of the core sample may be altered. Consequently the importance of proper core handling procedure in ensuring that the reservoir native-state wettability is preserved is highlighted. In a situation where the native wetting state has been altered, the need for adequate care in the process of/approach to reproducing wettability is also mentioned. Introduction The monotonic and geometric increase in world demand for energy in the face of rapid industrialization requires the production of increasing quantities of crude oil while maintaining acceptable cost levels. Many abandoned, matured fields have become the subject of novel EOR field trials in order to meet the energy demand. A lot of resources have gone into research and development, in a bid to better understand ways to manipulate factors at pore scale levels and higher, in order to improve oil recovery. Oil recovery efficiency depends on the interplay of many interacting factors, mechanisms, properties, etc at pore levels as well as macroscopic scales. Efficient and cost-effective oil recovery requires an in depth understanding of the nature and where possible, manipulation of these interacting forces. The study of these forces has been a subject of interest and research in the oil industry for several decades.

Summary The ensemble Kalman filter (EnKF), is a sequential data-assimilation technique that has been shown to work quite well in obtaining conditional facies models from assimilating production data. Because the problem of history matching geological facies is quite complex, most efforts at solving this problem typically assume that facies properties are constant and spatially homogeneous. In this paper, we propose a method for updating both the categorical facies variables and the spatially heterogeneous and nonuniform properties of the facies in a consistent manner within the EnKF framework. Tests of our proposed approach on two representative examples with different features of nonstationarity resulted in satisfactory history-match solutions and geologically consistent estimates of the nonuniform and heterogeneous petrophysical properties.