Substantial hydrocarbon reserves remain trapped in reservoirs that are characterized as tight, oil-wet, and fractured. The aforementioned reservoir characteristics are typical to shale formations, and significantly degrade hydrocarbon recovery efficiency because of well productivity, in addition to reservoir, capillary and sweep displacement efficiencies. In this paper an emphasis is made on identifying the governing reservoir force in tight oil formations at various development stages. The literature review in this paper captures scaling groups for capillary imbibition and several wettability modifiers. This is followed by an analysis, of scaling group limitations and the performance of wettability modifiers. A reservoir simulation model is built to evaluate capillary and viscous effects on oil recovery. Subsequently guidance for optimal reservoir development options is presented.
The optimization of well completion and well stimulation has significant impact on well productivity. It is noticed that there may be trade-off in tight formations between the dominance of viscous forces and the significance of decreasing capillary pressures. Although there is an increase in oil production rate, the cumulative oil production decreases slightly in all water wet conditions. The five well patterns can be categorized into well patterns comprising of three wells (shown in Figures 6a and 6c) and six wells (shown in Figures 6b, 6d and 6e). The highest cumulative oil production is well pattern (Figure 6a) duration 7 months, followed by well pattern (figure 6e) duration 3 months.
Oil-wet reservoirs hold considerable quantities of residual oil. However, during early development commercial quantities of available oil saturation are present in carbonate formations and pose low capillary pressures. Viscous forces govern oil recovery in tight oil formations during the initial stages of development (So >> Sor). Therefore, measures taken to reduce or overcome viscous forces yields higher incremental oil recovery compared with other reservoir forces. The precedence of well patterns should focus on well positioning rather than number of wells and operational expediency in managing draw-downs. Future work will evaluate the use intelligent completion technology to allow selective fractures stages in the horizontal well to undergo surfactant and low salinity water treatment by diffusion process during the well lifetime.