The effects of heterogeneity and wettability on oil recovery from laminated sedimentary structures

The sedimentary structure and wettability of clastic rocks at the laminaset scale may have an important influence on oil recovery by waterflooding. Previous work from this laboratory reported results for oil displacements in water wet laminated systems. In this paper, the results from a full cycle of drainage-imbibition floods in a cross-laminated rock slab are reported. The distribution of fluid saturation is monitored using CT scanning techniques. Results from a water wet laminated system are compared with those where the wettability of the slabwas changed by ageing the system with a "synthetic crude oil". The main purpose of this work is to investigate the effects of both the laminaset heterogeneity and wettability alteration on the displacement efficiency and oil trapping mechanisms for such systems.

In these experiments, the recovery efficiency significantly increased, due to the slab becoming more oil-wet. An analysis of the remaining oil saturation shows that (a) no significant oil trapping occurred in this flood, and (b) there was a higher remaining oil in the low permeability regions. Numerical simulations were performed to help our understanding and interpretation of the wettability changes. An excellent match of experiment with numerical simulation was obtained for a particular model case with the lower permeability laminae being more oil-wet than the highr permeability ones. We have termed this a heterogeneously wet (or het-wet) system. To our knowledge, this is the first time that such behaviour has been demonstrated and analysed in detail.