Wettability And Immiscible Displacement In Pembina Cardium Sandstone
Authors: Dulllen F.A.L. , Allsop H.A. , MacDonald I.F. , Chatzis I. 
Published: March 2010

Abstract
Imbibition tests, along with water floods and oilfloods, using various oils including Pembina crude oil, have been performed on Pembina Cardium sandstone core samples of homogeneous appearancess characterized by nitrogen permeabilities ranging from 3.9 md to 119 md. In the waterfloods the oil-la-water viscosity ratio was varied over the range of 0.23 to 15.2 and in the oil floods the water-lo-oil viscosity ratio ranged from 0.066 to 4.4. All the results obtained on the Pembina Cardium samples were compared with results of similar tests performed on strongly water-wet and strongly oil-wet Berea sandstone samples. The Pembina Cardium sandstone samples were found to have mixed wettability characteristics of the bicontinuous type because samples 100% saturated with brine spontaneously imbibed up to 53.4% pore volume 0/ oil, whereas oil sampler 100% saturated with oil imbibed up to 49.6% pore volume of brine. The average oil imbibition into eight samples was 40% pore volume and the average brine imbibition into six samples was 26% pore volume. Using styrene as the oil, the microscopic phase distribution after both types of imbibition, investigated by the phase immbolization technique, showed that the oil was mostly present in narrow pore crevices, whereas the water occupied most of the relatively large pore bulges. Waterfloods in Pembina Cardium core plugs of 3.9 md and 11.6 md permeability showed water breakthrough at 0.17pore volumes and 0.27pore volumes water satruation, respectively, and oil recoveries of 0.39 pore volumes in both samples after 6 to 8 pore volumes of water injection. By contrast, in the water flood of Pembina sample of 119 md permeability water breakthrough occurred at 0.44 pore volumes water saturation and a total oil recovery of 0.66 pore volumes was reached after injecting 13 pore volumes of water. The water flood and the oilflood histories of the Pembina samples display both water-wet and oil-wet characteristics. The shape of the characteristic top portion of the fractional flow curves of the Pembina samples occupies an intermediate position between the corresponding shapes of the fractional flow Clines obtained in strongly water-wet and strongly oil-wet sandstones, respectively. Toluene-methanol extraction of Pembina Cardium core plugs yielded water-wet samples with dramatically improved waterflood oil recovery efficiency. Ageing the extracted samples with Pembina crude oil resulted in mixed-wet samples with only a slight waterwet behaviour.

INTRODUCTION
The Pembina Cardium oilfield is the largest oilfield in Canada, covering 283 000 ha (700 000 acres) and containing estimated reserves of 1.2 billion m3 (8 billion barrels) of original oil-in-place (OOIP)(1). Expected recoveries from waterflooding are low, estimated at only 21% to 23% of OOIP. Early water breakthrough has caused declining production in many regions of the pool. Waterflooding is the main recovery method used in the Pembina reservoir with 70% of the approximately 4400 active wells being waterflooded(2,3).
Although macroscopic-to-megascopic reservoir heterogeneities may drastically affect waterflood performance, oil displacement ultimately occurs at the pore level, because the oil resides in the pore spaces and it must be displaced from there in order to produce it.