Imbibition Oil Recovery from the Montney Core Plugs: The Interplay of Wettability, Osmotic Potential and Microemulsion Effects

Abstract

This paper presents a series of rock-fluid experiments to investigate 1) wettability of several core plugs from the Montney Formation and its correlations with other petrophysical properties such as pore-throat-radius size distribution, and 2) effects of wettability, salinity and microemulsion (ME) additive on imbibition oil recovery. First, we evaluate wettability by conducting spontaneous imbibition experiments using reservoir oil and brine (with salinity of 141,000 ppm) on six twin core plugs from the Montney Formation. In addition, we investigate the correlations between wettability and other petrophysical properties obtained from MICP data and tight-rock analyses. Second, we inject oil into brine-saturated core plugs to arrive at residual water saturation. Third, we perform soaking experiments on oil-saturated core plugs using fresh water, reservoir brine and ME system, and measure the volume of produced oil with respect to time. We observe faster and higher oil imbibition into the core plugs compared with brine imbibition, suggesting the strong affinity of the samples to oil. The normalized imbibed volume of oil (Io) is positively correlated to the volume fraction of small pores, represented by the tail part of MICP pore-throat-radius size distribution profiles. This suggests that the tight parts of the pore network are preferentially oil-wet and host reservoir oil under in-situ conditions. The results of soaking experiments show that imbibition oil recovery is positively correlated to the water-wet porosity measured by spontaneous brine imbibition into the dry core plugs. Imbibition of fresh water results in around 3% (of initial oil volume in place) higher oil recovery compared with that of brine imbibition, possibly due to osmotic potential. Soaking the oil-saturated core plugs in ME solution after brine or fresh soaking results in 1-2% incremental oil recovery. Soaking the oil-saturated core plugs immediately in ME solution results in faster oil recovery compared with the case when the plugs are first soaked in water and then in ME solution.