Fundamental investigations into wettability and low salinity flooding by parameter isolation

Abstract

Improved oil recovery by low salinity waterflooding (LSF) represents an attractive emerging oil recovery technology, as it is relatively easy to implement and low-cost compared to other Improved and Enhanced Oil Recovery (IOR and EOR, respectively) processes. Even though LSF leads to extra oil recovery in most laboratory experiments and some promising data from the field have been presented, the mechanism underlying LSF is still unclear. Therefore it is difficult to predict a favorable performance of LSF in one field a priori, while dismissing others. This paper describes a series of spontaneous imbibition experiments on Berea outcrop core plugs, and some reservoir rock core plugs, that were designed to determine the impact of formation water, imbibing water and crude oil composition on wettability and on wettability modification by LSF. The data presented in this paper lead us to conclude that: Spontaneous imbibition experiments with formation brine and low salinity brine executed on Berea outcrop material aged with a crude oil show excellent reproducibility;An increasing concentration of divalent cations in the formation brine makes a Crude Oil/Brine/Rock system more oil-wet;The extent of wettability modification towards more oil-wet upon aging also depends on the types of cations in the formation brine;Improved oil recovery by exposure of the aged plugs to NaCl brines occurred when the imbibing phase was either higher or lower in salinity than the formation brine;Aging of the same brine/rock system with different crudes having diverse physico-chemical properties led to:○A spread in wettabilities after aging○A crude oil-dependent low salinity effect These results are discussed within the context of several mechanisms that have been put forward previously as an explanation for the low salinity effect.

Thin liquid films in improved oil recovery from low-salinity brine

“…However, they cannot explain all of the results. The purpose of this section is to discuss these limitations in order to stress that more careful studies are needed and to agree with the assessment in the literature that no one mechanism can explain all of the results [38,12].…”

“…Various mechanisms have been proposed, but none of them have definitively been shown to be the primary one [12]. This is due to the complex nature of the brine/oil/rock interactions, and is further complicated by a number of conflicting observations from experimental studies [4].…”

Extended DLVO-based estimates of surface force in low salinity water flooding

“…While several mechanisms have been proposed in low salinity water flooding based on multi-scale studies, from pore-scale to reservoir scale [6,20,47,48], detailed understanding is incomplete in nano-scale [5].…”

Effect of injection brine composition on wettability and oil recovery in sandstone reservoirs

“…In the recent years, extensive laboratory and field tests have showed that LSF can act as an attractive enhanced oil recovery technology [1][2][3][4][5][6]. The popularity of this technology is mainly because of its efficiency in displacing crude oil, low investment, easy operation, ease of injection, and environmental protection, all of which bring economic benefits compared to other chemical EOR methods [7].…”

“…Over the last decades, the wettability alteration has been widely believed to be an important contributor to LSF [1,5,7,10]. Wettability alteration of sandstone rocks by LSF is related to the minerals on sandstone surface, the polar components in crude oil and the ion composition of injected water [8,11,12].…”