Interactions of Fines with Oil and its Implication in Smart Water Flooding

Abstract

Migration of fines has been observed during water flooding in chalk reservoirs and has been suggested to play a key role in enhanced oil recovery (EOR). But, the exact role of fines is not well studied for carbonate reservoirs. This study shows that addition of water and crude oil on calcite fines leads to formation of soluble oil micelles in the water phase. Formation of these micelles and its implication in EOR has been experimentally analyzed.To study this phenomenon different water insoluble salts were used as fines including, Li 2 CO 3 , MgCO 3 , CaCO 3 , CaSO 4 , SrSO 4 and BaSO 4 to which oil and water was added. To study conditions of oil micelles formation, design oil was used consisting of hexane and hexadecane. Heptanoic acid and stearic acid were doped in various compositions to mimic the acid number of the oil. Experiments were conducted for pure crude oil and doped oil to understand its implications in EOR. Composition of initial and final floating oil was obtained through gas chromatographic (GC) analysis. The two were thereafter compared to obtain the composition of micelles formed.The experiments showed that oil micelles are only formed when polar hydrocarbons are present in the oil. Different mixtures of alkanes did not produce any micelle. In oil containing stearic acid it was observed that around 95% of the initial stearic acid was accumulated in the micelles and only 5% was found in the floating oil. In oil samples containing heptanoic acid only 50-60% of its initial amount was accumulated in the micelles. This indicates heavier acids can form more stable micelles. Oil micelles were produced in all the different fines used, but the composition of these micelles where dependent on the salt anions. In all carbonates, lighter acids preferred micelles formation with lighter alkane, (indicated by intensification of heavier alkane in the floating oil compared to the initial oil) and vice versa for heavier acids. While no such selectivity in micelles formation was observed in any of the sulfates. Results obtained with crude oil and doped oil and designed oil were consistent. These results show that fines (of insoluble carbonate) released during core fracturing, or (sparingly soluble sulfates) formed during smart water flooding can form mixed wet water soluble oil micelles and help in mobilization of trapped oil along with increasing sweep efficiency.The results clearly show oil micelles formation in the water phase from the interactions of oil with fines, and also provide a detailed understanding of its composition under different conditions. The study highlights the significance of fines during smart water flooding in carbonate reservoirs and shows how its role in EOR can be mistakenly underestimated.

Interactions of Fines with Base Fractions of Oil and its Implication in Smart Water Flooding

“…This is in agreement with the previously observed trend for carbonate fines. The results obtained with the basic hydrocarbons were in coherence with the acidic analogs (Chakravarty et al 2015) Emulsion formation between crude oil and reservoir fines (O3& D1) Furthermore these trends were examined for carbonate fines from reservoir rock (Dan field) and crude oil (O3). The carbonate fines of the reservoir rock were mixed with the deionized water and thereafter O3 was added.…”

“…Best grade chemicals were obtained for the fines and organic compounds to avoid any error in the conducted experiments. These experiments were conducted in coherence with the previous study for oil emulsion formation with acidic fractions of crude oil (Chakravarty et al 2015).…”

Importance of Fines in Smart Water Enhanced Oil Recovery (SmW-EOR) for Chalk Outcrops

“…The adhesion between mobile fines and these adsorbed polar compounds can help in desorption and release of the immobile trapped oil. Formation of fine can increase the mobility of the oil by formation of water soluble oil emulsion (Chakravarty et al 2015). This can lead to a more water wet state as observed in several experiments (Faith et al 2010a;Faith et al 2010b;Faith et al 2011).…”

“…The Extended UNIQUAC model is a thermodynamic model for aqueous solutions of electrolytes and non-electrolytes (Thomsen and Rasmussen 1999). The optimized parameters of this model are based on a large amount of experimental data (Christensen and Thomsen 2003;Thomsen et al 1996;García et al 2006;García et al 2005). And thereby enables the model to describe the phase behavior and the thermal properties of solutions containing electrolytes with great accuracy (García et al 2005).…”

Mechanisms of smart waterflooding in carbonate oil reservoirs - A review

“…The more seawater is mixed, the more CaSO 4 and SrSO 4 precipitates. Chakravarty et al (2015aChakravarty et al ( , 2015bChakravarty et al ( , 2015c analyzed existing imbibition and flooding experimental data. By extensive thermodynamic computations, it was demonstrated that additional production is observed whenever mixing of the formation brine and injected water under experimental thermodynamic conditions results in precipitation of the CaSO 4 .…”