Evaluation of Oil Recovery Performances of Surfactants Using Organic Conception Diagrams
Authors: Babadaglli T. , Boluk Y. 
Published: March 2010

Abstract
Capillary imbibition experiments conducted on sandstone, chalk, and limestone samples using different oils (crude and processed with different viscosities) and different surfactant solutions were evaluated for surfactant screening. In this evaluation, IFT, surfactant type, and concentration were considered. In addition to these, a new technique has been adopted to facilitate the surfactant screening process. This technique is based on assigning inorganic and organic property values and plotting Organic Conception Diagrams (OCD) for surfactants. OCD defines the property of a compound in terms of physical chemistry in such a way that the property that depends to a large extent on Van der Waals force is called "organic" and the one that depends greatly on electric affinity is called "inorganic." By using the OCD, hydrophilic and lipophilic characters of surfactants have been established to evaluate their potential to minimize oil/water interfacial tension.

Introduction
Using surfactant solutions as a displacement fluid to recover matrix oil in naturally fractured reservoirs (NFR) has gained a great deal of attention in recent years. Capillary imbibition recovery can be enhanced by the addition of surfactant into water to reduce the IFT(1). Typically an increase in the ultimate recovery with lowered IFT was observed for sandstones(2, 3). The imbibition rate also changes with reduced IFT
. Due to the less water-wet character of carbonates, in many cases, very low imbibition recovery was obtained with brine(4). Reduction of IFT by the addition of surfactant yielded a significant increase in recovery due to enhanced capillary imbibition and additional contribution due to gravity effect(3–4). More attention was devoted to chalky carbonates as they are found to be more responsive to low-IFT capillary imbibition recovery compared to the dolomitic carbonates(5–7).
It was observed that the response to the surfactant capillary imbibition recovery could be very different depending on the rock type and fluid properties even if the same surfactant type and concentration are used. For example, sandstones yielded initially faster recovery with high IFT solution (typically brine with no surfactant addition) but ultimate recovery becomes higher with decreasing IFT(1, 4). Carbonates, however, behaved in a different manner. It was previously reported that both the recovery rate and ultimate recovery increased with decreasing IFT for dolomitic limestone(3,4). Experiments on chalk samples showed that the type of surfactant plays a critical role on the ultimate recovery as well as the recovery rate(7–9).
In this paper, we present an analysis to correlate the capillary (spontaneous) imbibition recovery performance of surfactant solutions to surfactant, rock, and fluid properties. We also introduced a newly adopted technique known as Organic Conception Diagrams (OCD).

Experiments
In this study, experimental results obtained from different Studies(3, 4, 7, 9–12) were used. In addition, seven experiments were conducted on chalk samples using 17 cp oil at 20 °C. Four different surfactants were selected as a representative of non-ionic, anionic, and cationic types. Spontaneous imbibition experiments were conducted on 100% oil saturated cylindrical rock samples with all sides open to flow.