The Control of Apparent Wettability on the Efficiency of Surfactant Flooding in Tight Carbonate Rocks

Harris Sajjad Rabbani,Ibrahim Almaghrabi,Yossra Osman,Thomas Seers,Mohammad Azizur Rahman

doi:10.3390/pr7100684

Abstract

In this research, a state-of-the-art experimental core flooding setup is used to assess the efficiency of surfactant flooding as an enhanced oil recovery (EOR) technique in tight carbonate rocks. Specifically, we investigate the role of apparent wettability in governing the effectiveness of surfactant flooding. A series of flooding experiments with well-defined boundary conditions were performed on the low permeability core plug samples of Indiana Limestone (calcite-cemented carbonate grainstones). Experiments were conducted on three samples exhibiting differing apparent wetting characteristics: strongly oil-wet, moderately oil-wet and weakly oil-wet. Initially, the oil-saturated core samples were flooded with brine until the residual oil saturation was achieved, with surfactant flooding performed as a tertiary recovery technique. Interestingly, our experimental results reveal that the efficiency of surfactant flooding increases with the degree of oil-wetness of the tight carbonate rocks. The strongly oil-wet core showed the highest recovery, while the weakly oil-wet core manifested the least additional oil recovery associated with surfactant flooding. Moreover, we provided a pore-scale argument that explains the macroscopic role of surfactant flooding in tight carbonate rocks. We hypothesized that at the pore-scale the presence of thin film plays a critical role in controlling the effectiveness of surfactant flooding in the strongly oil-wet tight carbonate rocks. Overall, we believe that our macroscopic study provides novel insight into the dynamics of surfactant flooding in tight carbonate reservoirs and can aid in optimizing the field development plans for oil recovery.

Highlights

With increasing demand for energy globally remaining largely unperturbed, the development of effective and economic enhanced oil recovery (EOR) techniques may prove to be a critical component in meeting future energy requirements
We investigate the effect of the apparent wettability of tight carbonate rock on the efficiency of surfactant flooding at a fundamental level
One of the main issues with carbonate reservoirs is their wetting characteristics: commonly oil-wet in nature, strong capillary forces trap the majority of the oil behind the displacement front in small channels, such as grooves, edges and pore throats, limiting oil recovery

Summary

Introduction

With increasing demand for energy globally remaining largely unperturbed, the development of effective and economic enhanced oil recovery (EOR) techniques may prove to be a critical component in meeting future energy requirements. Carbonate reservoirs have formed an important focus for the deployment of EOR techniques. Constituting over half of the world’s conventional oil reserves, carbonate reservoir settings are commonly characterized by poor recovery efficiency compared to conventional clastic plays [2]. The restricted producibility of many carbonate reservoirs is often due to the presence of highly heterogeneous pore networks therein. Multifarious burial and fluid charge histories, coupled with the innate chemical susceptibility of carbonate rock forming minerals (especially calcite) can often result in a high degree of pore-scale complexity in such settings, in terms of pore size distribution, pore geometry and pore wall wettability [3]

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Results

Conclusion