Enhanced oil recovery by alkaline-surfactant-alternated-gas/CO2 flooding

Ranjan Phukan,Pankaj Tiwari,Subrata Borgohain Gogoi

doi:10.1007/s13202-018-0465-0

Ranjan Phukan, Pankaj Tiwari + Show 1 more

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https://doi.org/10.1007/s13202-018-0465-0

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Abstract

The volumetric sweep efficiencies of CO2 flooding for enhanced oil recovery (EOR) are generally low due to problems of viscous fingering and gravity override. This paper attempts to study a relatively new and promising method to reduce the mobility of CO2 flooding and increase oil recovery under reservoir conditions. Referred to as alkaline-surfactant-alternated-gas/CO2 (ASAG) flooding, this method is essentially the synergic combination of chemical and immiscible CO2 flooding. In this work, chemical formulations were identified through foam stability tests based on their foaming ability coefficients. The selected formulations were further tested for their capabilities to reduce oil–water interfacial tensions (IFT) to ultra-low value. With the best performing formulations, the laboratory-scale core flooding experiments were conducted to evaluate their EOR potential. The core flooding experiments were performed with sandstone reservoir core samples from two different depths of a major depleted oil field of Upper Assam Basin, India. This study reports the successful application of a natural anionic surfactant (black liquor) as a co-surfactant and foaming agent during ASAG flooding. It was observed that higher oil recovery of 14.26% original oil in place (OOIP) was obtained by surfactant-alternated-gas (SAG) flooding compared to 12.03% OOIP by immiscible CO2 alternated with brine (WAG) flooding. The highest residual oil recovery of 20% OOIP was obtained for ASAG flooding with the alkali, surfactant and black liquor in the chemical slug. Oil recovery performances during SAG and ASAG flooding were found to be better for core samples with lower porosity–permeability due to stronger foam formation in lower permeability cores.

Highlights

enhanced oil recovery (EOR) processes include all those methods that mobilize and recover the oil left behind or that cannot be produced economically by the conventional use of reservoir energy and pressure maintenance schemes with gas or water
The results of the experimental work highlighted the successful application of the synergic combination of alkali, surfactant and C O2 gas for improving recovery of medium gravity crudes
From the foam stability tests, it was observed that optimum concentrations of surfactants, alkali, crude oil, and salinities exist which corresponds to maximum foaming behavior

Summary

Introduction

EOR processes include all those methods that mobilize and recover the oil left behind or that cannot be produced economically by the conventional use of reservoir energy and pressure maintenance schemes with gas or water. The water-alternated-gas (WAG) technique had been accepted as the technology of choice to control C O2 mobility by the EOR industry (Enick and Olsen 2012). Injecting water with C O2 increases the water saturation and so decreases the C O2 saturation in the pore spaces This leads to a reduction of CO2 relative permeability making the mobility ratio favorable with the resulting better sweep efficiency and improvement in the oil recovery efficiency (Zekr et al 2011). The WAG method is the state-of-the-art technique for CO2 mobility control in porous media and is more efficient than CO2 injection alone, the process leaves behind 35–65% original oil in place (OOIP). The large volumes of brine injected along with C O2 prolong the life of the project, inhibit the contact of CO2 and oil, and result in the production of large amounts of water

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