Enhancing the Efficiency of Immiscible Water Alternating Gas (WAG) Injection in a Matured, High Temperature and High CO2 Solution Gas Reservoir - A Laboratory Study

Mohd Shafian, Siti Rohaida (PETRONAS Research Sdn Bhd) | Kamarul Bahrim, Ridhwan Zhafri (PETRONAS Research Sdn Bhd) | Abdul Hamid, Pauziyah (Petronas Research Sdn Bhd) | Abdul Manap, Arif Azhan (PETRONAS Research Sdn Bhd) | Darman, Nasir B. (PETRONAS) | Sedaralit, Mohd Faizal (PETRONAS) | Tewari, Raj Deo (Petronas Carigali Sdn Bhd)

OnePetro 

This paper discusses laboratory results of enhancing the performance of water alternating gas (WAG) injection process. Currently, field is under primary and secondary phases. It is light oil with moderate to good reservoir characteristics and relatively higher in reservoir temperature between 92 - 101oC and higher CO2 percentage in produced gas. Field is in decline phase and rise in water cut and GOR values. Redevelopment strategy of the field includes optimization of well spacing and WAG application to maximizing the oil recovery. One of the key challenges faced on WAG injection is gas overriding. Therefore, it becomes important to control the gas flood front during gas injection cycle of WAG and allowing the reservoir to reach to Sorg level.

The study will focus on measuring the variation of petrophysical parameters for surfactants that has bulk foam stabilization properties. In addition to classical foam Mobility Reduction Factor (MRF) determination, effect of foam on gas saturation has also been monitored along the core using in-situ X-ray monitoring tool.  Propagation of foam in porous media is less understood and application of X-ray monitoring for gas saturation in dynamic condition helps to understand this to great extent.

Experiments have been carried out on Berea and reservoir cores mounted on dedicated X-Ray-equipped core flood bench. The core, initially at Swi, is flooded up to Sorw with water followed by gas injection to Sorg level to establish the reference condition for WAG. A slug of surfactant solution is then injected followed by gas prior to co-injection of surfactant and gas (83 % quality foam).  Fluid propagation in core is correctly monitored for every 0.1 PV injection of fluids. The results suggest efficient mobility control by achieving required MRF in presence of ROS. High MRF is an essential ingredient for the success of the process. These results are also correlated with a homogenization of the gas front in presence of foam.