Numerical Investigation and Integrated Optimization of Solvent-SAGD Process
Authors: Ghasemi Mohammad , Whitson Curtis Hays 
Published: March 2015

The hybrid process is a technique which involves the co-injection of liquid solvent with steam in a similar steam assisted gravity drainage (SAGD) pattern. The combined process can significantly reduce the limitation of the pure SAGD process.

Numerous simulation studies have been previously conducted to understand the hybrid processes. However, most of the models suffer from the lack of an accurate equation-of-state (EOS)/viscosity models for the true estimation of the phase and volumetric behavior of solvent-bitumen-steam as well as the mixture viscosity at the edge oil-flow zone. The provided fluid model in this study is based on our extensive work done on the experimental analysis, and the modeling of viscosity and phase behavior of solvent and viscous oil mixtures for wide range of pressures and temperatures.

In this study, hydrocarbon additives such as C5, C6, C7, C8and C12are used as medium solvents and C15is selected as the heavy solvent. First, the mechanism of the medium and heavy solvents and their impact at the oil-gas interface is discussed. It is found that the development of the edge oil-flow zone is significantly controlled by solvent type where different mechanisms based on K-values behavior exist for different solvents.

Finally, we developed the integrated optimization model which includes the reservoir SAGD pattern and the surface facility process. Moreover, the pipeline used to transfer the mixture of heavy oil (or bitumen) and solvent from surface process to the market is integrated and optimized. The overall net present value (NPV) of the field is calculated and optimized by selecting the main regression variables. We found that for the specific solvent type; the solvent amount, the injection pressure of the solvent and steam are the main parameters which significantly determine the success of such processes.

Our findings are significantly important for the future development of the solvent-SAGD pattern i.e. both reservoir and surface/pipe-line facilities. In addition, it can be implemented for any type of heavy oil field which still requires thermal methods to increase the oil recovery.

Introduction

From last decades, SAGD process has been proven to be a promising oil-recovery process in bitumen deposits. However, the economics of SAGD is mainly influenced by first the natural gas used to generate the steam and second the water treatment and recycling. This is due to the consumption of a large amount of water and natural gas, which results in costly post-production water treatment and a significant amount of CO2emission. The Hybrid process is another technique which involves the co-injection of liquid solvent with steam in a similar SAGD pattern. The combined process can significantly reduce the amount of energy, water and greenhouse gases compared to the SAGD process. Moreover, the main purpose of solvent additives to steam in an SAGD process is to take the advantage of steam for bringing heat to cold bitumen and also the solvent to dissolve into the bitumen and increase the economic efficiency of the process.