Institute of Petroleum Engineering

Centre for Gas Hydrate Research Publications

Abstract 073
Gas Hydrate Risks during WAG Injection Operations: Numerical Simulation and Micromodel Experiments
Bashir, A., Harfoushian, H.J., Tohidi, B. and Anderson, R.
4th International Conference on Gas Hydrates, Yokohama, Japan, 19-23 May (2002).
Water Alternating Gas (WAG) injection is an oil recovery method aimed to improve sweep efficiency during gas injection. In recent years, produced hydrocarbon gas has been re-injected in water injection wells with the aim of improving oil recovery and pressure maintenance. However, little attention appears to be given to specific hydrate strategy requirements during WAG operations. This study aims to evaluate the risks associated with gas hydrate formation during WAG injection operations. Pressure-temperature profiles for various stages during WAG operations in a typical offshore field are calculated. The hydrate dissociation pressure has been correlated against temperature using experimental hydrate dissociation data for a typical natural gas and CO2. The data are used to calculate phase behaviour and gas hydrate stability zones for a typical injection of gas and CO2. In addition, the impact of cold seawater injection on hydrate formation during WAG operations is investigated. The results show that gas hydrates can form in the wellhead, tubing and the formation, depending on operating conditions. As expected, the risks increased during changeover from gas to water and water to gas. With the aim of investigating hydrate growth in the formation during WAG operations, a series of experiments has been conducted using a glass micromodel set-up. Images of hydrate formation during WAG processes were recorded. Experiments were conducted on a water-wet system, and showed that hydrate could be formed after the injection of free-gas inside reservoirs containing cold water.

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