Radially Symmetrical Heat Hydrate Dissociation Model with a Density Difference

Abstract

The hydrate dissociation is viewed as a phase change process in which hydrates transform from a solid phase into gas and liquid phase at a moving dissociation boundary. The boundary separates the dissociation zone containing gas and water from the undissociated zone containing the hydrates, leading to a density difference. Based on the assumption of a density difference between the dissociation zone and the hydrate zone, the authors propose a mathematical model to study hydrate dissociation under thermal stimulation in an infinite radially symmetrical reservoir. Analytical solutions to the temperature distribution are derived by using the self-similarity transformation. Considering the effect factors of the initial heated-water temperature and hydrate density, the authors conducted a thorough investigation of the temperature distribution and the location of the dissociation front for a sample hydrate reservoir. The results from our model show that the heated-water temperature and hydrate density exert significant influence on the hydrate dissociation. With the injection time unchanged, the dissociation distance tends to be increased as the heated-water temperature is increased, leading to a larger dissociation zone. Additionally, a smaller hydrate density can result in a larger dissociation distance. For hydrate thermal stimulation, a higher heated-water temperature and a lower hydrate density can lead to a larger dissociation distance with the injection time unchanged. As the hydrate dissociation proceeds, the dissociation rate is decreased.