Abstract
The Inflow Performance Relationship (IPR) of a well describes the relation between production rate and bottom-hole pressure, serving as an important tool to understand and predict well performance. For methane hydrate deposits, which account for twice of the total world's conventional oil and gas reserves, the challenge of predicting well performances belongs to the complex hydrate dissociation process and changing deposit condition.
In this work, we established the IPR model for Class II hydrate deposits developed by depressurization using numerical simulation method. To simplify the IPR correlations, the production process is analyzed and is split into different stages based on the production performance. On the other hand, we extend the existed IPR model to methane hydrate deposits by adding new indexes of production force, hydrate properties and deposit properties into the equation. The production process in Class II methane hydrate deposits is divided into three stages: I. Rapid increase stage, II. Rapid decrease stage, III. Stable decrease stage. The production performance of the former stage is affected greatly by the hydrate dissociation process, while the main production forces of the latter two stage are drawdown pressure and heat from surrounding rock respectively. The IPR curves in the same stage show similar shape. For stage I, the IPR correlation is a cluster of concave curves gradually away from the origin. The Fetkovich model is modified to describe the IPR correlation in this stage by changing the deposit pressure to a combination of deposit pressure and pressure drop. The ratio between these two pressures represents the effect of hydrate dissociation process. For stage II, the IPR correlation is a cluster of convex curves. The modified Vogel model is adopted in this stage and quadruple pressure in involved in its modified formula. The IPR correlation for stage III is not considered due to its low gas production rate and economic benefit. Finally, the new IPR model is applied using simulation results in the Mallik site, Mackenzie Delta, Canada. This work extend the current IPR techniques to methane hydrate deposits and proposed a new IPR study method for unconventional resources.
