Modifying the Hall Plot for Analysis of Immiscible Gas Injection Wells II: IOR

Abstract

The Hall plot is a graph of an injection well's cumulative pressure against its cumulative injected volume, ideally presenting as straight line. Changes in the gradient of this line can indicate a change in injectivity behavior. Developed for single-phase, steady-state, radial flow of liquids, it has proven useful in the surveillance of water injection wells. However, published studies into the validity of its equations and assumptions for gas injection scenarios are limited. Utilizing the Hall plot to analyze immiscible gas injection into an oil phase for improved oil recovery poses challenges due to the near-wellbore relative permeability of gas to the oil phase. This paper presents one useful and practical approach to achieve this correction.To account for the varying near-wellbore relative permeability of gas in the oil phase, a function relating the relative permeability of gas in the oil phase to the cumulative gas injection is developed and included in previously developed equations that account for compressibility and viscosity variations. These updated equations give a modified Hall plot that accounts for the non-linearity due to relative permeability effects and allows the Hall plot to be used qualitatively by engineers to identify changes in the injectivity of gas wells.

Performance Analysis of Water Injection Well BEL-13 and Production Well BEL-01 Using Hall Plot and Buckley-Leverett Methods

“…We can observe signs of the presence or absence of skin that influence whether the water injection goes smoothly and properly or not from this Hall Plot study. An upward, downward, or straight curve, respectively, denotes adverse skin conditions, normal skin conditions, or favorable skin conditions [10][11][12].…”