Well Test Interpretation in Faulted Reservoirs

Abstract

ABSTRACT Well test analysis for a well adjacent to a no-flow boundary or a fault presents a significant interpretation challenge. The interpretation difficulty stems from the fact that early-time skin- and storage-dominated period and the subsequent boundary-dominated period obscure the middle-time data. Consequently, conventional semilog or type-curve analyses are difficult to perform. Because of dominating influence of inner and outer boundary conditions, an appropriate interpretation model is necessary for the estimation of reservoir parameters. This work presents analytical models to analyze data for a well located at various distances from a fault, having wellbore storage and skin effects. The models are cast in the familiar graphical format with dimensionless variables – known as type curves. These type curves exhibit a different character than those of Gringarten et al for an infinite-acting reservoir. Both constant wellbore storage and exponential decline storage cases are considered in this work. The new type curves offer the potential for reservoir parameter estimation of permeability, skin and wellbore storage coefficient. Additionally, the distance to a fault could be estimated. Application of the new type curves, using an automated matching technique, is demonstrated through field examples. Data from several wells located in highly faulted off-shore gas and oil reservoirs in south-east Asia are used for the purpose. Difficulty of analyzing the data using conventional semilog analysis is also shown in this work. This study further shows that only the very early-time data (<10 minutes) that are affected by the wellbore storage effect are amenable to pressure-rate-time or convolution analysis, obeying the radial-cylindrical flow model.