Understanding First, Simulation Later

Abstract

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 132781, ’Understanding First, Simulation Later: Using Basic and Modern Reservoir- Engineering Techniques To Understand Reservoir Dynamics: A Proven Case,’ by Hector Gomez Alonso, SPE, Sarawak Shell Berhad, originally prepared for the 2010 SPE Annual Technical Conference and Exhibition, Florence, Italy, 19-22 September. The paper has not been peer reviewed. The full-length paper describes a mature field in which water production was seen very early in production life and rapidly increased to the current level of 80% water cut. At well level, a similar behavior has been noticed: high initial oil rates with subsequent strong decline once water breakthrough occurs. This type of behavior has been observed in most of the wells completed among the different reservoirs that make up the field. Long-term production data and modern decline analysis strongly indicated the presence of two systems in the reservoir. Introduction The full-length paper shows how important it is to have a strong understanding of reservoir dynamics before using 3D reservoir-simulation models and, especially in this case, how the use of simple and modern analytical techniques such as Chan plots, transient tests, and conventional and modern decline analysis can provide the reservoir engineer with sufficient background to take the next step confidently. The paper also describes how pseudosteady-state calculations provided information regarding the characteristics of the second system, which helped to optimize the original petrophysical interpretation in the static model. This represents a simple approach to consider how detailed a geological model need to be to reproduce production behavior. Usually, in mature fields, there is a considerable amount of information available regarding production, pressures, fluid samples, and transient tests, which sometimes is not analyzed properly because there is not sufficient time or the data are not easy to find. Reservoir engineers sometimes have the tendency to jump directly into dynamic simulation to understand the dynamics in the reservoir and generate predictions. The objective of following the methodology described, before engaging in the use of reservoir simulation, is to try to understand what really is going on at the subsurface level. If this is achieved, the reservoir engineer always will be ahead of the simulation model and not the other way around. Simulation models should be treated as tools in which equations are solved, by using input data (e.g., rates, pressures, pressure/volume/temperature, and relative permeability).