Proper Simulation of Chemical-EOR Pilots - A Real Case Study
Authors: Wilson Adam 
Published: February 2017

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper SPE 179659, “Proper Simulation of Chemical-EOR Pilots—A Real Case Study,” by Nariman Fathi Najafabadi, SPE, and Adwait Chawathe, SPE, Chevron, prepared for the 2016 SPE Improved Oil Recovery Conference, Tulsa, 11–13 April. The paper has not been peer reviewed.

A critical step in proper design and optimization of any chemical-enhanced-oil-recovery (CEOR) process is appropriate and precise numerical simulations. Addition of chemical species to the material-balance equations, along with finer resolution requirements for CEOR simulations compared with waterfloods, often makes it impractical to run full-field CEOR simulations to the required accuracy. Sector models, by their definition, are naturally suited for modeling of pilots. This paper presents a case study for appropriate simulation of a CEOR pilot.

Introduction

Chemical flooding (polymer flooding, surfactant/polymer flooding, and alkali/surfactant/polymer flooding) has improved significantly over the past decade because of vast research efforts to find practical solutions to specific field applications, improvements in the manufacturing and synthesis of new chemicals, field trials, and implementations by the industry.

Because of the complexity of CEOR and the inherent uncertainties regarding success of a particular CEOR process, extensive evaluations are required before decisions about full-field implementation can be made.

Numerical simulations are critical in CEOR evaluation and provide a realistic performance estimate, assuming that the underlying Earth model is reliable and appropriately calibrated. Usually, chemical floods are performed on candidate fields with a successful water flood history, but CEOR simulations are more complex and challenging compared with water flood modeling and history matching.

Sector-Model Generation

For the subject asset, which is a brown-field, the primary requirement in CEOR modeling is a representative, quality-controlled waterflood-history-matched full-field (or sector) model. Such a model should replicate the field performance (pressures and flow rates), at least on an overall basis and, preferentially, on a well-by-well basis. The model used for this study had high well density, was sufficiently reliable, and was used routinely for field development and performance prediction. The paper demonstrates the preparation and use of a sector model from this readily available waterflood full-field model for a polymer-flood pilot area.

The area of interest (AOI) for the pilot should be selected during an alternatives-analysis phase by a multifunctional team of field engineers and scientists and CEOR subject-matter experts after a project-framing exercise. In this case, this area is a seven-spot pattern containing a central injector and six surrounding producers. This is a small area compared with the full-field model. A local-grid-refinement (LGR) option was considered to create a sufficiently fine grid for CEOR simulation, but the resulting model was still deemed practically prohibitive.