Low-Tension Waterflood Pilot at the Salem Unit, Marion County, Illinois Part 2: Performance Evaluation
Authors: Widmyer R.H. , Satter A. , Frazier G.D. , Graves R.H. 
Published: December 2007

This paper evaluates a field test of a low-tension tertiary flooding process using a petroleum sulfonate surfactant. Observation-well data process using a petroleum sulfonate surfactant. Observation-well data showed that with proper formation conditioning and sufficient surfactant the process effectively displaced all oil remaining after waterflood. Over-all production was 25 percent of expected, and various explanations for this performance are discussed.

Introduction
A regular 2-ha (5-acre), five-spot pilot test of a lowtension waterflood process was undertaken in a previously waterflooded Benoist sand in the Salem field, previously waterflooded Benoist sand in the Salem field, Marion County, 111. Part 1 of this paper presents the process and pilot descriptions, injection and production histories, and associated field operations.
The objectives of this paper are to discuss parameters that may contribute to the process effectiveness and to evaluate the oil recovery performance. An accounting is made of flood components that were injected, produced, and retained in the formation. Both measured and predicted responses are reported. The use of tracers in predicted responses are reported. The use of tracers in allocating contributions from the four injectors to the producer and in detecting flow-path changes is described. producer and in detecting flow-path changes is described. Interpretation Techniques
A computer model simulating tracer and chemical flooding in a stratified pattern was used to interpret pilot performance data. The reservoir was divided into five performance data. The reservoir was divided into five layers to represent the heterogeneity, and stream tubes were used to account for areal distribution of liquid. Within each layer and tube, flow was considered one dimensional, and crossflow between layers and tubes did no exist. The model incorporated the following features:Chemical transport accounting for dispersion, adsorption, and partitioning.Incompressible flow of aqueous and oil phases, with flow considered high-tension (immiscible) or low-tension (miscible-like) depending on the chemical environment.Non-Newtonian flow of polymer solution and permeability reduction because of polymer adsorption on the permeability reduction because of polymer adsorption on the rock.
The following included in the pilot performance evaluation:Analysis of tracer data to verify quadrant flow patterns, fraction of production contributed by each patterns, fraction of production contributed by each quadrant, and vertical reservoir heterogeneity.The effect of the surrounding Benoist injectors and producers in conjunction with the adjacent aquifer. producers in conjunction with the adjacent aquifer.Estimation of chemical consumption based on tracer and chemical breakthrough volumes and concentration profiles at the observation and production wells.Comparison of simulated recovery performance with measured results.

Flow Distribution
Typical liquid distributions in vertically adjacent, high-and low-permeability flow intervals between one pilot injector and the producer are shown in Fig. 1. Also shown are the positions of the chemical banks at a given time.
JPT
P. 933