Reservoir Management Strategies For Optimizing Recovery From Zeigler Field: A Small Sized Field In Illinois, USA
Authors: Sim S.S.K. 
Published: March 2010

Abstract
One of the causes of the three-fold increase in the number of well abandonments in Illinois since 1987 has been difficulties encountered in waterflooding small heterogeneous reservoirs. This paper highlights some development strategies used in a successful waterflood project in Zeigler Field, Illinois, which should be applicable to other similar reservoirs.
Reservoir management strategies at Zeigler Field included obtaining core and log data from almost every well, detailed DST data, bottom-hole pressure surveys and production/injection surveillance. These information-gathering efforts enabled the operators to locate major permeability barriers; this allowed optimum placement of water injectors in the field and relatively high ultimate oil recovery.
The waterflood performance of the Zeigler Field was evaluated with an integrated 3-D geologic and reservoir simulation model. Direct linkage of the geologic model and reservoir simulator allowed both models to be greatly improved during the course of the simulation process. Results of the study included:geological model of the study areaevaluation of waterflood recovery efficiency and identification of a bypassed region,comparison of alternative oil recovery strategies for optimal incremental production.

Introduction
Most of the 42,000 oil wells in the State of Illinois are stripper wells that produce less than 0.5 cubic meters of oil per day. They are operated by small, independent companies which have limited financial resources and technical know-how to implement enhanced oil recovery methods. Almost 1,000 producing oil wells were abandoned and plugged in 1992 because they were no longer economical to operate. Since 1987, there has been a three-fold increase in the plugging of producing oil wells. One of the causes for this rapid increase in the rate of well abandonment has been the difficulties encountered in waterflooding small heterogeneous reservoirs. This topic has been discussed twice during monthly meetings of the Illinois Regional Society of Petroleum Engineers in the spring of 1993 and the following reasons were cited as the likely causes of waterflood failures:Reservoir heterogeneity or compartmentalization.The common practice of hydraulic fracturing during primary production may have created flow channels between injectors and producers causing early water-breakthrough.The rapid decline of pressure in small reservoirs after a relatively short period of primary production can create gas channels that allow injection water to bypass reservoir oil and cause premature water breakthrough.Adverse water-oil relative permeability effects.
FIGURE 1: Net pay contour map of Plumfield lease, Zeigler Field. (Available in full paper)
FIGURE 2: Production history of Plumfield lease, Zeigler Field. (Available in full paper)
This paper describes the experience gained from development of the Plumfield lease of the Zeigler Field, Illinois. It illustrates the benefit of acquiring and using geological, engineering and field data for reservoir management and demonstrates that some of the difficulties encountered in waterflooding a small reservoir can be overcome with prudent reservoir management techniques. The integrated geological and engineering study carried out on this field had the objectives of determining the reservoir architecture and developing a strategy for improved oil recovery for typical small reservoirs in the Illinois basin.