One of the causes of the three fold increase in the number of well abandonmentsin Illinois since 1987 has been difficulties encountered in waterl100ding smallheterogeneous reservoirs. This paper highlights some development strategiesused in a successful waterflood project in Zeigler Field, Illinois, whichshould be applicable to other similar reservoirs.
Reservoir management strategies at Zeigler Field included obtaining core andlog data from almost every well, detailed DST data, bottom-hole pressuresurveys and production/injection surveillance. These information gatheringefforts enabled the operators to locate major permeability barriers; thisallowed optimum placement of water injectors in the field and relatively highultimate oil recovery.
The waterflood performance of the Zeigler Field was evaluated with anintegrated 3-D geologic and reservoir simulation model. Direct linkage of thegeologic model and reservoir simulator allowed both models to be greatlyimproved during the course of the simulation process. Results of the studyincluded:
geological model of the study area
evaluation of waterfloodrecovery efficiency and identification of a bypassed region,
comparison ofalternative oil recovery strategies for optimal incremental production.
Most of the 42,000 oil wells in the State of Illinois are stripper wells thatproduce less than 2 barrels (0.32 M3) of oil per day. They areoperated by small, independent companies which have limited financialresources, and technical know-how to implement enhanced oil recovery methods.Almost 1,000 producing oil wells were abandoned and plugged in 1992 becausethey were no longer economical to operate. Since 1987, there has been a threefold increase in the plugging of producing oil wells. One of the causes forthis rapid increase in the rate of well abandonment has been the difficultiesencountered in waterflooding small heterogeneous reservoirs. This topic hasbeen discussed twice during monthly meetings of the Illinois Regional Societyof Petroleum Engineers in the spring of 1993 and the following reasons werecited as the likely causes of waterflood failures:
Reservoir heterogeneity or compartmentalization.
The common practice of hydraulic fracture during primary production mayhave created flow channels between injectors and producers causing early water break through.
The rapid decline of pressure in small reservoirs after a relatively shortperiod of primary production can create gas channels that allow injection waterto bypass reservoir oil and cause premature water breakthrough.
Adverse water-oil relative permeability effects.
This paper describes the experience gained from development of the Plumfieldlease of the Zeigler Field, Illinois It illustrates the benefit of acquiringand using geological, engineering and field data for reservoir management anddemonstrates that some of the difficulties encountered in waterflooding a smallreservoir can be overcome with prudent reservoir management techniques. Theintegrated geological and engineering study carried out on this field had theobjectives of determining the reservoir architecture and developing a strategyfor improved oil recovery for typical small reservoirs in the Illinoisbasin.
Zeigler Field is located in the southern half of Franklin County, in the southcentral portion of the Illinois Basin (Figure 1).