Abstract

A conventional waterflood of the Richardson Berea sandstone will yield a much greater than forecasted oil recovery. The very low permeability upper portion of the sandstone was ever considered pay but obviously a large portion of the recovery in the waterflood came from this "non-pay". Similar situations may exist in other oil fields, especially old or lugged oil fields that may present economical future development potential.

Introduction

Often oil recoveries for waterfloods and Improved Oil Recovery (IOR) projects are over-estimated and engineers must begrudgingly reduce reserves. Not a pleasant task. On the other hand, oil reserves for such projects are seldom underestimated and it is a much easier task for an engineer to add project reserves when justified. The Richardson Berea yield falls in the latter category although it is not completely obvious how the bonus oil has been produced.

Some of the most interesting and exciting times for an engineer or geologist working with old producing areas can be finding clues from old production records or production histories that lead to workovers, the development of IOR projects or new drilling. One only has to think of the many hydrocarbon zones that were drilled prior to hydraulic fracturing and were considered "too tight" to be economic. It is this theme that motivated the writing of this paper, especially for the Appalachian Basin area where many oil fields have been plugged without employing any improved recovery.

Waterflood Recovery

Based on average performance of waterfloods in reservoirs similar to the Richardson Berea, the waterflood recovery is often comparable to the primary recovery. If a reservoir had a recovery of 2000 BO per acre on solution gas drive, then it would be reasonable to estimate a waterflood recovery in the range of 2000 BO/AC. This, of course, is providing that other basic parameters for a successful waterflood are found in such a reservoir. The primary recovery for a solution gas drive reservoir with average or better permeability is in the range of 15 to 20 % of the STOOIP. Therefore, a similar percent recovery could be expected in a waterflood. There are exceptional cases where the waterflood recovery is much greater that the primary recovery. This could result from a reservoir, especially a shallow one, having a very limited amount of dissolved gas which would result in comparatively low primary recovery. However, a waterflood could be quite successful in such a case and recover much more oil than the limited primary mechanism.

The Richardson Berea is considered to be an average Appalachian reservoir with an average primary recovery of 20% of the STOOIP. Although the early high rate production was not available for the field, other Berea field averages suggest the above recovery estimate is valid.

Geology and Reservoir

The Berea sandstone of Lower Mississippian age produces in several areas of the Appalachian Basin and was deposited from several sources. The zone is an important producer of both oil and gas. One of the earliest successful waterfloods in the Basin was in the Chatham Berea field in the vicinity of Cleveland, Ohio. The subject reservoir (Fig. 1) is located in a down dip portion of the Gay-Fink Trend of central West Virginia.

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