Abstract

The Appalachian Basin, the oldest domestic United States producing area, is home to a number of active waterfloods and even more waterflood candidates. Efforts to evaluate existing floods and assess new opportunities, however, are often hampered by scant reservoir rock and fluid data, as well as incomplete, or nonexistent, fluid production and injection records.

The purpose of this paper is to illustrate, through the study of a case history, a practical methodology for evaluating a 30-year old Appalachian Basin waterflood, beginning with culling original in-house documents and well files and concluding with numerical simulation. The studied flood is the Richardson Unit Waterflood (Calhoun and Roane Counties, WV).

Introduction

The purpose of this paper is to provide a practical methodology for evaluating both existing waterfloods and waterflooding candidates located in the Appalachian Basin. Often, engineering efforts in such mature producing areas are hampered by incomplete reservoir rock, reservoir fluid, fluid production, and fluid injection data.

The methodology is illustrated through the study of the Richardson Unit Waterflood, a 30-year old Appalachian Basin waterflood located in Calhoun and Roane Counties, WV (Fig. 1). This producing area has been active for more than 100 years. The evaluation consists of:

  • a comprehensive examination of the available in-house material

  • a review of the literature

  • analytical analyses

  • decline curve analysis

  • numerical modeling.

Examination of In-house Material

The purpose of the examination of in-house material 1 was to gather, organize, and assess pertinent geologic, reservoir rock and fluid properties data, and the history of the project. While this first step in the evaluation may be sometimes tedious, early engineering and geological studies and operations records often provide significant data and insights.

Geology.

The Richardson Unit produces from a Lower Mississippian age Berea sandstone channel located in the Gay-Fink Trend system that crosses central West Virginia. The average depth to the top of the Berea in this producing area is 2350 ft subsurface. A typical log section (Fig. 2) reveals a permeable producing sand of some 14 ft gross thickness located in the main channel fill sandwiched between by a 10–14 ft thick hard, low permeability cap composed of fine-grained sandstone and an upper Devonian Shale barrier. The permeable pay sand is a poorly-cemented, coarse-grained sand and conglomerate. The Coffee Shale was deposited on top of the Berea sand, forming an upper barrier to the Berea sandstone.

Structurally, the reservoir is situated in a syncline with gas caps up-dip to the northeast and northwest. Structural folding subsequent to the accumulation of the in-place oil and gas resulted in the migration of the oil to the lower synclines and the gas to the structurally higher anticlines of the buried channel. The horseshoe-shaped Berea reservoir is bounded to the north and south by pinch-outs (Fig. 3) and further closed-off to the north by the plunging end of the Burning Springs Anticline. A structure map of the Berea top is shown as Fig. 4. The axis of the Burchfield Syncline runs through the center of this northerly-dipping oil reservoir.

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