Infill Reserve Growth Resulting From Gas Huff-n-Puff and Infill Drilling-A Case History
Authors: Wozinak David A. , Wing James L. , Schrider Leo A. 
Published: December 2007

Abstract
The economic exploitation of the East Canton Oil Field truly began with the technology advancement of hydraulic stimulation in the early to mid 1940's. This field which encompasses approximately 175,000 acres in Stark, Carroll and Tuscarawas Counties of northeastern Ohio, realizes the vast majority of its production from the Clinton Sandstone reservoir which is located at a depth of 4000-6000 feet. Primary development of this field on 40 acre spacing, has resulted in the drilling and completion of in excess of 3100 wells, a recovery to date of approximately 86 million barrels of oil and an expected Ultimate Recovery of 140 million barrels of oil or 9% of the 1.5 billion barrels of oil believed to be in place.
Due to the low recovery factors which are typical of low permeability, solution gas drive reservoirs, efforts have been underway to identity techniques capable of improving the ultimate recoveries from the field. Two (2) methods which Belden & Blake has been examining, target the improvement of recoveries from the existing drainage patterns as well as the infield reserve growth from development of undrained areas within the tight (&lt;0.1 md), stratigraphically compartmentalized reservoir. The "Marlboro Field", located in the extreme north of the much larger East Canton Field was selected as a pilot area for an initial study. Figure 1
Phase I of this study was to identity the impact that injecting natural gas into existing wells, repressuring the near wellbore/hydraulic fracture system, allowing for a "soak" period then returning the well to production would have on ultimate recovery. Computer simulations conducted by International Gas Consultants Inc. (IGC) indicated that the average drainage areas of this field were approximately 1/2 of the development spacing and that by injecting gas in a Huff-n-Puff fashion could result in incremental recoveries in the order of 1 new barrel of oil per 30 Mcf of injected gas. This study also indicated that in combination with infill drilling, overall oil recoveries within the field could increase by an estimated 100% over that achieved from primary recovery alone. Based on this study, two (2) Huff-n-Puff cycles were undertaken in a pilot area within the Marlboro Field resulting in incremental recoveries of 500 barrels of oil per well or 1 new barrel of oil per 40 Mcf of injected gas.
To address the infield reserve growth potential of this field from infill drilling, Belden & Blake drilled two (2) infill wells in late 1996 and identified commercial reserves in an area where some level of pressure depletion had occurred. In an effort to better identity high quality infill sites, S.A. Holditch and Associates was contracted to conduct a "Moving Domain Analysis" utilizing the reservoir and production data from the field. Based on this study, between 10 and 30 potentially economic infill sites have been identified within the Marlboro Field. Efforts are currently underway to validate that study. The study and its field validation will not be addressed in this paper but will be the topic of a future publication. The basis for the Moving Domain process has been well documented in previous studies.

Introduction
The geologic environment of the Clinton Sandstone has resulted in a stratigraphically complex reservoir. The Clinton sand unit is Lower Silurian in age and lies between the Dayton Limestone (Drillers Packer Shell) and the upper Ordovician Queenston formation (Drillers' Red Medina) at depths of 4,600 to 5,300 ft. Within the East Canton Field, which encompasses approximately 175,000 acres, the productive interval consists of interbedded shale, siltstones and sandstones ranging in thickness from 50 to 250 feet in thickness. These sandstone and siltstone lenses possess significant lateral and vertical discontinuity typical of a stratified reservoir. It is due to the interbedded sandstone and siltstone lenses, together with the inherently lower recoveries of this tight, solution gas drive reservoir that have resulted in low recovery efficiencies in the order of 8-10 % of the OOIP. Based on projected ultimate recoveries of 140 million barrels, the remaining hydrocarbons in place are expected to exceed 1.3 billion barrels. The magnitude of this remaining hydrocarbon resource has been the impetus for past and current IOR/EOR efforts.
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