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Considerable effort has been made by various research groups and exploration companies to improve completion techniques in the Devonian Shale. Completions in the Devonian Shale in the Big Sandy Field run the gamut from natural completions, shot-hole completions, Nitrogen fracturing, Nitrogen foam fracturing, CO2 foam fracturing, and gelled water fracturing, to the latest technique promoted by the DOE, sand-laden CO2 fracturing. Production rates from wells using the different completion techniques in this field vary widely. Of these techniques, Nitrogen foam fractured wells have been observed to have by far the lowest production rates. This paper compares production rates and well test results of the various completion techniques and attempts to quantify the problem with the Nitrogen foam fractured wells in terms of reservoir parameters. This will establish a base from which any improvement can be measured. The conclusions will be drawn from the case histories of approximately 105 wells located within the Big Sandy Field. A summary comparison of production data will allow a fair analysis of the techniques investigated. Well test data from a sampling of these wells will help define reservoir parameters and fracture geometry. Introduction Designing fracture treatments for the Devonian Shale in the Big Sandy Field has always posed a formidable challenge for research groups, exploration and production companies as well as service companies. Since activity in the field dates back to almost the turn of the century, several different stimulation methods have been tried with changing levels of technology. Extensive production records are available for comparing the various completion methods. The focus of this study is a group of wells located in eastern Martin and northern Pike Counties in Kentucky and western Lincoln and eastern Wayne Counties in West Virginia. This area was chosen because of the variety of stimulation methods used on these wells. The wells in Kentucky have been natural completions, shot-hole completions, fractured with Nitrogen, fractured with Nitrogen foam and sand, and fractured with CO2 foam and sand. P. 111

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This paper is a case study of a Coiled Tubing Drilling (CTD) project in which a lateral extension was drilled from an existing wellbore into a gas storage reservoir. The project took place in the Donegal Storage Field located in Southwestern Pennsylvania. The gas storage reservoir is the Gordon Stray Sandstone at a depth of approximately 2,680 feet true vertical depth (TVD) in the project well (Donegal #4621). The focus of this case study is on the geological and engineering considerations as part of pre-planning and candidate selection, drilling operations, problems encountered during the project, and the deliverability enhancement that was achieved. The drilling of a lateral extension using CTD technology was considered as a method to improve deliverability for several reasons: the failure of previous attempts to stimulate wells in the field using conventional and unconventional methods, geological considerations (including the extremely limited reservoir thickness of approximately four feet), the wellbore configuration, and the reduced footprint (environmental impact). Drilling operations used several technologies that are considered unconventional in the Appalachian Basin. Build rates and steering were controlled via an umbilical within the coiled tubing. The umbilical contained an electric line for the transmission of Logging While Drilling (LWD) data, and hydraulic lines to manipulate the direction of the bit. The well was also drilled in a constant state of underbalance using on-site generated nitrogen to reduce mud column weight and four-stage separation to control flow rates at the surface. Although several problems were encountered, and are discussed at length in the body of this paper, the lateral extension on Donegal #4621 was successful. A 698 foot lateral was drilled with approximately 450 feet located in the storage reservoir. Initial testing indicates that the horizontal extension has yielded over an 8,000% increase in deliverability from this well. Introduction Columbia operates a system wide program to maintain storage performance. Donegal Storage Field is operated as a peaking field; therefore deliverability maintenance/improvement is a priority. Since 1993, various recompletion and stimulation techniques have been utilized in the field as part of these efforts. These included increasing perforating shot density, high sand concentration fracs, Tip Screen - Out fracs, and Extreme Over-Balanced Technology (Perf- Surge and Perf- Stim)1. No method utilized provided an improvement in skin factor or deliverability. The drilling of a lateral extension in the storage reservoir from an existing wellbore to improve deliverability was first proposed in 1998. Various drilling methods were evaluated for price and feasibility. Coiled tubing was selected based on wellbore configuration, extremely limited reservoir thickness, and reduced footprint. If successful, the goals of this project would be to:Improve/maintain deliverability from the Donegal storage reservoirUtilize existing facilitiesMinimize environmental impactRemain cost effective