Abstract

During the summer and fall of 1994, CNG Transmission Corporation fracture-stimulated thirty (30) gas storage wells with a cross-linked gel fluid system. The work was done to increase late-season field deliverability. Individual well tests taken to date have shown that, on average, per-well deliverability has increased by a factor of five. The text that follows will detail the engineering and geologic aspects, procedures, results, and analysis of the project.

A discussion of the strategic placement of the storage fields involved will be presented, along with a review of FERC Order 636 and it's impact on the current gas storage business mechanics.

Overviews are presented on the geology, reservoir properties, and characteristics of the storage fields involved in the project. General well design and well completion configuration are discussed. Fracturing/refracturing candidate selection criteria are presented. Basic fracturing design criteria are discussed including: fluid parameters, geometry, proppant selection, and concentration. Discussions of observations and minor changes in treatment designs which occurred between the different fields are discussed,.

The treatments are summarized and compared on a pre and post fracturing deliverability test analysis. Explanations are offered for wells with exceptional results, as well as marginally successful treatments.

Introduction

As the Gas Storage business moves into the era of FERC Order 636 deliverability enhancement work has gone from being merely prudent to being absolutely necessary in order to successfully compete in the deregulated and "unbundled rate" business environment. Storage operating companies have looked at a myriad of techniques to maintain and enhance deliverability. There has recently been a marked increase in deliverability enhancement projects among Appalachian basin operators, in order to satisfy the growing demands of storage customers.

Based on the results of this project area, hydraulic fracturing remains one of the most cost-effective means of accomplishing deliverability enhancement. Knowledge of field history and reservoir characteristics, candidate selection criteria, job design, and project surveillance all combined to make this a successful project.

STORAGE FIELD PROJECT AREA

The project took place in five (5) storage pools operated by CNGT in northern Pennsylvania and southern New York. The fields are generally referred to as Leidy, Greenlick, Tioga, Sabinsville and Woodhull. Leidy and Greenlick fields are contained in the southeastern corner of Potter and north western Clinton Counties, Pennsylvania. Tioga and Sabinsville fields are located in the northern part of Tioga County, Pennsylvania. Woodhull field is located in the southern part of Steuben County, New York.

These fields range in size from 34 to 100 BCF, and maximum deliverability ranges from 350-1200 MMcfd. These fields are strategically located with respect to major pipeline hubs, and in near proximity to major industrial and residential markets in New York State as shown in figure 1.

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