Abstract

The Medina is a group of Silurian-age sandstone formations that have been dependable gas producing zones in Western New York since the late 1800's. Most of the production from the Medina has come from a combination of the Whirlpool and Grimsby formations. The method of how to most effectively complete these two formations is an ongoing topic of debate. The formations are separated by the Cabot Head shale formation that ranges in thickness from less than 5 feet to more than 70 feet in some places. One of the main questions with regard to completion of these formations is whether to 1) stimulate the Whirlpool and the Grimsby with separate treatments to ensure effective stimulation of both layers; or 2) stimulate both formations with one hydraulic fracture treatment, at a lower cost, that grows from the Grimsby through the Cabot Head and into the Whirlpool.

Microseismic monitoring of hydraulic fracture treatments is now a proven technique used to analyze hydraulic fracture geometry and azimuth. The New York State Energy Research and Development Authority funded a project in Chautauqua County, New York to use this technology to monitor a hydraulic fracture treatment in a Grimsby/Whirlpool well for the purpose of understanding hydraulic fracture development in these formations.

This paper uses the microseismic results obtained from the study to validate a hydraulic fracture model of the Grimsby/Whirlpool formations. A sensitivity analysis was then performed using this hydraulic fracture model to give direction as to when the Grimsby and Whirlpool formations should be stimulated simultaneously and when a two-stage completion would be more beneficial to obtain an effective stimulation in both zones.

Introduction

The Grimsby and Whirlpool formations have been drilled and completed using some basic log measurements and stimulation techniques for many years. Unbridled Energy sought to better understand this reservoir in order to maximize the effectiveness of the completions in their Lake Shore field in western New York. Seeing the advantage of this knowledge for the many other New York operators, NYSERDA agreed to help fund the project that was managed by Schlumberger Data & Consulting Services.

The log section below in Figure 1 covers the Whirlpool and Grimsby formations in the subject well located in Chautauqua County, New York. Both formations are gas bearing zones that have been completed via hydraulic fracturing for many years from eastern Ohio, through Pennsylvania and into New York. The ongoing question is how to most effectively stimulate these formations while best controlling costs. One method is to simply perforate the Grimsby and hope the hydraulic fracture reaches and develops into the Whirlpool. Another completion option is to treat the Whirlpool and Grimsby with two separate hydraulic fracture treatments. While this option ensures both zones receive their portion of the stimulation treatment, it does cost more than the previously mentioned method. This additional cost is made up of extra time on location the day of the treatment, the cost of an isolating bridge plug and separate perforation run between stages along with the rig time needed after the job to remove the bridge plug. The third completion option of treating both zones simultaneously by way of a limited entry perforation scheme is also used but was not modeled in this paper.

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