Abstract

The purpose of this paper is to provide a case history of methods used to work on an underground storage cavern containing butane. This refined product had become trapped behind the casing set point. The product was recovered using a mechanical casing cutter and a snubbing unit.

Introduction

In 1991, when a portion of the roof fell, it formed a trap for an estimated 100,000 bbls. of liquid butane. With extensive planning and project meetings, a thorough procedure was prepared. The workover consisted of first, pulling the tubing up +80' and rehanging it. Then, going in with a mechanical casing cutting tool through tubing, to cut the production casing at the newly formed roof. This would allow circulation of the trapped product. Three cuts were done, one at a time, in an attempt to insure the pipe fell into the cavern. A snubbing unit was used to control the pressure while working on the well. After the final cut was made, a tubing extension was snubbed in and hung off as a tail pipe to the tubing string. A blanket of nitrogen was maintained in the snubbing stack during snubbing operations. The work was performed without incident and saved a substantial amount of money by recovering 100,000 bbls. of butane and returning the cavern to operational status.

CAVERN OPERATION BASICS

Because there are differences between cavern operations and oil and gas production operations, a few basics will be covered…

How Caverns Work:

Storage caverns are for storing hydrocarbons to be used by downstream facilities as required. Caverns are created by drilling into a salt formation then dissolving it with fresh water, creating a void in the formation. Once in service, brine is used instead of fresh water to prevent cavity enlargement.

These caverns are developed in a flat, sedimentary laminated salt formation, not in a salt dome.

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