Abstract

Large volume underground storage of hydrocarbons has been developed and practiced in Saskatchewan. Canada for many years. Use of these facilities has gained importance in recent years, due mainly to economical and environmental reasons.

TransGas Limited currently has 42.8 billion cubic feet (Bcf) or 1206 million cubic meters (106m3) of working storage capacity. Of this total 14.1 Bcf (397 106m3) is held in solution mined bedded salt caverns and the remaining 28.7 Bcf(809 106m3) is held in depleted gas pools and gas caps. The total gas storage capacity, is 83.97 8cf(2366 106m3) of which 16.46 Bcf (463 106m3) is held in caverns and 67.51 Bcf (1902 106m3) is held in depleted pools. All of the depleted gas pools are located on the western side of Saskatchewan, mainly in Lower Cretaceous sandstone reservoirs. The washed salt caverns are scattered across Saskatchewan, all developed in the halite portion of the Middle Devonian Prairie Evaporite salt bed.

Traditionally, TransGas Limited has developed its solution mined salt storage caverns from start to finish to supply Saskatchewan customers.. However, in the increasingly competitive North American natural gas storage market, TransGas Limited has had to look for innovative methods to develop cost effective storage facilities while providing new market development opportunities, One method of prodding natural gas storage service, used in two recent cases, is to convert existing salt caverns, previously used to Store Liquefied Petroleum Gas (LPG) products, to natural gas storage.

TransGas Limited currently owns, leases and operates twenty-one (21) bedded sail caverns, of which six (6)caverns are currently LPG products, Three (3) additional bedded salt caverns are currently in the process of being Solution milled.

This paper presents a general overview of TransGas Limited's present experiences with the conversion of LPG salt caverns to sweet natural gas storage service.

Introduction

Some of you today will have knowledge of the storage operations within Saskatchewan.

TransGas pioneered the development of underground solution mined bedded salt caverns in Canada (and the United States as well) in the early 19605 at Melville, Saskatchewan. The sole purpose was for the dry or brine-free storage of natural gas. The equivalent caverns in the United States Were developed at Eminence, Mississippi in 1970. Prior to that time, salt caverns had been utilized by other companies for life storage of Liquefied Petroleum Gas (LPG) and other hydrocarbon liquid. Salt caverns permitted the highest rate of gas delivery; provided a secure and environmentally safe form of storage; permitted full product recovery; and required the least cost for construction; factors which still hold true today.

In the 1990s, TransGas purchased outright or leased a total of six(6) former solution mined bedded salt, LPG caverns and converted them to natural gas storage. Three (3) of these caverns are located at Regina North and three(3) at Melville South (see Figure 1). One quarter of all TransGas cavern storage comes from converted LPG caverns. The pre-requisites for cavern conversions are identified in Figure 2.

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