Abstract

This paper briefly describes the history of gas development in Western Australia (WA) and overviews the Harriet Gas Gathering Scheme now under construction, which ii the first project to collect associated gas in conjunction with non associated gas. The economics of gas gathering schemes are illustrated by reference to a case study and an approach to a gas flaring and gas gathering strategy for Western Australia is proposed. The implications of such a strategy for the petroleum industry and the development of WA are outlined.

Introduction

By the early 1970's large reserves of natural gas had been discovered in Western Australia and since the mid 1980's, increasing quantities of oil are being discovered. The State's combined crude oil and condensate output is presently 112,000 bbl/d (17.8 km3/d), presently 112,000 bbl/d (17.8 km3/d), representing a three-fold jump from the average levels of 36,000 bbl/d (5.7 km3/d) during the 1970's (see Figure 1). Much of this increased production flows from oil developments in the shallow waters around Barrow Island. This focussed attention on whether use could be made of the associated gas, which is produced with oil, and prompted studies into the alternative uses of this gas by utilising gas gathering networks to collect both associated and non associated gas and pipe it to market. Concurrently, increasing pipe it to market. Concurrently, increasing concern was being expressed about greenhouse gases and ways of and means to reduce emission levels.

Gas gathering, a concept which is widely pursued in many parts of the world, relates to pursued in many parts of the world, relates to the collection of both associated gas and non associated gas. In the context of this paper, the important State issue of developing a gas gathering strategy for associated gas which to date has either been flared, reinjected or used as plant fuel, is discussed.

Western Australia's natural gas development to date has however been based on non associated gas gathering, through the linking by pipeline of the onshore Dongara and Woodada gas fields as well as the offshore gas fields of North Rankin and Goodwyn.

The ability of WA petroleum developers to utilise commercially viable associated gas in shallow water offshore areas has only recently occurred. This situation has resulted from new gas market opportunities, and the presence of major onshore gas pipeline infrastructure which has been developed since the mid l980s. The Dongara to Perth pipeline and the Dampier to Perth pipeline currently deliver about 11 Mm3/d to gas users in WA.

The aim of this paper is to overview the history of gas development in WA and to outline the Harriet Gas Gathering Scheme now being constructed. The paper highlights economic and technical considerations flowing from gag gathering schemes and puts forward a possible approach to a gas flaring and possible approach to a gas flaring and gathering strategy. Finally, the paper reviews the implications for the petroleum industry and State development of such a strategy.

GAS GATHERING - THE OVERSEAS CONTEXT

In the overseas context, two areas which are in the forefront of gas gathering are the North Sea and the Gulf of Mexico. One of the most well known is the FLAGS scheme (North Sea liquids and associated gas system) which commenced in the mid 1970's and by the mid 1980s collected associated gas from eight fields via thirteen platforms standing in up to 200 metres of water.

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