Abstract

Since 1985 Bass Strait oil production has declined by over 100 KSTB/D (16 ML/d) to an average of 364 kSTB/D (58 ML/d) in 1988. To mitigate this decline Esso Australia has undertaken a coordinated program aimed at realizing the full production potential of existing reserves and facilities. This program centres on three fronts; major projects such as gas lift and waterhandling, a workover program and the removal of facility constraints. Over the next 4 years this rate enhancement activity is currently forecast to offset declining production rates by an average of 60 kSTB/D (10 ML/d).

Currently over 60% of available oil wells are capable of being gas lifted. including two wells with average angles in excess of 70 degrees, and it is planned to increase this number to over 75% in the near term. The strong water drive characteristics of Bass Strait reservoirs has resulted in increased formation water production. Waterhandling facilities have been installed to maximize production levels. Current waterhandling capacity production levels. Current waterhandling capacity is around 300 kSTB/D (48 ML/d) with half being achieved through use of hydrocyclones which provide improved portability and operating flexibility compared with conventional waterhandling equipment.

Since mid 1987 an average of over 4 workovers per month have been completed in an intensive program to achieve the full potential from all wells. This has been achieved through the use of alternative options to the conventional tubing pull workovers of the past. Extensive use has been made of coil tubing past. Extensive use has been made of coil tubing units (CTU), concentric rigs and a jack-up rig instead of conventional platform rigs, thus reducing costs and returning wells to production faster.

Platform facilities have been optimize through Platform facilities have been optimize through close liaison between operations and engineering personnel to locate and remove production personnel to locate and remove production constraints where possible. Integration of facilities for new developments has allowed production from existing reservoirs to be increased. production from existing reservoirs to be increased

Introduction

The Gippsland Basin lies offshore South Eastern Australia and contains the largest known reserves of oil in Australia, plus substantial reserves of gas. Gas was first discovered by Esso and BHP in 1965 and the first production platforms were started-up in Bass Strait in 1969. Since then 14 platforms have been installed and about 2.5 billion barrels (400 ML) of oil, 400 million barrels (64 ML) of LPG and 2.8 trillion cubic feet (100,000 Mm3) of gas has been produced.

Figure 1 illustrates Gippsland's oil production history. Production peaked in 1985 at an annual average rate of nearly 500 kSTB/D (80 ML/d) and has been steadily declining since then. Production from the remaining undeveloped reserves will partially offset this decline but they are relatively small reservoirs and difficult to develop economically.

Figure 2 shows the location of the major producing fields in Bass Strait. Marlin, Snapper and Barracouta are predominantly gas fields and the remainder are oil fields, the largest being Kingfish, Halibut, Mackerel, Fortescue and Cobia.

Since the early 1980's in particular, there has been considerable effort devoted to finding ways to optimise production from our aging reservoirs. The primary emphasis has been on gas lift and offshore primary emphasis has been on gas lift and offshore waterhandling facilities, and workovers. Many new and innovative techniques have been successfully introduced in recent years.

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