NEW DEVELOPMENT TECHNIQUES IN BASS STRAIT

Abstract

A total of 114 exploratory wells have been drilled in Bass Strait by Esso Australia Ltd. Prior to 1979 discoveries of hydrocarbon accumulations have been developed exclusively by the use of conventional platforms. During 1979 the use of subsea completions was introduced as a development technique. In addition, areal coverage by conventional platform development was extended by the drilling of a very highly deviated directional well.

Cobia-2, the first subsea completion in Bass Strait, was brought on production on June 30, 1979. During the installation of the subsea completion two 90 mm flowlines were successfully laid using the reel pipe-laying technique from the back of a workboat. Production of the well has been successfully controlled by one of the few operational electrohydraulic control systems in the world. Numerous pumpdown tool operations have been completed for dewaxing of flowlines. While on production the well has been producing 450 kl per day, flowing to the Mackerel ‘A’ platform.

In the early 1970's the location of platforms was determined by using a 45° to 50° angle of deviation limit for directional wells. This limit was gradually extended with each platform until a very significant change was achieved with the Mackerel A-14 well drilled with an average deviation angle of 69°. The significance of following good basic drilling practices was accentuated while attempting to reach a true vertical depth of approximately 2 400 metres by drilling 5 200 metres of directional hole. Production was commenced from this well on November 30, 1979.

These two techniques will pave the way for increased recovery in the 1980's, especially from the smaller reservoirs in Bass Strait. Perhaps more importantly, these techniques will have significance in the deeper water areas to which the industry is currently headed.