New Workover and Completion Technology Utilised in Bass Strait

Abstract

As production from the Gippsland Basin in Bass Strait Australia passes the 30 year mark, the need to find innovative techniques to maximise production from this world class maturing basin is a principle priority for the operator. To address this issue, Esso Australia, on behalf of the 50: 50 joint venture with BHP, recently embarked on a concentrated program to trial and evaluate several new technologies being developed by industry. This paper discusses several technologies that were employed to increase production, enhance reservoir recovery and improve well integrity. Varying degrees of success were achieved during these trials and the successes, failures and lessons learned will be outlined. The technologies discussed include:Scab liners with inflatable packers set through tubing in horizontal wells to isolate water/gas production;Gas and water shut off techniques utilising polymer technology;Wellhead leak sealing technology using differential pressure-set coagulating polymers;Wirelineless completions using expendable plugs and perforating gun hanger systems on space limited platforms (during infill drilling operations);Through-tubing deep penetration perforating charges used to stimulate production from wells with extensive near wellbore damage; andMini-fracturing gas stimulation technology used on poor performing reservoirs. The high level of mechanical success combined with encouraging reservoir success in some instances is promoting a continued search for further production enhancing techniques. Introduction Esso/BHPP's operations in Bass Strait, South Eastern Australia, include 16 production platforms, five sub-sea completions and two single mono-towers (Fig. 1). From these facilities there are 364 wells, the majority being oil and/or gas producers with the remainder injecting for reservoir management. Since production commenced from the Gippsland Basin in 1969 with the installation of the Barracouta platform, significant ongoing drilling and workover activities have enhanced and maintained production levels. Until the mid to late 1990s, traditional tubing pull, mechanical isolation and cement squeeze techniques have yielded high levels of mechanical and reservoir success with strong workover economics. An ever declining list of high quality opportunities, as evaluated using traditional techniques, made it necessary to embark on a search for technologies that would continue to achieve mechanical and reservoir objectives while at the same time reducing workover costs. After implementation of each new technology, an evaluation based on both mechanical and reservoir factors was performed. Mechanical success was defined as the completion of the required scope of work with appropriate testing successfully completed. Reservoir success was defined by long and short term reservoir performance compared against pre-job expectations. This paper concentrates on the mechanical aspects of each technology, however reservoir performance has also been discussed where appropriate. Each of the new technologies trialed are discussed in the following sections; Scab Liners with Inflatable Packers A number of horizontal wells in Bass Strait were identified as potentially producing either gas or water preferentially from the heel of the horizontal section. The cost of traditionally used methods for water or gas shut-off such as tubing pull re-completions for installation of mechanical isolation equipment or cement squeezes made them uneconomic.