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A Study To Identify Technologies That Could Be Applied To Improve Gas Field Recovery Resulting In An Updated Development Plan For The Toolachee Field, Cooper Basin South Australia

Chang, Brenda

Hosking, Lisa

Lovibond, Nicole

Engineering Honours Degree, 2010

University of Adelaide

Abstract

The Toolachee Field is a mature gas field located in the Cooper Basin, onshore South Australia. The field has been producing since 1984 with a total of 57 wells drilled. The West Patchawarra culmination holds the bulk of the original gas in place (OGIP), and is the main focus of this project. Water is a significant problem across the field and many wells have ceased production as a result. Low reservoir pressure adds to the difficulty of recovering the reserve.

Production data indicates significant volumes are potentially remaining. However current recovery rates are not operationally economic on a long term basis. The aim of this project is to understand the inflow direction, drive mechanisms and potential volumes remaining in the field. This knowledge will assist in generating a new development plan for the field, which will enable Santos to maximise recovery in the most cost efficient manner.

Further production enhancement is essential to future development of this mature field. Without it, it is likely that the Toolachee field will be prematurely abandoned. With this in mind, worldwide secondary recovery methods and other production enhancement methodologies have been reviewed in analogous fields, and proposed for incorporation into the future forward development plan. Infill drilling and waterflooding are suggested as potential methods of increasing production in the field.

A review of the pressure data was undertaken to facilitate the understanding of the drive mechanisms. P/z analysis determined that the field is highly compartmentalised, with deviation from simple tank depletion drive model evident in many wells. The explanation for this deviation is hypothesised to include partial water support and tight gas contribution. The pressure evaluation was coupled with generation of decline curves and analysis of rate transient data in order to provide an updated reserves position.

In addition, each well was reviewed to assess opportunities for production improvement. This enabled generation of an Inwellbore project seriatim. PROSPER analysis of high graded wells resulted in additional opportunities. The analysis process undertaken throughout this study helped identify well testing requirements, which were used to populate a surveillance seriatim.

Conclusions have been drawn from this project, including the likelihood that tight gas contributions are unlikely to have been previously mapped, thereby influencing the current mapped OGIP and recovery factor. Further development of the field by infill drilling and waterflooding is proposed in conjunction with optimisation opportunities.

These recommendations have been prepared for presentation to Santos, with proposal for further analysis and incorporation into future field development plans for the Toolachee Field.

Australian School of Petroleum
THE UNIVERSITY OF ADELAIDE

SA 5005 AUSTRALIA

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