Tirrawarra Oil Gas Lift Pilot Project
Aaron Fong Wei Shan and Minh Le Cong Nhat
Engineering Honours 2014
Australian School of Petroleum
The University of Adelaide
Reservoir and well performance for oil reservoirs generally deteriorates with time, either due to pressure depletion or elevated water production, and artificial lift is often employed to alleviate the situation. Careful screening of artificial lift methods by Santos for their Cooper basin fields has led to the conclusion that coiled tubing gas lift is to be implemented for the wells in the Tirrawarra field to extend the production life of the wells. In order to lower the risk of implementation, a field trial of using coiled tubing gas lift was first carried out on two wells in the Fly Lake field. After successful implementation in Fly Lake, a pilot program consisting of six wells was chosen for the Tirrawarra field. These six pilot wells will receive the injection gas via a new gas lift line from the compressor located at Fly Lake. However, the review of the artificial lift selection in this report has determined that Plunger lift should be considered other than coiled tubing gas lift. Hence, the report will further discuss the feasibility of plunger lift.
This study involves the refinement of the proposed coiled tubing gas lift design, requiring the optimization of injection rate and depth of gas injection. The study was performed by utilizing specialized modelling software (IPM Prosper), studying individual well performance using inflow performance relationships (IPR) - reservoir into the well, and vertical lift performance (VLP) in the tubing string. Optimization was achieved through sensitivity analysis. This optimization has led to the recommendation of a specific and optimum gas injection rate for each well. Secondly, it was found that optimum rate determination should also consider depth of injection, considering possible ballooning of coiled tubing and expansion due to downhole temperature. Thirdly, current production rates, after the implementation of coiled tubing gas lift, are forecasted for economic evaluation. Finally, a safety issue was discovered, with the recommendation of repositioning of the tubing hanger on the wellhead, a situation further elaborated in the report.