This paper presents an advanced method to accurately calculate oil and gas production from the Laminaria and Corallina fields produced by the Northern Endeavour FPSO on the Timor Sea, where direct metering has become unreliable or unavailable. The entire production data history was reconstructed, and results applied for better understanding of the reservoir and enabling better facility planning.
The newly developed allocation methodology is based upon PVT correlations that map liquid/gas ratios from production separator conditions to plant products. Mass balance at component level was applied to ensure sources and uses of gas + LPG were fully accounted for. Instead of the conventional approach where a simple oil shrinkage is applied, this method accounts for oil shrinkage which varies with process operating parameters, gas lift rate and back produced gas. The light oils from the Laminaria and Corallina fields are particularly susceptible to these effects.
Before any reconciliation, the total oil from these two fields calculated by this independent method compares closely with cumulative field life exported oil, and monthly reconciled rundown. Oil allocations between fields were rebalanced based on the mass allocation approach. Additionally, gas production figures were affected after discovering that a significant quantity of previously injected gas + LPGs had not been back-produced and was instead captured in the reservoir flow path. The reallocated production data and improved metering of current gas and LPG production rates enables a more representative reservoir model of remaining oil, gas and LPG ultimate recovery, well free-flowing limits, timing for infill wells and evaluation of the potential for alternate fuel availability based on mass reallocation of LPGs.
Insights from this work have provided key inputs into decisions on facility modifications and upgrade projects to maintain production and extend field life. The correlations and the workflow from this work have also been programmed into the Process Historian Database for better real-time monitoring and automation. The methodology described is applicable to other light oil or gas condensate fields to significantly improve metering, leading to better reservoir understanding and facility planning.