Disclose Hidden Hydrocarbon HC Reserves from Additional Zone of Interest AZIs Using dT LogR Method in Lunar Field, Gulf of Thailand

Abstract

Lunar field is a marginal gas field located in the Gulf of Thailand. A significant portion of reservoir sands is currently categorized as Additional Zones of Interest (AZI) which is not accounted in reserves. As for this kind of sand, the conventional petrophysical evaluation alone cannot certainly distinguish between hydrocarbon and water in the porous medium. The alternative method (dT LogR) for formation re-evaluation is therefore considered in attempt to reduce uncertainty in fluid classification and reveal hidden hydrocarbon potential from these AZIs. There are 2 phases in verifying the validity of dT LogR method. Phase I: dT logR method (Ref. Q.R. Passey et al., AAPG 1990) was tested against the unperforated AZI sands of 10 selected platforms in order to fine-tune scaling parameters in dT logR. The total of 12 gas-potential AZI candidates were selected for perforation test. Data acquisition was also planned to obtain the reservoir deliverability information in order to further calibrate the interpretation model. The production test results of these sands showed that the accuracy of the interpretation was 41% (5 sands of 12 candidates produced gas) but 33% (4 sands of 12 candidates) showed water flow. Phase II: The production test data from perforated AZIs in phase I and the well correlation were then incorporated in dT LogR assisted log reinterpretation. Additional 13 gas-potential AZI candidates were identified for 2nd perforation test to prove the correctness of the recalibrated petrophysical model. The results showed success in model improvement of which its accuracy increased to 61% and no high water production was observed in any of them. After using dT LogR method to assist petrophysical evaluation, a total of 469 metres of unperforated AZIs were reconsidered to be productive gas bearing formation. In other words, 22 BCF of gas reserves and 873 MSTB of condensate reserves from these upgraded AZIs were added. In addition, it is foreseen that the remaining AZIs of other platforms are to be further reevaluated and therefore improves the confidence in reserves booking and field development planning of Lunar Field. In conclusion, the dT LogR method is a very useful tool for Lunar Field to significantly reduce uncertainty of fluid classification which in turn provides lots of benefits in gas field management adding immeasurable value to Lunar Field.