Lessons from the History of Jasmine Oilfield, Gulf of Thailand
Carter, David; Houtzager, Fred; Limniyakul, Theeranun; McClure, Jason; Oglesby, Chris; Platt, Chris; Siefert, Ole; Tabmanee, Piyatad; Watcharanatakul, Rattana
Pearl Oil (Thailand) ltd., Bangkok, Thailand.
Jasmine Field comprises multiple oil and gas bearing fluvial and lacustrine sandstone reservoirs contained within a complex en echelon fault zone. Despite the field's success, its potential was overlooked, due to a perceived lack of oil reserves, during a 30 year period prior to oil production which began in 2005.
Three important factors that influenced the field's history were (a) a non-optimum exploration and field delineation program, (b) initial use of inappropriate field analogues, and (c) application of improved field development methods and technologies. Crestal oil accumulations were missed by discovery wells drilled on 2D seismic data, and delineation wells drilled non-optimally on 3D seismic data by a previous operator due to a geodetic datum error. Prior to field development, the estimated ultimate recovery was only 8-9 MMBO, compared to a current estimate of 50-70 MMBO.
The initial application of inappropriate field analogues resulted in the dominant reservoir drive-mechanism being misunderstood and recovery factors being underestimated. Reservoir character and production performance are controlled by depositional history and oil properties. 3D seismic images and core data indicate that the Miocene fluvial sandstone bodies are dominantly meandering river deposits where extensive lateral accretion during deposition has resulted in reservoirs with large width to thickness ratios.
These reservoirs possess individual hydrocarbon contacts controlled by separate mudstone top seals. Although these reservoirs behave as separate compartments both stratigraphically and between adjacent fault blocks, their lateral extent provides strong aquifer support.
The combination of water-drive, oil mobility, fining upward reservoir character and numerous case histories, support the use of horizontal wells to drain the larger oil accumulations. The deeper succession is interpreted to contain lake-shoreline clastic reservoirs.
These lacustrine reservoirs commonly possess common hydrocarbon contacts within a single fault block. Evidence of pressure depletion during production from these reservoirs initially suggested that they behaved as isolated reservoirs on a production time scale.
However, pressure data from recent and shut-in wells now suggests that these reservoirs are also connected on a production time scale. The history of Jasmine field provides an opportunity to learn from both its positive and negative aspects for use in future field development plans.