--> Structural Uncertainty of Parigi Carbonate Platform Due to Velocity Model Pitfall and Its Impact to Development Drilling: A Case Study of XPA Development Wells, PHE ONWJ

AAPG Asia Pacific Technical Symposium

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Structural Uncertainty of Parigi Carbonate Platform Due to Velocity Model Pitfall and Its Impact to Development Drilling: A Case Study of XPA Development Wells, PHE ONWJ

Abstract

We investigated Parigi carbonate platform features at the base of Late Miocene isolated using three-dimensional seismic and exploratory well XP-1 data from Offshore Northwest Java. Brightened seismic reflections and flat spots evidence of fluid accumulation occur at the top of carbonate features. Various thickness of gas column due to carbonate surface has become challenging issue to structural uncertainties that have a direct impact in development, production, and in drilling decisions. Post-stack migration data has pitfalls in processing seismic data, which causes artificial features on seismic images and might mislead the structural interpretation. The post-stack migration fails to properly image the undulation of carbonate surface caused by limitation in seismic resolution. In the presence of the strong lateral velocity variation in carbonate body, layer cake velocity model was applied based on XP-1 exploratory well to suppress the velocity-related artifacts and provided better carbonate geometry that resulting depth structure map. This study aims to illustrating the pitfalls in the structural interpretation on XPA development wells. The curvature anomalies related to the lateral variations has misinterpreted as real structure while drilling. XPA-1 and XPA-2 has been drilled 15 ft below the prognosis while XPA-2 drilled 30 ft below the prognosis and has not yet penetrated the Top Parigi. XPA-2ST was planned to penetrate relatively higher structure at 400 meters to the northern from original trajectory. XPA-2ST penetrated to Top Parigi higher 10 ft than prognosis. Considering the various gas column and production length of XPA developments wells, chock management was applied to maximize recovery factor and gas production rate as expected.