PETROPHYSICAL ASSESMENT FOR EARLY WATER PRODUCTION IN THE UJUNG PANGKAH FIELD, EAST JAVA, INDONESIA

摘要

Kujung reservoirs in the Pangkah Field demonstrate very complex carbonate system including depositional setting, facies variation, structures and reservoir properties. Early water production in the field has been suspected caused by mobile water coming from a combination of transition zone and aquiver through fractures and vuggy porosity. Petrophysical assessments discussed in this paper include log interpretation, SCAL data evaluation, Pressure data analysis, and image log interpretation. Various special core analysis data, post ageing, relative permeability, and USBM analyses that indicate an oil-wet system combined with a considerably long transition zone suggest the presence of mobile water within the transition zone. Pressure data taken in some wells after experiencing depletion demonstrate water gradient in oil zone confirm an oil-wet system. Open fractures observed and identified from resistivity and image logs in the productive zone are suspected to be conduits to the water leg and transition zone causing higher water produced than expected. Meteoric water leaching was also recognized to be prominent through out the field in some zones providing high permeability vuggy porosity system. A tendency of an oil-wet system plays an important role that results in more mobile water condition than that in a water-wet system, one of ways to mitigate this natural cause is by moving the produced interval much further up away from the transition zone. Production data combined with fracture density map are used to determine which factors contributing to water production. Fracture density map and its relative proximity to faults have been also used as a mitigation strategy for well placement to avoid fracture zone and expect less water to be produced. If the well still penetrates fractures, a method of isolation needs to be implemented in the completion strategy.