ANALISIS TEKANAN LUAP DAN MEKANISME PEMBENTUKANNYA MENGGUNAKAN DATA SUMUR DAN KECEPATAN SEISMIK PADA LAPANGAN “SKW”, CEKUNGAN JAWA TIMUR UTARA
The drilling in the North East Java Basin, known as one of the prolific hydrocarbon basins in Indonesia, is often experiencing several problems due to the presence of overpressure. This study aims to predict overpressure and analyze the generating mechanism using well and seismic data in SKW field in the basin, so that overpressure-related drilling problems could be avoided. Based on pore pressure analysis, we found that there are 5 pressure zones in the study area, i.e: hydrostatic pressure in Zone A and C, occurring in Lidah to the upper of Mundu formation and Ledok Formation; first appearance (top) of overpressure at Zone B occurring in the middle to lower Mundu Formation; moderate overpressure in Zone D occurring in upper – middle Wonocolo Formation; high overpressure in Zone E occurring in middle Wonocolo – Ngrayong formations. Our analysis also shows that sediment thickness controls overpressure magnitude in the study area, indicating that overpressure is due to loading mechanism.
The interpretation of loading mechanism as the main generating mechanism of overpressure in the study area is also supported by constant effective stress behaviour as observed in wells analysed in this paper. Burial history analysis also shows that rate of sedimentation in the study area is about 113 m/mY, in favour of supporting the loading mechanism interpretation. We also found that starting at the depth of 4000 ft, smectite starts to transform into illite, however, this transformation does not give substantial impact to overpressure magnitude in the study area.