EVALUASI TEKANAN PORI PADA AREA LUBUK KERTANG, LAPANGAN PANGKALAN SUSU, CEKUNGAN SUMATERA UTARA

• Main Author: Sijabat, Hitler
• Format: Theses
• Language: Indonesia
• Subjects: Geologi, hidrologi & meteorologi
• Online Access: https://digilib.itb.ac.id/gdl/view/74655
• Institution: Institut Teknologi Bandung

The southeast area of Aru sub-Basin is one of the areas identified to have overpressure zones in the North Sumatra Basin. Regionally, overpressure in this basin is identified in the Baong Formation. The purpose of this study is to determine the mechanism of overpressure, analyze the lateral distribution of pore pressure, define the stress regime, and build a three-dimensional model of pore pressure in the study area. Wireline log data from seven wells and 3D seismic of 156 km2 are used to evaluate overpressure in the southeast area of the Aru sub-Basin. Hydrostatic pressure is obtained from a hydrostatic gradient of 0.433 psi/ft and overburden stress is derived from density data. Pore pressure is calculated using Eaton’s method and its distribution is determined using 3D seismic velocity. The results of this evaluation are validated by pressure data such as Drill Stem Test (DST), Leak-Off Test (LOT) and mud weight. The mechanism of overpressure is identified from wireline log evaluation, especially sonic and resistivity logs, density-sonic cross-plot, sedimentation rate analysis and maturity evaluation (Ro). Meanwhile, the stress regime is determined by calculating the maximum stress value (SHmax), minimum stress value (Shmin), and overburden stress (????). The result of evaluation and 3D pore pressure modelling show that overpressure consistently occurs at the top of the Upper Baong Formation, relatively hydrostatic in the Middle Baong Sands (MBS) and towards hard overpressure in the Lower Baong Formation, then returns to hydrostatic in the Belumai Formation. The cause of overpressure are the non-loading mechanism in the form of smectite to illite mineral transformation and loading mechanism (disequilibrium compaction). The lateral distribution of pore pressure in all formations is heterogeneous. The pore pressure values are larger in the deeper part (central area) and smaller in the shallower part (western area). With SHmax > ???? > Shmin, the study area is classified as having a strike-slip fault stress regime. The main stress (SHmax) runs southwest - northeast and forms a northwest-southeast lineament pattern of thrust faults and folds.