ESTIMATING THE CONTRIBUTION OF LOADING AND NON-LOADING MECHANISMS TO THE GENERATION OF OVERPRESSURE IN THE TELUK ARU AREA, NORTH SUMATRA BASIN

• Main Author: ANWARI - NIM: 22016025 , JAKSON
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/28215
• Institution: Institut Teknologi Bandung

<p align="justify">The North Sumatra Basin is an overpressured petroleum basin. The top of overpressure is located at the top of Baong Formation or at the lower part of the Keutapang Formation. The combination of loading and non-loading mechanisms is thought to be the cause of overpressure in this basin. This study is aimed at estimating the contribution of both mechanisms to the generation of overpressure in the Gulf of Aru. <br /> <br /> <br /> This study uses pressure data (DST/MDT, mudweight, drilling events, etc) in identifying overpressure zone. The interpretation of overpressure generating mechanisms is based on wireline log characteristics combined with Dutta and Bowers cross plots, and is also supported by clay mineral composition (XRD analysis result), source rock maturity (VR data), temperature, and geological/stratigraphic data. The estimation of the contribution of loading and non-loading mechanisms is performed by using the “Budge-Fudge” method. <br /> <br /> <br /> The top of overpressure zone is identified at the depth of ±4,000’-4,200’, at the Lower Keutapang Formation, while the top of high/hard overpressure zone is at the depth interval of ±6,500’-6,900’ (near the base of middle part of the Baong Formation or near the top of lower part of the Baong Formation), with a transition zone located at the depth interval of 5,000-6,000s feet. The well X-6 has shallower overpressure zone with the top of overpressure located at the depth of 1,160’. The top of transition zone and high/hard overpressure are at the depth of 2,500’ and 6,350’, respectively. This circumstance indicates that this well experienced greater uplift reflected by the formation found on the surface, as well as higher log value at the surface. <br /> <br /> The log-depth profile, Dutta and Bowers cross plots, clay mineralogy, and source rock maturity show the combination of loading and non-loading mechanisms as the cause of overpressure found in the study area. The overpressure estimation by using “Budge-Fudge” method shows that the contribution of loading mechanism is dominated at low overpressure zone. In the transition zone to high overpressure zone, non-loading mechanism becomes more dominant reaching up to several times compared to loading mechanism. <p align="justify">