OVERPRESSURE DISTRIBUTION AND ITS GENERATING MECHANISM IN THE ONSHORE NORTHERN PORTION OF EAST JAVA, EAST JAVA BASIN

• Main Author: HAKIM, FAHMI
• Format: Theses
• Language: Indonesia
• Subjects: Geologi, hidrologi & meteorologi
• Online Access: https://digilib.itb.ac.id/gdl/view/15601
• Institution: Institut Teknologi Bandung

The northern portion of East Java is a part of The East Java Basin. This area is chosen as the research area because it has indications of the presence of overpressure and possessing complex geological conditions such as: variation in basement depth and the occurrence of several sedimentation zones. Such geological conditions will affect the distribution and generating mechanism of overpressure. Well data analysis comprising formation pressure data, drilling mudweight data, drilling report, final well report, wireline log, 2D seismic line, is used to know overpressure distribution and generating mechanisms in the research area. The result of this research shows that distribution of pore pressure is controlled by geologic condition which in this case is basement depth. The pore pressure regime in basement high is hydrostatic – low overpressure, while it is high overpressure in basement deep area. The explanation for this circumstance is that we have relatively thick shale sequence due to rapid sedimentation as well as sufficient thermal regime to generate overpressure in the basement deep, while such conditions do not exist in the basement high area. The mechanism generating overpressure in the research area is both loading and unloading mechanism. The loading mechanism relates to the inability of sediments to expel fluid in response to rapid sedimentation, while the unloading mechanism is caused by transformation of smectite into illite under the influence of temperature. The Eaton’s method with the exponent of 1.5 – 4.5 can be used to estimate overpressure magnitude in the research area. < The map of basement configuration shows a rapid variation of basement depth over a short distance in the research area. The consequence of this circumstance is that pore pressure regime will also vary over a short distance. Traditionally, the closest well will be chosen as an offset well for the next well to be drilled. Based on this research, such traditional approach can lead to unsuccessful pore pressure prediction, if the closest well and the next well to be drilled are located in the different basement configuration.