WELLBORE INSTABILITY ANALYSIS THROUGH GEOMECHANICAL FACIES MODEL IN CISUBUH SHALE, BAMBU BESAR STRUCTURE, NORTHWEST JAVA BASIN, INDONESIA

• Main Author: Hanafiah, Anas
• Format: Theses
• Language: Indonesia
• Subjects: Geologi, hidrologi & meteorologi
• Online Access: https://digilib.itb.ac.id/gdl/view/53149
• Institution: Institut Teknologi Bandung

Bambubesar Field is Pertamina's oil and gas field located in Karawang district, West Java. Four exploration wells and 6 development wells have been drilled, with the cumulative oil production up to July 2020 of 1.37 MMBO. From the drilling that has been done, the main problem that occurs is causing NPT (non-productive time), the biggest one is the instability of the drill hole which is closely related to the failure mechanism that occurs in the drilled rock, especially in the Cisubuh and Cibulakan formations which are the focus area of this research. Regionally this area is located in the North West Java basin, at Kepuh Low subbasin which was formed behind the arc at the Eocene to Oligocene age due to the subduction system in the south of Java Island. Along with the filling of the basin to the backarc sediment, the Cibulakan and Cisubuh deposit from the Middle Miocene to Pleistocene. In this sedimentary layer, the research was carried out to consider the instability issue that occurs when drilling penetrates this layer. The orientation of minimum horizontal stress has an angle of N 110 ° E (NW-SE), while the direction of maximum horizontal stress is perpendicular to the minimum horizontal stress at N 20 ° E (NE-SW). Geomechanical parameters were obtained with pore pressure equivalent to 1.03-1.20 SG, s v 1.82-2.25 SG, sHmax 1.73-1.95 SG, shmin 1.57-1.72 SG, and UCS 0.53-63.63 SG. Principal stress S1, S2, S3 shows sv > sHmax > shmin which is the normal fault regime. The method used in this research is to analyze the causes of borehole instability with facies analysis, determine the geomechanical parameters and associated rock mechanics based on the facies, and make a final wellbore stability model. This study hypothesizes that (1) the problem of wellbore stability requires geomechanical calculations, (2) proper facies analysis is needed to specifically model geomechanics based on rock properties, to obtain an appropriate geomechanical model approach in overcoming borehole instability. The research conduct XRD analysis then determines the focus of geomechanical modeling based on its facies characteristics, create a geomechanical model to prevent potential borehole instability, and evaluate and test the model in drilling activities in Bambubesar. The results show that the Cisubuh and Cibulakan facies have different rock characteristics. Each gradation that is owned has a different response to the geomechanical model that is made. Each different character in a facies body and has a certain prediction of shale pressure so that facies must be distinguished, then a geomechanical model of each facies must be made to accommodate the balance stress needs at each point on the borehole wall as a model of stability to its in situ stress. From the results of this study, a geomechanical model can be applied in the drilling activity of the next Bambubesar structure. Evidenced by the results of the successful drilling in BBS-010 test well without any problems with borehole instability.