APPLICATION OF RESISTIVITY LOG IN PALEOGEOGRAPHIC RECONSTRUCTION, AZP BLOCK, CENTRAL SUMATRA BASIN

• Main Author: Putra, Azarico
• Format: Theses
• Language: Indonesia
• Subjects: Geologi, hidrologi & meteorologi
• Online Access: https://digilib.itb.ac.id/gdl/view/78569
• Institution: Institut Teknologi Bandung

Biostratigraphy analysis plays an important role in defining the bio-marker, used as the primary guide in the well and seismic correlations as well as the determination of the depositional environment and facies changes to construct paleogeographic maps. However, not all the wells and only a certain interval has biostratigraphy analysis. This is in contrast with the well logs, since the well logs always present in almost all wells. In this study, addressed the role of the well log that is associated with the subsurface data in search of a correlation between the resistivity log and bathimetry that directed from biostratigraphy analysis and utilization of these correlations in the paleogeographic reconstruction of the study area. The subsurface data i.e: mikropaleontologi reports, wireline log, dipmeter log, 2D seismic, cuttings and sidewall core description, final well report, and regional study references. Biostratigraphy analysis on four (4) exploration wells obtained study interval age range at P21 – N14 or equivalent to the age of Late Oligocene - Middle Miocene and bathimetry that range from marginal marine - upper bathyal. Biostratigraphy analysis is combined with the gamma-ray logs pattern and mud logs to define the sequence marker. There are four sequence markers, SB-0 is equivalent to the top of basement and the upper limit of Kelesa Group (late phase syn-rift), MFS-0 is equivalent to the maximum transgression of Telisa formation at the early age of Early Miocene, SB-1 is characterized by strict boundary in the early Middle Miocene equivalent with Binio Formation, and MFS-1 is the last maximum transgression before shallowing regionally. Based on the calculation of formation water salinity from all wells, the results calibrated to paleo-bathimetry from biostratigraphy data in four wells (AZP-1, AZP2, AZP-3, and AZP-5). The obtain chloride concentration, then plotted and compared with formation water salinity from the well log. In the four wells, the obtained value and trends of salinity are similar in intervals that do not contain hydrocarbons. While in the interval that indicates the presence of hydrocarbons, the value of salinity on the well logs indicate an anomaly (as if the salinity is reduced significantly). This anomaly occurs because the value of the resistivity of the hydrocarbon is almost equal to the value of fresh water resistivity (high resistivity values). Paleogeographic interval SB0 - MFS0, suggesting the existence of two depocenter separated by local high (inter basinal ridge). The western depocenter interpreted as braided delta deposits as part of incised valley and the eastern depocenter in the northeast are interpreted as braided delta deposits. In the interval MFS0 - SB1, depocenter is thickening to the south as slope turbidite deposite. Depocenter that grows in inter basinal ridge deposited as delta complex. And at SB1 - MFS1 interval, two depocenter located in the eastern part of the high are constrained by a relief which is interpreted as the sand bar deposits from the previous period. Both depocenter is interpreted as delta complex.