PALEOMORPHOLOGICAL CONTROL OF THE GROWTH OF THE LOWER CIBULAKAN CARBONATE UNIT IN THE JB AREA, NORTH WEST JAVA SUB BASIN

• Main Author: Wasonoaji, Andi
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/62112
• Institution: Institut Teknologi Bandung

The study area or known as the JB area is located in the northern part of the West Java Basin. This study area is located in the Offshore North West Java (ONWJ) Block which is now operated by Pertamina Hulu Energi (PHE). This area is known as a producer of oil and gas from the Upper and Lower Cibulakan Formation. The study target is limestone unit located in the Lower Cibulakan Formation or known internally as the Baturaja Formation. The results of the drilling show at the southeast, there is the B-South field with the BF-1 exploration well as an oil field in the Limestone of the Lower Cibulakan Formation which has a limestone thickness of more than 300 m, on the other hand at the tops of structures such as the E-Main Structure with Exploration Well A-1 and Structure B. -North with Exploration Well BW-4 has Limestone with a thickness interval of 200-299 m. To the west of this field, there are clusters of well data showing a thickness of more than 300 m, namely: Esploration Wells A-15 and DH-1 and their location is not at the top of the structure. The concept of limestone exploration in general is looking for a basement high with a limestone thickness interval of 200-299 m. The general assumption is that the development of limestone reservoirs due to the leaching process has a high chance of occurring in this area, but with the production of the BF-1 well with a thickness of 300 m, it is possible for reservoir formation to occur in areas that are not at recent high. The purpose of this research is to understand the distribution of limestone and paleomorphology at the time of its growth. Identification of Cibulakan limestone Unit characters from well logs data, grouping, structure mapping and thickness maps was carried out to analyze paleomorphological conditions when carbonates grew. One of the keys to determine the distribution of limestones for the Lower Cibulakan Formation is the post-deposition paleomorphological form of the Lower Cibulakan Marin Unit as a basis for limestone growth. To understand this, a relatively deep or shallow approach is used from the thickness data of the Lower Cibulakan Marin Unit using a certain thickness reference. This data is then integrated with the pattern of limestone distribution to gain an understanding of limestone growth from one area to another. The results of this study indicate that the paleomorphological form of limestone growth will be affected by the shape and thickness of the sediment below it and the influence of sea level on limestone growth. Paleomorphology will affect the nature of limestone growth into three patterns, namely: (1) limestone whose position is close to sea level in shallow areas or close to paleo high will tend to grow laterally, this occurs in shallow ramps carbonate exposure buildups, (2) limestone that grows not too close to sea level or is located on an attached platform with paleo high can grow optimally laterally and vertically provided that its lateral movement is not limited by the presence of faults, and (3) limestone which when growing is in a local elevation area caused by structural or because of the thickness of the sedimentation below it and is not connected (detached platform) with paleo high it will have a tendency to grow optimally to vertical direction.