GEOPHYSICAL ANALYSIS TO IDENTIFY FRESHWATER AND SALTWATER ZONES IN THE PLAN FOR THE CONSTRUCTION OF A NEW OPERATIONAL WELL BY PT X ON THE COASTAL SHORE OF SEUMADU ISLAND, LHOKSUMAWE, ACEH

• Main Author: Anggita Sari, Arash
• Format: Theses
• Language: Indonesia
• Subjects: Teknik (Rekayasa, enjinering dan kegiatan berkaitan)
• Online Access: https://digilib.itb.ac.id/gdl/view/77048
• Institution: Institut Teknologi Bandung

This study aims to provide optimal recommendations for the location and depth of aquifer extraction for a new production well for PT X. These recommendations take into consideration the operational needs of the company as well as the potential intrusion of seawater into the groundwater. The potential intrusion is inferred from the chemical data of groundwater from existing wells, which indicates a dominance of sodium (Na+), potassium (K+), and chloride (Cl-) ions, suggesting a "Sodium Chloride Type" chemical composition. This implies the presence of seawater mixing within the groundwater, posing a potential threat to the availability of fresh water resources for PT X. The research objectives encompass two key aspects. Firstly, to develop recommendations for the location and depth of through geoelectric and wireline logging, while considering the intrusion of seawater. This aims to establish detailed guidelines regarding the depth of fresh and saline water zones, screen placement, and well location, ensuring the acquisition of high-quality groundwater supply that meets PT X's operational requirements. Secondly, this study aims to conduct a subsurface geological assessment, particularly focusing on the characteristics of rock formations in the study area. This objective seeks to gain a deeper understanding of regional and local geology and hydrogeology, as well as rock formations that may impact groundwater quality. The research methodology employs a geophysical survey approach utilizing VES measurement and geophysical well logging. This method is employed to gather essential data and information for assessing groundwater potential beneath the surface. VES measurements at four points in the northeast-southwest axis of the PT X site reveal a pattern of low resistivity values indicating the presence of seawater intrusion. Conversely, VES interpretation at two measurement points in the southeast area of the research site indicates the presence of fresher water at depths of 70–110 meters. Based on these findings, the decision is made to select a southeastern location for the new well. Once a potential well location is identified, wireline logging is conducted to provide a more detailed understanding of subsurface conditions. Correlations between lithology interpretation, gamma ray logs, resistivity logs, and VES measurements reveal the presence of a saline aquifer zone at depths of 20–40 meters. Consequently, the desired aquifer target is recommended to be situated at depths of 80–120 meters, where the water quality is slightly brackish yet fresher than the overlying aquifer. This suggests the potential for better water quality at this depth, making it more suitable as boiler feedwater as required by PT X's power generation facility. Based on the conducted study, a new well location is determined at coordinates X 288071 Y 576650 with a screen installation depth of 87–117 meters. In conclusion, this study offers vital recommendations for aquifer location and depth, taking into consideration both the operational needs of the company and the potential intrusion of seawater. These recommendations are grounded in the analysis of geophysical data, water chemistry, and lithology correlations. It is anticipated that these recommendations will provide valuable guidance to PT X in developing a new production well.