IN-SERVICE AND LIFTING ANALYSIS OF OFFSHORE JACKET WITH SOIL ADHESION LOADS IN RELATION TO MUDMAT AREA VARIATIONS DURING THE DECOMMISSIONING PHASE

• Main Author: Adipratama Putra, Rifa
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/86401
• Institution: Institut Teknologi Bandung

Fixed platforms play a crucial role in supporting offshore oil and gas production activities, especially considering that over 70% of Indonesia's oil and gas reserves are located in these areas. As these platforms reach the end of their operational life, decommissioning becomes a critical process. Decommissioning refers to the procedure of shutting down operations on the structure and in its surrounding environment. The uplift force required to remove the structure from the seabed during decommissioning is influenced not only by the weight of the structure but also by the adhesion of the soil beneath the mudmat. This study aims to evaluate the effect of mudmat area variations on the uplift force and stress of the jacket structure during decommissioning. Using numerical modeling in ABAQUS, the interaction between the mudmat and the soil is analyzed using non-linear spring elements to represent the soil’s mechanical properties. The simulated uplift force for five mudmat variations ranges from 2.44 to 3.50 times the submerged weight of the structure, with structural feasibility checked during the underwater lifting operation by applying safety factors in accordance with DNV ST N001 and DNV OS H205 standards. The simulation results demonstrate a strong linear relationship between mudmat area and uplift force. A 34.7% reduction in mudmat area decreases the uplift force by 21%, while a 21.4% increase in mudmat area raises the uplift force by 13.6%. Additionally, changes in mudmat area influence the maximum stress in the structure, following a second-order polynomial relationship. This non-linear relationship indicates that a reduction in area has a more significant impact on stress reduction compared to an increase. A 34.7% reduction in mudmat area lowers the maximum stress by 42.3%, whereas a 15.23% increase in mudmat area only raises the stress by 8.3%.