INSTALLATION ANALYSIS FOR MANIFOLD AND SUCTION PILE SUBSEA STRUCTURE

• Main Author: Alexander Zebua, Reynard
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/84981
• Institution: Institut Teknologi Bandung

The world's energy demand continues to grow in tandem with population growth. One of the most dominant energy sources used globally is oil and natural gas. To meet this demand, robust supporting facilities are required. Various types of oil and gas exploration and production facilities have been developed, each with its own advantages. Gradually, oil and gas exploration is moving towards deeper waters, necessitating support facilities capable of facilitating exploration and production activities under such conditions. Subsea facilities are introduced to address these challenges. An in-depth analysis of the stages and methods to be used in the installation of subsea facilities is essential. A sensitivity analysis was conducted based on wave scatter for the installation site. Guided by DNV-RP-H103, a ship response analysis was performed for environmental loading directions ± 15? from the ship's heading as stated in the installation procedure. For each environmental loading, an analysis was also carried out for several installation stages, including when the module is in the air, when the module enters the splash zone (with part of the structure submerged), when the entire structure is submerged, when the structure reaches several depth steps (25%, 50%, 75%), and when the structure is 10 meters above the seabed. Additionally, an extra analysis was performed for certain steps, including the analysis of the wave shield effect produced by the ship's diffraction when entering the splash zone, and analysis when the Active Heave Compensator (AHC) is turned on and off when the structure is 10 meters above the seabed. This series of analyses was conducted to determine the permissible environmental conditions for the installation of the manifold and suction pile structures The analysis was performed using OrcaFlex 11.d and OrcaWave 11.d. From the analysis, the permissible environmental conditions for the installation of the manifold and suction pile were determined. Several stages were identified as critical during the installation, including when the structure is in the air, when entering the splash zone, and when the structure is close to the seabed (10 meters above the seabed step). To address these challenges, it is necessary to ensure safe limits for each installation stage. During the splash zone crossing step, an analysis of the wave shield effect produced by the ship's body was conducted. The analysis results indicate that the wave shield can help reduce the loads experienced by the module when in the splash zone. This is evident from the lower crane tip DAF values compared to those without considering the wave shield. However, the wave shield is only effective for wave periods shorter than 8 seconds, while it has little effect on longer periods. For longer wave periods (over 8 seconds), the wavelength becomes larger, and the diffraction effect diminishes as the waves tend to pass the ship more easily without much interference from the ship's body. At the 10 meters above seabed step, an additional analysis was performed (AHC on and AHC off). When the AHC is activated, the structure's movement in the Z-axis is relatively small (more stable), while when the AHC is turned off, the structure's movement in the Z-axis tends to be larger. During the landing stage, this large movement can lead to installation failure (a collision between the structure and the seabed). To minimize the risk of failure, it is recommended to activate the AHC during the landing stage.