THE RELEVANCE OF SURVEY APPLICATION IN OFFSHORE CONSTRUCTION

INTRODUCTION Construction activities are vital to developing our environment and economy. Various engineering projects are executed for different reasons in diverse environment with survey input being fundamental to successful planning & execution. The marine environment is dynamic and it requires peculiar/specialized engineering solutions. The hydrographic surveyor is tasked with the responsibility of providing solutions to survey deliverable required for construction in the marine environment. A good knowledge of various construction activities and survey methodology is required to successfully provide solutions to support successful execution of construction works. This short presentation is aimed at highlighting survey activities relevant to various construction activities in offshore (and by extension marine) environment.

WHAT IS OFFSHORE CONSTRUCTION? Offshore construction is the installation of structures and facilities in a marine environment, usually for the production and transmission of electricity, oil, gas and other resources. It is also called maritime engineering. It includes: Foundation engineering Structural design Construction Repair of offshore structures etc. All activities listed above require application of survey for successful execution.

OFFSHORE SURVEYING Offshore surveying is concerned with meeting the survey requirement of the offshore industry. Broadly speaking, these are: The positioning of vessels, drilling-ships, platforms, etc. The surveying of seabed and sub-seabed features prior to and after exploration, rigs move, drilling, trenching or installation of platforms, pipelines, wind farms, communication/power masts etc. The ongoing inspection/monitoring during installations.

APPLICATION OF SURVEY TO OFFSHORE CONSTRUCTION Offshore construction requires survey application to aid design, installation and post installation of offshore facilities among other things. Survey is carried out during offshore construction in application to the following activities: Pre-engineering Pre-installation Construction support (Pipe-lay, Jacket Installation, Rig move, SBM Installation, Meteorology etc) As-built survey Post installation Decommissioning Types of survey services rendered in application to construction activities are discussed below.

BATHYMETRIC & GEOPHYSICAL SURVEY Analogue Geophysical & bathymetric survey services are carried out to aid civil/construction engineering activities such as pre-engineering design, pipeline pre-installation, pipeline as- laid/as-built, pre-dredge, post dredge, navigation clearance, pre-jacket installation etc. Geophysical surveys varies from seismic and high resolution surveys in application and methodology. It is essential to carry out a analogue geophysical survey on the proposed/selected location to obtain information that will aid design and methodology before installation. Geophysical surveys are also essential to identify potential hazards that could impede operations prior to installation works. Bathymetry information is required for navigation hazards, construction design, etc. Analogue Geophysical Survey services among others include: Seabed mapping using a Side Scan Sonar Sub-bottom profiling to detect sub-seabed debris, hazard & stratigraphy Seabed Bathymetry using the Echo Sounder Magnetometer survey to detect magnetic seabed debris

GEOTECHNICAL SURVEY Geotechnical survey services for various applications such as pre-engineering design, pipeline pre-installation, pre-trenching, pre-dredge, structural foundation analysis, pre- jacket installation etc. It is essential to know the soil type and depth/thickness in different layers of the sub-seabed in other to know the type of foundation and methodology to employ for installation. Geotechnical Survey services among others include: Surface soil sampling (Grab sampling, box coring etc) Shallow stratigraphy sampling (Piston coring, vibro coring etc) Comprehensive foundation sampling (Shallow sampling methods & borehole sampling) Soil tests and correlation with analogue & seismic profiling.

NAVIGATION, SURFACE AND SUBSEA POSITIONING FOR CONSTRUCTION Navigation, Surface and Sub-sea positioning survey services are applied for various construction works on Pipelay Barges, Dive Support Vessels, Rigs, Lift Boats, Construction Barges, Anchor Handling Tugs etc. SURFACE POSITIONING A surface positioning system and navigation suite shall be installed on the vessel, construction barge and Anchor Handling Tugs for real-time positioning during installation works. The system includes a DGPS, Gyro, Navigation Software and Telemetry for real-time monitoring and communication with the remote monitoring system installed on a jacket/platform and the Anchor Handling Tugs. JACKET INSTALLATION MONITORING SYSTEM (JIMS) A remote Jacket Installation Monitoring System (JIMS) is a system that will be set up on the jacket to track its precise position and heading in real time during installation. The system contains a DGPS for positioning, Gyro for heading, MRU for attitude (roll & pitch), alternative power and a telemetry system to communicate with the installation barge. With the JIMS, the exact location and heading of the jacket shall be confirmed before the jacket or template is lowered to the seabed. Land survey techniques are also applied for dimension control surveys and as secondary positioning method. SUBSEA POSITIONING Under water acoustics positioning plays a vital role in construction support. Survey aids precise subsea installation works, diver tracking, ROV tracking, underwater repairs etc mainly through the use of acoustics positioning systems (USBL and LBL) and sonars ( 2D- mesotech, blueview etc and 3D- Echoscope , MBES).

PICTURE GALERY OF SOME SURVEY ACTIVITIES EXECUTED (BY GOSL) IN APPLICATION TO OFFSHORE CONSTRUCTION

Thank you!