Site Surveys and Investigation services is a process of surveying a location where a drilling rig or a platform will be positioned/installed. The process ensures that the location is free of debris, junk, wrecks and shallow gas pockets and flat seabed is identified. A number of other geohazards and environmental risks and manmade seafloor hazards are identified during the surveys, with recommended mitigation actions. These surveys called interchangeably 1) marine site survey, 2) geophysical and geological survey, 3) seabed and subsurface conditions survey, 4) drilling hazard survey 5) seabed survey.
Used in various capacities and combinations during every stage of an oil and gas project, below is a breakdown of the services and type of surveys.
Not only the surveys are required technically, they are also a mandatory requirement to provide to insurance companies, when procuring drilling or project related insurance, be it well insurance, drilling insurance or BAR insurance. The geotechnical survey is critical and compulsory for a jack-up drilling rig operations when legs of a drilling rig penetrate the seabed. The survey data allows understanding the loads to be applied, as well as to ensure that shallow gas pockets (gas accumulation) are not encountered. During rig moves, the site survey should be conducted at all times, as subsurface data tend to change over time and offset data obtained from a nearby location might not be accurate. Yet, this may not always be the case and highly dependent on the field and the information available.
At the exploration and appraisal phase, the site survey (seabed survey, hazard survey and geotechnical soil testing when a jack-up drilling rig is deployed) is used during every rig move. Normally at this stage, the survey area covers the entire block/field, unless earlier acquired data is available.
At the development stage, the survey scope includes site and pipeline route survey, geotechnical coring and platform foundation engineering analysis. This is usually part of an EPC contract to deliver a facility. Yet, there might be cases at redevelopment stages, when this is done by an operator, to help in decision making or FEED scoping.
The industry of marine surveys is known to be a hi-end technology user with multi-discipline skills. Each serving a different purpose and deployed from a dedicated survey vessel, a number of different tools used to conduct a survey. Those include echo sounders, side scan sonars, profilers, magnometers shallow seismic, remotely operated vehicle (ROV) and autonomous underwater vehicle (AUV), drilling spread for seabed and soil testing, to name a few.
Any survey is a relatively long process and done in stages:
- Scope of Work and Tender Management
- Survey Planning
Execution and Data Acquisition
- Equipment and Vessel Mobilization
- Change Management
Interpretation and Analysis
- Data validation and Integration
- Data Interpretation and Analysis
This BIBBY Hydromap's schematic shows a typical equipment layout.