The Exploration and Evaluation stages are a period of ‘prospecting’. High resolution seismic exploration surveys and geotechnical data acquisition, are among the requirements of this stage.
The Development stage is a collection of different survey activities. Prior to the installation of an offshore platform or seabed pipeline, bathymetric and geophysical surveys must be undertaken to assess the suitability of the proposed drill site. A bathymetric map of the area is produced from echo sounder and side-scan sonar data. Shallow gas detection is an important safety aspect to consider when planning the emplacement of the rig and accompanying anchors. The sub-bottom conditions are studied using seismic, magnetic or gravity techniques to allow the seabed foundation behaviour to be predicted. Seabed sampling systems such as gravity corers or grabs provide data to assist the interpretation of shallow soils.
Other factors to consider in planning stages are :
- Possible change of surface location to include alternative locations.
- Existence of specific exploration licence requirements for the proposed well location, such as a requirement for an environmental survey?
- Possible restrictions limiting the time of year that seismic surveys can be undertaken?
Once the value of the explored reservoir at the different drill sites has been established, the field development is extended to the laying of engineering structures. Initially pipelines and control modules and umbilicals connect between wells and floating and fixed production environments. As the field grows the seabed equipment becomes extensive.
Survey tasks for pipe laying activities are firstly, in support of ‘lay’ vessel and submersible requirements, and secondly, for the determination of the position of the pipeline. Each operation relies on precise positioning.
The Production Stage is characterised by the requirement for operational support. Inspection surveys of the pipeline and cables, and engineering structures, are performed regularly. Video footage of ‘events’, informational or damage, are used to document potential problem areas.
Surveys carried out in the Abandonment stage, are largely for environmental purposes. Oil companies may be required to carry out site surveys for debris in the vicinity of abandoned wellheads and seabed pipeline construction lines.
Oil and Gas survey work has proven at times to be the largest commercial sector for survey markets and technology. The industry however is characterised by major fluctuations of activity, usually as a result of reductions in the price of oil.