Provides important Geological information for Engineering Design purposes
Provides consistency in interpretation of Geological Features
Has the potential to save significant costs in medium to longer term (may not require additional boreholes)
The knowledge of the geological characteristics of the formations within the foundation layers (nominally up to 100 metre depth below seabed) is critical for the successful construction and safe functioning of Jacket installations and emplacement of Jack-Up Drilling Rigs.
The sites for both Jackets and Drilling Rigs are chosen based on the oil or gas bearing zones which are usually many thousands of metres below the seabed, with little initial consideration given to the topmost sedimentary layers. Once the site or sites are chosen, Site Hazard Surveys and Borehole Drilling are performed to provide the requisite information on the near surface foundation layers to determine their suitability for production platforms or exploration drilling rig locations. If the sites prove unsuitable, then additional work is required to identify an acceptable location.
A large amount of useful but uncorrelated data exists within an Oil Company’s records within currently producing concession areas. With careful analysis and correlation, this data can be utilised to provide advance notice of potential hazards prior to performing site hazard surveys and borehole drilling. The potential exists, therefore, for significant cost savings.
GeoModel, a near-surface Geological Database Model developed by Meridian Surveys, provides this information by combining all available data into one complex database which is then analysed by experienced Geophysicists to correlate the various data forms. The final data is presented as a series of profiles or sections throughout the area of interest as well as a colour coded plan view. These depict the various geological features such as channels, faults, crustal layers etc., all of which are important for accurate engineering decisions.
The provision of the data in this form provides an important tool for advance planning of site locations, with the increased probability of the site proving suitable for the intended use prior to hazard surveys or borehole drilling.
A regional review of the available data provides a significantly improved understanding of the geology of the area, the processes that formed the various geological structures and the post-depositional processes that may have occurred.
The objectives of the Geological Model are to provide:
An analysis and explanation of the regional geological history.
A comprehensive and consistent interpretation of the regional geological formations.
Regional charts (plan view) and profiles (sections) for use in advance planning procedures.
Three types of data are usually available. These are:
Sub-bottom profiler (boomer) seismic
2D and 3D seismic
Borehole information
Interpretation of Boomer data and Digitising utilising Meridian’s Seismertise software.
Interpretation and Digitising of channels from 3D Time slices from 3D seismic data.
Correlation of channels with the appropriate horizon on boomer data.
Correlation of horizons with borehole data to enhance the accuracy of interpretation.
In order for the model to be successful there must be good coverage of all three types of data over the region of interest, plus regional boomer tie lines must link the various sites to ensure consistency of interpretation.
The Geological Model (GeoModel) data is produced as a single or series of regional charts and a set of regional profiles in both hardcopy and CAD format.
The Geological Model provides:
An upgrade in the quality and accuracy of the interpretation of sites through the enhanced understanding of the regional geological processes.
Consistency in interpretation between disparate locations.
An excellent method to assist in the quality control monitoring of future surveys through prior knowledge of existing conditions.
Once sufficient coverage of an area is completed the GeoModel provides the ability and potential to:
Clarify and define the geological constraints and/or hazards for jacket installation and jack-up rig emplacement.
Define the potential for conformable and predictable soil development in the Jacket foundation zone.
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