OEMG Digital Geophysics is a resistivity based method that has been highly modified and extensively tested for use in marine and freshwater environments including both shallow (approximately 30m water depth)  and deep water (up to 200m) projects.

Multi Channel cables are trailed behind the survey vessel and either float or are towed on the seabed depending on the conditions, though seabed towed cables are always preferred. Real time measurements are transmitted to the survey vessel every 900 milliseconds, which allows the operator to immediately assess the quality of the data and adjust parameters as required. This results in significant saving in the data acquisition costs and plus higher quality data is collected as all aspects of a survey are optimized on site.

Classical acoustical methods for shallow sub-bottom surveys are often limited by prevailing geological and environmental conditions, these include:

• Gravel in the subsurface obscuring information due to the appearance of diffractions
• Multiple reflections in shallow water that obscure real data
• “Gas masking” occurring in sediments rich in organic matter
• Strong shallow reflectors such as “cap rock” reflecting almost all acoustic energy preventing the exploration of lower geological formations
• The inability of refraction to provide information about softer layers underlying hard layers

OEMG Digital Geophysical studies provide depths, thicknesses, information about the nature of the geology and the presence of soft sediments underlying compacted sediments or rock.

Key Projects include:

Djibouti, NSW Metro Cross Harbour Tunnel, Eden Port Redevelopment, NSW, Gold Coast Water Strategic Integrated Digital Ground Model.

OEMG global provides Digital Geophysics for land in Australasia. Our Digital Geophysical method is a high resolution sub-bottom profiling system modified from the proven principles and methods of land based geoelectrical survey, and offers the same operational and processing benefits of our marine systems. This includes enhanced acquisition and processing techniques that provide high resolution quantitative (i.e. depths and thicknesses) and qualitative (i.e. quality or resistivity) data about sub-bottom structures. It has brought resistivity to the forefront of land and freshwater sub-bottom investigations.

Key benefits of an OEMG Digital Geophysical survey is that data can be acquired:

• Through gravels
• Through gaseous muds
• In complex geological environments (Hard-Soft-Hard, undulating, vertical and discontinuous layering).

Key outcomes from an OEMG Digital Geophysical Survey include:

• Accurate Qualitative and Quantitative data
• Three dimensional Modelling
• Significant reduction in the number of required boreholes and increased confidence that all geological structures have been sampled
• Enhanced understanding of the geological setting and an associated reduction in overall project risk

The OEMG Fluid Mud Mapping is a new and totally unique method for determining the nautical depth in the presence of fluid mud. Breaking away from traditional acoustic and density based systems, this method relies on viscosity changes at the fluid mud/solid mud interface to precisely map this rheological boundary.

The unique ability of the OEMG Fluid Mud Mapping method to map the true nautical depth in the presence of fluid mud sees the possibility for new and efficient dredge management. It works by dragging a sensor package behind a survey vessel at the end of an umbilical data cable.

Our method is a proven and efficient method for determining the nautical depth as defined by the discontinuity in the vertical viscosity profile, separating fluid mud and solid mud. The method allows Port Managers to confidently optimise dredging operations by knowing exactly where the solid mud begins. In addition the thickness of the mud layer can be determined with additional techniques.

OEMG-Global undertakes seabed and sub seabed mapping for scientific bodies, oil and gas companies and civil construction. We will work with your company and use your equipment, or we can utilise strong relationships with hire companies around the world to arrange the most cost effective and practical solution possible.

OEMG global utilises and has access to latest technology, acoustic and geo-electric sub-bottom profiling systems. We will work with your systems or assist in the preparation of tenders or planning to ensure that the goals of the survey are understood and met.

Choosing the system that will meet the objectives of the survey can be difficult as many of the systems overlap in their capabilities and/or are complementary to each other. Often two or more systems are used in parallel, however on smaller jobs, employing multiple systems can be prohibitively expensive. Read more to understand the common technologies available and their pros and cons. Here we examine the practical application of pingers, parametric echo sounding, chirp and sparker and boomer systems. We will also touch briefly on seismic refraction

OEMG undertakes targeted geotechnical studies as part of an Integrated Digital Ground Model and view Geotechnical surveys as an integral and indispensable component of any robust ground study providing key engineering data. However, as with all studies, the purpose and potential contribution to upside and down side risk should be assessed.

Targeting geotechnical studies with high resolution and advanced geophysics, improves the accuracy and interpretation of sampling. Most importantly, Geotechnical studies targeted with OEMG’s Integrated Digital Ground Model, have saved proponents 10’s of millions of dollars through the realisation of opportunities and the avoidance of emerging risks such as latent geological conditions.

“Defining sampling targets is the single most important value of a geophysical campaign, when considering ownership of opportunity risk”

The selection of geotechnical methods is just as important as the sampling locations. Vibracoring has become one of the quickest and most effective tools for sampling soft sediments. It can be used in conjunction with or instead of rotary coring and is most effective when targeted with our Digital Geophysical Methods.

The acquisition and analysis of Vibrocores has been a valuable tool in geotechnical investigations for many years. Early vibrocorers were cumbersome and required large vessels for deployment. In the late 1970s Associate Professor Charles Phipps designed a lightweight portable Vibrocorer that could be deployed from small vessels and still acquire up to 6m, largely undisturbed core samples from unconsolidated to lightly indurated sediments in water depths up to 200m.

Vibrocores can provide valuable geotechnical information including sedimentological, engineering, and geochemical data quickly and in a cost-effective manner. The lightweight equipment can be transported by air for rapid mobilisation into remote areas and assembled in various configurations depending on the specific requirements of the job. Core samples can be analysed on-site and/or in a laboratory.

Contact us for More Information