Companies will have to adapt and innovate to prosper in this challenging new environment caused by the financial crisis within the global economy and it is worth examining how these environmental pressures will influence the focus of offshore activity.
Up until 2008 Controlled Source Electromagnetic (CSEM) surveying had experienced year-on-year growth. This technique offers the prospect of direct detection of hydrocarbons via their resistivity signature and has tremendous potential to reduce the risk when making decisions on drilling. However, it is a technology in its infancy and the cost of acquisition of EM data is high compared to conventional seismic. Therefore, in these times of relatively low oil prices it is one of the areas which have suffered a notable drop in investment.
At the same time industry projections were indicating a major shortfall in capacity of towed streamer seismic and in particular multi-streamer 3D vessels. Many companies had embarked on ambitious new-build programmes and a number of these vessels have come on-stream in the last 12 months compounding the overcapacity that has now engulfed the market. Hopefully, this surplus will be short-lived as confidence gradually returns to the industry.
Enhanced oil recovery
In the current cautious climate the focus is very much on enhanced oil recovery (EOR) from existing fields. Even relatively modest improvements of 5 per cent additional recovery can equate to a major financial return and this offers a relatively low risk investment for companies that have already invested heavily in developing fields and establishing the infrastructure of rigs, pipelines, etc. Key to this activity is 4D time lapse seismic and 4C multi-component seismic.
4D seismic aims to track changes in reservoir properties over time, based on subtle changes detected in periodically acquired seismic datasets. There are many variations on the method ranging from towed streamer to permanent and retrievable ocean bottom seismometers, either cable (OBC) or nodes (OBN).
The repeatability of towed streamer 4D has been enhanced considerably by recent improvements in streamer steering technology which have significantly reduced positioning errors. This is vital as variations in source and receiver positioning can generate differences in the resultant seismic data of the same order of magnitude as those caused by changes in the state of the reservoir itself.
The new streamer technologies also include single channel acquisition, and recording of a broader bandwidth, both at the high and low end of the spectrum, which has enabled greater resolution of target horizons.
However, one significant limitation of towed streamer data is that it only records compressional P-wave data. Important additional information, such as fluid movement and variations in reservoir lithology, can be determined by recording the converted shear or S-wave. Shear waves can only be detected by geophones which are in direct contact with the seafloor using ocean bottom seismic techniques.
These 4C multi-component systems have receivers consisting of a hydrophone and three orthogonally orientated geophones; and increasingly conventional geophones are being replaced by micro-electro-mechanical system (MEMS) devices that can record seismic signals with a significantly broader frequency content than was previously attainable.
Permanent reservoir monitoring
Permanent reservoir monitoring (PRM) is an area that is destined to expand significantly over the coming decades. Permanent systems installed to acquire Life of Field Seismic (LoFS) have obvious advantages over towed seismic as regards repeatability and although initial installation costs are high, these costs reduce significantly over time as repeat surveys only require the deployment of a source vessel.
Early implementations in the mature oil provinces of the North Sea and Gulf of Mexico have demonstrated their potential and new fibre optic technologies are at the forefront of the development of robust, low maintenance PRM systems that are now commercially available.
One final area that has garnered significant interest as a possible direct hydrocarbon indicator is the presence of coherent anomalies in the background low frequency seismic spectrum (1-6Hz). These anomalies have been detected over a number of hydrocarbon reservoirs and research is ongoing to determine if they are a diagnostic feature that can be used in the future determination of as yet undiscovered reservoirs. This could potentially lead to further applications for low frequency ocean bottom passive seismic acquisition.
This year marks the 200th anniversary of the birth of Charles Darwin. His profound insight into the way life adapts over successive generations to challenges in the environment is also applicable to the way our industry is evolving and will continue to develop in response to the challenges it faces.
The natural selection of the best new technologies and acquisition methods will play their part in the discovery of new reserves and improving production from existing fields.
Enter X at www.engineerlive.com/ihss
Dr Neil Grosse is Business Development Team Manager, Geomotive Inc, Tortola, British Virgin Islands. www.geomotive.net
