Jeff Cunkelman discusses field-proven technology to optimise survey data, efficiency and safety
Benefits of streamer steering have been widely recognised for several years. ION's DigiFIN lateral control system has made steerable streamer technology more widely available, enabling service providers to acquire higher resolution data more efficiently and safely. Increasing productivity and reducing costs are paramount in today's economic landscape.
For years service providers have been steering vessels to pre-determined survey routes. High resolution imaging requires these vessels to tow up to 18 streamers kilometres long. Ideally, the cables would remain straight and parallel behind the vessel throughout the survey.
However, environmental variables, such as ocean currents, cause streamers to feather and form irregular shapes.
Uncontrolled cable movement heightens safety concerns about streamer entanglement, resulting in streamer separation values set by risk mitigation instead of geophysical objectives.
HSE risk
The lack of cable control also increases HSE risk around a growing number of in-field obstructions. As the number and length of streamers continues to rise, the necessity to maintain tight, uniform positioning increases.
Steerable streamers enable operators to counteract environmental effects by laterally controlling cable movement.
DigiFIN, ION's universal streamer steering system, leverages customers' existing infrastructure for low total cost of ownership and immediate adoption.
The plug and play, open-source architecture provides flexibility to customise the network.
DigiFIN is comprised of both in-water and on-board components. The in-water equipment easily attaches to cables and has one vertical wing dedicated to lateral movement for maximum functionality with minimal noise. The wing dynamically changes angles to displace water and drive the cable direction and intensity desired.
The devices are neutrally buoyant on the cable, eliminating ballast adjustments or increased depth keeping activity. Frequency Shift Key (FSK) communication ensures universal compatibility.
System intelligence and control
Orca, ION's next generation command and control software, works with the shipboard lateral controller to steer the streamers to the user's desired separation.
- Orca provides streamer separation estimates to the lateral controller;
- The lateral controller calculates wing angles required to achieve the desired separation.
Depending on the operation mode, multiple cable shapes and parameters can be selected for the ideal configuration.
Combined, DigiFIN and Orca enable operators to automatically fine tune positioning and control in a dynamic marine environment.
Streamer steering benefits
Steerable streamer technology enables seismic contractors to improve productivity by minimising time spent on offline operations. DigiFIN enables faster line changes by straightening cables coming out of a turn more quickly. In addition, the system can maneuver closer around obstacles near start of line, decreasing cycle time. Crews can deploy and retrieve multiple cables simultaneously instead of one at a time. During deployment, DigiFIN provides increased control to both slot final streamers more easily and control longer streamers better.
The unpredictability of the marine environment not only affects the in-water equipment, but also infill. Infill may be required if all bins were not acquired with all offsets during the first pass. Re-shoots are time-consuming for service providers and costly to oil companies. DigiFIN adjusts or induces a feather angle in the spread to reduce trouser effect and maximise coverage.
However, steerable streamer benefits far exceed operational efficiencies. Tighter, more uniform cross-line separation enables denser spatial sampling. The increased control aligns source and receiver positions to pre-plots or prior surveys to improve 4D repeatability. More constant source and receiver positions eliminate guesswork in data post-processing.
In addition, spread control mitigates the risk of obstructions and entanglement. Acquisition on existing fields is becoming more common to maximise production. Close-passes heighten safety concerns because if the spread deviates far enough from the plan near an in-field hazard, the results could be disastrous. In addition, DigiFIN maintains a constant, user-defined cross-line separation to mitigate the risk of cable entanglement.
Orca and DigiFIN, which enable streamer steering, are critical to ION's Intelligent Acquisition approach to simplify and automate operations. By integrating our technology into a seamless system, the spread can be optimally positioned while reducing complexity, cycle time, and cost. ION is committed to making these advanced acquisition techniques widely available to mitigate risks, reduce costs, and enhance image quality. As the cost and complexity of towed streamer surveys rise, streamer steering will be an invaluable asset to marine acquisition.
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Jeff Cunkelman is with ION Geophysical, Houston, TX, USA. www.iongeo.com
