Surface towed streamers and ocean bottom nodes are usually considered competing solutions. Geophysical contractors specialize and offer either method. However, if data processing can put the data together these methods are complementary, with nodes covering the minority are that is obstructed or where shear waves are required and streamers cover the majority of the area.
In a week or two, a streamers crew can acquire data to image the subsurface under an area of hundreds of square km. The transit time and the time it takes to deploy and retrieve the streamers is days to weeks to months. If we get a streamer crew to acquire a monitoring survey over a field, we would have the crew cover the whole area and perhaps adjacent fields if applicable. Obstructions can be undershot with a separate source vessel shooting into streamers towed on the other side of the platform. Streamers have to keep a safety distance of hundreds of meters from obstructions to allow for feathering. Source vessels, whether shooting into nodes or into streamers, can get closer to obstructions; tens of meters.
Nodes provide much better image under the platform because they can be deployed very close and even under platforms. Compared to streamers, nodes provide wide azimuth coverage, imaging with multiples, recording of shear waves, and better repeatability if they are deployed with remotely operated vehicles (ROV). The productivity of a node crew in square km per day is a small fraction of that of streamers. Depending on the obstructions and whether a streamer crew of opportunity can be in the area for neighboring fields, the most economical solution may be either streamers with undershoot, or pure nodes, or a combination. The added value of data quality depends on the target and the overburden. Usually node data are better, but in some cases streamer data may be better. Whether these differences in quality are significant depends on the target.
An interesting possibility with nodes is to deploy the nodes in an area of interest, and shoot into them twice. Once before and once after an activity such as the start of production or water injection, or a production test from a discovery well. It is often possible to see flow barriers via pressure effects and fluid motion.
The economy must be examined on a case by case basis. If the capital investment in deploying a permanent reservoir monitoring system is similar to the capital investment in a node crew, it will be more economical to use redeployed nodes. Especially if the nodes can be deployed and retrieved by an ROV vessel that is anyway resident in the field.
Although the basic idea of using the best of both streamers and nodes is simple, the implementation is not. Totum Geo can help with the following challenges, opportunities, and risk mitigations.
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