A technology scientific discipline developed past times Stanford scientists for passively probing the seafloor using weak seismic waves generated past times the bounding main could revolutionize offshore crude oil together with natural gas extraction past times providing real-time monitoring of the subsurface spell lessening the touching on marine life.
“We’ve shown that nosotros tin generate images of the subsurface nearly every twenty-four hr flow instead of taking snapshots simply ii or iii times a year,” said Biondo Biondi, professor of geophysics at Stanford’s School of populace Sciences.
Currently, many unloosen energy companies purpose a technique called time-lapse reflection seismology to monitor offshore crude oil together with gas deposits to optimize production together with await for hazards such every bit hidden gas pockets. Reflection seismology involves ships towing arrays of “air guns” that explode every 10 to xv seconds to arrive at loud audio pulses. The pulses bounce off the seafloor together with geological formations beneath, together with then journeying dorsum to the surface, where they are recorded past times hydrophones. The information are together with then deciphered to bring out details nigh subsurface structures.
Each survey tin terms tens of millions of dollars, together with every bit a upshot they are only conducted ii to iii times a year. Environmental groups together with marine biologists convey expressed concerns nigh the purpose of air guns for contributing to dissonance pollution inward the bounding main that tin disturb or fifty-fifty hurt marine animals, including humpback whales together with giant squid.
The novel technique developed past times Biondi together with Sjoerd de Ridder, a educatee of Biondi’s who is right away a postdoctoral scientist at the University of Edinburgh, is different. It exploits naturally occurring seismic waves generated past times Earth’s oceans that are several orders of magnitude weaker than those produced past times earthquakes.
As bounding main waves collide amongst i another, they practise pressures on the sea floor, where they generate seismic waves that together with then propagate inward every direction. Scientists convey known nigh this “ambient seismic field” for nearly a century, but it was only of late that they understood ways to harness it.
“We knew the ambient seismic unloosen energy was there, but nosotros didn’t know what nosotros could practise amongst it,” De Ridder said. “That agreement has only been developed inward recent years. Our technique provides the commencement large-scale application to harness it for crude oil together with gas production.”
The technique that Biondi together with De Ridder developed, called ambient seismic champaign noise-correlation tomography, or ASNT, uses sensors embedded inward the seafloor. The sensors, which are typically installed past times robotic submersibles, are connected to i unopen to other past times cables together with arranged into parallel rows that tin bridge several kilometers of the seafloor. Another cable connects the sensor array to a platform inward fellowship to collect information inward existent time.
The sensors tape ambient seismic waves traveling through Earth’s crust. The waves are ubiquitous, continuously generated together with traveling inward every direction, but using careful signal-processing schemes they developed, Biondi together with De Ridder tin digitally isolate only those waves that are passing through i sensor together with and then unopen to other i downstream. When this is done repeatedly, together with for multiple sensors inward the network, what emerges is a “virtual” seismic moving ridge designing that is remarkably like to the form generated past times air guns.
Because the ASNT technique is solely passive, pregnant it does non request a controlled explosion or a loud air gun smash to practise a seismic moving ridge signature, it tin live on performed for a fraction of the terms of an active-reflection-seismology survey together with should live on far less disruptive to marine life, the scientists say.
Since 2007, Biondi together with De Ridder convey been testing together with refining their technique inward a real-world laboratory inward Europe. The scientists worked amongst the unloosen energy companies BP together with ConocoPhillips to written report recordings from existing sensor arrays inward the Valhall together with Ekofisk crude oil fields inward the North Sea that are capable of recording ambient seismic waves.
The proof-of-concept experiment has been successful, together with the scientists convey demonstrated that they tin icon the subsurface at Valhall downward to a depth of nearly 1,000 feet. “We’ve right away shown that our technique tin real reliably together with repeatedly hollo upwards an icon of the near-surface,” De Ridder said. “Our promise is that they tin also bring out changes inward the rocks that could indicate an impending problem.”
The Stanford scientists outlined their technique together with detailed unopen to of their results from Valhall, every bit good every bit from Ekofisk, inward a serial of technical papers, the latest of which was of late published inward the journalGeophysical Research Letters.