Featured Research

from universities, journals, and other organizations

Views From Space Help Oil Prospectors See Deep Underground

Date:
February 2, 2005
Source:
European Space Agency
Summary:
Those searching for oil and gas have used varied methods to send sound energy into the ground and to record the waves reflected by the geological features beneath the surface. Today, seismic surveys planned with satellites are yielding clearer, deeper subterranean views at reduced cost.

This still image from a fly-through covering 500 square kilometres of west central Algeria illustrates the massive amount of varied topographic and geological information that satellites can provide in order to more effectively pre-plan a seismic survey campaign for oil and gas exploration.
Credit: Image courtesy of European Space Agency

It takes seismic force to make the ground give up its secrets. Through the years, those searching for oil and gas have used varied methods to send sound energy into the ground and to record the waves reflected by the geological features beneath the surface. Modern methods include large vibrator trucks and many thousands of surface sensors called geophones, all precisely located to obtain the most useful information with which to explore for hydrocarbons. Today, seismic surveys planned with satellites are yielding clearer, deeper subterranean views at reduced cost.

Often carried out in the remotest parts of the planet, these surveys are almost military in scale and expense; a seismic crew exploring a 500-square-kilometre area can require 400 people with up to 50 small and 15 large vehicles working with up to 600,000 geophones, and carrying out 600 seismic 'shots' daily.

Seismic surveyor WesternGeco, has been working with ESA for the last three years to integrate satellite data into its working practices. What Earth Observation can provide is a detailed preview of a region's topography and geology, valuable for assessing areas that will produce the best and worst seismic quality – meaning the sending and receiving of vibration signals – far in advance of commencing the survey.

"Working on the surface, we deliver imaging and structural characterisation of the subsurface, down to 6000 metres or deeper," says Andreas Laake of WesternGeco. "Technology has moved on since the days of heavy explosives, but the principle remains the same."

Elastic waves are excited at the surface and propagate through the subsurface, partly transmitting, partly reflecting, and partly scattering. The reflected waves are then detected on the surface by a pre-planned array of geophones. Sophisticated processing of these sensor data creates a three-dimensional picture of the underlying geology of the survey area.

"The modern vibroseis technique has spatial resolution sufficient not just to identify oil and gas reservoirs, but also to show internal details such as their fracture geometry," Laake adds. "This is vital, because our customers do not make money for the amount of hydrocarbons theoretically in the ground, but what they actually recover.”

"The vibroseis method uses trucks with heavy masses and baseplates that vibrate the ground to provide a far more controlled source," Laake explains. "Depending on the target, the trucks can be tuned to work across a pre-defined frequency spectrum, providing 'multicoloured' views in terms of elastic waves."

To achieve high-fidelity reservoir characterisation, the surveyors aim to exclude as many variables as possible. Around 80% of acoustic signal distortion comes from propagating through the top 100 metres of ground, with the most problems encountered nearest the surface.

"For satisfactory results, we must achieve very good coupling of both the vibration source and the receivers with the ground," Laake recounts. "The mechanical energy generated by a vibrator truck is only useful if it gets converted into elastic energy in the ground. And elastic energy coming back out of the ground must be converted into electrical signal in order to be measured, so here we must have good coupling of the geophones with the ground as well.

"Very hard rock has poor coupling with the baseplate, and the returning signal is low-quality because receivers cannot be placed satisfactorily. Coupling cannot take place on uneven ground. And with soft ground, the baseplate may just sink, or the soft ground may just absorb high frequencies at the receiver end to reduce the potential image resolution.

"But, until we started using satellite imagery, we could only guess at the coupling and data quality in advance of an actual survey. Space-derived topographic information is also important because rises or falls in the landscape delay signal arrival time, and if they are not compensated for, they cause blurring of imagery.

"These two variables set the scene for a broad range of information we require. For example, we must know if there is anywhere we can't go due to steepness and roughness of terrain. Also, we need to know if there are any rivers to cross or infrastructure to avoid such as oil wells or pipelines whose activities may interfere with our signal."

No single space-borne instrument can supply all the data required. Instead, data from a variety of different satellites are collected and combined within a geographic information system to yield information on accessibility, data quality, and source and receiver coupling.

The process begins with a digital elevation model, available from many sources including space shuttle mapping and ESA's ERS-tandem mission. This provides topographic and gradient information for logistics and safety planning. Next comes radar imagery – from spacecraft such as Envisat and ERS – to measure surface roughness, forming the basis of a map of coupling potential.

Visible light images provide infrastructure and land use information that help determine accessibility for vehicles and people. Also, surface vegetation detected in this imagery may indicate sediment-buried water channels that weaken signal propagation.

The ground reflects short-wave infrared (SWIR) light immediately, revealing the spectral characteristics of minerals at the surface. SWIR imagery, obtained from hyperspectral satellite sensors, is particularly sensitive to carbonates such as limestone and basalt and occurrences of softer materials such as gypsum or quartzite gravel.

Advancing further into the infrared spectra permits surveyors to peer deeper beneath the surface. Thermal infrared (TIR), or heat radiation from the surface, is a delayed response to incoming solar radiation, coming from the top half-metre of subsurface.

"It is important to characterise this area, as this is where most of that 80% of data distortion comes from," says Laake. "In particular, TIR is useful for identifying underlying layers of basalt, which radiate strongly in thermal energy, so much so that we can interpret its presence indirectly from well below a half a metre.

"Basalt is a massive reflector, functioning like a shield between the surface and the hydrocarbon reservoirs. We can't work on surface basalt – the baseplate simply jumps back – but there are optimal design geometries we can use for buried basalt layers using selected angles of incidence for the seismic waves to ensure that not all the signal is reflected and that some goes through."

WesternGeco has so far used remote sensing data for sites in Algeria and Argentina. "We have started with desert areas because they are a relatively simple case with unchanging landscapes," Laake concludes. "But, the technology we are developing here can fully apply to other locations.

"What Earth Observation represents for us is a means of carrying out seismic survey feasibility studies prior to defining survey programmes for our clients, and ensuring enhanced data quality for even the most challenging environments."

UK-based Infoterra and WesternGeco have jointly developed a seismic-quality mapping service as part of an ESA Earth Observation Market Development (EOMD) project. EOMD is a programme aimed at strengthening the European and Canadian capacity to provide geoinformation services based mainly on Earth Observation data, with a particular emphasis on addressing the needs of small value-adding companies.


Story Source:

The above story is based on materials provided by European Space Agency. Note: Materials may be edited for content and length.


Cite This Page:

European Space Agency. "Views From Space Help Oil Prospectors See Deep Underground." ScienceDaily. ScienceDaily, 2 February 2005. <www.sciencedaily.com/releases/2005/01/050128215109.htm>.
European Space Agency. (2005, February 2). Views From Space Help Oil Prospectors See Deep Underground. ScienceDaily. Retrieved September 15, 2014 from www.sciencedaily.com/releases/2005/01/050128215109.htm
European Space Agency. "Views From Space Help Oil Prospectors See Deep Underground." ScienceDaily. www.sciencedaily.com/releases/2005/01/050128215109.htm (accessed September 15, 2014).

Share This



More Earth & Climate News

Monday, September 15, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Conservationists Face Uphill PR Battle With New Shark Rules

Conservationists Face Uphill PR Battle With New Shark Rules

Newsy (Sep. 14, 2014) — New conservation measures for shark fishing face an uphill PR battle in the fight to slow shark extinction. Video provided by Newsy
Powered by NewsLook.com
Pakistan's 'killer Mountain' Fails to Draw Tourists After Attack

Pakistan's 'killer Mountain' Fails to Draw Tourists After Attack

AFP (Sep. 12, 2014) — In June 2013, 10 foreign mountaineers and their guide were murdered on Nanga Parbat, an iconic peak that stands at 8,126m tall in northern Pakisan. Duration: 02:34 Video provided by AFP
Powered by NewsLook.com
Solar Storm To Hit This Weekend, Scientists Not Worried

Solar Storm To Hit This Weekend, Scientists Not Worried

Newsy (Sep. 11, 2014) — Two solar flares which erupted in our direction this week will arrive this weekend. The resulting solar storm will be powerful but not dangerous. Video provided by Newsy
Powered by NewsLook.com
The Ozone Layer Is Recovering, But It's Not All Good News

The Ozone Layer Is Recovering, But It's Not All Good News

Newsy (Sep. 11, 2014) — The Ozone layer is recovering thickness! Hooray! But in helping its recovery, we may have also helped put more greenhouse gases out there. Hooray? Video provided by Newsy
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
 
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:  

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

    Technology News



    Save/Print:
    Share:  

    Free Subscriptions


    Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

    Get Social & Mobile


    Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

    Have Feedback?


    Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
    Mobile iPhone Android Web
    Follow Facebook Twitter Google+
    Subscribe RSS Feeds Email Newsletters
    Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins