|WikiProject Geology||(Rated Start-class, Low-importance)|
|WikiProject Earthquakes||(Rated Start-class, Low-importance)|
The claims regarding direct detection of hydrocarbons via such low frequency or passive-seismic techniques (also known as Anshar and ADD-HR) are completely without foundation. While low frequency seismic waves can be useful in the understanding of mega-scale features of the earth's interior (on the scale of hundreds of miles), such as the mantle and core, they have no valid application in the identification of hydrocarbon reservoirs. Any and all competent geophysicist or physicist will confirm that the theoretical and empirical basis of the claims are false. Geophuzzy (talk) 22:57, 5 November 2008 (UTC)
- The most known European company, Spectraseis, exists, grows and keeps receiving new and new contracts to do the acquisition and analysis. The direction is the important research topic in the geophysical department of ETH (Zurich), being covered by multiple scientific publications and several successfully defended PhDs. There are also other companies, including Gradient and your mentioned Anshar. It may be oponents, of course, but "any and all competent geophysicist or physicist" sounds far too strong for me. Audriusa (talk) 20:10, 20 May 2009 (UTC)
I will make a comment or two on the above statements: It is true that low frequency passive techniques for hydrocarbon exploration are very controversial in the oil industry right now. However, no one has shown that it is completely without basis. It is also true that Spectraseis seems to be getting a lot of business and ETH is awarding doctorates for work in this subject. However, it is not the geophysical department of ETH, but the structural geology group. In fact, a recent rebuttal of this method was published by an eminent geophysicist who is in the geophysics department of ETH. This was published as a comment to a Spectraseis/ETH paper recently published in the oil industry journal called Geophysical Prospecting. What is low frequency? To earthquake seismologists, probably less than 0.1 Hz. Then, it is true that these low frequency waves probe deep scales not relevant to hydrocarbon reservoirs. However, the frequency range of the microseismic method in question is 1-10 Hz. As for surface waves, these frequencies only probe depths to a few 10's of meters. But, as propagating body waves in the reflection seismic method, they can probe reservoir depths. However, the reflection method does not currently do well for frequencies below 6 Hz or so. The real question is - are body waves an issue? Spectraseis claims yes. Now, the (entirely legitimate) subject of passive seismic interferometry can take ambient noise and synthesize reflections from reservoir depth layers. Hence, poroelastic effects could show up in this case as amplitude anomoalies. It might be that this is what Spectraseis claims to be seeing. However, there are many problems. For example, surface waves in ths frequency range will swamp any body waves potentially arriving from the reservoir. Also, it is not been currently shown by anyone how to model the expected signatures under any conditions. Such results have been claimed, but later debunked by others. One problem is that the subject is not receiving serious scrutiny by industry geoscientists. Why is this? Becuase, as stated above, most serious geoscientists are not taking the method seriously. This is primarily due to the unconvincing empirical evidence shown, and even more unconvincing theoretical arguments. However, this does not prove, in itself, that there is no underlying effect. In fact, no such proof is possible in principle. In time, this will all get sorted out. Will low frequency passive seimic be seen as a legitimate method for oil exporation, or one of the longest cons run in the oil industry? Either way, one this in clear - the Wikipedia article I am commenting on, as is, is a piece of crap. 188.8.131.52 (talk) 06:42, 1 June 2010 (UTC)
I fully agree with the previous negative statements made herein the discussion for the article on passive seismic. The article is pure advertising for a company promoting with any means their minor passive seismic method. It was shown by several authors (Aki & Berteussen, Hanssen & Bussat, Broadhead, and Martini et al.) that an around-3-Hz Direct Hydrocarbon Indicator (DHI) does not exsist. It was shown that a peak around 2-6 Hz can be produced either by regional natural sources (storms, surf,...) or by artificial anthropogenic sources (traffic, drilling,...). The frequency of the peak drifts around 3 Hz which is controlled by the thickness of the unconsolidated surface layer. The recorded 3 Hz energy is a Rayleigh wave and its wavelength is correlated to the penetration depth/thickness of the unconsolidated layer, which can be exploited with the well-known Nakamura method.
Additionally, the term ‘passive seismic’ is foremost used for microseismic monitoring, where an indirect source (human-caused pressure change) is used than the standard sources of ‘active seismic’ like explosives, air guns, vibroseis trucks and similar. Furthermore, a range of passive seismic methods exist which are not at all listed in this article. I will therefore in due time change this article, adding several other, scientifically proven and more important methods, and add critical references to the existing Spectraseis ad. — Preceding unsigned comment added by Likelooks (talk • contribs) 19:33, 23 June 2011 (UTC)
I am glad to see that the proper definition of passive seismic will soon replace this blatent case of advertising for the company. Previous attempts to create a new page on "Microseismic Monitoring" were rejected and so if there is any way I can help to provide sources or material for a comprehensive summary of passive seismic/microseismic I am happy to do so. KayeJezz (talk) 21:32, 12 February 2012 (UTC)