Vibroseis versus Dynamite
I’m currently on a 2D job which is mainly flat but it does have one portion in the middle which has some hills requiring bulldozer cutting. The client emailed me the other day asking about using vibes in the hills as somebody at the office had asked if it wouldn’t be better to use dynamite. On this job dynamite is not a realistic option as importing the stuff is difficult and drills are just not available to get it down to a decent depth so I needed to answer in such a way that he would be able to convince the doubters.
The first thing that I normally do in these cases is look for an expert opinion that has been published in a respected journal but as I looked around the Internet for any sort of scientific comparison between vibroseis and dynamite on flat terrain I came up empty, far less a comparison on steeper grades.
I know from several recent projects that vibes can be used pretty effectively in some steep areas but I am also perfectly aware that the laws of physics even apply to seismic crews and vibrators. The simple fact of the matter is that as we get to steeper angles the force that the vibe exerts is working at an ever increasing angle to the force exerted by the vibes weight which normally holds the machine down so the output power can never be equal to that on level ground so there must be a limit to what can be done with a vibe. The problem is to demonstrate that this limit will not be reached in the hills that we have.
As mentioned earlier my recent projects include two jobs in mountainous country. One of the jobs was a 3D done completely with vibes and the other was a 2D where there was dynamite available and some pattern holes could be drilled in the hard rock areas that were completely inaccessible to the vibes.
On the latter job the dynamite shots were not as good as the vibe records for adjacent shots. Penetration was poorer and the noise was far more noticeable due to the lack of stacking and correlation which favours the vibes. The terrain in that area was far worse than anything that we are up against here and the data was acceptable. I know that it isn’t really a fair dynamite versus vibes comparison using pattern holes but then again the vibroseis were being used in places that they were never designed to go.
Here on this project the same vibes are being used and the data we have been getting is very good but the question remains, would it be better to drill and use dynamite. Cost is a big part of the consideration when it comes to seismic, especially with the oil prices at current levels.
Maybe somebody out there has been involved in some sort of comparison testing that could be of help. Let me know in the comments below.
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