I sent the PDF file to a family member who is a Geophysicist and here is his response.
I’ve been buried under a ton of work so I didn’t spend a lot of time reviewing the link ( it’s too bad you didn’t have the PowerPoint, those .pdf files are really slow!) but I can tell you that PGS is a good company, the acquisition parameters look sound (a high enough filter and long enough hydrophone cable, tight grouping, etc.) and the seismic profiles included showed some interesting and complex geology that has potential for structural trapping of hydrocarbons, plus we know Nigeria’s plumb full of oil. The inline and xline plots show vertical slices down into the earth and when you pack a bunch of them next to each other they form a “cube” of data which is made of seismic traces which are just strings of floating point numbers. So the first three dimensions are length and width of the survey as mapped on the earth’s surface with depth down into the earth as the third dimension. The 4th “D” in 4D refers to time. Here’s where it gets tricky: seismic traces take time to penetrate downward so the depth of a data cube is commonly referred to as time, as in the two way time for the source signal (an air gun in this case) to penetrate down an reflect back up to the streamer (hydrophone cable). When the data is depth converted then the third dimension can rightfully be called depth. The time referred to in 4D refers to re-shooting the survey and noting changes from the previous. I’m not a big believer in 4D as it’s really hard to get two shootings apple to apple. A better method is AVO analysis where you look at seismic traces in a zone of interest sorted by offset (distance between source and receiver) and note amplitude changes taking place going from near to far offset, these can be a pretty good indicator of fluid content as liquids screw with the signal strength in various ways – P-waves penetrate just fine but fluids absorb and dampen shear waves. In other words trying to see if there’s any hydrocarbon actually down there occupying that great structural trap? To do that you need pre-stack seismic data meaning the offsets at each trace location have not been summed together (they have in these pictures) and an AVO interpreter who knows what he’s doing.
Any thoughts?
Bayfisher
