To continue the column from last month, I was reviewing the types of explosive sources used over the years, particularly for the benefit of the “new breed” of geophysicists and their field staff.
A very interesting source used in some areas was the linear source, namely Aquaflex for water applications and Geoflex for land and surface applications.
Rupert Goodhart was responsible for designing and having built what we termed the Geoflex plow. The explosive source was usually 50 grain to 200 grain detonating cord plowed 18" to 48" below the surface with a special plow not unlike that used to plow telephone cable underground. The length and strength could be varied to suit the conditions. The detonator was added when the line was shot.
Variations of this approach were used in the winter by covering the detonating cord with snow, both on land and a considerable amount was used on the ice in the Arctic. Again, patterns of cord could be laid out, usually parallel, with a slight stagger to the lines.
Before the plowing was completed there was quite a lot of surface shooting going on using various combinations of low grain, fire retardent cord with “bumps” of various sized cartridges of explosives along its path. In lieu of a fire retardent cord, there was a period where up to I" diameter continuous lengths of water gel explosive tubing was used.
These products were used not only as a seismic energy source but also as “fire-break-cord”, to flow a path clear of vegetable matter so that forest fire fighters could get down to clay to stop a ground fire. Some efforts were more successful than others, but you sure knew the blasters were in the country.
Probably the most widely used version of the detonating cords was the system which properly termed became known as “Vertical Ice Aquaflex”. This was usually used in the arctic. The general idea was to drill a hole through the ice, suspend a primed length of cord with a weight at the lower end. As you can see the variations here were many. The most popular cord ended up as 25 grains per foot but cords up to multiples of 200 grain were also tried.
A very short variation of surface cords in the arctic was built around the “Geopad”. This was a rectangular sheet of 50 grain cord, cut at one foot lengths with the ends sealed, then about 50 pieces glued together to make a flexible pad or mat of continuous explosive. This was used by stretching out 50 grain cord on the surface of the snow (or ice) in any configuration desired. The “Geopads” were added again wherever desired to give whatever type of energy wave was required. (There were a lot of wierd and wonderful arrays of both source and geophones).
Generally speaking the arctic (land) was shot conventionally using deep and heavy charges. The 3" diameter by 100 lb. plastic couplable cartridge was developed specifically for the arctic areas to reduce the total column rise of explosives.
Several tries were made to use other than Nitro-glycerine based explosives but none of these ever caught on to any great extent, mostly due to the extra care needed to transport, store and handle explosives with “fussy” characteristics.
Stories abound about the “close calls” or “near misses” using explosives in other than standard, well established means. All of these special use trials started in some oil company’s board room with the “chief’ and his SUbordinates, along with some explosive types and someone saying,”what if …“. Sometimes it took many months to bring a”what if’ to trial in the field. Some of those “what ifs” actually solved problems and everyone was pleased. The other times someone usually said “those explosives sure are damned expensive!”
I’ve purposely left out a couple of areas where we have used explosives and here’s why. Shaped charges have been used off and on in many configurations for years. Many theories abound about how good and how bad they are.
The Poulter System is also a type of shooting that has been with us for many years and is still in use as a good seismic energy source under certain conditions. I’ll do a column on the Poulter System at a later date and include a lot of safety tips on its use.
I’ve purposely not gone into detail on the “old” systems and I’m sure my comments will generate discussion among some of the 01’ boys over coffee. I’ll be glad to answer questions from anyone regarding some of the techniques used. But - I still advocate 5 at 60, or something very similar.
’Til next time, at work or leisure LIVE SAFELY!