The first step of a refraction survey was deciding on an area and laying out a grid work of lines to survey. The area was usually
chosen from known geological data. ARAMCO had drilled many stratigraphic wells in the area and knew the general geology of the area.
Once an area was chosen, a grid work of lines was drawn on a map as to where the seismic lines would be placed. In Bir Hadi the lines
ran East-West and had one North-South line to tie the other lines together. The term lines just comes from the fact they were lines
drawn on a map. It was important that ARAMCO knew where the lines were located on the ground so they could go back later to a spot if
they decided to drill a well or do more detail exploration. There was no GPS in those days; all surveying was done with theolites taking
off from a known location. ARAMCO had also done an extensive survey in the area setting up benchmarks in various locations. A camp
would be set up that was centrally located to the current line being surveyed and shot. The first people to arrive were the surveyors.
They would survey the line to make sure it was straight and to determine the elevation of each station for the placement of geophones and
shot holes. The stations were 1000 feet apart in this area and were numbered using the first two digits. The survey stakes were simple
1" x 2" wood lathes about 4 feet long. Each stake had the station number on it. The surveyors would get up before daylight to start work.
They would quit about mid-day when it started getting warm and the heat waves interfered with their readings. In the Sand Mountains area,
the surveyors would stop working before noon in the summer time.
After the lines were surveyed, the explosives would be placed at the shotpoint locations along the line. In Bir Hadi, the charges were
bags of ammonia nitrate soaked in diesel oil. Same stuff used in the Oklahoma City bombing. Without some type of detonator, the ammonia
nitrate was safe. In the Sand Mountains, the explosive material was a more powerful explosive in metal canisters. This was because most
of it was delivered by helicopter, while in Bir Hadi, the charges were delivered by trucks. We had to keep an accurate record of
the explosives we used because the Saudi Government was concerned that extremist might get them to use against the government. The caps
primers and boosters were kept under lock and guarded at the powder dump until they were ready to go to the line.
While the explosives were being delivered to the lines, the drill crews would start their work. The main drill used was the Mayhew 500
which was mounted on trucks. A smaller version was mounted on a sand buggy for use in the Sand Mountains. If the sand was deep, a
puffer would be used instead of a rotary drill. A puffer was a truck-mounted compressor. A large metal tube would be lowered into the
sand and the compressor would blow the sand out of the tube. This way, a deep enough hole could be formed. After the hole was drilled
or puffed out, it would be loaded with the explosive charges. Usually the charge also had the booster, primer and caps attached to it
at this point. The charges were buried because a smaller charge could be used. Four shots would be detonated for each set up of a
single seismic spread (24 geophones, 1000 feet apart). We were mapping two formations (Hith and Rus) and each required a different offset.
For the Hith Formation, the shots were about 20,000 feet off the end of the spread and consisted of about 2000 pounds of explosives. For
the Rus Formation, the shots were about 5,000 feet off the end of the spread and consisted of about 500 pounds of explosives. Each spread
was shot off both ends in order to be able to use the ABC method when interpreting it back in the office. Each spread overlapped the
adjacent spreads by two stations to time tie each spread to the previous spread. This insured that the spreads and shots were in the right
When it was time to start recording, the cable was laid out. There were geophones every 1000 feet. They were low frequency Dayton geophones.
That meant a number of problems could stop the crew from recording. Rain, wind and camel herds could generate enough noise to interfere with
the recording by generating noise that was as great as the actual data being recorded. When the geophones were connected to the cable,
each one had to be checked to verify the polarity was correct. Otherwise peaks would be troughs and troughs would be peaks on the seismic
record. The doghouse (recording truck) was called that because it looked like a small house on the back of a truck or sand buggy. The
observer was the person who ran the recording equipment in the doghouse. He would verify everything was set up properly. The doghouse
would move to the center of the cable to connect to it in preparation for recording.
At this time the shooter who was responsible for detonating the shotpoint would move to the shotpoint being shot for the current record.
There were two shooters on the crew. Each worked off one end of the recording cable. Otherwise, it would have been about 15-mile drive
to get to the two shotpoints off each end of the line. The shooter would arrive at the shotpoint and connect the blaster box to the charges
for the current shotpoint. Because of the long distances involved, the shooter would sent out a tone on the radio that was recorded on the
seismic record. When the charge was detonated, the tone was broken and a negative spike would occur on the record giving the time for the
shot. This was time zero. When the shooter was ready to shoot, he would radio the observer to let him know the shot was ready to go. Then
the shooter would say he was shooting on the count of five. The observer would then count to five and start the recording. One time the
observer started to record and nothing was coming in. He turned the radio on and heard "Threeeeeeeeeeeee". The shooter was from the Southern
USA and had a Southern drawl. Another time he started to record and data was already coming in. The shooter was from the UK and talked
very fast. The shooters would not shoot if the wind were blowing too much. Not for the noise, but for the static electricity. The wind
blown sand created enough static electricity that it could set off the charge while the shooter was connecting to the charge. If the charge
did not go off for some reason, or the recording was not good, then a surface charge had to be set off. It was usually double the size of
the normal charge. The drills were too far away to come back to drill a new shotpoint. Another problem was earthquakes. A few times, the
observer started recording only to see data already coming in on the cable. It was energy from an earthquake. It did not happen very often.
More on Page Three.