Landlocked Marine Shoot
Complex Locale Gets Unique Plan
Geophysical contractors sometimes find themselves in the darndest situations.
Yet they’re often adept at zeroing in on solutions.
This was the case in Uganda, when U.K.-based IMC Geophysics International was faced with the challenge to acquire a seismic survey across a large part of a water body for its Canada-based client Heritage Oil Corp., which has been actively drilling in Uganda for a number of years.
The assignment was an upgrade from the land 2-D and 3-D and the transition zone 2-D activity IMC had been pursuing in the region.
Even though IMC had the expertise to design the survey it lacked certain assets, i.e. gear, to acquire it in the most effective manner.
The company called on Houston-based Global Geophysical, and the two entities ultimately struck a synergistic deal: Global would supply the equipment and a number of key personnel, e.g., senior navigators, observers, and IMC would supply the labor and local logistics.
A Complex Environment
The program target area is Lake Albert in northwest Uganda.
“Geographically, it’s a very complex environment for a conventional marine survey,” said Duncan Riley, vice president worldwide marine at Global. “Lake Albert is a textbook horst and graben geologic feature everybody reads about when studying geology.
“The lake is bordered on the east by a mountain range that’s been thrust upward almost vertically,” Riley added, “so the eastern border of the lake is roughly a near-300 meter vertical cliff. The lake is about 150 kilometers long and averages 35 kilometers in width, and the water depth is a fairly uniform 50 meters. The surface area is some 5,300 square kilometers.”
In other words ...
“It’s a marine environment in the middle of a land-locked country,” Riley noted, “so it’s stretching the expertise of anyone that’s done significant work there in the past because they’ve been working in savannah and thick bush.”
The inhospitable locale itself -- hot and wet, in the middle of the continent -- is a considerable challenge for personnel.
IMC designed the survey, which encompasses 15 square kilometers on land and 315 square kilometers in the marine environment. Rather than trying to implement two separate surveys and marry the data post acquisition, a recording system designed to work in both land and shallow marine environments made far more sense.
Mustang Experience Pays Off
This was right up Global’s alley given the successful transition zone survey it acquired late last year on Mustang Island in the south Texas coastal area near Corpus Christi. There, the company worked in a number of operating environments -- crossing the transition zone, the island and back into the bay -- using one recording system.
The company transported many of that job’s assets, which were initially put together for a coastal transition zone environment, to Uganda where they’re being deployed to acquire a seamless data set across the water, the land component (including the logistics base) and the gap between.
Moving the equipment to its destination was a major logistical challenge.
Riley noted they amassed a variety of modular boats and equipment that could be disassembled, shipped and reassembled at the shore -- problem is, the shore is a long, long way from the Entebbe airport where the containers were unloaded from the plane.
About 20 trucks loaded with gear traveled 10 hours to reach the central part of the lake, which has a port of sorts where the gear could be loaded onto barges.
It then took about six hours for the barges to reach the base camp on a depressed piece of land, which is accessible only by small plane or boat. A small dock was available for unloading the equipment.
The survey is being implemented using the Sercel 408 UL recording system onshore, where dynamite will be used. Offshore, the 408 ULS is being used along with airguns.
The 330-square-kilometer program will require about three months, according to Riley.