During a recent field trip to Uganda associated with oil and gas exploration, a cross section of journalists had the opportunity to ask some pertinent questions.
For instance, why drill horizontally rather than the usual vertical?
One expert said horizontal wells introduce a new variable: a single well can penetrate and produce oil from multiple parcels.
He said it is the only way one can follow a rock layer to maximize penetration distance.
Using the horizontal method, a single drilling pad can be used to drill a number of wells. This reduces the footprint of drilling operations. In 2010 the University of Texas at Arlington drilled 22 wells on a single platform.
These wells are draining the natural gas from about 1100 acres beneath the campus. Over a 25-year life-time the wells are expected to produce a total of 110 billion cubic feet of natural gas.
A Geologist and Field Monitor at Uganda’s Petroleum Exploration and Production Department (PEPD) from the Energy Ministry,Mr Wilson Tumushabe said the alternative would be to drill many wells, each requiring a drilling pad, pond, access road and gathering line.
“Horizontal wells are better producers and are the best in terms of environmental conservation rather than vertical which is cheap,” Tumushabe told East African Business Week at the Total ESP oil field.
He said with horizontal drilling, you access many oil pockets within the ground from the same point.
He said if a vertical well is drilled through a 50-foot (about 16 metre) thick reservoir rock then natural gas or oil can seep into the well through 50 linear feet of ‘pay zone’.
However, he added if the well is turned to horizontal (or the same inclination as the rock unit) and drilled within that rock unit then the distance of penetration within the pay zone can be much greater. Some horizontal wells have over one mile (1.6 kilometres) of pay zone penetration.
He said they have adopted the horizontal oil drilling technique so as to lessen impact on the environment and wildlife in the environmentally sensitive Albertine Graben.
Commercial deposits of oil, which currently stands at 3.5 billion barrels, have been discovered in the Albertine Graben. Although this is an opportunity for the country to make money, it can also endanger animal species like elephants and lions.
But Tumushabe said horizontal drilling reduces the environmental impact compared to vertical drilling.
A representative from BG Group, Fred Kibodya told East African Business Week in Dar es Salaam recently that horizontal drilling is one form of directional drilling which has been an integral part of the oil and gas industry since the 1920s.
Kibodya said wells are drilled at multiple angles, not just vertically, to better reach and produce oil and gas reserves.
Horizontal wells begin at the surface as a vertical well. Drilling progresses until a specifieddepth above the target rock unit where the well is diverted to move horizontally.
Total E&P Uganda has been the first oil firm in Uganda undergoing oil exploration within the Murchison Falls National Park to launch horizontal drilling in Jobi-6 appraisal well. Tullow also developed a deviated well in the Jobi field.