There have been many innovations by North Slope oil producers over the 30 years since production began in 1977. One of the lesser known, but of great importance, is development of what may be the world's first “zero-discharge” procedure for oil field wastes.
John Reeder, retired chief attorney for BP Exploration (Alaska) Inc., believes development of techniques for disposing of used drilling fluids and other waste materials by injecting them underground, through special disposal wells, may be among the North Slope industry's most enduring accomplishments.
It demonstrated that drilling and oil field development could be done in ways that minimized the industry's impact on the local environment.
Drilling fluids, or “mud,” is a liquid used during drilling to lubricate the drill bit as it bores down through the underground rock. The fluids also keep a high pressure in the hole as a precaution against gas or oil flowing uncontrolled from the reservoir into the well-bore, a condition that can cause a blowout of the well.
The mud is circulated through the hole with pumps on the drill rig, bringing rock cuttings from drilling to the surface for storage. The used fluids and cuttings, which can amount to a significant amount of material from wells drilled several miles into the earth, must be stored or disposed of.
Much of this is benign from an environmental standpoint, but some of it isn't. Drilling fluid is made mostly barite, a natural material, and rock is, well, rock. But drill fluids can also contain chemicals, such as heavy metals, and the rock cuttings can also become contaminated in various ways.
The safe storage of these wastes was a serious issue for the industry, Reeder recalled, until a solution was developed in the late 1980s and 1990s, when the drilling and environmental departments of the producing companies, Arco Alaska Inc. and BP Exploration (Alaska) Inc., adapted technology developed in the mining industry for oil field use.
Originally the drilling fluids were stored in reserve pits, large rectangular pits that were built adjacent to the pad where the drilling rig operated. The practice at Prudhoe Bay and several other fields on the Slope, like Kuparuk, was to drill several production wells on one large drill pad so that all of the support infrastructure — pipelines, well control facilities, utilities and roads — could be concentrated.
The reserve pit built next to the drill pads had to be quite large, since they stored fluids from many wells. The pits were lined to prevent any leakage of the fluids, and berms were built around them.
However, problems did develop as the years went by and more and more wells were drilled. The reserve pits filled up and when water accumulated in the spring from melting snow and ice, they started to overflow onto the tundra. While most of the spilled fluids consisted of water, there were small quantities of chemical and other contaminants. Environmental groups, with the Natural Resource Defense Council taking the lead, sued to force federal and state agencies to require the producers to find a solution.
One solution was actually being developed by BP at the nearby Endicott field, Reeder recalled. Endicott is an offshore field produced from two artificial gravel islands in shallow water just offshore the Prudhoe field. Given its location, there was no room for a conventional reserve pit, Reeder said, so BP developed an alternative of injecting the wastes, again mostly water and rock, back underground.
The technique was to be employed at Prudhoe Bay and eventually all other oil fields on the North Slope, Reeder said. In a settlement agreement with the Natural Resource Defense Council and other environmental groups, the Prudhoe producers, which included BP, developed a variation of the underground injection procedure to be used for all future drilling and also agreed to clean out all of the old reserve pits and to reclaim them to as near as possible to their original natural condition.
For the large Prudhoe field, the companies built a central plant facility to which all drill fluids and wastes are trucked, Reeder said. The plant grinds all of the rock cuttings into a fine powder, which is then injected underground — mixed with the fluids — through production wells that were converted to serve as injectors, he said.
Drill wastes are now trucked from some other fields on the Slope, but in fields that are too distant for trucking to be economic, the wastes are injected through wells designated for that purpose at the drilling location.
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