Title: From Colorado to the North Sea: A New World of Wellsite Work
Author: Terrilyn Olson
Publication: The Outcrop, June 2000, p. 1, 8
Editor’s Note: This is one of a continuing series of articles by RMAG members who have interesting oil-field experiences to share. Unsolicited submissions are welcome.
When I accepted Amoco’s transfer from Denver to Norway, I hoped my assignment would entail offshore work. When just such an opportunity arose in 1998, I jumped at the chance. I was to serve as consulting geologist and petrophysicist for coring and a complicated logging program. Special dispensation was needed because I hadn’t been through the rigorous safety-training program where you practice ocean-survival techniques. After acquiring new orange coveralls and a hardhat, and gathering the necessary well data, I was off to the rig.
The Maersk Guardian rig is a jack-up attached to the Valhall Field complex of platforms. Valhall sits in the middle of the North Sea, close to the border between the Norwegian, Danish, and British sectors. I flew from Stavanger to Valhall in an 18-passenger helicopter wearing a “gumby” suit. It was May, and the weather was calm for the 100-minute flight. From the air I could see numerous other platforms, including the Ekofisk complex and several others in the British sector.
The helicopter landed at Valhall Field on the accommodations platform helideck, which meant that I must trek across four platforms (accommodations, drilling, facilities, and new drilling) to reach the rig. Lugging safety equipment, data, and a few clothes, and wearing an insulated safety suit, I was quite warm and damp when I arrived. Despite the ocean swell visible below the metal grating of the catwalks between the platforms, crossing between the platforms wasn’t bad—it was the trip up the steep latticework of stairs to the rig that was a challenge.
Once I was at the rig, the medical officer offered a tour and a safety orientation. The rig housed a diverse community of people in a maze of offices, sleeping quarters, mess hall, lounge area, and even a workout area that you got to by traversing part of the noisy drilling substructure.
How was this rig different any other? First, much of the crew spoke Danish or Norwegian, so signing and conversation often were incomprehensible. The company man was a Texan; the other drilling supervisor was a Norwegian. I’m not sure which one had the stronger accent. The scale of the operation also was outside my experience. More than 75 people lived on the rig. Daily rig rates were over $80,000. One surprising disappointment was the food. In contrast to offshore installations in the Gulf of Mexico, the food (while quite edible) was very unexciting: spaghetti with meat sauce, overcooked cod, and such.
But then, there were the rocks. The Valhall reservoir is a chalk. Reservoir pressure is several thousand psi below the bubble point. The well was drilling vertically on the crest of the anticline to replace a well that was expected to fail soon due to chalk collapse. Cores and a full suite of logs were being collected to improve understanding of the central, most prolific part of the field. Reservoir characteristics of interest included fractures, effective porosity, chalk compaction (and porosity loss) with depletion, fluid segregation, and matrix and fracture permeability.
Coring was underway when I arrived, with variable results. Most of the fractured chalk was shattered in the core barrel, so the best reservoir was seldom represented. A new, lightweight coring fluid was being used to optimize recovery; it was a gooey, light gray slime that obscured core characteristics and was only partially successful in increasing recovery.
This was the first chalk well in which Amoco ran magnetic resonance (MR) logs. Many last-minute operational adjustments to logging parameters were required. Fortunately, the onshore operations geologist, the Amoco MR expert in Tulsa, and the Western Atlas MR expert in Houston all were willing consultants over the phone at all hours. We got much good data and useful experience for future log runs.
My three days in the middle of the North Sea were a horizon-expanding experience that I’d like to repeat. My Norwegian is much better now, for one thing! Tusen takk!