An Engineering Challenge - Cook Inlet, Alaska

ABSTRACT In the search for and the development of petroleum reserves under the turbulent [and at times ice-covered] waters of the upper Cook Inlet, Alaska, many new and difficult engineering and operating problems have been encountered. These problems are directly attributable to the severe environment, particularly the unusually swift tidal currents and the extended low winter temperature regime. Following a brief resume of the progress of the oilfield development, the pertinent environmental-characteristics and some of the effects these characteristics have on engineering and operating practices are examined. Particular emphasis has been given to the difficulties of measuring tidal currents, and the phenomenon of flutter that has been experienced as a result of the swift currents. A summary of the results of three current measurement programs is presented along with a description of some special tools and techniques that were evolved to make the measurements. The use of spoilers on pipelines, pipelaying stingers, marine conductors and diver tubes to control or mitigate the effect of flutter is documented and illustrated with sketches and photographs of equipment used in the Inlet. The more significant influences of the environmental conditions on the design of structures and operational practices are enumerated. Remedial measures to reinforce a structure from the erosive action of ice and corrosion in the tidal zone are described. Although environmental conditions have posed unusually difficult engineering and operating problems, adequate solutions have been developed by the industry and its associated consultants and contractors. INTRODUCTION The development of petroleum reserves underlying the SWift, and in winter months ice-covered, waters of upper Cook Inlet, Alaska continues to challenge the engineering and operational capabilities of the oil industry. Previous papers have described the successful accomplishment of specific projects and have reviewed the chronological development in the Inlet in considerable detail.1–4,5 This paper describes some of the more significant environmental conditions peculiar to the upper Cook Inlet, methods and equipment used to obtain quantitative data on those conditions, and various engineering and operational practices that have been employed to satisfy the environmental requirement. Although many problems encountered in the Inlet have been resolved to the extent necessary to permit development, the accumulating experience will undoubtedly lead tc improved methods and equipment for application in other parts of the world. The first commercial oil discovery in Alaska was completed on the Kenai peninsula in the Swanson River field in Sept., 1957, some 11-1/2 years ago. Following extensive exploration in the intervening years, the upper Cook Inlet was first tested with the drill in 1962; three exploratory wells were drilled and eventually abandoned. However, these initial tests were encouraging enough to justify the drilling of four additional exploratory wells in 1963, one of which resulted in the discovery of the Middle Ground Shoal field. As shown in Fig. 1, the number of fields in the Inlet has grown to five. They are the Middle Ground Shoal, Granite Point, Trading Bay; McArthur River and North Cook Inlet fields, the latter being a gas field, whereas the other are oil fields.