Echo sounding, side scan sonar and seismic profile records in the canadian Beaufort Sea provide evidence of trench\;!s or "scours" on the continental shelf sea bottom. These are generally believed to be caused due to grounding of ice masses. Records obtained over a three year period by government and industry were analyzed with particular regard to frequency of scouring and scour azimuth, depth and width. Approximately 1100 n. miles of echo sounding records and 1900 n. miles of side scan sonar records obtained in 1970, 1971 and 1972 were examined in detail during-the study. These totals were made up by choosing every third or fifth mile of available records. The variations of these parameters with location are shown on maps and their relationship with water depth are presented on histograms. SpeCUlative discussion regarding causes of scouring, scour rates and sedimentation within scours is also presented. Two areas were selected where parellel side scan sonar tracks were run to prepare mozaics of the sea bottom. These areas were later resurveyed to determine the number of scours added over several years. It has been found that the preferred orientation of the scours is 105 0 -285 0 • Scouring is most common in water depths between 50 and 150 ft. where many areas are nearly saturated with scours. Maximum activity occurs at approximately 100 ft. Normally scours do not exceed 6 ft. but in places they occur up to 20 ft. in depth. Scour widths range from tens of feet to hundreds of feet. The tendency is for scours to become deeper in deeper water. The depth of scouring is particularly important in design of protection for offshore wells and future pipelines. The most important parameters in this regard are the depth of scours and the rate of new scouring.

Accurate interpretation of geophysical data, design of safe casing strings for drilling and production operations, and determination of the potential for existence of gas hydrates in and immediately below the permafrost zone are only possible if the thickness of the permafrost zone can be accurately determined.Freezing of interstitial water in soils has little effect on many of the physical properties of the soil, however, large changes in elastic properties and electrical resistivity do result. This makes it feasible to determine the thickness of the permafrost zone using techniques which measure changes in acoustic and electrical properties of the soils adjacent to the wellbore. This paper discusses the characteristic response which occurs as the borehole logging tool passes upwards from unfrozen sediments into the permafrost zone. It is this response which indicates the base of the permafrost zone and allows determination of permafrost thickness.Conclusive evidence of permafrost thickness and confirmation of permafrost thickness inferredfrom acoustic and electrical data is obtained from temperature data obtained subsequent to well suspension. Techniques utilized to obtain these temperature data are outlined in this paper.L'interpretation precise des donnees geophysiques, le calcul de tubages securitaires pour les operations de forage et de production, et l'examen de la presence possible d'hydrates gazeux dans la zone de pergelisol ou immediatement en dessous ne sont possibles que si on peut determiner l'epaisseur de la zone de pergelisol avec precision.Le gel de I'eau interstitielle dans les sols n'a que peu d'effets sur plusieurs des proprietes physiques du sol, mais, par contre, des changements importants de proprietes elastiques et de resistivite electrique se produisent. Ce fait rend possible la determination de l'epaisseur de la zone de pergelisol en utilisant des techniques qui mesurent les changements de proprietes acoustiques et electriques des sols au voisinage d'un forage. Cet article discute la reponse caracteristique qu'on observe dans un forage lorsqu'une sonde remonte des sediments non geles vers la zone de pergelisol. C'est cette rkponse qui indique la base de la zone de pergelisol et permet d'en determiner l'epaisseur.Les releves de temperature apres la completion d'un forage apportent des donnees concluantes sur l'epaisseur de pergelisol et sur sa verification par les methodes acoustiques et electriques. On decnt aussi les techniques utilisees pour obtenir ces mesures de temperature.

A study of a 70-mile chain of prolific Leduc D-3 reef pools situated on a common aquifer is presented. The primary objective of the study was the prediction of the future performance of the centrally located Westerose D-3 Pool, as influenced by other pools in the trend. A two-dimensional mathematical model of the Acheson-Homeglen Rimbey Leduc D-3 reef chain was developed. Values of resistance and capacitance, characterizing reservoir parameters, were assigned to the grid points in the reservoir simulator. These were adjusted until a satisfactory match with twenty years of performance history was obtained. The future pressure performance and water influx or efflux under many combinations of producing rates were predicted for a ten-year period. The study indicated unusual trends in pressure and water influx behaviour resulting from interference effects. Further movement of Westerose oil into the underlying aquifer was predicted with continued injection of produced solution gas. These results were instrumental in the recent termination of gas injection into the Westerose D-3 Pool. The study also predicted the withdrawal rates necessary from the Westerose D-3 Pool to maintain the oil-water interface at its current position and to control its further movement.

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OFFSHORE PRODUCTION Ice management to support the Kulluk drilling vessel J. HNATIUK and B.D. WRIGHT Gulf Canada Resources Inc. ABSTRACT A second-generation drilling vessel has been constructed to extend the drilling season in the Beaufort Sea through the use of a unique hull design, moori.ng system and icebreaking support vessels. The unique designs of the drilling vessel, icebreakers and supply boats are described. The Kulluk vessel, designed to drill in open water or newly-formed ice, commenced drilling in August 1983. It was soon called on to cope with the most severe ice conditions in nine years. The ice surveillance and ice management procedures employed in coping with the prematurely severe 1983 ice conditions arepresented. Depending on the severity of the ice hazards colour code alerts were triggered which dictated the nature of the drilling operations permissible.A pre-requisite for operations is a knowledge of which icefeatures present a hazard to the drilling vessel-opera-tionally, the hazards must be detected using radar and visual reconnaissance from aircraft or vessels. Predictions of the veh)city, trajectory and time of arrival of the hazardous features are made based on plots of radar and other information. Action is taken to mitigate the hazards through the use of the four powerful icebreakers and supply bo,ts, biased tensioning of the mooring system, disconnecting the riser or, in the extreme event, moving from the location. The icebreaking vessels work at assigned dis-tances from the drilling unit to either break floes and pressure ridges into less hazardousfeatures or to deflect thefloes away from a collision course. The ice management system for the Kulluk was put to a severe test in its first year of Keywords: Kulluk drilling vessel, Beaufort Sea, Mobile arctic caisson, Retained islands, Icebreaking support vessels. operation but it performed admirably well. Introduction The continental shelf of the Beaufort Sea has long been considered to have the _ potential for major oil and gas accumula-tions. During the period 1963 to 1969, offshore permits to explore for oil and gas were issued for the majority of the shelf which extends some 125 km to 175 km from shore to water depths of 200 m. The Geological Survey of Canada's aver-age expectations of the hydrocarbon potential of the Beaufort Sea -Mackenzie Delta area are 1347 million M3 of oil and 1865 billion M3 of gas(l). Numerous encouraging hydrocarbon discoveries have been made in the Beaufort Sea since offshore drilling commenced in 1973. The commerciality of reserves will depend on many factors such as pay thickness and other reservoir character-istics, well productivities, i,eservoir depth, water depth, distance from shore, environmental forces, sea bottom condi-tions, capital and operating costs, crude oil prices and the fiscal regime.Sea ice conditions in the Beaufort Sea are such that the drilling season from conventional ice reinforced drillships is -only 3 to 4 months. The second-genera-tion drilling vessel, BeauDril's Kulluk, was constr...