Guidelines for Stable Foam Drilling Through Permafrost

Abstract

SPE Members Abstract Stable foam was used successfully on ten wells in the Canadian Arctic to drill near gauge holes through permafrost. During the program, important practical information on foam drilling guidelines and operational considerations were obtained. The results indicate that the optimum foam quality for ensuring good hole cleaning varies with drilled depth and lithology. The data is presented in a graphical format which can be applied directly in the field. Introduction During the winter of 1985 - 1986 an aggressive eleven well drilling program was undertaken on the Tuktoyaktuk Peninsula in the Canadian Arctic. Stable foam was used on all but one well to drill surface hole through the permafrost. The use of foam was spurred by the possibility that one or two of the wells may be kept for future gas or oil production. It was essential for a potential production well that a near guage, fully cementable surface hole be drilled. Full length surface casing cement is required to provide stability and prevent buckling of surface casing due to thaw subsidence of the permafrost adjacent to the wellbore. On all previous wells in the vicinity, surface holes had been drilled with conventional mud systems. These wells had been plagued with problems such as excessive washouts, sloughing hole and in some cases stuck pipe. Surface hole cement jobs on these wells were generally conducted in two stages and required between 150 and 200 tonnes of cement per well. In such cases full length support of the surface casing could not be guaranteed. Stable foam was considered as a substitute for the conventional mud system because of its excellent insulating properties, low heat capacity and poor heat conductance. In the early 1970's foam had been used in the Arctic to drill through permafrost with very encouraging results. Stable foam is a mixture of air, water and surfactant (soap). The air and liquid are injected from two separate lines into a foam generator. The mixture passes through baffle plates within the foam generator to produce a thick shaving cream like substance. The foam continues down the drillstring to the bit where it carries cuttings to surface and out the discharge or blooie line. In most cases the foam is not reused. P. 67^