Abstract

Hole enlargement is a serious problem while drilling in permafrostconditions. The hole enlargement problems leads to lost circulation. Irregularand unstable holes also affect the quality of cement jobs. The drilling fluidis generally at a higher temperature than the permafrost formation. This causesa heat transfer from the drilling fluid to the formation. The ice particlesbinding the sediments together start to melt. This loosens up thesediments and causes caving. This paper proposes to minimize this problem witha low thermal conductivity fluid.

The drilling fluid can be cooled at the surface after it comes out of theannulus and before it is circulated back into the drill string. Cooling reducesthe temperature gradient between the fluid and formation. But this cooling isnot enough since the permafrost is at subzero temperatures and cooling to suchlow temperatures is not economically and practically feasible. This is wherethe innovative drilling fluid comes in. The drilling fluid shall have hollowmicrospheres. These microspheres are easily available commercially undervarious trade names. These microspheres lower the heat transfer coefficient ofthe fluid. This means that a significantly small amount of heat will betransferred from the drilling fluid to the formation. Low temperaturegradient and low thermal conductivity will work in conjunction.

The drilling fluid shall have a low heat transfer coefficient of 2.9-3BTU/hr.ft2.°F. The composition of the fluid and the heattransfer coefficient measuring experimental setup shall be discussed in thepaper. The paper shall also discuss the effects of heat transfer coefficient, circulation rates etc. on the thawing of permafrost.

The technique in this paper could go a long way in mitigating drillingproblems in permafrost regions.

Introduction

Conventional oil and gas reserves are fast depleting and becoming scarce dayby day. Hence, there is a need to find oil and gas reserves in previouslyunexplored areas of the earth. Arctic regions present one such area with hugepotential of untapped oil and gas reserves. Producing oil and gas in such harshenvironments require special techniques designed for these conditions. Everyoperation in the arctic has its own set of challenges.

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