Bit stick-out calculation for the deepwater conductor jetting technique

Abstract

In view of the absence of a theoretical model for choosing the bit stick-out in deepwater conductor jetting operation, and the existing operational blindness and risks, a bit stick-out calculation model was built up through theoretical derivation and field tests to provide the theoretical basis for the design of reasonable bit stick-out. Theoretical analysis assumes that bit stick-out is the best when the upper edge of the jet flow sprayed from the bit nozzle tip is internally tangent to the lower edge of surface conductor, based on which a formula to calculate the reasonable bit stick-out was derived, and the rationality of the theoretical assumption and correctness of calculation model were proved through field tests. Field test results show that the conductor running speed is in positive correlation with bit stick-out, while the restoration of friction between the conductor and surrounding soil body is in negative correlation with bit stick-out. The calculation model was applied in the drilling operation of 12 deepwater wells in the South China Sea and got good application effects. It saved 14.96 h per well on average, enhanced operational efficiency, and met the safety requirements at the same time. Key words: deepwater, jetting, surface conductor, bit stick-out, calculation model, field test