Flow of Mud During Drilling Operations

The development of rotary rock bits with jet nozzles required means of estimating pressure losses in the drilling fluid flowing throughout the well being drilled and through the associated equipment. The initial tabulations were based on Newtonian fluids. Subsequent authors developed descriptions of drilling fluids based on Bingham or power law non-Newtonian fluid models. Because optimum-hydraulics theories dictate that hydraulic horsepower, impact, or impact force must be maximized, we made the difficult decision to determine these pressure losses by actual tests. A total of 119 water-base drilling fluids were pumped through capillary tubes up to 2 in. in diameter and through six standard sizes of drillpipe tool joint combinations. Drilling fluids were flowed through jet bit nozzles and were flowed up two annulus-size combinations as well as an annulus with hole enlargements. The annular tests included cuttings, which aided in determining flow patterns. This paper includes development of friction factors and empirical corrections for current theories to model flow of highly non-Newtonian fluids more reasonably. Procedures and equations are offered to help estimate pressure losses in a drilling operation, even with very limited fluid property information typical of our industry.