Bit Run Optimization through Simulation

Weight on bit, rotary speed, bit hydraulics and more importantly bit types, are the most important parameters affecting rate of penetration and consequently the economics of drilling. Pulling a worn bit is necessary to make the drilling operations more efficient. Cost per foot calculation is a popular criterion used to predict when to pull a bit.
In this paper, some first 3 thousands feet of a reservoir lithology including four bit runs are analyzed so that factors affecting penetration rate are optimized and the lowest possible well cost is achieved. The effects of using other bit types, weight on bit, rotary speed and bit hydraulics are simulated in an attempt to determine the optimized parameters, which result in the lowest drilling cost.
Overall, it was found that in bit runs 2, 3 and 4 some lower cost per foot can be achieved using milled tooth bits instead of tungsten carbide types. Furthermore, it can be concluded that by increasing weight on bit and reducing rotary speed in harder rocks, more favorable results are obtained while in softer rocks it is vice versa. In addition, by lowering both mud flow rate and nozzle sizes, hydraulic horse power dissipated at the bit is increased, hence decreasing cost per foot.