Real-time optimization of drilling parameters based on mechanical specific energy for rotating drilling with positive displacement motor in the hard formation

- A MSE model for rotating drilling with PDM is established.
- A method for real time optimizing drilling parameters for rotating drilling with PDM is presented.
- The new MSE model estimates MSE values with a reasonable approximation.
- The optimum WOB is low for rotating drilling with PDM, increasing WOB does not always increase ROP.
- The method can real time estimate optimum WOB with varying RPM to drill a specific formation with PDM.

Mechanical specific energy (MSE) has been widely used to quantify drilling efficiency and maximize rate of penetration (ROP) in oil and gas wells drilling. Given currently there are few effective MSE models to precisely model the actual downhole drilling for rotating drilling with positive displacement motor (PDM), in this work a new MSE model for rotating drilling with PDM is established based on the analysis of PDM performance. Meanwhile a method for real time optimization of drilling parameters based on MSE for rotating drilling with PDM in the hard formation is also presented. Field data presented in this paper indicate that when drilling with a high efficiency and free of drilling complications, the MSE(min) estimated by the new MSE model is roughly equal to the confined compressive strength (CCS) of the formation along the well depth, it can meet the needs of applications in the field. It also shows that ROP is sensitive to high weight on bit (WOB) for rotating drilling with PDM and the optimum WOB is low, increasing WOB does not always increase ROP but is more likely to decrease ROP. The method for optimizing drilling parameters can real time estimate optimum WOB values with different RPM to drill a specific formation interval with PDM. It can be used to maximize ROP and allow operators to drill longer and avoid unnecessary trips.