Abstract

We present in this paper a comprehensive and universal tool/model for the mud motor power section. The model includes performance, fatigue, and hysteresis heating simulation capability. It can be used for improved and optimized power section design, motor selection prior to jobs, drilling parameters optimization, failures analysis, and training. Model predictions are compared with real field cases with good accuracy.

There are many challenges to build a proper model of the power section: a geometry that involves complex kinematics with progressive cavities moving in a spiral motion, unusual contact mechanism with high deformation from the elastomer, the elastomer itself being a highly nonlinear material that experiences hysteresis heating, the fluid aspect with complex 3D path, the interaction between the fluid and the elastomer, the sliding and rotating operating modes, and the load fluctuation in typical downhole instable conditions. To build an adequate model we have developed a set of modules with a unique apparatus helping to make cross-interacting links between them.

The present simulation capability allows us to predict the performance and the fatigue life of the power sections with good precision. We have already run many different power section simulations under different conditions showing good correlation with field data. We provide here direct field operation applications with comparative results between some field failures and model predictions. In addition, we expose how combining accurate profile measurements of the rotor and the stator with the modeling capability can prevent failures due to wrong interference fit or incompatibility between rotors and stators. Besides that, a comparative study with different elastomers in the same power section is also considered. We show also how we can use the model for well planning by selecting the right motor for the right application. Moreover, during the well execution, by combining its prediction and the monitoring system to derive optimized drilling parameters for performance and reliability, one can achieve higher shoe-to- shoe rate of penetration (ROP).

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