Improper hole cleaning is a major cause of non-productive time (NPT) in drilling. Current hole cleaning practices are mostly based on experience, rules of thumb and simplistic calculations. Hence, they are not reliable and do not work as expected in all scenarios. There is the need for a robust, fast, and accurate approach to simulate cuttings transport, and provide reliable and useful estimations of the hole conditions in real-time.

In this paper, a transient cuttings transport model is presented for real-time hole cleaning simulations. The model solves the transient conservation equations using a drift-flux modeling approach, which is applied to describe the multiphase flow of cuttings and fluid in the wellbore. The model uses experimentally derived equations that account for the effects of pump rate, pipe rotation, eccentricity, fluid rheology, inclination, etc. on cuttings transport. A fast numerical solver is used to enable real-time simulations, while providing numerical stability that is crucial to maintain the modeling convergence under area discontinuities. Using small time-steps, the model captures pressure wave behavior, which is necessary for simulating managed pressure drilling (MPD) operations. Pressure-dependent mud density, non-Newtonian viscosity, and cuttings slip velocity models are used to estimate downhole parameters such as pressure, cuttings concentration, bed height, drilling fluid and cuttings velocities, etc. The model can provide a drilling crew with accessible real-time simulation results on the rig for monitoring the hole cleaning operation and preventing problems from happening.

Case studies are performed based on field experiments to analyze the effectiveness of the developed model on avoiding operational problems such as pack-off and stuck pipe. Results show that by monitoring the real-time cuttings concentration and bed height along the wellbore, the developed model can detect improper hole cleaning conditions and provide optimum drilling parameters to resolve problems, thereby minimizing NPT. The robust numerical scheme allows for simulations that are several times faster than the real-time operation on a standard desktop PC, providing the crew with enough time to take preventive actions. Clean-up cycles can also be simulated by the model to calculate and optimize the required parameters for optimum hole cleaning results. Required clean-up times are calculated for the field cases to ensure that cuttings are effectively removed from the wellbore before pulling out of hole and running casing. Moreover, MPD operations can be simulated using the model that consider the effects of cuttings concentration and bed blockage on the pressure profile.

The developed model can provide valuable real-time information on downhole conditions to the drilling crew during the drilling process and give adequate time to the crew to take timely corrective action if necessary. Moreover, the model can simulate the planned drilling process and calculate optimum drilling parameters to avoid hole cleaning problems.

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