Optimized Downhole Mud Motor Delivers Outstanding Performance Improvement in Alaska Coiled Tubing Drilling

Abstract

For almost two decades, coiled tubing drilling (CTD) has proved to be a successful method to reach the un-swept portions of Alaska’s North Slope reservoirs. This method of drilling has evolved over the years with new technologies and efforts from contractors and operators striving to improve performance from lessons learned. Despite these improvements in equipment and processes, operators and contractors must still deal with certain inherent deficiencies of this drilling method when compared to conventional rotary drilling – suboptimal weight transfer, sometimes troublesome hole cleaning — due mainly to lack of string rotation and low flow rate range, etc. These shortcomings have the potential to induce other drilling performance problems that affect the smoothness of coiled tubing drilling operations. Severe lateral vibration and severe stalling have become acceptable evils over the years, resulting in undesirable trips for failure and unacceptable non- productive time (NPT), both undermining one of the key benefits of coiled tubing drilling – rapid pace operations compared to rotary drilling. This paper introduces a new lower-speed downhole positive displacement motor (PDM). The technology is equipped with high-performance elastomer and was engineered to improve drilling and drill-bit performance in CTD applications. Recent field deployments in Alaska’s North Slope CTD operations proved this design by eliminating earlier performance problems for improved CTD project economics. For example, the technology’s ability to allow for about 10gal/min higher flow rates (compared to other motor designs) significantly improves hole cleaning; a key aspect in CTD operations. Up to today, this downhole mud motor design has been utilized on 13 wells, accumulating 1,303 circulating hours, 577 drilling hours and over 20,700 ft drilled. Performance improvements in depth of cut, reduced lateral vibration, reduced amount of stalls, and other benefits were achieved. There was no trip for PDM failure in all of the 34 runs, traversing different formation zones. The corresponding paper will provide additional information on application benefits by investigating two recent field deployments.

Positive Displacement Motor Condition and Performance Prediction Using Surface and Downhole Sensor Data

“…Downhole measurement technologies have demonstrated that the mud motor's expected rotational speed differs from the actual [19]. The elastomer (stator) deteriorates and reduces the motor's volumetric efficiency; as a result, there is a decrease in the differential pressure in the power section, which affects the output mechanical energy at the bit [20]. A standard method to evaluate the condition of the mud motor is to perform a wear-off test and calculate the overall efficiency change for a specific interval.…”

Drilling Monitoring System: Mud Motor Condition and Performance Evaluation

“…Motor wear is primarily a function of operating hours and operating parameters. Elastomer damage reduces the motor's volumetric efficiency, resulting in a reduction of the differential pressure and, thus mechanical energy at the bit (Anyanwu et al, 2012).…”

A Fuzzy Inference System for Detection of Positive Displacement Motor (PDM) Stalls during Coiled Tubing Operations

“…PDMs are prone to failure, particularly due to stalling and the overpressure that this event produces. As more stalls are accumulated over time, this interruption to drilling can amount to significant losses of productive drilling time [5]. A damaged motor downhole can lead to a loss up to hundreds of thousands of dollars in an offshore drilling rig.…”