Design of New, Fit-For-Purpose, Downhole Positive Displacement Motor Improves Reliability and Enhances Performance in 16-in. Vertical Sections

Abstract

Abstract Saudi Aramco operates several deep gas reservoirs in the Kingdom of Saudi Arabia (KSA). Both vertical and horizontal K2 gas development wells have long 16-in. vertical sections. The 16-in. section is drilled as quickly as possible through several mid-depth hydrocarbon reservoirs to a competent seat in a dolomitic limestone. Since this section is fairly long (±5,000 ft) it represents one of the biggest challenges in the continuous drive for better rate of penetration (ROP) as well as reliability of downhole drilling assemblies. These sections are typically drilled with various positive displacement motors (PDM) in a simple performance bottomhole assembly (BHA) setup with two roller-reamer type stabilizers to mitigate mechanical stuck pipe risks. Drilling through the interbedded formations with varying hardnesses using very aggressive 16-in. bits has proven to be challenging in terms of wear and tear on the drilling motors. Damage to the motors, such as stator chunking, bearing failures and even catastrophic connection twistoffs have occurred during these drilling operations. One service provider currently uses 9½-in. motors in the 16-in. wellbores. To address tool integrity issues, the service provider upgraded to their standard offering, 12¾-in. motors. While incidences of housing and stator failure were eliminated, the combination of large, high flow rate tools in a land-based operation has not delivered the required performance on bottom. The drilling rigs currently employed for gas development drilling were not capable of pumping more than 1,300 gpm while optimum performance from the standard 12¾-in. motor comes with flow rates above 1,500 gpm. As a result, bit speed was too low, and ROP did not meet or exceed the 9½-in. motor runs and the standard 12¾-in. tools did not find widespread acceptance from the client. A new, more robust 12¾-in. motor was developed, which was also designed to provide higher rotary speed output at available flow rates and pressures. To evaluate the performance of this new motor, a drilling dynamics diagnostic tool was run in a field testing program. To date, several runs have been made with the new 12¾-in. motor in various fields in the Kingdom of Saudi Arabia. Various BHA incorporating different motor configurations and newly designed bits have been used. The drilling dynamics diagnostic tool was positioned directly behind the motor to obtaining a better understanding of the BHA and bit response for the various configurations. This paper will focus on the significant reliability and performance improvements achieved through the introduction of the new motor, which was specifically designed for this challenging environment.