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

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.

High Frequency Downhole Dynamic Measurements Provide Greater Understanding of Drilling Vibration in Performance Motor Assemblies

“…The use of downhole mud motors to improve drilling performance in vertical wells is becoming more common throughout the oil and gas industry 1 . The additional torque provided by a downhole mud motor allows for a more aggressive drill bit design to be selected, and achieve a greater Rate Of Penetration (ROP).…”

5-Axis CNC Milling Method on Complex Helical Surfaces of PDMs

“…The positive displacement motor (PDM) designed by applying the reverse function of the Moineau pump [1,2], plays a great role in drilling directional wells, horizontal wells and oil well workover operations throughout the world for some decades. It is driven by high pressure drilling fluids or other flow media.…”

“…It is driven by high pressure drilling fluids or other flow media. PDM is simple in structure and is made up of four main components such as dump valve assembly, power section, connecting rod assembly and bearing section [1][2][3]. All of them, the power assembly is a key component of PDM and there is a conjugate rotor-stator coupling inside it.…”

“…Then the sealing curves move down and the enclosed cavities progress along the sealing curves. The drilling fluids go through the cavities orderly and, finally, discharge out power section [1][2][3][4].…”

“…Thus, the energy efficiency of conjugate pairs between the stators and rotors will be improved. It is well known that the mechanical efficiency of PDMs from Baker Hughes INTEQ, is up to 72% [2,3]. Some practical application has indicated that, in machining rotors and stators, 5-axis linkage CNC machine tools is effective to eliminate the over-cut and intervene on finish surfaces and to save auxiliary time.…”