A turbodrill is a hydraulic downhole motor in which the hydraulic thrust provided by high pressure pumped mud is converted into mechanical energy to impose rotary motion to the drill bit. The mud passes through the nozzles at a high velocity, impacting the stator blades and rotating the outer housing and the bit. Axial-flow multistage turbine is the working tool in which the energy is converted in drive force to impose rotary motion just to the drilling tool at the bottom hole instead of moving the entire column of rods in the well.
The first filed patent of a downhole turbodrill motor (or, downhole drilling motor) mud-powered and single-stage impulse dates back to 1873 by C.G. Cross in the United States. It was a forerunner and experimental technology for the time that could have undermined the diffusion of the rotary drilling system, which in that moment was still rarely used in petroleum fields. Given that the rotary drilling rods column may weight several tons and is long as the entire depth of the well, the turbodrill would have provided significant energy saving and reduction of breakage of the rod joints. Unfortunately, the engineering efforts poured in this system did not find correspondence with the advancement of the contemporary science of materials and high-pressure pumping technology. Erosion problems with the nozzles and stator resulted because of the high fluid flow velocity; furthermore, the power output of the single-stage turbo drill was low, and the bits were not aggressive enough with harder rocks strata.
In 1884, M.C. Baker patented a single-stage axial flow turbo drill, and this design was the forerunner of the groundbreaking multistage axial-flow turbodrill, developed 40 years later by Scharpenburg. In Baker's project, the stationary stator blades are attached to the outer housing while the runner (or rotor) blades are attached to the rotor which turns the bit. This single stage turbodrill also delivered too low power output, which make of it another technology stuck into the laboratory. The issues emerged from Cross, Baker, and other developers prevented the introduction of turbodrill technology in the petroleum fields, but they did not halt the development of the technology, soon to be experimented also outside the United States.
In 1901 (after a decade of utilization and improvements) the rotary drilling system was successfully used to hit the greatest gusher well of the world until then in Spindletop near Beaumont, Texas, the turbodrill machine was still a troubled technology on hold on the workbenches of designers. In consequence of that, rotary made a giant step ahead in the commercial drilling technologies, while interest and investments in downhole drilling motors diminished substantially. Eventually, they were extensively tested in the 1920s, when the interest in the technology was revitalized by researchers working on directional drilling. Dedicated development projects started at the same time in the United States and Russia.
In 1922, C. Scharpenburg with Standard Oil of California began designing improved turbodrills and testing the multistage axial-flow turbo drills which (the forerunners of those used today in directional drilling applied to hydraulic fracturing). In 1924, he patented the multistage axial-flow turbodrill and successfully tested it in 1926. This turbodrill contained many advanced features not used in commercial drilling motors including a sealed lubrication system which allowed the ball thrust bearings to operate in lubricant.
However, the technology then was still young and with many flaws. Contemporary seal design limits caused the pressure to drop to only 100 to 300 psi across the drill bit, which was far below the 1,000 to 2,000 psi required. Bearings limitation consisted in that they were short-lived at high temperature environments, particularly when exposed to drilling mud rather than lubricants (gear failures due to loss of lubricant were inevitable already only after 3-4 hours running time). Hence, bit weights and mud flow rates both must be reduced from optimum conditions as concessions to using a downhole motor. Also, harsh erosion problems were encountered at very high nozzle velocities. Consequently, in 1935, the Scharpenburg turbodrill was equipped with rubber radial bearings and the seal were removed to allow the mud to leak continuously through the ball thrust bearings to cool and lubricate them. The thrust bearings were moved to the bottom of the turbodrill to faci1itate repair and to simp1ify the turbodril1. In spite of all those difficulties, this machine found widespread use in the 1930s in the United States for drilling directional holes – but was not yet widely used for straight hole drilling because of problems with the bearings and seals.
Outside the United States, scientists in the Russian Empire, and later the Soviet Union, worked on high-speed, single-stage turbines which utilized speed reducers to produce lower, more efficient, bit speed. The first turbodrill engineered on the base of this different approach was the model of the Russian petroleum engineer Matvey Alkunovich Kapelyushnikov. He first experimented early prototypes in turbodrill in 1912 in Baku (modern-day Azerbaijan) and from 1914 to 1937 was director of the bureau established to develop turbodrill technologies. Between 1922 and 1925, Kapelyushnikov in cooperation with engineers S.M. Volokh and N.A. Kornev from the Mechanical Department of Tomsk Technological Institute developed and patented the single stage geared working through a high-speed (1800 to 2000 rpm) mud turbine equipped with a reducer set to drive rock bits at speeds of 50 to 100 rpm. This machine was featured by a complex planetary gear system (1 to 3 stages) operating into a sealed lubrication system. 200 up to 300 Gpm (gallons per minute, corresponding to 757 to 1135 litres) of mud were pumped through the nozzle at velocities of about 200 feet per second (corresponding to 61 metres per second) producing power outputs of 12 to 15 horsepower. This invention laid the foundations for the history of turbo drilling in Russia, and it is remembered as the Kapelyushnikov’s turbodrill. Results were satisfactory, but because of the problems encountered with the complex speed reducers working with combined with improved high-speed turbines, it was decided to produce also the low-speed multistage turbo drills during the 1930s.
In 1941, Standard of California drilled five wells with a 95/8-inch turbo drill (30 stage) which delivered 92 horsepower at 700 rpm. Mud was pumped through the turbine at a flow rate of 550 Gpm and with a pressure drop of 580 psi across the turbine. This corresponds to an input power of 186 horsepower and an overall turbodrill efficiency of 49%. The bits drilled at average penetration rates of 51 feet per hour with bit weights of 4000 to 5000 pounds. In 1945, Standard Oil of California modified their turbodrill with rubber thrust bearings. These mud-lubricated, multi-disk rubber thrust bearings revealed to be very efficient, at this feature was utilized since the 1980s. These bearings had a service life of 100 to 150 hours when operated near the balanced condition where the bit weight equals the hydraulic down thrust on the rotor. In conclusion, this long moment of research and development started in the 1920s merged into the real drilling marked in 1950s, when turbodrills begun to be used in large extent in Russian petroleum fields. By the early 1960s, 85 percent of the wells in the Soviet Union were being drilled with turbodrills; in the 1970s the rate decreased to about 70 percent because conventional drills were used in most Russian wells deeper than 4,000 meters. That happened because turbodrills were not economically convenient to be used in deep drilling because of the increased downhole trip time required to replace worn turbodrills.
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