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New tools for downhole drilling, with high strength stainless steel drive shafts

Carpenter Technology Corporation : 09 May, 2006  (New Product)
NQL Energy Services, Nisku, Alberta, by thinking outside the box and switching to a high strength, corrosion resistant stainless steel, has multiplied up to 10 times the service life of drive shafts used on its well known Black Max downhole drilling tools for oil and gas exploration. Partial view of a Black Max motor, with cutaway revealing the Custom 465 stainless steel drive shaft.
NQL Energy Services, Nisku, Alberta, by thinking outside the box and switching to a high strength, corrosion resistant stainless steel, has multiplied up to 10 times the service life of drive shafts used on its well known Black Max downhole drilling tools for oil and gas exploration.

Partial view of a Black Max motor, with cutaway revealing the Custom 465 stainless steel drive shaft.

For drill rigs using the longer lasting mud motors, the savings in rig downtime required for tool replacement can be spectacular. With so much equipment dependent on performance of the drilling tool, Robert Roszak, NQL Energy engineering manager, estimates that drilling rigs could save tens of thousands of dollars a day for tool replacement.

The Black Max mud motors made by NQL Energy Services, one of the largest independent drilling tool suppliers in the world, are used in very harsh drilling environments. They are subject to great vibration, with shafts operating at speeds up to 1500 rpm under heavy rotational load, and transmitting up to 20,000 ft. lbs. torque while drilling. In the process, the tools are penetrating deep in the earth, exposed to the attack of abrasive mud and debris, and severely corrosive sour gases.

Such operating conditions were too much for the EN30B and Astralloy alloy steel that NQL Energy formerly used for drive shafts. Shafts of these steels, traditional choice for this type of application, would last no longer than 150 hours in service before requiring a replacement.

Shafts made from these alloys exhibited problems with corrosion and torque handling, as well as short service life. Inspection first revealed evidence of surface pitting, then cracking that progressed until twist-off occurred under heavy torque loads. The strength capability of both alloys was relatively low at 135 to 140 ksi (930 to 965 MPa).

After changing to Custom 465 stainless steel, a specialty alloy developed by Carpenter Technology Corp., Wyomissing, PA, USA, the Canadian manufacturer found that its mud motor shafts were lasting up to 1,500 hours under the most demanding service conditions before replacement was needed.

Custom 465 stainless is a premium-melted, martensitic, age-hardenable alloy capable of about 255 ksi (1758 MPa) ultimate tensile strength when overaged to the H950 condition, which is nearly twice the ultimate tensile of the alloy steels replaced. In addition, the Carpenter alloy is designed to have excellent notch tensile strength and fracture toughness in this condition.

Further overaging this stainless alloy to the H1000 condition provides a superior combination of strength, toughness and resistance to stress corrosion cracking compared with other high strength, precipitation hardenable stainless alloys such as Carpenter Custom 455 stainless and Carpenter 13-8 stainless. The general corrosion resistance of Custom 465 stainless approaches that of Type 304 stainless.

NQL Energy obtained its Custom 465 stainless bar stock from Carpenter in solution annealed condition, in diameters ranging between 1/2 in. and 6 in., and lengths of 12 in. to 48 in. Material then was turned and milled to finish size as needed.

NQL Energy Services' Black Max drilling motors, many with their upgraded stainless steel shafts, are designed for maximum performance in

(a) directional, horizontal, straight line and short radius drilling;
(b) under-balanced, air, nitrogen and coil tubing drilling;
(c) river crossings, trenchless construction and utility boring; and
(d) methane release drilling and mining, pipeline and environmental applications.

Black Max drilling motors feature a sealed, oil-lubricated bearing assembly that ensures a contained bearing stack for greater reliability and power transmission, thus longer motor life and efficiency. The motors are made in 80 different configurations, in a wide range of sizes from 1-11/16 in. diameter to 11-1/4 in. diameter.
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