Drilling Stabilizer ( Drilling Rig ) – Readyzone

 Drilling Stabilizer and Reamers

Drilling stabilizer and rolling cutter reamers are special thick-walled drill collar subs that are placed in the BHA to force the drill collars to rotate at or near the center of the borehole. By keeping the drill collars at or near the center of the borehole the drill bit will drill on a nearly straight course projected by the center axis of the rigid BHA. Stabilizers and rolling cutter reamers have blades or rolling cutter that protrude from the sub wall into the annulus to near the borehole diameter. The space between blades or rolling cutters allows the air or natural gas flow with entrained rock cutting to return to the surface nearly unobstructed.

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Fig. 1 – Rotating blade stabilizers

Figure 1 shows three rotating blade drilling stabilizers. These three stabilizers are, respectively, the integral blade (usually a spiral blade configuration) stabilizer, the big bear drilling stabilizer 9a large type integral blade drilling stabilizer), and the welded blade (spiral blade) drilling stabilizer. The blades on these three stabilizers are machined into (integral) the stabilizer body or are rigidly attached to the stabilizer body and, therefore, rotate with the body of the drilling stabilizer and, thus, with the drill string itself.

Figure 2 shows two sleeve types of blade stabilizers. These stabilizers have replaceable sleeves (with blades). These two stabilizers are, respectively, the sleeve type drilling stabilizer and the rubber sleeve stabilizer. The sleeve type stabilizer has a metal sleeve with attached metal blades (sleeve rotates) and can be replaced on the stabilizer body when the blades wear. The rubber sleeve stabilizer has a sleeve that has a rubber sheath over a metal substructure (sleeve does not rotate). The rubber sleeve can be replaced on the stabilizer body when the blades wear.

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Fig. 2 – Nonrotating blade stabilizer

In general, the rotating blade stabilizers are shop repairable. The integral blade stabilizers have gauge protection in the form of tungsten-carbide inserts or replaceable wear pads. Integral blade stabilizers can be used in abrasive, hard rock formations. When the blades are worn, the stabilizers can be returned to the machine shop and the inserts or wear pads replaced. Welded blade stabilizers are not recommended for use in abrasive, hard rock formations. When their blades become worn or damaged, they can be returned to the machine shop for repairs.

Nonrotating blade stabilizers can be repaired at the drilling rig location. Worn sleeves can be removed and new ones placed on the drilling stabilizer body. This is an important advantage over the rotating stabilizer. The nonrotating stabilizer is most effective in abrasive, hard rock formations, as the sleeve is stationary and acts like a drilling bushing. This action decreases wear on the metal sleeve blades.

Stabilizers are used extensively to improve the straight hole drill capability of a BHA for both mud drilling operations and air drilling operations. However, care must be exercised in using stabilizers in air drilling operations. The wear rate on drilling stabilizer blades in air drilling operations will be greater than in a mud drilling operation (assuming similar geologic conditions).

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Fig. 3 – Three – point rolling cutter reamer

Figure 3 shows a three-point rolling cutter reamer. These reamers have the roller cutters 1200 apart on the circumference. The rolling cutter reamers is a special type of stabilizer tool that provides “blades”, which are cylindrical roller cutter elements that can crush and remove rock from the borehole wall as the drill bit is advanced. Often the reamer is placed just above the drill bit (replacing the near bit stabilizer, see Figure 4). Reamers are also available in a four-point rolling cutter reamer. These reamers have the rolling cutters 900 apart on the circumference.

Such rolling cutter reamers are used when drilling in abrasive, hard rock formations. The gauge of the rolling cutter reamers can be adjusted by replacing the rolling cutter elements on the drilling stabilizer body with different outside diameter elements. Also, damaged rolling cutters can be replaced. These replacement can be accomplished at the drilling rig location. When drilling abrasive, hard rock formations, the gauge of the rolling cutter reamers is usually adjusted to be slightly under the drill bit gauge or at the drill bit gauge. The reamers provide the near-bit stabilization needed for straight drilling in abrasive formations.

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Fig. 4 – Typical bottom hole assembly for direct circulation rotary drilling operations.

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Reference : William C. Lyons, Air and Gas Drilling Manual (Applications for oil and gas recovery wells and geothermal fluids recovery wells), Third edition

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