Drilling stabilizer types & design is the main subject of this article. First we will introduce to you the definition of stabilizer. Then we will move to stabilizer application. And Finally we will talk about the its types. This article is a part of the series explaining Drilling Bottom Hole Assembly Components, Types & mechanism
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Drilling Stabilizer Definition
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A stabilizer is a piece of down hole equipment used in the Bottom Hole Assembly BHA of a Drill String. It mechanically stabilizes the Bottom Hole Assembly BHA in the borehole in order to avoid unintentional Sidetracking (check also: sidetrack Drilling), vibrations, and ensure the quality of the hole being drilled. Stabilizer is composed of a hollow cylindrical body and stabilizing blades, both made of high-strength steel. The Stabilizer blades can be either straight or spiraled, and are hard faced for wear resistance.
Drilling Stabilizer Applications
- Stabilizers are mandatory for centralizing the Drill Collars in the hole.
- As stabilizer numbers increased in the Drill String as the stiffness or rigidity of the Drill String increases which increases the ability of the Drill Collars to drill a smooth and straight hole and reduces the undesirable Drilling Bits movement, such as bit wobble, which reduces bit life.
- Also because of the large diameter of the stabilizer, it will provide some reaming action and wipe the walls of the hole to ensure a full-gauge hole.
What Is The Major Drilling Stabilizer Types Used In The Drill String?
The Steel Body Spiral Stabilizer
This kind of stabilizer have wings or blades that are an integral part of the stabilizer body. The blades make a 360 degree contact with the well bore. The outer surfaces of the blades are curved to fit the curvature of the well bore wall. This bearing surface provides bore hole wall contact and permits the stabilizers to hold the Drill Collar assembly centered in the hole
There are two types of spiral blade Drilling stabilizer Design:
- The integral blade stabilizer; The blades of the integral blade stabilize are an integral part of the stabilizer body. Whenever the stabilizer has worn down to an unacceptable condition the entire stabilizer is sent to the shop for reconditioning. this one is suitable for hard and abrasive formations. It is used in the small hole sizes
- The replaceable sleeve stabilizer; Which consists of the mandrel and the spiral sleeve. When the blades wear out, the sleeve can easily be detached from the mandrel at the rig and replaced with a reconditioned or new sleeve.It is used in large holes.
The Replaceable Wear Pad (RWP) Stabilizer
This type of stabilizer consists of four 3 ft long vertical (straight) replaceable pads. Large diameter, pressed-in tungsten carbide compacts on the surface of the pad prolong wear and keep the stabilizer in gauge. The long pads provide large contact area which make the stabilizer suitable for areas of extreme deviation tendencies. The wear pads can be changed easily at the rig. The stabilizer may be resized to a different hole size by replacing the pads with a set that has been manufactured to a different diameter.
The RWP drilling stabilizer Design is good for deviation control. However, the RWP drilling stabilizer is difficult to wash over because of the inserts used and it generates higher torque than the spiral drilling stabilizer because of its longer pad length.
The Non-Rotating Stabilizer.
Non Rotating Drilling Stabilizer Design consists of a mandrel and a polyurethane stabilizer sleeve which is free to rotate on the mandrel Since the polyurethane stabilizer sleeve does not rotate during drilling (only the mandrel rotates).
The non-rotating drilling stabilizer design is used for reducing drilling torque by employing the ease of rotation between the polished mandrel and the polyurethane sleeve. Its use is most common in the very large hole sizes where the use of spiral steel drilling stabilizers would generate excess torque.
Non rotating drilling stabilizers Design are rarely used as near bit stabilizers because their radial stiffness is no more than the drill bit itself. Rather, they are used two or three collars above the bit.
Advantages of the non-rotating stabilizer are low cost and low torque and drag. The disadvantages include low radial stiffness, rapid wear and tearing of the urethane pads and inability to ream under-gauge holes.