Stabilizers are an indispensable part of almost all rotary directional BHAs.
Near-bit stabilizers have BOX x BOX connections. They are usually bored out to accept a float valve.
String stabilizers have PIN x BOX connections.
Most stabilizers have a right-hand spiral.
Stabilizers are used to:
Control hole deviation.
Reduce the risk of differential sticking.
Ream out doglegs and keyseats.
Here we are going to discuss the following types of stabilizer :
Integral Blade Stabilizers
Welded Blade Stabilizers
Sleeve Type Stabilizers
INTEGRAL BLADE STABILIZERS (IB)
I.B. stabilizers are made from high-strength alloy steel as a single piece tool. They are rolled and machined to provide the blades.
The unitized construction features three spiraled ribs designed to minimize down hole torque, reduce damage to the hole wall and ensure maximum fluid circulation.
The IBS is well suited for use in most formations from soft and sticky to hard and abrasive.
It is available in both bottom-hole and string designs, providing the flexibility to run it anywhere in the BHA.
When the blades wear down to an unacceptable diameter, the tool should be removed from the drilling assembly and returned for servicing where it can usually be redressed to full gauge size.
They can have either three or four blades.
I.B. stabilizers normally have tungsten carbide inserts (TCIs). Pressed-in TCIs are recommended in abrasive
Features and Benifits :
The blades are an integral part of the tool body, eliminating the risk of leaving components or pieces in the hole.
Available in both “open” and “full wrap” designs, providing optimum hole wall contact while ensuring maximum fluid bypass area.
Application in Directional Drilling :
A packed hole assembly typically requires the placement of multiple IB stabilizers throughout the three zones of stabilization. Contact a OTI - representative for BHA recommendations.
A pendulum assembly is a recommended application for the IBS due to its unitized design. For the most effective pendulum assembly, two stabilizers should be run separated by one drill collar.
Vibration and drill collar whip can be reduced through the placement of stabilizers in the BHA and upper drill collar string.
Extended Life IBS Specification :
Standard IBS Specification :
WELDED BLADE STABILIZERS (WBS) :
The Welded Blade Stabilizers used in the B.H.A for drilling soft to medium hard formation holes are available in three types (straight, straight-offset or spiral design).
They are best suited to large hole sizes where the formation is softer because they allow maximum flow rates to be used.
Stabilizer bodies are manufactured from AISI 4145 H Modified Steel with mechanical properties in accordance with API Specification 7.
Mid steel blades are welded onto the body using strictly controlled pre-heating, post weld heat treatment and weld application techniques.
All areas affected by the process of welding are subject to full non-destructive examination to assure the mechanical integrity of the joint.
Standard Welded Blade Stabilizers are available in 3 or 4 blade configuration with the spiral type available with open or tight spiral.
HF 1000 or HF 2000 Hardfacings are most commonly applied to Welded Blade Stabilizers.
Standard dimension of WBS :
Welded blade stabilizers are available in following three configurations:
NOTE : IBS are more expensive than welded blade type stabilizers, since they are machined from one piece of metal.
SLEEVE TYPE STABILIZERS :
These consist of replaceable sleeves that are mounted on the stabilizer body. They offer the advantage of changing out a sleeve with worn blades or replacing it with one of another gauge size. The blades can be dressed with tungsten carbide inserts for abrasive formations.
There are two main designs of sleeve-type stabilizer as shown in figure below:
Two-piece stabilizer (mandrel and sleeve):
The sleeve is screwed onto the coarse threads on the outside of the mandrel and torqued up to the recommended value.
Sleeve makeup torque is low.
There is no pressure seal at the sleeve.
It is convenient to change sleeves on the drill floor.
This design of stabilizer is manufactured by several companies.
It is in wide use today.
Three-piece stabilizer (mandrel, sleeve and saver sub):
The sleeve is screwed onto the mandrel first, by hand.
The saver sub is then screwed into the mandrel and this connection is torqued up to the recommended value.
In this case, there is a mud pressure seal at the mandrel/saver sub connection. Makeup torque of this connection is the full value for that size of API connection.
Great care must be taken (clean and dope the shoulders properly, use correct makeup torque), otherwise downhole washouts etc. will result.
It can be quite difficult any time-consuming to change/service the sleeve. For these reasons, this design of sleeve-type stabilizer is not as widely used today as it was some years ago.
Clamp-on stabilizers allow more flexibility in BHA design.
They can be positioned on NMDCs, MWD, PDMs etc. at the required spacing to maintain directional control.
Nonmagnetic clamp-on stabilizers are available on request Some clients are apprehensive about running clamp-on because of the danger of them moving position downhole. Sometimes they’re difficult to take off after POOH.
NON- ROTATING STABILIZER
These stabilizers are used to centralize the drill collars, but the rubber sleeve allows the string to rotate while the sleeve remains stationary. The wear on the blades is therefore much less than in other stabilizers and so they can be used in harder formations.
Stabilizers can be installed just above the bit (near-bit stabilizers) or at any point within the BHA (string stabilizers).
Two stabilizers can also be run in tandem if necessary ("piggy-back"). Stabilizers are inserted at drill collar connections. This limits their spacing to 30 ft or multiples of 30 ft.
Closer spacing can be achieved by using shorter drill collars (pony collars) that are 10-15 ft long.
"Clamp on" stabilizers can be used to provide support at some point along the length of a collar.
Any stabilizer that is placed near a magnetic surveying tool must be made of non-magnetic material, to prevent distortion of the survey results.
Hardfacing is a metalworking process where harder or tougher material is applied to a base metal. It is welded to the base material, and is generally takes the form of specialized electrodes for arc welding or filler rod for oxyacetylene and TIG welding.
Hardfacing may be applied to a new part during production to increase its wear resistance, or it may be used to restore a worn-down surface.
Crushed tungsten carbide held in a nickel bronze matrix. The 3mm grain size ensures greater concentration of carbide which is ideal for soft formation drilling.
Trapezoidal tungsten carbide inserts held in a sintered carbide nickel bronze matrix. This will give a greater depth of carbide coverage – ideal for high deviation drilling in abrasive formations.
Tungsten carbide inserts set in a powder spray deposit ideal for abrasive formations. 97% bonding guaranteed, certified by ultrasonic report. Recommended for non-magnetic stabilizers.
Tungsten carbide inserts (button type). The inserts have been developed to allow cold insertion and maintain close fit. A greater concentration of inserts on the bottom third of the blade and leading edge will increase surface contact to reduce wear in highly abrasive formations.
This oxy-acetylene process applies tough molten carbide particles of varying sizes held in a nickel chrome matrix which provides excellent bonding properties and greater surface wear characteristics are achieved. Surface hardness levels over 40 HRC. Ideal for GEO-THERMAL applications over 350°.
This process is a highly automated way of applying hardface and utilizes a combined arc/plasma stream on the work piece surface. This results a low base metal dilution and a dense, uniform coating, the filling medium can be variety of hardfacing consumables.