Spiral Drill Collars for BHA Weight and Stiffness Control

Description

Goldenman API 7-1 Spiral Drill Collars are heavy-wall rotary drillstem components designed to provide weight on bit, bending stiffness and directional stability within the bottom-hole assembly.

The spiral grooves reduce the continuous external contact area between the drill collar and the wellbore while providing additional flow paths around the collar. This configuration is commonly selected for directional, deviated and extended-reach wells where differential sticking, cuttings accumulation and borehole contact require additional consideration.

Available outside diameters range from 79.4 to 279.4 mm, equivalent to approximately 3-1/8 to 11 inches. Standard rotary shouldered connection options include NC23 through NC70, together with selected REG connections for larger drill collar sizes.

Each Spiral Drill Collar is manufactured according to the selected OD, bore, connection, length, bending-strength ratio, spiral-groove geometry and bottom-hole assembly requirements.

Product Short Description

Goldenman Spiral Drill Collars combine the weight and rigidity of a conventional drill collar with machined external spiral grooves that reduce continuous borehole contact.

The product is available with project-specific OD, bore, connection, length, spiral profile, stress-relief features and handling grooves. Each order is manufactured and inspected according to the approved API 7-1 datasheet and dimensional drawing.

Product Highlights

• Manufactured to applicable API Spec 7-1 requirements
• API-certified Drill Collar product scope
• Outside diameters from 3-1/8 to 11 in
• NC23–NC70 and selected REG connections
• Standard reference lengths of 9,150 or 9,450 mm
• Heavy-wall construction for BHA weight and stiffness
• Spiral grooves reduce continuous borehole contact
• Improved annular flow paths around the collar
• Smooth and spiral configurations available
• Optional slip and elevator recesses
• Optional stress-relief grooves and box bore-back
• Project-specific spiral number, width, depth and lead
• Full-length bore drift inspection
• Rotary shouldered connection gauging
• UT, MPI, hardness and dimensional inspection
• Heat and product traceability
• Third-party inspection support

What Is a Spiral Drill Collar?

A Spiral Drill Collar is a thick-wall drillstem component with external helical grooves machined along part of its outside surface.

Like a conventional slick Drill Collar, it is installed in the bottom-hole assembly to:

• Provide weight on bit
• Maintain axial compression near the bit
• Increase BHA stiffness
• Transmit drilling torque
• Carry drilling fluid to the bit
• Support stabilizers and directional tools
• Help control hole trajectory
• Reduce buckling in the drill pipe above the BHA

The spiral profile adds another function by reducing the amount of collar surface that remains in continuous contact with the wellbore.

The grooves also create additional passages around the collar for drilling-fluid and cuttings movement.

A Spiral Drill Collar is not the same as a spiral stabilizer. A stabilizer normally has larger blades intended to control BHA gauge and lateral position, while a Spiral Drill Collar remains primarily a weight and stiffness component.

Main Applications

Goldenman Spiral Drill Collars can be configured for:

• Vertical drilling
• Directional drilling
• Deviated wells
• Horizontal and extended-reach drilling
• Bottom-hole assemblies
• Weight-on-bit control
• BHA stiffness transition
• High dogleg drilling programs
• Wells with differential-sticking risk
• Wells with restricted annular flow
• Replacement of existing spiral-grooved Drill Collars
• New drillstem equipment packages

The number, size and position of Drill Collars should be determined from the complete BHA design rather than from hole size alone.

General Technical Specifications

Parameter	Available Specification
Product name	Spiral Drill Collar
Applicable standard	API Spec 7-1, applicable current edition
API product category	Drill Collars
Outside diameter	79.4–279.4 mm / 3-1/8–11 in
Bore	31.8–76.2 mm / 1-1/4–3 in
Standard reference length	9,150 or 9,450 mm
Connection range	NC23–NC70 and selected REG connections
Structure	Spiral-grooved heavy-wall Drill Collar
Spiral geometry	According to approved drawing
Bending-strength ratio	Approximately 2.37:1–3.18:1 in the listed configurations
Connection orientation	Box up and pin down unless otherwise specified
Material	Quenched-and-tempered alloy steel according to approved specification
Slip recess	Optional
Elevator recess	Optional
Stress-relief features	Optional when specified
Internal coating	Project-specific
Sour-service option	Subject to material and service review
Certification	Applicable API certificate
Inspection	API and purchase-order requirements

The exact material grade, mechanical properties, spiral dimensions, connection features and product weight must be confirmed through the approved manufacturing datasheet.

Complete Drill Collar Size Table

Connection	OD	Bore	Length	D_F Reference Diameter	Bending-Strength Ratio
NC23	79.4 mm / 3-1/8 in	31.8 mm / 1-1/4 in	9,150 mm	76.2 mm	2.57:1
NC26	88.9 mm / 3-1/2 in	38.1 mm / 1-1/2 in	9,150 mm	82.9 mm	2.42:1
NC31	104.8 mm / 4-1/8 in	50.8 mm / 2 in	9,150 or 9,450 mm	100.4 mm	2.43:1
NC35	120.7 mm / 4-3/4 in	50.8 mm / 2 in	9,150 or 9,450 mm	114.7 mm	2.58:1
NC38	127.0 mm / 5 in	57.2 mm / 2-1/4 in	9,150 or 9,450 mm	121.0 mm	2.38:1
NC44	152.4 mm / 6 in	57.2 mm / 2-1/4 in	9,150 or 9,450 mm	144.5 mm	2.49:1
NC44	152.4 mm / 6 in	71.4 mm / 2-13/16 in	9,150 or 9,450 mm	144.5 mm	2.84:1
NC44	158.8 mm / 6-1/4 in	57.2 mm / 2-1/4 in	9,150 or 9,450 mm	149.2 mm	2.91:1
NC46	158.8 mm / 6-1/4 in	71.4 mm / 2-13/16 in	9,150 or 9,450 mm	150.0 mm	2.63:1
NC46	165.1 mm / 6-1/2 in	57.2 mm / 2-1/4 in	9,150 or 9,450 mm	154.8 mm	2.76:1
NC46	165.1 mm / 6-1/2 in	71.4 mm / 2-13/16 in	9,150 or 9,450 mm	154.8 mm	3.05:1
NC46	171.4 mm / 6-3/4 in	57.2 mm / 2-1/4 in	9,150 or 9,450 mm	159.5 mm	3.18:1
NC50	171.4 mm / 6-3/4 in	71.4 mm / 2-13/16 in	9,150 or 9,450 mm	159.5 mm	2.37:1
NC50	177.8 mm / 7 in	57.2 mm / 2-1/4 in	9,150 or 9,450 mm	164.7 mm	2.54:1
NC50	177.8 mm / 7 in	71.4 mm / 2-13/16 in	9,150 or 9,450 mm	164.7 mm	2.73:1
NC50	184.2 mm / 7-1/4 in	71.4 mm / 2-13/16 in	9,150 or 9,450 mm	169.5 mm	3.12:1
NC56	196.8 mm / 7-3/4 in	71.4 mm / 2-13/16 in	9,150 or 9,450 mm	185.3 mm	2.70:1
NC56	203.2 mm / 8 in	71.4 mm / 2-13/16 in	9,150 or 9,450 mm	190.1 mm	3.02:1
6-5/8 REG	209.6 mm / 8-1/4 in	71.4 mm / 2-13/16 in	9,150 or 9,450 mm	195.7 mm	2.93:1
NC61	228.6 mm / 9 in	71.4 mm / 2-13/16 in	9,150 or 9,450 mm	212.7 mm	3.17:1
7-5/8 REG	241.3 mm / 9-1/2 in	76.2 mm / 3 in	9,150 or 9,450 mm	223.8 mm	2.81:1
NC70	247.6 mm / 9-3/4 in	76.2 mm / 3 in	9,150 or 9,450 mm	232.6 mm	2.57:1
NC70	254.0 mm / 10 in	76.2 mm / 3 in	9,150 or 9,450 mm	237.3 mm	2.81:1
8-5/8 REG	279.4 mm / 11 in	76.2 mm / 3 in	9,150 or 9,450 mm	266.7 mm	2.84:1

The values above are reference dimensions from the existing Goldenman product range. Final tolerances, mass, connection geometry and spiral profile are governed by the approved product drawing.

Spiral Groove Configuration

The spiral profile must be defined separately from the basic Drill Collar OD and bore.

A complete Spiral Drill Collar specification should state:

• Number of spiral grooves
• Groove direction
• Groove width
• Groove depth
• Groove lead or pitch
• Spiral start and stop positions
• Groove-bottom diameter
• Length of the spiral section
• End-transition radius
• Remaining land width
• Surface-finish requirement
• Maximum external gauge diameter

These values affect:

• External contact area
• Annular flow area
• Collar weight
• Bending stiffness
• Wear distribution
• Fishing and handling clearance
• Stress concentration at the groove transitions

The spiral profile should be machined with smooth transitions. Sharp groove ends or abrupt section changes can create undesirable local stress concentration.

Spiral Drill Collar vs Slick Drill Collar

Comparison	Spiral Drill Collar	Slick Drill Collar
Outside surface	Machined helical grooves	Smooth cylindrical OD
Borehole contact	Reduced continuous contact area	Greater continuous contact area
Annular flow path	Additional flow channels around OD	Standard annular clearance
Differential-sticking exposure	Can be reduced in suitable applications	Greater contact area may increase exposure
Weight per joint	Slightly reduced by groove machining	Higher for the same base OD and bore
Manufacturing complexity	Higher	Lower
Inspection	Includes groove transitions and groove-bottom areas	Focuses on smooth OD and connection areas
Typical selection	Deviated, directional or sticking-sensitive wells	General vertical and conventional drilling

The spiral design does not eliminate differential sticking. Mud properties, overbalance pressure, filter cake, hole cleaning, BHA geometry and operating practices remain important.

Selecting the Correct Outside Diameter

Drill Collar OD affects:

• Weight per joint
• Bending stiffness
• Hole and casing clearance
• Annular velocity
• Differential-sticking contact area
• Fishing clearance
• Compatibility with stabilizers and BHA tools

A larger OD provides more weight and stiffness but reduces annular clearance.

Selection should consider:

• Hole size
• Casing ID
• Liner ID
• Stabilizer gauge
• Fishing tool requirements
• Planned BHA OD
• Maximum dogleg severity
• Expected cuttings size
• Required circulation area

The spiral lands and maximum external diameter must remain compatible with the most restrictive bore through which the collar will pass.

Selecting the Internal Bore

The Drill Collar bore affects:

• Hydraulic flow area
• Pressure loss
• Drill Collar weight
• Torsional capacity
• Tensile area
• Bending-strength ratio
• Compatibility with drop balls and internal tools
• Full-length drift diameter

A smaller bore increases metal cross-sectional area and joint weight but creates more hydraulic restriction.

A larger bore can reduce pressure loss but changes the connection balance and mechanical properties.

The selected OD, bore and connection must therefore be reviewed as one configuration.

Understanding Bending-Strength Ratio

The bending-strength ratio compares the relative bending resistance of the pin and box connection sections.

A properly selected ratio helps avoid concentrating fatigue damage disproportionately in one side of the rotary shouldered connection.

The ratio is influenced by:

• Drill Collar OD
• Internal bore
• Pin dimensions
• Box dimensions
• Connection type
• Counterbore and stress-relief features
• Remaining metal area

Two Drill Collars with the same outside diameter may have different bending-strength ratios because their bores or connection designs differ.

The required configuration should be selected from the API dimensional table and the connected BHA components.

Connection Selection

Available connection families include:

• NC23
• NC26
• NC31
• NC35
• NC38
• NC44
• NC46
• NC50
• NC56
• NC61
• NC70
• 6-5/8 REG
• 7-5/8 REG
• 8-5/8 REG

The connection must match the adjacent Drill Collar, HWDP, stabilizer, sub or bottom-hole tool.

The purchase specification should confirm:

• Connection designation
• Box-up and pin-down orientation
• Bevel diameter
• Bore
• Make-up torque basis
• Thread surface treatment
• Stress-relief groove requirement
• Box bore-back requirement
• Thread-root cold-working requirement where specified
• Thread protector type

Connection names alone should not replace dimensional gauging and approved interface drawings.

Optional Slip and Elevator Recesses

Slip and elevator recesses can be machined to improve handling of heavy Drill Collars at the rig floor.

The order should define:

• Slip recess location
• Elevator recess location
• Recess OD
• Recess width
• Transition radius
• Surface finish
• Handling equipment compatibility

These recesses remove material from the Drill Collar body and therefore must be included in the approved mechanical and dimensional design.

They should not be added in the field without engineering review.

Spiral Drill Collar Position in the BHA

A typical lower drillstring may include:

1. Standard drill pipe
2. Heavy Weight Drill Pipe
3. Spiral or slick Drill Collars
4. Stabilizers
5. Directional tools or mud motor
6. Bit

The Drill Collar section is commonly used to keep the drill pipe above it in tension and transfer compressive weight toward the bit.

The required quantity depends on:

• Desired weight on bit
• Buoyancy factor
• Hole inclination
• Neutral-point location
• Drill Collar weight per meter
• BHA length
• Stabilizer placement
• Dogleg severity
• Dynamic drilling loads
• Rig hook-load limits

A fixed number of Drill Collars should not be applied to every drilling program.

Material and Heat Treatment

The Drill Collar body is manufactured from alloy steel meeting the approved API and project mechanical-property requirements.

Manufacturing controls should address:

• Raw material chemistry
• Forging or rolled-bar quality
• Quenching and tempering
• Tensile properties
• Yield strength
• Elongation
• Impact toughness
• Hardness
• Through-section uniformity
• Heat identity and traceability

The exact steel grade and mechanical-property requirements should be shown on the purchase datasheet and material certificate.

For H₂S or low-temperature service, additional material, hardness and impact requirements may be necessary.

H₂S and Corrosive Service

For sour-service applications, provide:

• H₂S concentration or partial pressure
• CO₂ concentration
• Chloride content
• Operating temperature
• Drilling-fluid chemistry
• Well pressure
• Applicable NACE MR0175/ISO 15156 requirements
• End-user hardness limitations

The material and heat-treatment review must confirm that the selected Drill Collar is suitable for the specified environment.

A standard alloy-steel Drill Collar should not automatically be described as sour-service qualified.

Replacement and Interchangeability

A replacement Spiral Drill Collar should not be ordered using only OD and connection.

Provide:

• Existing manufacturer
• Product part number
• Overall length
• Outside diameter
• Bore
• Connection
• D_F reference diameter
• Spiral groove quantity
• Groove width and depth
• Groove lead
• Spiral-section length
• Slip and elevator recess dimensions
• Stress-relief features
• Product weight
• Existing drawing and photographs

Two 6-3/4 in NC50 Spiral Drill Collars may connect to the same equipment but still differ in bore, weight, spiral geometry and fatigue performance.

Manufacturing and Quality Control

Goldenman manufacturing and inspection procedures can include:

• Raw material certificate verification
• Heat-number traceability
• Chemical composition review
• Mechanical-property verification
• Heat-treatment record review
• Ultrasonic examination
• Magnetic-particle examination
• Hardness testing
• Outside diameter inspection
• Bore inspection
• Full-length drift inspection
• Straightness inspection
• Overall length inspection
• Spiral-groove dimensional inspection
• Groove-transition inspection
• Slip and elevator recess inspection
• Rotary shouldered connection gauging
• Seal-shoulder inspection
• Surface-imperfection inspection
• Product marking verification
• Final documentation review

Inspection criteria should follow the applicable current API 7-1 requirements, including relevant addenda and errata.

Product Marking and Traceability

Product identification can include:

• Manufacturer’s name or identifying mark
• Drill Collar outside diameter
• Bore
• Connection designation
• API 7-1 identification
• Heat or traceability number
• Customer-specific marking
• Serial number where required

Marking must be positioned so that it does not damage threaded, sealing or highly stressed areas.

Available Documentation

The order documentation package can include:

• API certificate
• Certificate of Conformity
• Approved product datasheet
• Dimensional drawing
• Spiral-groove drawing
• Material certificate
• Heat-treatment record
• Mechanical test report
• Ultrasonic inspection report
• Magnetic-particle inspection report
• Hardness report
• Dimensional inspection report
• Bore drift report
• Straightness report
• Connection gauge report
• Surface inspection report
• Product traceability list
• Packing list
• Third-party inspection report

Frequently Asked Questions

What is the main difference between a Spiral Drill Collar and a standard slick Drill Collar?

Both products provide weight and stiffness in the BHA.

The Spiral Drill Collar has machined helical grooves that reduce continuous borehole contact and provide additional annular flow passages. A slick Drill Collar has a smooth cylindrical outside surface and normally retains slightly more weight for the same base OD and bore.

Can a Spiral Drill Collar eliminate differential sticking?

No.

The reduced contact area can help lower sticking exposure in suitable conditions, but differential sticking is also influenced by wellbore overbalance, mud filter cake, formation permeability, hole inclination and operating practices.

The complete drilling program must be considered.

Does the spiral groove diameter equal the nominal Drill Collar OD?

The nominal OD normally refers to the maximum external diameter across the spiral lands.

The groove-bottom diameter is smaller and must be specified separately. Groove depth, land width and spiral lead should be confirmed on the manufacturing drawing.

Can a Spiral Drill Collar replace a slick Drill Collar with the same OD and connection?

Not automatically.

The spiral version normally has a different weight, external contact profile and hydraulic clearance. The BHA calculation, fishing clearance and weight-on-bit requirement should be reviewed before replacement.

Is a Spiral Drill Collar the same as a spiral stabilizer?

No.

A Spiral Drill Collar is primarily a heavy-wall weight and stiffness component. A stabilizer has defined gauge blades intended to control lateral BHA position and hole trajectory.

The two tools have different dimensional and functional requirements.

How should the correct connection be selected?

The connection must match the adjacent BHA components and provide an appropriate bending-strength relationship for the selected OD and bore.

The complete connection designation, bore, bevel diameter and optional stress-relief features should be stated in the order.

Why are two bore options available for some Drill Collar sizes?

Different bores allow the buyer to balance joint weight, hydraulic flow area and bending-strength ratio.

For example, a smaller bore increases metal area and weight, while a larger bore provides more internal flow area. The selected bore must be matched to the connection and BHA design.

Can this Spiral Drill Collar be used near MWD or magnetic survey tools?

A standard alloy-steel Spiral Drill Collar is magnetic and can interfere with magnetic survey instruments.

Where magnetic interference must be minimized, a dedicated Non-Magnetic Drill Collar should be selected and qualified separately.

What areas require the most attention during used Drill Collar inspection?

Critical areas include:

• Pin and box threads
• Seal shoulders
• Stress-relief grooves
• Box counterbores
• Spiral groove bottoms
• Groove start and stop transitions
• Slip and elevator recesses
• External wear areas
• Internal bore
• Areas exposed to bending fatigue

Inspection scope should reflect operating hours, dogleg exposure, over-torque events and previous repairs.

What information is required for a replacement Spiral Drill Collar?

Provide the OD, bore, length, connection, weight, complete spiral geometry, handling recess dimensions, connection features and existing drawing.

A sample photograph is useful, but a fully dimensioned drawing is the preferred replacement basis.

Information Required for Quotation

Please provide:

• Required quantity
• Drill Collar outside diameter
• Internal bore
• Overall length
• Connection at each end
• Required bending-strength ratio
• Number of spiral grooves
• Groove direction
• Groove width
• Groove depth
• Spiral pitch or lead
• Spiral-section length
• Slip recess requirement
• Elevator recess requirement
• Stress-relief groove requirement
• Box bore-back requirement
• Thread-root treatment requirement
• Material specification
• Mechanical-property requirements
• Operating temperature
• Drilling-fluid conditions
• H₂S and CO₂ conditions
• Applicable NACE requirements
• NDE requirements
• API certificate requirement
• Third-party inspection requirement
• Required documentation
• Destination country
• Delivery schedule

For replacement orders, also provide the existing drawing, part number, product markings and clear photographs.

Request a Technical Quotation

Goldenman supplies API 7-1 Spiral Drill Collars for vertical, directional and extended-reach bottom-hole assemblies.

Available configurations cover outside diameters from 3-1/8 to 11 inches with NC and REG rotary shouldered connections, project-specific bores and custom spiral-groove profiles.

Send your required OD, bore, connection, length, spiral dimensions and inspection requirements to:

Email: info@goldenman.com

Goldenman will review the BHA requirements and prepare the dimensional drawing, technical datasheet, inspection plan and commercial quotation.