Directional Drilling

Drillstring Components

Sperry-Sun 2004

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Directional Drilling

Drill Collars

Sperry-Sun Drilling Services

2004

Drill Collars

Sizes (OD) :2-7/8” – 12”

ID range :1”– 4”

Weights :

19 – 342 lb/ft

Material (σfmin):≤6-7/8” 110 kpsi

≥7” 100 kpsi

Drill Collar Materials

Comparison of properties – 8” OD x 2” ID drill collars :

SG lbs/ft EI = (x 1010 lb-in2)

• Steel AISI 4145H 7.68 160 0.57 • Tungsten Carbide 17.8 326 0.43 • Uranium, depleted 18.4 367 0.90

• Notes :• Tungsten carbide featured memory effect, brittle• Uranium consisted of 2% Mo + 98% U – corrosive,

needed a steel jacket, dangerous material

• SG = Specific Gravity• AISI 4145H as per API Specification 7• EI = Stiffness Coefficient (Young’s Modulus of Elasticity x Moment of

Inertia (l))

Selection of Drill Collars

Issues :

• Weight

• Stiffness

• Hydraulic resistance

Using Drill Collars

• Provides WOB (weight - on – bit) with a stiff tubular

• When keeping neutral point of tension within DC column (use approx. 90% of the DC weight only)

• Minimum effective hole diameter (after Lubinski) :

MEHD = (D bit + D dc) / 2

• Minimum required drill collar diameter (after Koch) :

min DC = 2(Dcsgcoupling) – D bit

MEHDD bit

2

D dc

2

running casing

Stiffness

• Moment of Inertia (l) :

(note: – if you use radius in place of diameter = /4 in place of /64)

(Polar Moment of Inertia (J) = 2 x Moment of Inertia (l) =/32)

Valid for thick wall cylinders, when OD/ID > 1.7

44 IDOD64

I

In4

• Young’s Modulus of Elasticity : Strain (Deformation) = ∫ (σ / E)

(function of (σ = stress) / (E = Young’s modulus of Elasticity))

Valid within the elastic strain region

Values : 29 x 106 psi for common steels (29,000 kpsi) 51.5 x 106 tungsten carbide 10 x 106 aluminium

26 x 106 Monel K500

• Stiffness Coefficient : SC = E x I lb-in2

Triangular Drill Collar for Increased Stiffness

Note : there are rectangular drill collars, too

Spiral Groove on Drill Collar

Drill collars can be spiral grooved to reduce differential sticking (approx. 4% weight loss)

DC Connections• Thread profile : V-038R (V-065 is obsolete)• Preferred connections : REG, NC, FH, H-90 (IF and XH are not preferred but are common in the

oilfield)• Bending Strength Ratio : BSR ~ 2.5 (stiffness of box / stiffness of pin)• Make-up torque : essential • Low- torque connection features• Pipe dope

Stress Reduction on Pins

stress relief groove

Note : not recommended for connections smaller than NC-38

Stress Reduction on Box

Low torque shoulder on the box

Bore - back

Drill Collar Lbs / Ft

Non-Magnetic Drill Collars

• NM drill collars, hang-off collars and hang-off subs - house the survey probes in non-magnetic environment

• NM extension bars – keep the survey probe in the (NM) drill collars far enough away from the steel components to avoid or minimize interference

• NM orienting subs (e.g. UBHO) to reduce interference

• NM string stabilizers, flex collars are available, too

• NM pressure cases and other parts for survey instruments

• Regular steel for drill collars : AISI 4145H (API Spec 7)

• Non-magnetic steels :

– chrome-manganese alloys (P530, P530HS, P550) – chrome-nickel alloys (SMI SM2035, SCF-19)– copper/copper-nickel alloys (MONEL K-500)

• Material strength (σy) :

steel (DC) AISI 4145H 110/100 kpsi (3-1/2” to 6-7/8”; 7” to 11” OD)

nm P530 110/100 P530HS 120/110 P550 140/130

SCF-19 100Staballoy 100

Monel K-500 115 SG 8.44 !

Note : Make-up torque depends on the yield strength, too

Non-Magnetic Materials

Composition of the Most Common NM Alloys

Monel K-500 27-33% Cu + 63% Ni+ (expensive)2.30-3.15% Al + 2.00% Fe

Cr-Ni steel ~ 18% Cr + >13% Ni (tend to gall)

Austenitic Cr - Mn alloys (SCC) used for LWD steel (>18% Mn + 4%Cu-Be)

Be-Cu bronze (expensive)

AUSTENITIC STEELSteel which, because of the presence of alloying elements, such as manganese, nickel, chromium, etc., shows stability of Austenite at normal temperatures.

AUSTENITEPhase in certain steels, characterized as a solid solution, usually off carbon or iron carbide, in the gamma form of iron. Such steels are known as “austenitic”. Austenite is stable only above 1333°F. in a plain carbon steel, but the presence of certain alloying elements, such as nickel and manganese, stabilizes the austenitic form, even at normal temperatures.

NM Drill Collars and Flex Collars

Spiral NM Drill Collars

NMDC End - Without SRG

no SRG

low-torque shoulder

• Problems with non-magnetic LWD and drill collars are:

• Galling on tool joints• Corrosion• Cracking• Frequent re-cutting the tool joints might be needed

(hard on tooling)• Occasionally Hot spots could be developed• Price is high

Non-Magnetic Drill Collars

Non-Mag Galled Threads

Corrosion-Erosion Pitting

Drill Collar Abrasive OD Wear

Non-magnetic Pup Joints

Note the 18° shoulder on tool joints

Directional Drilling

Hevi-Wate Drill Pipe

Spiral-Wate

Sperry-Sun Drilling Services

2004

Hevi-Wate Drillpipes

• Intermediate weight pipes with longer tool joints and additional upset (s) on the pipe body (1 or 3)

• Size range available : 3-1/2” – 4” – 4-1/2” - 5” – 5-1/2” – 6-5/8”

• ID and weights are depending on manufacturer

• Standard, spiral- and non-magnetic versions

• Manufacturers / suppliers : Drilco, Grant-Prideco, Weatherford

• Not covered by API Specification

Comparison of DP to HWDP

• 5” 19.50 lb/ft Grade G NC50 drillpipe approx. wt. 21.92 lb/ft

• 5 x 3” HWDP ( Drilco), standard, adjusted wt. 49.70

• Weight increase 2.27x

• Grant – Prideco standard 5 x 3” 49.3 lb/ft 1 upset

• Drilco - standard 5 x 3” 49.7 1

• - spiral 5 x 3” 54.0 3

• Weatherford - standard 5 x 3” 50.6 1

• - spiral 5 x 3” 53.8 1

Comparison of Hevi-Wate Drillpipes

Hevi-Wate Drillpipes

long TJ

large bore

pipe upset

SRG

HWDP Pin

SRG

HWDP – Pipe Upsets

hardfacing hardfacingupset

HWDP and DP Racked Back

HWDP DP

long TJold API marking :

hi-strength DP

wt and grade codes in slots