Drillstring Components and Course Assessment

Course Assessment

• To be eligible for the final exam, registration for the course and 90% attendance is required.
• Passing the course requires a minimum of 40% marks in the coursework component.
• A minimum of 40% marks is also required in the final examination component.
• Overall, a minimum of 40% marks is needed from the combination of coursework and the final exam.

Learning Objectives

• Drillstring components can be described.
• Standard and non-standard BHA configurations are explained.
• Drillstring components can be designed.

Drillstring Components

• A drillstring is a combination of tubular pipes run in a hole for drilling.
• Common drillstring components include drill pipe, heavy weight drill pipe (HWDP), drill collars, stabilizers, subs, float valve, and jars.
• A BHA is the lowermost part of the drillstring, and a BHA has components such as drill bit, mud motor, MWD/LWD, stabilizers, and subs.

Drill Pipes

• A drill pipe extends well depth.
• There are many grades, weights, and sizes, but three length ranges exist.
• A joint of pipe is broken down into three sections, comprising the box, tube ("body"), and pin connection.
• Only Grade E, G, and S are actually used in oilwell drilling.
• API RP7G has guidelines for Drill Pipe as follows:
• New = no wear, never been used.
• Premium = uniform wear with 80% wall thickness.
• Class 2 = 65% wall thickness.
• Class 3 = 55% wall thickness.
• Drill pipe sizes include 3-1/2", 4", 4-1/2", 5", 5-1/2", and 6-5/8".
• Annular capacity between the casing or hole and drill pipe, tubing, or casing is calculated as: Annular capacity, bbl/ft = (Dh²- Dp²)/1029.4.

Heavy Weight Drill Pipes (HWDP)

• Heavy Weight Drill Pipe (HWDP) is a thick-walled pipe, similar in appearance to DP but heavier, with a smaller internal diameter.
• HWDP is used for several reasons, including keeping the transition zone out of the drill pipe.
• HWDP is used in high-angle and horizontal wells instead of drill collars, and it helps maintain tension on the drill pipe while drilling.
• HWDP is identifiable by its oversized center and the amount of hard banding on the tool joints and can be ordered in Range 2 and Range 3.
• HWDP comes in the same sizes as drill pipes which is from 3-1/2" to 6-5/8".

Drill Collars (DC's)

• Drill Collars (DCs) are heavy, stiff steel tubulars, much heavier than DP and HWDP.
• DCs are located at the bottom of a BHA to provide weight on the bit and rigidity.
• The primary function of DCs is to provide the necessary weight on bit (WOB).
• DCs ensure the DP is kept in tension to prevent buckling and can be slick (flush) or spiral.
• There are two types of DC which are Slick DC and Spiral DC.
• Spiral DC should be used in areas where differential sticking is a possibility to minimize contact area with formation.
• DC sizes can measure from 3 1/8" to 11".
• The Buoyancy Factor (BF) of the mud weight is determined using: BF = 1 - (Mud Weight (MW) / 65.5).
• The drill collar weight to desired WOB is as follows: Weightdrill collar = (WOB*Safety Factor (SF)) / Buoyancy Factor (BF), for vertical wellbores.
• For inclined wellbores: Weightdrill collar = (WOB*Safety Factor (SF)) / Buoyancy Factor (BF)*cosθ.
• The length of the required Drill Collar is as follows for vertical wellbores: Drillcollariength = (SFWOB) / BFDrill collar weight in air (lb/ft).
• For inclined wellbores: Drillcollariength = (SFWOB) / BFcosθ*Drill collar weight in air (lb/ft).

Stabilizers

• Stabilizers center and stabilize drillstring components in the drilled hole and reduce the contact area of components with the borehole.
• Stabilizers are applicable for any type of drilling assembly, while stabs control hole deviation.
• Correctly used stabs may improve hole quality and rate of penetration. They also help to prevent undesirable drilling scenarios like stuck pipe, hole spiraling, and harmful vibration.
• Types of Stabilizers are Welded, Integral, String and nearbit, Straight Blades/ Spiral blades, Replaceable sleeves / non-rotating sleeve, and Variable gauge/diameters.

Jar & Accelerator

• Jars free stuck drill strings or recover stuck components.

Shocks Absorber, Subs & Crossovers

• Subs are short tubular pieces that increase the main drilling string component's versatility.
• Crossover subs are mechanical parts with threaded connections used to connect components with different sizes or thread characteristics.
• Crossover subs are typically found in the drill string between the drill pipe and drill collars or other points.

Mud Motors

• Mud Motors are typically positioned right above the drill bit
• Employed to enhance drilling performance across various well types
• Furnish rotation to the drill bit without necessitating the rotation of the entire drillstring
• Pivotal in directional drilling, facilitating deviation from vertical, angle construction, and subterranean target steering
• Augment the energy imparted to the bit
• Facilitate the conversion of hydraulic to mechanical power
• Boost the rate of penetration

Drillbits

• The two main categories of drill bits are roller cone bits and fixed cutter bits.
• Roller Cone Bits have three metal cones that rotate independently as the bit turns.
• The cutting structures on each cone gouge and crush the rock as the cone rotates.
• Roller cone bits include milled tooth bits and tungsten carbide bits.
• Fixed Cutter Bits have no moving parts or bearings with cutters permanently mounted onto blades e.g Polycrystalline Diamond Compact (PDC) bits.
• PDC bits, also known as "Drag Bits," shear and drag the rock as they cut.
• Originally designed to drill formations with soft to medium hardness (strength).
• PDC bits are able to drill at high Rates of Penetration (ROPs), and have low abrasivity on lithology types such as shale and claystone.
• For Rotary/ top drive they typically use low-medium WOB & medium high RPM's
• Mud Motor: high power (high torque) & medium speed (RPMs)

Bottom Hole Assembly (BHA)

• The Bottom Hole Assembly (BHA) is one of the drill string components.
• The components are Drilling Bit, Drill Collars, Drilling Stabilizers, Reamers, Jars, Shock subs and The hole opener.
• Other components in the Bottom Hole Assembly are a downhole mud motor, a rotary steerable system (RSS), measurement while drilling (MWD, and logging while drilling (LWD) tools.
• "Subs" are used to connect items with dissimilar threads together.

BHA Configurations

• There are three BHA configurations that concern the use or layout of drill collars, heavy weight drillpipe, and standard drill pipe.
• Type 1, standard simple configuration: Uses only drill pipe and drill collars, where the drill collars provide the necessary weight on the bit.
• Type 2: It uses heavy weight drill pipe as a transition between the drill collars and the drill pipe, with the weight on bit achieved by the drill collars.
• Type 3: Uses the drill collars to achieve directional control.
• The three configurations usually apply to straight/vertical wellbores at most low to medium angle wellbores.

MWD & LWD Tools

• Measurement While Drilling (MWD) is used to measure and record the physical properties of the drilling process.
• The physical properties are temperature, inclination, azimuth and tool's vibration.
• LWD, or logging while drilling is a methodology that records, stores, and transmits information during drilling operations.
• Valuable formation evaluation data that its uses include pore pressure estimates & mud weight.
• The key difference between LWD and MWD tools is that LWD data are recorded into downhole memory and retrieved when the tools reach the surface.
• MWD data is transmitted through the drilling fluid within the drill pipe by a modulated pressure wave (mud pulsing) at ~3 bits/s monitored in real time.

This lesson describes drillstring components such as drill pipes, heavy weight drill pipes, and drill collars. It also states the requirements for course registration, attendance and passing marks.