Drill String and Drill Collars Teams members:Maricela Pérez Gómez.Diana Ramos López.Rosaida Suarez Sánchez.Juan Sebastián Palacios Reyes.Jesús Manuel Hernández González.

At the end of this lecture YOU will be able to describe:

• Functions of Drill Pipe , Drill Collars and BHA selection

• Grades of Drill Pipe and strength properties• Thread types and tool-joints• Drill collar weight and neutral point

Objectives

The drill string is the mechanical linkage connecting the drill bit on bottom to the rotary drive system on the surface.

The drill string serves the three main following functions :

1. Transmit and support axial loads - WOB2. Transmit and support torsional loads - Torque3. Transmit hydraulics to clean the hole and cool

the bit. WOBDC

DP

Functions of the Drill String

The Drill String includes all tubular equipment between the Kelly Swivel and the bit

• Kelly• Surface Safety Valves• Drill Pipe• Heavy Walled Drill Pipe• Drill Collar• Jars – Shock Subs – Bumper Subs – Junk Baskets – Accelerators etc…

Drill String Components

  Strictly speaking, Kelly/ Topdrive are not components of the drill string; however, they provide the essential requirements for drilling a well:

The Kelly/Top Drive

1) Transmit rotation to the drillstring.

2) Provide access to the drilling fluid into the drillstring.

3) Support the weight of the string.

• Transmits rotation and weight-on-bit to the drillbit

• Supports the weight of the drillstring • Connects to the swivel and allow

circulation thru pipe.

The Kelly is the rotating link between the rotary table and the drill string.

The Kelly comes in lengths ranging from 40 to 54 ft with cross sections such as hexagonal (most common), square or triangular. Connected to a Kelly Saver Sub

The Kelly

The Kelly cock is used to close the inside of the drillstring in the event of a kick.

The upper & lower Kelly cocks operate manually.

IBOP / DPSV/FOSV are not run in the drill string but kept handy on the rig floor

The Kelly is usually provided with two safety valves, one at the top and one at the bottom, called Kelly cock.

Kelly Cock

Advantages over the kelly system:1. Efficient reaming and back reaming.

2. Circulating while running in hole or pulling out of hole in stands

3. The kelly system can only do this in singles; ie 30 ft.

The top drive is basically a combined rotary table and kelly.It is powered by a separate motor and transmits rotation to the drill string directly without the need for a rotary table.

Top Drive

Stabilizers

Reasons for Using Stabilizers:

1. They are used as a fundamental method of controlling the directional behavior of most BHAs.

2. Help concentrate the weight of the BHA on the bit.

3. Minimize bending and vibrations which cause tool joint wear and damage to BHA components such as MWDs.

4. Reduce drilling torque by preventing collar contact with the side of the hole and by keeping them concentric in the hole. (FG!!)

5. Help preventing differential sticking and key seating.

Stabilizers

Drill Collars

Drill collars are used to apply weight to the bit. Their large wall thickness gives them a greater resistance to buckling than DP. Their large wall thickness gives them a greater resistance to buckling than DP. The neutral point should be located at the top of the drill collars section (never in the DP section), 75 to 85% (maximum) of the drill collars section should be under compression (this will include HWDP if utilised).

The lower part of the drill collar section is under compression, therefore subject to buckling. This generates high stresses and potential fatigue failure, particularly at the connections.

In deviated holes, to avoid sticking of the drilling assembly, the minimum number of drill collars should be used (and these should be of the spiral type). Heavy Weight Drill Pipe in conjunction with undergauge stabilisers, should be used be used to substitute the drill collar weight.

Drill CollarsDescriptionThey are heavy walled metal tubesThe ends are threaded (box and pin)

FunctionsTo put weight on bit (WOB)To keep the drill string from buckling

TypesComes in many OD and ID sizesTypically 4 ¾” to 9 ½” ODMost commonly in lengths of 30-31 feetSquare collars where the holes tend to be crookedSpiral collars where there is chance of getting stuckCollars with elevator and slip recesses

Characteristics• DC connections are rotary shouldered connections and can mate the various DP connections• The shoulder provide the only positive seal against fluid leakage• The lubricant is Copper based dope• The connection is the weakest part of the entire BHA• The DC connections go through cycles of tension-compression and are subject to bending stresses• Improper M/U torque, improper or insufficient lubricant, galling can all lead to connection failure

Drill Collar Connections

Low Torque Feature•The low torque feature consists in removing part of the shoulder area of the pin and box.•This allows for lower make up torque maintaining adequate shoulder loading.•It is a common feature in large OD connections.

Torsion limits for DC Torque is rarely limited by the DC connection because it

is usually higher in the DP at surface and lower in the DC.

If DC make-up torque >Dp make-up torque you have no routine problems.

BH Torque at any point should not exceed 80% of make-up torque for the connections in the hole to avoid over tightening connections which can lead to damage of seals.

Torque Limits for DCM/U Torque as % of total torque

API recommended make-up torque for connections is a percentage of the total torsional yield of the connection

DC< 7 in DC>7 inPAC 79.5% N/aH-90 51.1% 56.2%API NC 56.8% 62.5%

CONCLUSIÓN

The drill string and drill collars are very important in the drilling, the drill collar is connected to the drill string to provide greater rigidity, greater weight and stability to the entire drill string and thus achieve a more efficient drilling both were designed to work together.