Drillbits OIl and Gas

8/12/2019 Drillbits OIl and Gas

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UNIVERSITI TEKNOLOGI PETRONAS

PETROLEUM ENGINEERING DEPARTMENT

Section 4

Drillbits


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PAB 2033 DRILLING ENGINEERING JANUARY 2014

Contents

4.1 Introduction

4.2 Purpose

4.3 Bit classification4.4 Bit dull grading

4.5 Bit economic


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4.1 Introduction

Proper bit selection for a well is an important

decision that affects the overall well cost

We must consider a lot of factors;

Bit cost Rig and overall operation spread costs

Expected parameters

Formation types and properties

Mud systems


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4.2 Purpose

To facilitate rock removal/ failure by

Exceeding rocks shear strength

Exceeding rocks compressive strength

The broken rock is removed by rotary scraping or

hydraulic cleaning

Main functions


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4.3 Bit classification

Bit Classification

Fixed cutter

Impregnated

Diamond

Rolling cutter

InsertMilltooth

Friction

bearing

Natural

DiamondT.S.P

DiamondP.D.C.

Roller

bearing


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Also known as rock bits, roller cone and Tri-cone

Has cones that roll when the drill bit turns

There are two types- tooth bits (steel tooth or mill tooth bits)

and insert bits (carbide or button bits)

Made up 3 major components;

Rolling cutter

3 Lugs Component parts 3 Cutters




The cutters are attached to the lugs.

Then the 3 lug and cutter assemblies are welded

together to make a drill bit

Rolling cutter




Rolling cutter (Milltooth) Also known as steel tooth bit

It has steel tooth to gauge the rock

It is best in soft formation and

generally less expensive than otherbit types




Rolling cutter (Milltooth)

Advantages

Fast ROP

Good stability

Streerable

economic

Consideration

Tooth wear rate

Bearing life




Rolling cutter (Insert) Tungsten carbide insert bit aka

button bit

One of the hardest material known

Can drill in most hardest andabrasive formation




Rolling cutter (Insert)

Advantages

Cutting structure durability

Range of formations

Interbed tolerance

Steerability and stability

Consideration

Slower ROP

Bearing life




Rolling cutter (roller bearing)




Rolling cutter (friction bearing)




Fixed cutter No moving parts, but drilling occurs because of

rotation of the drill string

It has two types; diamond and PDC




Fixed cutter(PDC-Polycrystalline Diamond Compact)

More expensive than roller cone but

drill faster and longer bit life




Fixed cutter(PDC-Polycrystalline Diamond Compact)

Advantages

Very fast ROP Long life potential

Consideration

Impact damage

Abrasiveness stability


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Fixed cutter (Natural diamond)

Industrial rated diamond set on

surface to create an abrasive cutting

face

Use in hard and abrasive formation


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Advantages

Very durable Hard rock capability

Low junk in hole risk

Consideration

Slower ROP High cost applications


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Fixed cutter(T.S.P- Thermally Stable PDC)


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Fixed cutter (Impregnated diamond)

Has PDC cutter but straight out of

the body

Soft and hard formation


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Fixed cutter(Impregnated diamond)

Advantages

Very durable Hard rock capability

Low junk in hole risk

Consideration

Slower ROP High cost applications


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Bit Cutting Mechanisms

Fixed cutter bits

Continuous shearing(shear failure)

Roller cone bit

Cyclic compression(compressive failure)


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Bit Cutting Mechanisms

Gouging and scraping Milltooth

Chipping and crushing Insert

shearing PDC

ploughing Natural diamond

grinding Impregnated diamond


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4.4 Bit dull grading


Why grade dull bit?

Engineering information database

Information about suitability for the chosen bit

Guidance for next/future bit selection

Review four bit wear categories

Cutting structure (T)

Bearings and seals (B) Gauge (G)

Remarks


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Bit Selection Process Collect data

Geology

Offset bit records, mud logs, well logs

Analyze the proposed well plan

Length of hole sections

Drilling fluids

Directional drilling needs (tricone-good steerability control)

Geology

Consider rock properties Hardness

Abrasiveness

Stickiness

Compressive strength


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4.5 Bit economic

=+ +

= overall cost per foot ($/ft)

= cost of bit ($)

= rotating time with bit on bottom (hrs)

= round trip time (hrs)

= rig operating cost ($/hrs)

= Footage (ft)


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4.5 Bit economic

Bit

Type

Bit Cost

($)

Depth In

(ft)

Depth Out

(ft)

Rotation

HoursA 8,500 8100 8306 15

B 15,000 8250 8982 58

C 15,000 8000 8983 96

Example4.5

Select the best performing bit

= $120,000/

= 1/1000


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4.5 Bit economic

Bit

Type

ROP

(ft/hr)

A 206/15 13.7

B 732/58 12.6

C 983/96 10.2

Answer4.5

Rate of Penetration (ROP)


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4.5 Bit economic

Bit

Type

Bit Cost

($)

Footage

(ft)

ROP

(ft/hr)

Cost/Foot

($/ft)

A 8,500 206 13.7 606.94B 15,000 732 12.6 478.02

C 15,000 983 10.2 549.25

Example4.5

=$120,000

24 = $5,000/

Bit A is the cheapest and give highest ROP,

but it is the least economical

Bit B should be selected as the best bit for this hole section


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Drillbits OIl and Gas

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