EMB 5433 / MAB 4643DRILLING AND PRODUCTION

TECHNOLOGY

DRILLING BIT

Faiza MN – July07

LESSON OBJECTIVES

� To describe the basic types of drill bit and their differences

� Select drill bit for specific application

� Describe the bit evaluation process and IADC system

� Describe the techniques to evaluate bit performance

� Calculate cost per foot of a bit run

� Select a bit on a basis of a previous bit run data

Faiza MN – July07

CONTENTS

� INTRODUCTION

� TYPES OF DRILLING BIT

� BIT SELECTION

� BIT EVALUATION

� BIT PERFORMANCE

Faiza MN – July07

Drill Bit

INTRODUCTION

Faiza MN – July07

INTRODUCTION

� Drill bit is the cutting or boring tool which is made up on the end of the drill string

� It drills through the rock by scraping, chipping, gouging and grinding

� How well a bit drills depends on:

� Type and condition of the bit

� The weight applied to make it drill

� The rate at which it is rotated

� The type of drilling fluid used for circulation

� The kind of rock/formation it is drilling

Faiza MN – July07

TYPES OF DRILL BIT

DRILL BITS

FIXED CUTTERROLLER CONE

FISHTAIL

PDC(POLYCRYSTALLINE

DIAMOND

COMPACT)

NATURAL DIAMOND

MILL TOOTHTUNGSTEN CARBIDE

INSERT

Faiza MN – July07

ROLLER CONE BIT

� The cones are mounted on bearing pins, or arm journals, which extend from the bit body

� The cones rotate and drill hole with a crushing and/or gouging action

� Require high WOB to fail the rock with high compressive loads

� Major advances:

� Jet nozzles to improve cleaning

� Tungsten carbide for hardfacing and gauge protection

� Sealed bearings

Faiza MN – July07

NATURAL DIAMOND BIT

� Employ natural diamonds set into tungsten carbide matrix body

� Cutting action is by scraping/grinding

� Very resistant to erosion and abrasion and are especially effective in harder formations.

� Expensive and care must be exercised when running in the hole since they are not resistance to impact loading or drilling on junk.

� Normally requires high RPM for better performance due to the limited depth per cut per rev

Faiza MN – July07

PDC BIT

� Use small discs of synthetic diamond

� Use shearing or grinding action

� In relatively plastic, sedimentary rocks as shales, limestone, and weakly cemented sandstones the shearing action is most efficient cutting mechanism requiring the least energy to drill.

� The PDC cutter’s self sharpening effect results in long bit life and high rates of penetration.

� Thermally Stable Polycrystalline (TSP) is similar to PDC bits but are tolerant of much higher temperatures

Faiza MN – July07

BIT SELECTION

� Must consider both mechanical and geological factors

� Useful to have condition of previously used bit in that hole or in the same section of an earlier drilled hole

� Cutters - offset, journal angle,

tooth or insert bits

� Fluid Circulation - regular, jet

fluid, air cooled

� Bearing Assemblies

� Soft Fmn – soft clay, unconsolidated

� Medium Fmn – shales, gypsum, salt,

chalk, siltstone, limestone, sandstone

� Hard Fmn – limestone, dolomite,

lime, hard compacted sand, quartzitic

MECHANICAL FACTORS GEOLOGICAL FACTORS

Faiza MN – July07

BIT SELECTION (cont’d)

Not critical40 - 100High

(6000 – 10000 lb/in)

HARD

High150 - 250 (shales)

100 - 150 (chlk/soft ss)

Low

(3000 – 6000 lb/in)

MEDIUM

High since ROP high

(500 – 800 gpm)

125 - 150Low

(3000-5000 lb/in)

SOFT

FlowrateRotary Speed (rpm)

WOB (per in of bit diam)

Formation Type

BIT OPERATING PARAMETERS

Faiza MN – July07

BIT SELECTION (cont’d)

� Many variations in the design of drill bits

� IADC has developed a system of classifying drill bits, based on formation type and design variations.

� One for Roller Cone and one for Fixed Cutter

Series # - Type – Features – Additional

Example: 1-2-4-E

5-1-7-X

Faiza MN – July07

ROLLER CONE IADC CHART

Mill Tooth

TC insert

Faiza MN – July07

Faiza MN – July07

IADC - example

A Smith F2 bit has an IADC classification of 517X:

� 5 indicates that the Smith F2 has tungsten carbide inserts,

� 1 The bit is designed for use in soft formations with low compressive strength;

� 7 indicates that the cones on this bit have sealed friction bearings, and that the bit is designed for protection against gauge wear;

� X indicates that the inserts have a chisel tooth configuration (asopposed, for example, to a conical shape) – there are 10 other characteristics.

Faiza MN – July07

BIT EVALUATION

� As each bit is pulled from the hole, its physical appearance is inspected and graded according to the

wear it has sustained

� Why evaluate bit?

� To improve future bit type selection

� To identify effects of WOB, RPM etc.

� To improve ability of personnel to recognise when a

bit should be pulled due to wear

� To improve bit design

� Using IADC Dull Grading system

Faiza MN – July07

Faiza MN – July07

IADC BIT DULL GRADING

Inner / Outer Cutting Structure Location of Dull Characteristics

Faiza MN – July07

BIT PERFORMANCE

� A good drill bit should gives:

� Good Rate-of-Penetration (ROP)

� Longest possible number of rotating hours

� Drill hole the same as the bit (true-to-gauge)

� Lowest cost per foot of hole drilled

� ROP is affected by:

� WOB

� Rotary Speed (RPM)

� Mud Properties

� Hydraulic Efficiency

Faiza MN – July07

BIT PERFORMANCE (cont’d)

� Cost per foot of hole drilled

( )

F

CTRCC

rttb++

=

C = Overall cost per foot ($/ft)

Cb

= Cost of bit ($)

Rt

= Rotating time with bit on bottom (hrs)

Tt

= Round trip time (hrs)

Cr

= Cost of operatiing rig ($/hrs)

F = Length of the bit run (ft)

� The equation can be used to:

� Post drilling analysis to compare one bit run with another in a similar well

� Real-time analysis to decide when to pull the bit – theoretically when the cost per ft is at its minimum

Faiza MN – July07

BIT SELECTION FROM OFFSET WELLS

� The process requires several assumptions:

� The lithology encountered in the offset bit runs must be

similar to that expected in the proposed well

� The depth of the offset bit runs are similar to that in the

proposed well

� The bit runs in the offset wells were run under optimum

operating conditions

� Having made the assumptions, the best bit will be selected on the basis of footage drilled, ROP and Cost-per-foot of bit run