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Errors And Failures During Oil Well Drilling Engineering Essay

Paper Type: Free Essay Subject: Engineering
Wordcount: 4476 words Published: 1st Jan 2015

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This paper provides a general overview of errors and failures during drilling and tripping operations in the oil industry. The overview is presented in a tabular format for quick and easy reference. The work makes a clear distinction between errors and failures and how errors may possibly lead to drilling failures. A classification of drilling failures with their signs and symptoms as well as the possible causes of these failures is included in the overview. The overview may help during a thorough audit of failures that are encountered during a drilling operation. Developing a list of possible failures during drilling with a description of basic observatory signs and symptoms of their occurrence is the crucial first step in minimizing Non Productive Time (NPT) during drilling operations.

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Keywords: Drilling, Error, Failure, Tripping

1. Introduction

The oil industry is unarguably one of the most complicated industries which face so many challenges yet functions as efficiently as possible. This assertion is true because the primary object of interest to the petroleum engineer cum the industry is located thousands of feet beneath the earth’s surface. This is accompanied by varying conditions of temperature and pressure as well as other geological factors. A combination of these factors makes the subject of understanding the process of getting at the object of interest complex to drilling engineers. The elusive nature of this understanding makes drilling operations encounter failures. These failures range from drill tool/equipment breakdown, wellbore or formation collapse, lost circulation, kicks and blowouts.

Suffice it to say that these failures cost the industry valuable drilling time running into billions of dollars annually. It is against this background that this work on drilling failures is looked into. The primary focus of this work therefore is to improve the drilling process, by designing a good approach to identify all possible failures, how and when they occur, and most importantly their root causes. This would be done from a taxonomic perspective. This would involve classifying failures in the industry in their natural groups and isolating their possible causes, the key indicators to such failures as well as the errors leading to the failures.

2. Reported Cases of Failures in the Oil Industry

To put the cases of failure in the right perspective, it is necessary to first define failure and error as it applies to oil well drilling operations. Schlumberger (2012) in their oil field glossary webpage defines failure in drilling as:

Failure to meet the defined drilling objective.

Deviation in the expected TD depth /run length

Deviation in the expected performance (penetration rates, directional, power use)

Error as defined by Oxford Advanced Learners Dictionary, is a mistake especially one that causes problems or affects the result of something.

In today’s error classification systems, error can mean several things:

Error as the cause of failure. For example: This event was due to human error. Classifications rely on this definition when seeking the cause of operator error in, for instance, a supervisor’s “failure to provide guidance” (Shappell & Wiegman, 2001.).

Error as the failure itself. For example: The operator’s decision was an error (e.g. Helmreich, 2000). Classifications rely on this definition when categorizing the kinds of observable errors operators can make (e.g. decision errors, perceptual errors, skill-based errors) (Shappell & Wiegmann, 2001).

Error as a process, or, more specifically, as a departure from some kind of standard. This standard may consist of operating procedures. Violations, whether exceptional or routine (Shappell & Wiegmann, 2001), or intentional or unintentional (Helmreich, 2000), is one example of error according to the process definition. Depending on what we use as standard, we of course come to different conclusions about what is an error.

Based on the above definitions, the following are the reported cases of failures in the oil industry.

The most recent case is the Gulf of Mexico oil disaster in 2010. Though the immediate and remote causes of the incident still remains a subject of controversy, the fact remains that the incident makes the subject of failures in the oil industry a relevant one.

Shokir (2004) listed the following actual failure cases that occurred in Gulf of Suez Petroleum Company (GUPCO) in Gulf of Suez area and Western Desert area. These are cases 1 to 5.

Case #1

This development well drilled in the Western Desert Concession in the onshore Abul-Gharadig area in 1991. Egyptian drilling company Rig No.8 (EDC-8) was used to drill this well to a total depth (TD) of 10,616 ft. While drilling 12.25-inch hole from 10,503 ft to 10,616 (TD) through the Limestone of Abu Roash formation with rotary bottom hole assembly and water base mud, lost 350 psi. When pulling out of hole, washout in Shock Sub was detected

Case #2

This development well drilled in the Gulf Of Suez Concession in the offshore Ramadan area in 1993. Pyramid drilling Rig (Bennevis) was used to drill this well to a total depth (TD) of 12,504 ft. While drilling 12.25-inch hole from 10,805 ft to 10,823 through the Shale and Limestone of Mheiherrat formation with rotary bottom hole assembly and water base mud, lost 300 psi. Pull out of hole, found vertical crack in the top joint of heavy weight drill pipe.

Case #3

This development well drilled in the Gulf Of Suez Concession in the offshore Hilal area in 1993. Sonat Offshore drilling Rig (Mercury) was used to drill this well to a total depth (TD) of 10,267 ft. While drilling 12.25-inch hole from 8,747 ft to 8,961 through the Limestone of Rudeis formation with rotary bottom hole assembly- and water base mud, lost 600 psi. Pull out of hole, found hole in the drill pipe near the surface.

Case #4

This development well drilled in the Gulf Of Suez Concession in the offshore October area in 1995. Sonat Offshore drilling Rig (Comet) was used to drill this well to a total depth (TD) of 16,080 ft. While drilling 12.25-inch hole from 10,035 ft to 10,239 through the Anhydrite of South Gharib formation with rotary bottom hole assembly and oil base mud, lost 300 psi. Pull out of hole, found the short drill collar cleaned smooth cut 0.3 ft from the boxfish neck area.

Case #5

This Exploratory well drilled in the Gulf Of Suez Concession in the offshore Badri area in 1995. Santa Fe International Rig No.124 was used to drill this well to a total depth (TD) of 12,480 ft. While drilling 12.25 inch hole from 12,417 ft to 12,480 through the Salt with Shale, Limestone and Sand Streaks of Ayun Musa formation with rotary bottom hole assembly and water base mud, had very hard back ream and very high torque, pump pressure dropped 1200 psi. Pull out of hole; found the drill string backed off at the short drill collar.

CASE # 6

Horbeek et.al (1995), in their work cited Shell Expros effort in 1991 to tackle drillstring failures in their operations. This they did by carrying out autopsies.

The autopsies confirmed what they had long been suspected: fatigue particularly BHA connection fatigue was the main cause of failure. Table1 briefly summarizes the autopsies carried out from 27/5/1992-1994.

Failures in the BHA accounted for 79%, whilst drillpipe accounted for 21%of the total failures for this period. BHA connection fatigue alone accounted for 58% of the BHA failures and was attributed to poor inspection criteria, poor drilling practices and lack of stress relief features. Other learning points from the autopsies were:

Majority of failures, 46%, occurred in the 12 1/4″ hole section.

Greater attention should be paid to rig torque gauge calibration;

MWD shock logs can warn of impending drillstring failure.

New drillstring components were not being specified to Shell specifications.

Use of stabbing guide will reduce failures associated with connection damage.

Avoid slip cutting drillpipe.

Improved pipe identification system needed.

Once a downhole pressure loss is established POOH immediately.

From interviews they carried out during the autopsy process it quickly became clear that a general lack of understanding of cause, effect and cost of fatigue failures existed.

The failures are summarized in the Table 1.

Table 1: DRILLSTRING FAILURE AUTOPSIES 1992-1994 (Horbeek et al, 1995)





Twist off at HDIS

BHA connection fatigue


Twist off at crossover

BHA connection fatigue


Twist off at MWD crossover

BHA connection fatigue


Twist off at stabilizer

Combination torsion/tension overload


Twist off at MWD

Tensile overload


Washout at crossover

BHA connection fatigue


Cracked mud saver sub

Overtorque of new connection


Twist off at MWD

BHA connection fatigue


Twist off at HWDP

Accidental over-torque by top drive


Twist off at jars

Tension/torsion overload


Twist off at bit sub

BHA connection fatigue


Washout at HWDP

Connection damage/bad handling


Twist off at shock sub

Connection fatigue


Washout at HWDP

Shoulder seal damage/bad handling


Washout at jars

BHA connection fatigue


Washout at crossover

BHA connection fatigue


Twist off at jar -intensifier

BHA connection fatigue


Twist off at jars

Insufficient hole cleaning


Twist off at mud motor

BHA connection fatigue


Twist off at hole opener

Poor hard banding application & inspection


Washout at drillpipe connection

Tool joint connection fatigue


4 washouts from split boxes DC’s and HWDP

Age &condition of equipment


Washout at drillpipe connection

Overtorqued connection





Twist off at drill collar

Torsion/tension overload when stuck


Twist off at jars

BHA connection failure


Washout in HDIS

Fatigue and vibration


Washout in drillpipe

Fatigue and vibration


Washout in drill collar

Fatigue and vibration


Washout in drill collar

Fatigue and vibration


Washout in HWDP

Age and condition


Washout in drillpipe

Slip cuts


3washout in drillpipe

Stabbing damage


Twist off NM drillpipe

Stress corrosion cracking


Twist off SHWDP

Brittle failure


Twist off in drillpipe

Drillpipe tube fatigue


Twist off NB stabilizer



Drillpipe parted

Tensile strength exceeded


Washout in jars


3. Errors Contributing to Drilling Failure

The error leading to a drilling or tripping failure may be caused by the abnormal state of either the formation being drilled, the wellbore itself or the equipment used in the drilling or tripping operation or caused by other external factors. It must be stated here that these errors may be attributed to either human, manufacturing or mechanical errors.

Human Error

Here are just a few generic definitions for human error:

An inappropriate or undesirable human decision or behavior that reduces, or has the potential for reducing, effectiveness, safety, or system performance

An action that led the task or system outside its acceptable limits

An action whose result was not desired by a set of rules or an external observer

To put things into context, there are three primary stages of cognition (planning, storage, and execution), which relate to the three error types (mistakes, slips, and lapses).

The three human error types are:

Mistakes: Mistakes occur when an intended outcome is not achieved even though there was adherence to the steps in the plan. This is usually a case in which the original plan was wrong, was followed, and resulted in an unintended outcome.

Lapses. Lapses are associated with our memories (e.g., lapses of memory, “senior moments,” etc.). These are generally not observable events.

Slips. Slips are generally externalized, observable actions that are not in accordance with a plan. These are often referred to as Freudian slips, in which a person may be thinking something but inadvertently says it so that someone else can hear it. Slips are most often associated with the execution phase of cognition.

Manufacturing Error

Variation caused by the manufacturing process that affects the size of the part. Manufacturing error is part of measurement value. From a design perspective the engineer or designer produces a piece of equipment or a system with intentions to function in a certain way. When it doesn’t function that way (it breaks, catches on fire, messes up its output or is befallen of some other mishap) they try to find the root cause.

Typically the cause can be identified as a:

Design deficiency – when the mechanical, electrical or other components of the design has a problem that caused the mishap

Manufacturing defect – when the material or assembly has an issue that causes it to fail

Environmental hazard – when an outside factor such as the weather causes the hazardous condition

Mechanical Error

Mechanical error is a deviation from correctness in computer-processed data, caused by equipment failure. This error can often be attributed to a range of different problems on both the manufacturer and the user side, as well as to the unpredictable forces of chance. When equipment malfunctions or falls short of its intended purpose, it may cause delays and lost funds. In rare cases, however, the results can be catastrophic. Serious injuries, loss of life and long-term negative repercussions can emerge from the failure of a seemingly innocuous industrial component. Such events may emphasize the importance of manufacturing standards and safety considerations, or highlight certain industrial concerns that influence the outcome of a project. These errors are related to drilling operations as shown in Table 2.

Table 2: Errors during drilling & tripping operations






Abnormal state of an Entity


Fractured &faulted formations

Natural fracture, geological fault, cavernous formation, permeable formation

Human /Mechanical Errors

Tectonically stressed formations

Stressed formation

Abnormal pore pressure

Under compaction of shales

Reactive formation

Dissolving limestone, reactive shale

Mobile formation

Drilling salt fomations

Unconsolidated formation

Poor sediment cementation

Naturally over pressured shale collapse

Under compaction of shales


Material accumulation in the wellbore

Cuttings accumulation,cavings accumulation

Human/Mechanical Errors

High hydrostatic wellbore pressure

High pore pressure

Low hydrostatic wellbore pressure

Low pore pressure

Crooked wellbore

Doglegs, keyseat


Hardware error

Age of equipment, design errors

Human Error, Mechanical & Mechanical Errors

Software error

Limited knowledge of software by drilling crew members, typo errors

Technical error

Lack of technical know-how by drilling personnel

4. General Classification of Drilling Failures

The classification of drilling failures in this paper is broadly categorized into three namely: equipment failure, wellbore failure and then formation failure. Table 3 lists these failures and their potential causes.

Table 3: Summary of drilling and tripping failures, causes &Errors

Failure Type


Potential Causes

Errors Leading to failure

Error type


Failure class

Failure sub class

Drillstem failure

Failure to acquire evaluation data, high torque &drag

Shocks &vibrations

Drillstem design

Manufacturing error

Drill pipe washouts

Loss of hydrostatic pressure, Low SPP

Deviated holes and doglegs, corrosive mud or gases,CO2& H2O in mud

Running drill pipe in compression, in-correct make up torque of tool joints

Human/operator error

Drillpipe corrosion

Contaminants in drilling fluids

O2 in drilling fluids

Human error

Drillpipe fatigue

Pipe leakage

High cyclic loads

Shallow doglegs in conjunction with high tension and slow penetration rates

H2S &CO2 in mud

Drillstring buckling

Compressive load in pipe exceeds a critical value

Cracked pipes

Sudden drop in pressure

Over torqued threads

Swelled or mushroomed box end shoulders,pin connection breaks

When enough torque is not applied at the table

When enough torque is not applied at the table

Human error

Pipe twist

Torque exceeding pipe’s ultimate shear strength

Pipe parting

Ultimate tensile strength exceeded


Metal to metal contact b/w the pin &box threads, stabbing

Human error

Failure Type


Potential Causes

Errors Leading to failure

Error type


Failure class

Failure sub class

Casing failure

Thermal failure

High temperature during steam injection

Sulphide stress corrosion cracking failure

Stress & corrosion by H2O &H2,high strength steels

Poor design of steels

Manufacturing error

External corrosion failure

Exposure of casing to wet air and/or saline fluids

Human error

Helical buckling failure

axial load and compressive forces exceeds the casing’s load carrying strength

Casing collapse fail

BHA hangs up when RIH, Calliper log shows collapsed casing

high external formation pressure

Centralizer failure

Inefficient mud displacement

Under-reamed wells, using an incorrect unit for the job

Using an incorrect unit for the job

Human error

Mud motor failure

Mud motor stalling

A sudden severe increase in SPP , ROP ceases

operating parameters exceeding the capability of the motor

Motor Failure during reaming

extended reaming operations

Motor Failure during tripping

key seats, ledges

Motor failure due to downhole temperatures

downhole temperatures increase beyond 225° F


Lost circulation

Induced fracture LC

Volume of mud in mud pit reduces

High mud density, ,increase in annular pressure

Failure Type


Potential Causes

Errors Leading to failure

Error type

Failure class

Failure sub class


Lost circulation contd

Natural fracture LC

Volume of mud in mud pit reduces

Natural fractures, high permeability formations, cracks,vugs, fissures

Incorrect estimation of annular pressures

Human error


High pore pressure kick

Geo-pressured formations

Operational related kick

Swab & Surge during tripping

Inefficient ROP

Formation related Low ROP

Cuttings accummulation

Operational related Low ROP

Low WOB,Bit balling


Wellbore wall related

Cementing failure

Stress cracking

Appears as “no cement” on bond logs

stress changes caused by casing expansion

Gas migration

un-cemented channel, low overbalance pressure before and during cementing

Cement shrinkage

Cement cracks

Exposure to air of low humidity

Micro annulus

Inter zonal Communications,

Well Leakage

Hydrostatic Pressure Reduction inside the Casing,

Cement Shrinkage

Borehole caving

Angular, Splintery cavings

Highly tensional/compressive stress

Failure Type


Potential Causes

Errors Leading to failure

Error type


Failure class

Failure sub class

Solids induced pack off


Sudden overpull

Cyclic overpull at tool joint intervals on trips.

High tensional side forces

Underguage hole

Pulled bit or stabilisers are undergauge.

Sudden set down weight.

Circulation is unrestricted.

Bit stuck

PDC bit run after a roller cone bit,

When drilling abrasive formations

Ledges and doglegs

Sudden erratic overpull or set down

Running an unsuitable BHA,changes in BHA


Missing hand tools / equipment.

Circulation unrestricted.

Sudden erratic torque.

Inability to make hole.

Poor housekeeping on the rig floor.

The hole cover not installed

Cement blocks

Cement fragments.

Erratic torque.

Hard cement becomes unstable around the casing shoe

Green cement

Increase in pump pressure.

Loss of string weight.

Sudden decrease in torque.

Green cement in mud returns, discoloration of mud.

drill string is inadvertently run into cement

Bit jamming

Poor hole cleaning ,fluid is too thin

Differential Sticking

Bit balling

Reduced ROP,Increased SPP, Overpull on tripping

Swellable soft clays

Failure Type


Potential Causes

Errors Leading to failure

Error type


Failure class

Failure sub class

Hole collapse

Little or no filter cake

Wellbore washouts

Excessive hole fill,cuttings

Swelling shale, hole erosion, insufficient mud weight

Reactive formations

Hydrated or mushy cavings. Shakers screens blind off, clay balls form. Increase in LGS, filter cake thickness, PV, YP, MBT

When using WBM in shales and clays in young formations.

When drilling with an incorrect mud specification

When using WBM in shales and clays in young formations.

When drilling with an incorrect mud specification

Unconsolidated formations

Increase in pump pressure.

Fill on bottom.

Overpull on connections.

Shakers blinding

Little natural cementation

Mobile formations

Overpull when moving up, takes weight when running in

Drilling salt formations

Fractured &faulted formations

Hole fill on connections.

Possible losses or gains

natural fracture system in the rock

Tectonically stressed formations

Pack-offs and bridges may occur.

Cavings at the shakers (splintery).

Increase torque and drag

highly stressed formations are drilled

Naturally over-pressured shale collapse

Cavings (splintery) at shakers.

Increased torque and drag.

Hole fill.

An increase in ROP.

Cuttings and cavings are not hydrated or mushy.

under-compaction, naturally removed overburden

5. Conclusions

This work has been a modest attempt at classifying downhole failures and errors during drilling and tripping operations. Though not exhaustive, the work has been able to group failures and errors into their natural groups and then elucidated their symptoms and their potential causes. Finally, it is concluded that:

Failures during tripping and drilling operations may be naturally classified into: wellbore related, equipment related and formation related failures

That errors leading to these failures may be broadly classified into errors located in the formation, errors located in the equipment or errors located in the formation or wellbore being drilled

That these errors may result from misinterpretation of test data, improper use of hardware or software, ineffective monitoring of events, under maintenance of equipment


BHA = Bottom Hole Assembly

BOP = Blowout Preventer

CO2 = Carbon (IV) Oxide

H2O = Water

H2S = Hydrogen Sulphide

HWDP = Heavy Weight Drill Pipe

LC = Lost Circulation

LGSC = Low Gravity Solids Content

MBT = Methylene Blue Test

MWD = Measurement While Drilling

O2 = Oxygen

PDC = Polycrystalline Diamond Compact Bit

POOH = Pull out of Hole

RIH = Run in Hole

ROP = Rate of Penetration

SPP = Stand Pipe Pressure

TD = Total Depth

WBM = Water Based Mud

WOB = Weight on Bit

YP = Yield Point


A work of this magnitude must have been culled from other writers’ work; hence I wish to express my sincere gratitude to all the authors whose works were consulted in the course of writing this paper.

This acknowledgement would essentially be incomplete if I fail to extend my deepest appreciation to the Almighty God-Jehovah, for without Him, there would have been no me.

To others whom I have not mentioned due to space or the lack of it, I remain your debtor in gratitude.


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