Errors And Failures During Oil Well Drilling Engineering Essay
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.
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)
DATE
FAILURE
ROOT CAUSE
27/05/92
Twist off at HDIS
BHA connection fatigue
23/07/92
Twist off at crossover
BHA connection fatigue
24/07/92
Twist off at MWD crossover
BHA connection fatigue
02/11/92
Twist off at stabilizer
Combination torsion/tension overload
05/11/92
Twist off at MWD
Tensile overload
21/11/92
Washout at crossover
BHA connection fatigue
22/11/92
Cracked mud saver sub
Overtorque of new connection
26/11/92
Twist off at MWD
BHA connection fatigue
08/12/92
Twist off at HWDP
Accidental over-torque by top drive
02/01/93
Twist off at jars
Tension/torsion overload
19/02/93
Twist off at bit sub
BHA connection fatigue
24/02/93
Washout at HWDP
Connection damage/bad handling
12/03/93
Twist off at shock sub
Connection fatigue
19/03/93
Washout at HWDP
Shoulder seal damage/bad handling
21/03/93
Washout at jars
BHA connection fatigue
04/04/93
Washout at crossover
BHA connection fatigue
10/08/93
Twist off at jar -intensifier
BHA connection fatigue
20/08/93
Twist off at jars
Insufficient hole cleaning
05/10/93
Twist off at mud motor
BHA connection fatigue
23/10/93
Twist off at hole opener
Poor hard banding application & inspection
08/11/93
Washout at drillpipe connection
Tool joint connection fatigue
24/11/93
4 washouts from split boxes DC’s and HWDP
Age &condition of equipment
24/11/93
Washout at drillpipe connection
Overtorqued connection
DATE
FAILURE
ROOT CAUSE
02/12/93
Twist off at drill collar
Torsion/tension overload when stuck
02/12/93
Twist off at jars
BHA connection failure
03/01/94
Washout in HDIS
Fatigue and vibration
05/01/94
Washout in drillpipe
Fatigue and vibration
09/01/94
Washout in drill collar
Fatigue and vibration
11/01/94
Washout in drill collar
Fatigue and vibration
14/02/94
Washout in HWDP
Age and condition
11/03/94
Washout in drillpipe
Slip cuts
09/05/94
3washout in drillpipe
Stabbing damage
28/06/94
Twist off NM drillpipe
Stress corrosion cracking
23/08/94
Twist off SHWDP
Brittle failure
23/08/94
Twist off in drillpipe
Drillpipe tube fatigue
07/11/94
Twist off NB stabilizer
Fatique/vibration
04/12/94
Drillpipe parted
Tensile strength exceeded
04/12/94
Washout in jars
Fatigue
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
ERROR
WHERE ERROR IS LOCATED
SOURCE OF ERROR
POSSIBLE CAUSE OF ERROR
CONTRIBUTING FACTORS LEADING TO FAILURE
Abnormal state of an Entity
Formation
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
Wellbore
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
Equipment
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
Observations
Potential Causes
Errors Leading to failure
Error type
EQUIPMENT FAILURE
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
Galling
Metal to metal contact b/w the pin &box threads, stabbing
Human error
Failure Type
Observations
Potential Causes
Errors Leading to failure
Error type
EQUIPMENT FAILURE CONTD.
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
FORMATION RELATED FAILURE
Lost circulation
Induced fracture LC
Volume of mud in mud pit reduces
High mud density, ,increase in annular pressure
Failure Type
Observations
Potential Causes
Errors Leading to failure
Error type
Failure class
Failure sub class
FORMATION RELATED FAILURE CONTD
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
Kicks
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 FAILURE
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
Observations
Potential Causes
Errors Leading to failure
Error type
WELBORE FAILURE CONTD.
Failure class
Failure sub class
Solids induced pack off
Keyseating
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
Junk
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
Observations
Potential Causes
Errors Leading to failure
Error type
WELBORE FAILURE CONTD.
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
Nomenclature
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
Acknowledgement
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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