Errors And Failures During Oil Well Drilling Engineering Essay

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 earths 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 todays 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 supervisors failure to provide guidance (Shappell Wiegman, 2001.). Error as the failure itself. For example: The operators 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 DCs 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 doesnt 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 pipes 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 casings 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 225Â ° 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.