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overview of DRILLING OPERATION.pptx

  2. CONTENT • Definition of drilling • Types of wells drilling • Types of drilling rig & personnel • Rig components • Casing & cementing • Hole problems • Fishing operation. • Conclusion
  3. Drilling operation  Definition: application of science and technology to make a hole through the earth crust.  Equipment that drill is called the rig.  The unit of measurement is feet (meter)  Rig are mobile, they can be assembled (rig up) or rig down at the location  Different environment require different types of rig.
  4. Application of drilling • Drilling is the only means to ascertain the presence of oil in the formation. • Drilling provides a means of producing reservoir fluid. • Drilling provides a means of communicating with the reservoir or subsurface. • For water and mineral, construction e.t.c.
  5. Pre-spud meeting • The opco advertises to contractors to submit tenders • After rig/contractor is decided, meetings are held to discuss things like: mud program, bit program, casing program, various contractor needed to supply things like water, catering services, laundry, security e.t.c. • Well engineering is planned and data from offset well that can help the drilling company is provided to aid planning.
  6. Factors considered in Well planning. Selection of the location • After the prospect to be drilled has been identified, the exact location for drilling is chosen based on various factors like accessibility, level ground, ease of communication e.t.c. This is the first step in well drilling.
  7. Collect pressure data • Once the location has been identified, geological data of adjoining wells is collected and analyzed. • Special emphasis is laid on pressure data like expected formation pressure, fracture gradients and formation stability • In cases where no wells have been drilled previously these pressure are estimated from geophysical data collected while prospecting.
  8. Decide target depth • Before any drilling activity can begin, the target depth of the well to be drilled is decided. • This is because an oil well is usually drilled in three or less section known as phases if there is no hole problem. • This is to ensure optimum use of men and materials
  9. Decide hole geometry • An oil well is usually drilled in phases – each succeeding phase being smaller in diameter than the preceding phase. • The exact configuration of these phases i.e the hole diameter and the exact depth to which each phase will be drilled is decided. • The casing sizes are based on the hole sizes
  10. Decide casing setting depth • Once a particular diameter hole is drilled it is cased and cemented to prevent formation collapse. • The formation strength, the fracture gradient and the possible formation pressure is considered to determine when it is safe to set casing to prevent formation breakdown or influx of formation fluid to the well bore.
  11. Decide cement plan • Cementation is done to hold the casing in place. • This helps to hold the casing by forming bond between the formation wall and the casing. • To do this, the volume of slurry required to fill up the annulus has to be calculated, the type of cement to be used, the cement additives, the composition of the cement slurry must be well planed and documented.
  12. Mud program • Drilling fluids are required to drill an oil well. • Details about the type of mud, the mud properties and the various mud additives to be used for drilling the well are laid out in mud program.
  13. Design drilling program • Detailed specifications about the various drilling parameters at various depths like weight on bit (WOB), rotation per minute (RPM), pump pressure and flow rate of the drilling mud are taken into consideration in well plan. • In addition the type of drilling whether vertical or deviated is also specified in the drilling plan
  14. Design bit program • Specification of the various drilling bits to be used at various depths are mentioned here. • The type of bits to be used, the size of bit & nozzle sizes to be used and the various hydraulic parameters to be maintained are also discussed.
  15. Design formation evaluation program • The process of identification, location and appraisal of formations containing oil, by the well site geologist as the drilling continues is known as formation evaluation. • Formation evaluation is done with the help of logging techniques such as wire line logging, mud logging, coring & cutting analysis. • Details of the kinds of logging to be done, their frequency and depths to which electric logs will be run are mentioned in the formation
  16. Completion plan • A general idea about the method to be used to produce the well after completion of drilling is itemized in the completion plan. • Completion can be open hole, cased hole with single tubing or cased hole with multiple tubing’s and packers.
  17. Testing program • The kind of testing which will be done upon completion of drilling is specified in testing plan. • The type of testing to be done and at which depth, may be open hole testing or cased hole, it must be specified here.
  18. Select rig • The rig selection is primarily based upon the total depth to be drilled. • This is because the drilling capacity of a rig will depend upon its load carrying capacity as it will have to lift a heavier load to drill deeper. • Thus to drill a deeper hole a higher capacity rig is used
  19. Project drilling time • Based on the various factors, the total time required to drill the well and complete it are estimated. • In addition to the total time, a detailed break up of drilling days versus depth and the time required for various activities like casing e.t.c is also made. • This estimate is generally very accurate and drilling is usually completed according to plan
  20. Estimate costs. • An accurate estimate of the cost of drilling the well is made. • These costs falls into two broad categories, for consumables and for services required. • The cost of services required is usually dependent on the total number of days required to drill the well. • The amount of consumables will depend on the target depth of the well.
  21. Drilling contract • For effective drilling operation both in terms of cost, safety and timeliness, a detail contract is entered into between the operator and the drilling contractor. • This is aimed at drilling usable hole for the operator efficiently, safely and economically. • Different types of contract are available depending on the agreement between the operator and the drilling contractor
  22. Day rate • The rentals for rig and personnel charges are based on the number of days that the rig is on site irrespective of the number of meters/feet drilled per day. Footage/Meterage rate • The rental for rig is based on the number of meters/feet that the rig drills at a particular location, irrespective of the number of days on location.
  23. Turnkey • Here all the services required to drill and complete a well are to the drilling company. • That is the sum total of the cost required to drill the well to TD is paid the contractor irrespective of number of days spent on location and the number of feet/meter drilled per day. • This contract type is more popular as it increases the efficiency of drilling company.
  24. Types of oil wells drilled.  Exploration Well - A well drilled for the purpose of ascertaining or confirmation of oil accumulation.  Appraisal wells are drilled to determine the extent of the reservoir, so as to know volume of the oil reserve.  Development wells (Infill drilling or Well) – This is a well drilled to optimize oil production form a given reservoir or field.
  25.  Directional Well. This is the science of directing a wellbore along a predetermined trajectory to intersect a designated sub – surface target.  Horizontal Well drilling is the science directing a wellbore along a predetermine trajectory usually at an angle of 900 to the vertical to intersect a designated sub- surface target
  26. TYPES OF DRILLING RIGS It is always desired to drill in different geographic and climatic environment. However, the basic drilling operation remains essentially the same regardless of the types of rig used or the environment where the rig is used.  LAND LOCATION (ON SHORE)  land rig is used which consist of derrick or mast, substructure, mud pit, drillers cabin, prime movers, hoisting equipment, rotating equipment, circulating equipment and crew residential cabin.
  27. WATER DRILLING EQUIPMENT (MODU) • Inland water equipment – Inland water drilling includes swamp, dredged marsh, bay and lagoon locations where water is relatively shallow and protected from appreciable wave action. • Submersible (Inland Barge) drilling barge is used. Inland barges are designed for drilling in 10 – 20 ft of water. • Drilling in deeper water with submersible barge is accomplished by construction of a shell gravel fill for the barge to rest on.
  28. Jack – up rig  May be used from 50 ft to 350 ft of water.  The cost of such installation is enormous, but may be quite economical on a per well basis, since numerous wells may be directionally drilled from its deck.  They are very useful in development drilling and poorly adapted to exploratory work
  29. Jack – up rig
  30. Semi submersible Rig  These types of rig are often refers to as semi for short.  They are floating barge.  They use anchors on the sea floor to keep the rig stationary.  They can be used in water up to 7000ft (2100m).  Water is allowed to enter the barge so as to lower the rig to the sea level for drilling.
  31. Semi submersible Rig
  32. DRILLING SHIP (Floater)  This is a large self contained ship, which contains substructures, drawworks, rotary table, engines, mud pits, dry mud, chemicals etc, pipe racks, cementing equipment, fuel and water and crew quarters.  The ship can operate in any weather short of hurricane. It can be used for a deep offshore drilling and in remote areas.  It uses dynamic positioning to keep them on station (it uses computer controlled motors or thruster and sensors)
  35. Crews may consist of four, five, six, or more individual depending on the size and service rating of the rig itself. TOOLPUSHER The Tool pusher – sometimes called the rig superintendent or rig manager – is the man in charge of the rig and overall drilling operations. Driller - is directly in charge of drilling activities; he supervises other workers in the rig. He is next to the tool pusher.
  36. DRILLING RIG PERSONNEL  Derrick man or assistant driller – he is next to the driller, stays at the monkey board to control the pipe during tripping.  After tripping he monitors the mud.  Floor man or roughneck – they are in charge of making up and breaking out drill pipe while drilling or tripping.  Motorman, Mechanics, Crane operator and roustabout e.t.c.
  37. MAJOR COMPONENT OF DRILLING RIG  Power system (prime mover)  Hoisting (Drawworks, Blocks and drilling line, Derrick)  Rotary system (Swivel, (Kelly, Rotary Table) Top Drive system , Drill pipe, Drill collar & Bits)  Circulating system (Drilling fluid, Mud pumps, Mud tanks, The mud cycle (desilter, dessander, degasser))  Well Control system (Blowout Preventer, Accumulator, Diverter)
  38. PRIME MOVERS  Prime mover provide power for the rig.  It is usually an internal combustion engine. POWER  1 hp = 33,000ft – lb/min. The amount of power required for drilling varies with the job, but most rigs require from 1,000 to 3,000hp, usually provided by two or more engines.  Shallow or moderate – depth rigs need from 500 to 1,000hp for hoisting and circulating, heavy-duty rig may require 3,000 hp or more. The power requirements for rig auxiliaries such as lighting and air conditioning may be from 100 to 500 hp.  Power Transmission: A rig may have a mechanical drive or an electric drive (which may be an AC – DC drive or DC – DC drive).
  39. HOISTING SYSTEM Derrick or Mast  Derricks and portable masts provide the clearance and structural support necessary for raising and lowering drill pipe, casing, rod strings, etc., during drilling and servicing operations.  The derrick or mast must be designed to safely carry all loads that are likely to be used during the structure’s life.  Wind load and compressive load.  Wind load is given as: P = 0.00338 (V2)(Ch,)(Cs) P = pressure in. lb/ft2 V = wind velocity in knots Ch = height coefficient Cs = shape coefficient (1.25 for derrick)  Derrick load* = 1.5(Wh + Wc + Wt + 4FL)
  40. HOISTING SYSTEM DRAWWORKS  The drawworks, is a big heavy piece of machinery that consists of a revolving drum around which the wire rope, called the drilling line is spooled or reeved.  It also has a cat shaft, a kind of axle that crosses through the drawworks that has a revolving drum (called a cathead spool) on either end or two special catheads.  Several other shafts, clutches and chain and gear drives facilitate speed and direction changes. COMPONENTS PARTS  Drillers Console, brake lever, drum shaft, sprocket, gears and chains. It also contains drum brake and equalizers, cat shafts with cat heads.
  41. Functions of Drawworks  Transmit power from the prime mover to its hoisting drum to lift drill string, casing string or tubing string or to pull in excess of these string loads to free stuck pipe.  Transmit power to the catheads for breaking out and making up drill string, casing and tubing string.  Transmit power from the prime movers to the rotary drive sprocket to drive the rotary table.  The hoist contains brake systems which enable the driller to easily control a load of thousands of pound of drill pipe or casing. There may be at least 2 types of brake system.  1) The mechanical and (2) Hydraulic or hydrodynamic or electric
  42. The drawworks on the rig floor
  43. BLOCKS AND DRILLING LINE  The drilling line supports the entire drilling assembly by means of pulley – style devices and grasping implements, which are collectively called the overhead tools.  Included among these are the crown block, traveling block, the hook, drilling line and the elevators. CROWN BLOCK  The crown block is an assembly of sheaves mounted on beams at the top of the derrick. Most crown block has 4 to 7 (seven) sheaves which may be as large as 5 – feet in diameter mounted in line on a common centre pin.
  44. Crown block
  45. TRAVELING BLOCK • The traveling block moves between an up and a down position on the line. • It carries the hook that support drill string when drilling and the elevator bail that holds the elevator when tripping in or out of the hole. • Selecting a block for a certain rig or for a certain job depends on the block load capacity in tons
  46. HOOK  The hook is a large joining device suspended from the traveling block to grip the various piece of equipment needed in drilling and in making trips.  It rotate on bearing in its supporting housing and can be locked into many as twelve different position.  The hook has a safety latch for the swivel and locking arms or link ears at both sides for elevator – bail attachment.
  47. Hook schematics
  48. DRILLING LINE  Drilling lines are made of steel wires that are made into strands and the strands into rope in action similar to braiding.  The outer strands are laid spirally around a central core.  The wire rope generally ranges from 1 1/8 to 11/2 inches  The important things to watch out for to prevent wear to drilling line are: the tread diameter of the block sheaves, the critical points, groove radius, fleet angle and prevent sudden loading.
  49. ROTATING SYSTEM  The rotating equipment from top to bottom consists of the swivel, Top Drive System (TDS) (the Kelly), the rotary table, the drill stem and the bit.  The drill stem is the assembly of the swivel and the bit (i.e. drill pipe and drill collars, stabilizer e.t.c.) SWIVEL  Swivel in a device joining two parts so that one or both can pivot freely. It is attached to the traveling block by a large bail. It may rotate more than 200rpm. FUNCTION OF SWIVEL  It supports the weight of the drill stem  It allows the drill stem to rotate  It provides a pressure – Tight seal and passage way for the drilling mud to be pumped down the inside of the drill stem  Pronounced on a Kelly rig.
  50. KELLY  The Kelly is a square, hexagonal or triangular piece of pipe, usually about 40 ft long, which serves the purpose of transforming the rotating motion of the rotating table to the drill string FUNCTION OF KELLY  It serve as a passageway for drilling fluid on its way into the drill pipe .  It transmits the rotating movement to the drill pipe and bit.  It may serve as well control equipment through upper and lower Kelly cock.  The Kelly fits into a corresponding square or hexagonal opening in a device called a Kelly bushing or drive bushing. The Kelly bushing fits into a part of the rotary table called the master bushing or rotates and as the Kelly rotates, the drill string and bit rotate.
  51. THE ROTARY TABLE The function of rotary table is to: • To turn and rotate the Kelly (or any equipment attached to it) • To support the weight of the drill string or the casing during make up or break out • When drilling is going on, the rotating turns to the right or clockwise. • When the pipe is pulled from the well bore, the rotary table supports the string on slip during intervals when pipe is not being suspended from hook. • The rotary table rotates through a working range of 40 – 50 to 200 revolutions per minute (rpm). As the hole deepens the Kelly descends through the bushings, which are mounted in the table openings.
  52. Rotary table
  53. TOP DRIVE SYSTEM (TDS) • It provides rotation for the drill string instead of rotary table in Kelly rig. • It consists of gear box, one or two hydraulic motors, a pipe handler or grabber which includes torque arrestor. • It also has guide and torque track which terminates 7-9 feet above drill floor and elevator links including elevator. • The speed can be up to 600 rpm.
  54. DRILL STRING  The drill string is made up of the drill pipe and special heavy – walled pipe called drill collars. DRILL PIPE  Each length of drill pipe is about 30 ft long and is called a joint of pipe.  Drill pipe is attached to Kelly at the top (on a Kelly rig) but connects to the TDS and to the drill collar (HWDP) at the bottom. Function of Drill Pipe  Permit rotation  Allow fluid passage to the bit.  Provide necessary length of the well drilled Each end of each point is threaded.  The end of the joint with interior threads is known as the box, and the end of the joint into the exterior threads is called a pin.  The joints are welded to the body of the pipe.
  55. DRILL COLLAR  These are heavy walled pipe of small diameter steel tubes, like drill pipes, through which mud can be pumped. ROUNDED OR SQUARE (Drill collars)  Drill collars are about 30ft long and unlike the drill pipe that has tool joints welded on, they have the boxes and pins cut into them. FUNCTION OF DRILL COLLAR  To transfer rotary action to the bit  To allow passage for drilling mud  To put weight on the bit  To provide good stabilization for the bit to drill a straight hole.
  56. Rotating equipment.  Heavy wall drill pipe (HWDP) - consist of heavy wall tubes with an upset in the middle, called the center wear pad.  It is a transition between the drill collar (DC) and the drill pipe (DP) to make the crossover gradual.  Stabilizers. These are drill string components with blades that protrude from the body.  They are usually almost the same diameter as the bit and are located in a drill string at various points in the drill collars of the BHA, including just above the bit for directional/deviated hole and far up or in the middle for vertical hole drilling.
  57. SUBS  These are short sections of drill collars materials about two feet (2 ft) or longer, which provides crossovers between different diameters and types of threaded connection.  They are available in different connection configuration such as: box / box, pin / pin, pin / box and box / pin subs  Crossover subs  Float subs – a non – return valve run just above the bit (to prevent kick through drill string)  Dart sub – a landing sub for a drop in and pump – down back pressure valve.  Its function is to prevent kick through drill string like float sub.  Bent sub.
  58. BITS  The drilling bit is attached to the drill collar through the bit sub. This is the part of the rotary system that does the actual hole making.  THE DRAG e.g. FISH TAIL.  it does not have a moving pact.  It drills by shoveling action against the formation.  The water course opening is directed against its blade so that it can remove any shale that may be attached to the cutting surface.  It is used mainly to drill a soft formation, especially at a shallow depth. ROLLER CONE BIT  It has cone – shaped steel devices called cones that are free to turn as the bit rotates. Most bits have 3-cones, but some have 2 and some have 4 cones
  59. There are two types of Roller cone bits: • The steel tooth bit and (b) Tungsten – carbide inserted bit • All bits have passage drilled through them to permit drilling fluid to exist. • Jet nozzle opening. • They can be used for both soft, medium hard and hard formation depending on its design. • Roller bearing and journal bearing.
  60. Tungsten carbide insert
  61. DIAMOND BITS  Since diamonds are so hard, diamond bits are specially suited for drilling hard rock formations but may also be used effectively on soft formation.  A PCD (polycrystalline diamond bit) is also a type of drag bit.  A cylindrical Coring bit is also available with diamond studded.
  62. A PDC bit for soft formation
  63. CIRCULATING SYSTEM  For the rotary drilling system to function, fluid must be circulated downward through the drill stem, around the bit and upward in the annular space between the drill stem and the wall of the hole or the casing. (The circulation route). THE DRILLING MUD (FLUID)  The term “drilling fluid” includes air, gas, water and mud.  The term “mud” refers to a suspension of solids in water or oil or of solids and droplets of one of these liquids (emulsion) dispersed in the other. The mixture of clay (Solid bentonite) and water or oil is a mud. The drilling mud consist of phases  i. The liquid phase (water or oil) (may be fresh or salt water)  ii. The colloidal fraction (bentonite or Wyoming clay)  iii. The inert fraction (barite, weighting material etc)
  64. Functions Of Drilling Mud To transport bit cutting to the surface To clean the bottom of the hole (bit) To cool and lubricate the bit and drill stem To support the walls of the wellbore To prevent entry of formation fluids into the well i.e. control subsurface pressure. To suspend cutting when circulation is stopped.
  65. THE MUD PUMP  The function of the mud pump is to circulate the drilling fluid from the tank, through the drill stem, to the bit (where hydraulic power is expended for jetting), back up the annulus and back to the tank.  The mud pumps are either Duplex, double – acting pumps or triplex pump.  The term “duplex” refers to the number of pistons (2) and term “ double – acting” denotes that each side of piston does work. Pulsating discharge and high pressure.  Triplex has 3 pistons and single acting. High flow with smooth discharge.
  66. Schematic valve operations for double acting duplex pump . Piston Piston rod P2 Discharge P1 inlet or suction
  67. Pressure control system  Pressure control system includes Blowout Preventers (BOP), diverters, choke and kill line and accumulator unit.  Types of Blowout Preventer (BOP) (Annular Preventer and Ram Preventer)  Ram preventer has three types of rams (pipe ram, blind ram and shear ram). Functions of BOP  To close the wellbore and contain pressures  Allow wellbore fluids to be control vented.  Allow pumping into the well (when usual means are not available)  Allow tripping of drill pipe into and out of the hole
  68. CASING  Casing is a strong cylinder steel pipe used in an oil well to ensure a pressure tight connection from the surface to the oil or gas reservoir. FUNCTIONS OF CASING  To prevent cave-in or washout of the hole  To prevent contamination of fresh water sands by fluids from lower zone  To exclude water from the producing formations  To confine production to the well bore  To provide a means of controlling well pressure  To permit selective production of the pay zone  To furnish a permanent borehole of precisely known diameter
  69. TYPES OF CASING Drive Pipe  It is used to prevent shallow formation damage and collapse.  It also provide support and passageway for the conductor casing (Not always used especially in a consolidated formation).  Installed by driving the pipe to a point of refusal. Off shore consideration  Slip joint takes care of heaving up and down of the water body  Slip joint is connected to the marine riser at the bottom and the vessel body.  Flex Joints. A flex joint is installed between the lower end of the riser and the BOP stack.  This joint essentially acts as a pinned connection to minimize bending stresses in the riser as the drilling vessel is moved by wind, wave and current action.
  71. TYPES OF CASING CONDUCTOR CASING  Conductor pipe is used as a channel to raise the circulating fluid high enough to return to the pit.  It prevents erosion of the hole around the base of the rig.  It protects the subsequent casing strings from corrosion and may be used to support some of the wellhead load on location where ground support is not enough.  May be set 300ft or more. SURFACE CASING  Surface casing is set deep enough to protect the well from cave- in and washout of loose formations that are often encountered near the surface.  It provides a point of attachment for casing head and other fittings that will be left on the completed well.  Surface casing is usually set from 300ft to 4000ft.
  72. INTERMEDIATE CASING  The intermediate casing is to protect the hole (called production or salt casing).  It is used to seal off weak zones that may rupture with heavy mud usually needed for deepening a well. PRODUCTION CASING  This string of casing serves to isolate the producing reservoir from undesirable fluids in the producing formation and from other zones penetrated by the well bore.  It is the protective housing for the tubing and other equipment in a well. LINER STRING  A liner is an abbreviated string of casing used to case open hole below existing casing.  Production liners are sometimes suspended in the well without cementing.
  73. FORCES ON CASING • The major forces acting on casing are: • Tension: this is a downward pull of the weight of the casing string on the pipe body and on the coupling created at the top of the casing string Burst • Burst pressure occurs when the pipes internal pressure is greater than the external pressure Collapse • This is an unbalanced external pressure imposed on pipe.
  74. PRIMARY CEMENTING  Primary cementing is the process of mixing and placing cement slurry in the annular space between a string of casing and another casing or casing and the open hole.  The cement sets, bonding the pipe to the formation.  Cement slurry is the mixture of dry cement with water and necessary additives to condition the slurry to suit the hole characteristics.
  76. CEMENTING TOOLS  Cementing head, top plug, bottom plug, float collar, centralizer, Guide shoe, Scratchers, cement pump, cement mixer. Guide Shoe  A guide shoe is a round-nosed device installed on the first joint of casing with thread – locking compound.  It has opening in the bottom to allow drilling mud to enter the casing as it is lowered.  It is always used.  There are three types of guide shoes:  1) Plain guide shoe, 2) The combination of float and guide shoe, 3) Automatic fill-up guide shoe.
  77. Float Collar  This is similar to float shoe, it permits the casing to float into the hole.  The float collar may be installed on top of the first joint or on top of the second or third joint to go into the hole.  Most operators employ a float collar at a distance of one or more joints above the casing shoe in order to provide space inside the casing for contaminated cement.  Provide a stop point for bottom plug
  78.  Centralizers  These are steel metals used to keep the casing pipe away from the borehole wall.  They must be spaced close together enough to prevent the casing from contacting the formation wall even in a deviated hole. They are used to:  Ensure a reasonably uniform distribution of cement around the pipe  Obtain a complete seal between the casing and the formation. Cement Scratchers  These are mechanical wall cleaning devices attached to casing.  They abrade the hole when worked by reciprocating or rotating the casing string  Ensure good bonding between the casing and the formation.
  79. Bottom plug (Wiper plug)  The bottom plug is a cylindrical hollow molded rubber body.  It contains diaphragm at the top which rupture to allow cement slurry to flow through and also has wipers protruding from its side that removes mud.  It is the first plug to go into the casing from the cementing head.  It wipes mud off the inside of the casing and keeps the mud separated from the cement. Top Plug (Wiper plug).  The top plug is a solid cylindrical core with four wipers protruding from its sides.  The top plug follows the cement into the casing and wipes cement off the inside wall of the casing.  It also prevents the mixing together of cement and the displacement fluid behind the cement.  This plug is solid. When it seats or bumps on the bottom plug at the float collar, pump pressure increases since no fluid can get pass the top plug.
  80. Cement Head.  This house the wiper plugs and also the cementing line is attached to it.  The cement flows into the casing through the well head and also provides a channel through which the drilling mud in the annulus flows to the surface.
  81. A centralizer, scratchers, guide shoe and float collar.
  82. DRILLING PROBLEMS  A lot of hole problems are encountered and may be avoided or overcome by proper control of mud properties. These are:  Salt section hole enlargement  Heaving shale problems  Blowouts  Lost circulation  Formation damage  Key seating  Bit balling
  83. HOLE EROSION CAUSE  Hole erosion results from the hydraulic impact on formations with poor inter-grain cementation.  Generally it is caused by turbulent fluid flow in the annulus or excessive circulation in one place with the bit off bottom. Effect  The annular fluid velocity will be reduced in enlarged hole sections. If the drilling fluid is not highly pseudoplastic, the cuttings can concentrate in this area.  Eventually they may form a 'mud ring' or ball of agglomerated cuttings, which in severe cases can lead to hole pack-off and stuck pipe.  Good cementing practice requires turbulent flow to ensure proper drilling fluid removal.  Large washed out sections may cause the flow to become laminar and poor drilling fluid removal.
  84. PREVENTION  -Keep the flow regime laminar, where possible. Maintain highly pseudoplastic rheology  -Low shear rate viscosity along with the reduced flow rate requirements this makes an excellent fluid for unconsolidated formations.  -In silty formations examine the possibility of water sensitive clays causing further destabilization. If suspected, test with small treatments of inhibiting chemicals or polymers.
  85. SALT SECTION HOLE ENLARGEMENT  When salt domes are penetrated, they dissolved, eroded, thus causes an excessive hole enlargement, which in turn may be a source of future trouble and expense  In case of drill string failure, the enlarged hole makes fishing operation (attempts to retrieve the drill string) exceeding difficult  Larger mud volumes are required to fill the system hence treating cost are higher  Large cement volumes are required for casing operation if fill – up through the section is to be attained Solution.  The principal means of avoiding these problems is to prepare a salt saturated mud system prior to drilling the salt, thus avoiding the dissolving effect.
  86. HEAVING SHALE PROBLEMS  Some areas are characterized by shale sections containing bentonite or other hydrated clays, which continually absorb water, swell and slough into the hole.  This often occurs in the younger formations in the upper hole sections. It is the result of water imbibition by a smectitic shale.  They can cause pipe sticking, excessive solids build up in the mud and the hole bridging are typical resultant problems.  The annular diameter is reduced. The drill string, logging tools and casing may not easily pass through.  Increased annular friction pressure losses may raise the ECD above the fracture pressure for a lower zone. .  Sloughing shale can also be caused by brittle failure resulting from differential rock stress.
  87. Heaving shale. This can be due to tectonic activity or deviation of the well bore from vertical.
  88. Hole collapse by caving in The rock can fail in either tension or compression depending upon the orientation of the stresses to the wellbore wall
  89. SOLUTION TO HEAVING SHALE  Changing mud system to inhibitive type e.g. lime, gypsum which reduces tendency of the mud to hydrate water sensitive clays  Changing to oil emulsion mud or oil base mud  Increase circulation rate for rapid removal of particles  Maintaining a positive pressure overbalance against the formation pressure will help to hold the failed rock pieces in place
  90. DIFFRENTIAL PRESSURE STICKING  This is the force that holds pipe against the wall of the hole, due to the differential between formation pressure and hydrostatic pressure  Circulation is not hindered. For differential sticking to occur the following criteria are required:  Hydrostatic pressure must exceed formation pressure.  A zone of permeability must exist, over which a thick filter cake has been deposited.  There must be contact between the pipe and the filter cake
  91. Differential pressure sticking
  92. KEY- SEATING  A key seat results when drill pipe under tension wears a slot into the wall of the hole during drilling and tripping operations.  It often occurs when drilling a directional well.  The slot diameter is usually the same as the diameter of the drill pipe tool joints.  The drill collars are therefore most likely to get jammed in a key seat when pulling out of hole. Recognizing key-seating  Key seating is indicated by an increasing over pull, normally during tripping.  Here again the circulation is not impeded after the string has become stuck.
  93. Key seating The development of a key seat
  94. BLOWOUTS  A blowout occurs when formation pressure exceed the mud (hydrostatic) pressure which allows the formation fluid to flow out of the hole.  This is one of the most expensive and highly feared hazards of drilling Blowout may occur due to:  Swabbing i.e. pipe pulling (suction) out of the hole too rapid  When a zone of high pressure (gas zone) is encountered Solution.  The solution is to drill with proper mud density to overcome the encountered subsurface pressure
  95. LOST CIRCULATION Lost circulation is defined as the loss of substantial quantity of mud or whole mud to an encountered formation.  This is shown by complete or partial loss of returns (annular mud return)  Drop in annular mud volume may also cause kick Types of formation to which circulation may be lost are:  Coarsely permeable rocks e.g. gravels, reef, and irregular limestones  Faulted, jointed and fissured formations such as  Those with naturally occurring fractures  Those in which the fractures are induced or caused by column pressures  Cavernous and open fissured formations Prevention  Minimum overbalance of hydrostatic head, plus ECD.  Cure  Cut down the pump rate , reduce the overbalance , block the permeable channels by pumping LCM.
  96. FORMATION DAMAGE  Formation damage is caused by the invasion of foreign fluids and / or solids into the exposed section adjacent to the well bore.  Generally, the drilling mud is the main source of such contaminants.  Fluids used in stimulation treatment (acidizing, hydraulic fracturing etc) may also have some undesirable effects, which partially nullify their beneficial actions.  This damage when it occurs in the pay zone hinders or prevents the flow of oil or reservoir fluid into the well bore or production tubing. JAMMING A NEW BIT  An undergauge hole is a section of a hole with a smaller diameter than the diameter of the new bit used to drill ahead.  The most common cause of under-gauged holes is gauge wear on the previous bit run
  97. DRILLING LINE SERVICE  (Ton – miles of Drilling line) uses Lb-ft  The amount of wear a drilling line suffers is closely related to the amount of work it helps accomplish.  Ton – miles of service are accumulated on:  round trips ,  in drilling,  coring,  reaming,  fishing and  running casing – in fact, during any operation that entails putting any load on the drilling line.  Tables are available to assist in calculating drilling line service
  98. Fish and fishing operation • Fishing is the act of retrieving any lost or stuck tool from the well bore. Tools used includes: • Free point detector • String shot back off • Jet, chemical cutters • Wash over pipe • Overshot • Spears • Jars and accelerators • Impression block • Tapered tap e.t.c.
  99. DOWN HOLE MOTORS Turbine Motors  The activating drilling mud or freshwater is pumped at high velocity through the motor section, which, because of the vane angle of each rotor and stator (which is a stage), causes the rotor to rotate the shaft of the motor.  The kinetic energy of the flowing drilling mud is converted through these rotor and stator stages into mechanical rotational energy.  The rotors are forced to turn, causing the bit to rotate.  The major advantage of turbine is that they can operate at higher temperature than the PDMs.
  100. Positive Displacement Motors  A positive displacement motor (PDM) also drive the drill bit independent of the drill string rotation.  Soft, medium and hard rock formations can be drilled with a positive displacement motor using nearly any type of rock bit.  Rather moderate flow rates and pressures are required to operate the positive displacement motor.  Thus, most surface pump systems can be used to operate these downhole motors.  Rotary speed of the positive displacement motor is directly proportional to flow rate.  Torque is directly proportional to pressure. Thus, normal surface instruments can be used to monitor the operation of the motor downhole.  High torques and low speeds are obtainable with certain positive displacement motor designs, particularly, the higher lobe profiles.
  101. DIRECTIONAL DRILLING  The common method of drilling a directional well is to use a downhole motor with a bent sub.  The bent sub is directly placed above the motor.  It is the bent sub which makes the deflection assembly, its lower thread is inclined 10 to 30 from the axis of sub body.  Downhole and the bent sub assembly can be used for kicking off wells, for runs correction and for side tracking.  Whipstocks (standard removable & permanent casing whipstock) can be used to kick off well by applying weight to set it and shear its pin.  But may lead to severe dogleg and lots of rig time in tripping and opening the rat hole.
  102. DIRECTIONAL DRILLING • Jetting (or badgering) is a technique used to deviate wellbore in soft formation. • A special jet bit is used and the formation must be soft enough to erode by the action of drilling fluid. • Also adequate rig hydraulic horsepower must be available to erode the formation.
  103. conclusion We have seen different types of:  Rigs  Drilling techniques (onshore & offshore)  Vertical and directional well  Hole problems and possible solutions  Fishing operations Let us complete the well.