stuck Pipe

1. Stuck PipeCauses, Prevention & Treatment

2. Objectives • To provide an understanding of the sticking causes contained under the category solids. • How they are identified at the early stages. • Provide guidance on the best methods to overcome the mechanism. • Establish the relationship that certain job positions have with stuck pipe prevention.

3. Stuck Pipe A stuck pipe refers to a situation in oil and gas drilling where the drill String cannot rotate, move up, or down. As we all know, to drill a well, you will need a string to transmit the produced torsion force & load from the surface to the bit. The directional driller and driller direct the well by several parameters: the torque, pulling, and rotating of the drill string. This can result in significant disruptions to drilling operations and can be a costly and time-consuming problem to resolve. A pipe sticking mechanism is something that is happening in the hole, which causes the force required to pull the string to be greater than the weight plus the expected friction. In addition, the supporting force while running in will be less than the weight minus the expected friction. Sticking mechanisms can act while raising the string, or while lowering it, or both. A string of tubulars plus the incorporated equipment is subject to the normal laws of physics, including friction. When a drill string is pulled, the force required is the weight (in fluid) plus the friction. When running into the hole, the supporting force equals the weight minus the friction. This is a fact of life and cannot be avoided. It does not mean that frictional forces cannot be controlled to some extent by using a drilling fluid with more or less lubricating properties, but the statement is still true.

4. Stuck Pipe Problems • Stuck pipe can be caused by mechanical or differential pressure effects • Mechanical effects include: • wellbore instability • unconsolidated formations • mobile formations • fractured/faulted formations • geopressured formations • reactive formations • poor hole cleaning • key seating • undergauge hole • junk in hole • green cement • cement blocks • collapsed casing

5. Stuck Pipe Stuck pipe can be caused by differential pressure or mechanical effects Mechanical effects include: • wellbore instability • unconsolidated formations • mobile formations • fractured/faulted formations • geopressured formations • reactive formations • poor hole cleaning • key seating • undergauge hole • junk in hole • green cement • cement blocks • collapsed casing

6. Troublesome Formations Mobile Like toothpaste, can flow into the wellbore. This can cause geometry related stuck pipe. Soft clays and squeezing salts. Reactive Reacts with water and swells. Gumbo. Soft clay and shale. Pressured Shale which contains geopressured fluids. Commonly appear as splintery shale and sharp caving over shakers. Depleted Sands which have been produced to the point that the pressure is depleted. Overbalance hydrostatic can cause differential sticking Abrasive Sharp sands can wear bit and stabilizers down and cause the hole to become undergauged. Leads to tight hole conditions. Fractured Limestone, dolomites, and other brittle formations may be naturally fractured. Large blocks may fall into the hole.

7. Categories Of Stuck Pipes • There are 3 categories of stuck pipes as follows: • Pack off and bridging: Pack off and bridging are occurred when there is something in the wellbore as formation cutting, junk, etc accumulating around drilling string/BHA and that stuff blocks the annulus between drill string and the wellbore. You should remember that either big or small debris can stick the pipe. • Differential sticking: Differential sticking happens when drill string is pushed against permeable formations by differential pressure between hydrostatic and formation pressure. The frictional force between drillstring and formation is so high that you will not be able to move the pipe. The differential sticking tends to easily happen when drilling through depleted reservoir is conducted. Moreover, this stuck mechanism almost always happens when the drill string has been stopped moving for a long time. • Wellbore geometry: Wellbore geometry stuck pipe mechanism occurs when the shape of the well and the bottom hole assembly (BHA) don’t match each other. Therefore, the drill string is not able to pass through that section.

8. Hole pack off and bridges • PACK OFF: • The actual mechanism works through a combination of contact between the string and a build up of material in the annulus and the effect of compaction caused by the subsequent restriction of flow. • BRIDGE • Bridging often refers to the hole being blocked by material when the string is out of the hole. Hole pack off/Bridges, causes • Hole pack off • Settled cuttings (poor hole cleaning, excessive ROP) • Settled cavings (Reactive, Geopressured shales, Overburden stress, Tectonic stress, Unconsolidated formation, Fractured or Faulted formation, cement related). • Hole bridging • Settled cavings (Overburden, Tectonic stress). • Unconsolidated formations • Fractured formations

9. Solids induced Pack-off • The following formation types could lead to the occurrence of stuck pipe: • Unconsolidated Formations (unconsolidated, mobile, fractured, faulted…) • Reactive Formations • Mechanically Stressed Shale

10. Unconsolidated Formations • Causes: • Poorly cemented sand or pea gravel falls into the wellbore and pack off the drill string. • Usually occurs at shallow depths. • Little or no filter cake and insufficient hydrostatic support. • Warning signs: • Rough drilling • Seepage losses • Fill on trips • Increase in drag & torque • Pump pressure fluctuations. • Shakers and desander overload. • Cavings back at shakers

11. Identify sand or porous formations Maintain a high gel mud in the slug tank Monitor pump pressure and drill cuttings Use high viscosity sweeps (often) Spot gel pill prior to POOH Control fluid loss if applicable Case off known problem zones Control ROP Keep flow rate to minimum Ensure low permeability filter cake Pick off bottom and circulate Unconsolidated Formations • Preventive actions:

12. Reactive shales (Gumbo) Causes: Water sensitive shales drilled with inadequate mud inhibition Shales absorb water and swell into wellbore Reaction is time dependant. Mobile Formations • Warning signs: • Funnel viscosity, PV, YP increases • Torque and Drags increases • Clay balls, softy mushy cuttings at shakers • Overpull and swabbing • BHA balling (mud rings)

13. Preventive actions: Maintain sufficient mud weight or use inhibited mud (high salt, polymers, OBM). Use eccentric/bi-centre PDC bits Ream and wipe frequently Keep pipe moving in Open Hole Spot freshwater pills Pump lubricant/base oil Mobile formations

14. Drill hole section and case off quickly (Keep an inhibitive mud in specification) (Monitor the methylene blue test(MBT) closely) Minimise the BHA length Wipe the hole regularly Utilise dump anddilute procedures as required when using WBM. Consider using OBM Reactive Formations

15. Causes: Naturally occurring fractures Pieces of formation fall into the wellbore and jam the Drill string Warning signs: Prognosed limestone or fractured shales and/or faults. Mud logger sample interpretation. Large cavings at shaker. Hole fill on connection and trips. Erratic and high torque and drag Pump pressure fluctuations Fractured or Faulted Formations

16. Preventive actions: Control drilling. Circulate hole clean before drilling ahead. Minimise mud seepage losses. Check the hole condition constantly, looking thru cuttings shape changes, erratic torque and pressure. Wash and ream constantly Restrict tripping speed when BHA is near suspected zone Limit circulating and surge pressures Minimise drill string vibration Ream fractured zones cautiously Fractured or Faulted Formations

17. Which types of formations can we drill through? Mechanically Stressed Shale • Shale Formations • Geo-pressured • Hydro-pressured • Overburden Stress v Hole angle • Tectonic Stress • Hole Enlargement • Hole cleaning problems

18. Causes: Drilling pressured shales with insufficient mud weight. Shales fracture and cave into the wellbore. Warning signs: Mud loggers trend indicate increasing pore pressure. ROP increasing when drilled. Torque increase and drag on connections. Hole fill, splintery shale over shakers. Gas trends increase. Pressured shales • Preventive actions: - Increase mud weight as pore pressure increases. - Minimise surge/swab pressures. - Minimise exposure time.

19. Causes: Naturally occurring lateral forces in the formations. Stressed shales fracture and fall into the wellbore causing an elliptical shaped bore Warning signs: Mountainous locations. Active tectonic plate movements. Salt domes. High and erratic torque and drags. Large shale cavings. Mechanically Stressed Shale

20. Preventive actions: Keep hole clean Circulate high density sweeps. Monitor pore pressure (warning signs will be increase in gas, signs of cavings). Increase mud weight as soon as possible Avoid mud weight reduction (careful when diluting/bleeding into active system, dump/dilute process). Minimise open hole exposure time Minimise Swab/surge pressures Mechanically Stressed Shale

21. Initial action: Attempt to regain full circulation. If total pack off, leave 500 psi pressure on stand pipe and monitor bleed off Have string at free hanging weight and work maximum torque to stuck point and then release. Repeat torque/release until circulation is regained or pipe is free. Secondary action: Work torque into string and jar with maximum loads. Continue initial and secondary actions until pipe is free. When pipe is free, circulate hole clean and continue to clean the hole. Freeing Pack Offs/Bridges

22. Causes: Poor hole cleaning results in overloading the annulus with cuttings, potentially sticking the drillstring. Improper Flow parameters used Hole Cleaning • Bore hole stability is dependant on: • Porosity • Permeability • Pore Pressure • Rock stress • Balance (mud Weight)

23. Review of Definitions: Porosity is the ratio of the fluid to the total rock volume. Permeability is the ability of fluid to travel through rock/formation. Hole Cleaning • Pore pressure: The pressure of fluids within the pores of the reservoir (also called reservoir pressure or formation pressure) • Rock stress: Vertical and horizontal forces acting on formations • Overburden/tectonic forces

24. Cuttings and cutting beds, effect of mud density Hole cleaning is much less problematic in high density mud due to increase of buoyancy of cuttings A 1 ppg increase in mud weight has more benefit on hole cleaning than any changes in mud rheology. Above 15 ppg, it is very unusual to have hole cleaning problems. Hole Cleaning

25. Turbulent flow: High velocities can erode beds and transport cuttings Turbulent flow is effective in high angle, small diameter intervals in competent formations Laminar flow: Lower flow rates, rheology is critical Laminar flow is preferred if formation is sensitive to erosion Hole cleaning capacities in laminar flow is improved by low shear rate viscosity and gel strengths. Hole Cleaning

26. Hole Cleaning, effective length concept Divide well into sections per hole angle Multiply actual length by section factor (table) to obtain effective length Volume required= (total effective length* bottom up volume)/ measured depth

27. Hole Cleaning, effective length concept

28. Low Angle Holes < 35° High Angle Holes > 35° Causes of Settled Cuttings • Excessive ROP • Insufficient Annular Velocity • Poor Mud Parameters • YP, Gels • Insufficient Circulating Time • High Hole Angle • 55 Most Difficult

29. Hole Cleaning vs. Flow rate (> 35º) Hole cleaning rate at 120 rpm rotation Point of diminishing benefit CUTTINGS FLOW Hole cleaning rate with no rotation Minimum threshold flow rate needed for hole cleaning FLOW RATE The illustration above points out the benefit of rotation in conjunction with circulation when attempting to clean a deviated hole. Rotation should always be used in conjunction with a sweep – especially in deviated holes.

30. Hole Cleaning Guidelines (> 35º) • Maintain sufficient MW for hole stability • Circulate at maximum rate for hole size • Limit ROP to the max. recommended value • Back ream each stand drilled with motor • Rotate at high RPM (120+) • Continue back reaming if hole conditions dictate • Consider wiper trip after long hole section drilled w/motor • Consider low viscosity/ high viscosity tandem sweeps

31. Ensure penetration rate is controlled to allow optimum hole cleaning (booster line f/ floaters). Do NOT limit circulation to bottom up, ensure shakers are clean. Maintain checks on cutting volume changes at shakers. Maintain correct mud specifications. Maintain programmed Annular Velocities. Recognize the significance of increasing overpulls. Always reciprocate and rotate while circulating. Select the optimum (recommended) viscous sweeps (directional or straight hole). Hole Cleaning guidelines VERTICAL Section

32. Deviated Wells: Increase flow rate with hole angle 30oinclination requires 20% higher velocity 50o to 60o requires twice the AV of a vertical well Use lower viscosity mud to induce turbulence Consider cleaning cutting beds < 350 with: high viscosity sweeps Consider cleaning cuttings beds > 350 with: low viscosity sweeps followed by high viscosity (or weighted) sweeps Rotation and reciprocation are critical > 450 Hole Cleaning guidelines HIGH Angles Section

33. Disturb cutting beds mechanically with frequent wiper trips, rotation and back reaming. Control ROP to avoid overloading the lowside with drill cuttings. Minimize low flow rate circulating. High annular velocity and pipe rotation cleans the hole. If the hole is tight on connections, circulate long enough to move cutting beds to the vertical section of the hole. SOMETIMES YOU HAVE TO SLOW DOWN TO SPEED UP! Maintain a “zero gel”(3 rpm) value to approach the hole size in inches. Maintain annular velocity around Drill pipe above 180 ft/min (studies). Pump Low vis sweeps to stir cutting beds in high angle sections followed by Hi vis sweeps to transport cuttings in the near vertical section. Hole Cleaning guidelines HIGH Angles Section

34. Stuck pipe mechanisms Mechanical and Well bore Geometry

35. Causes: Excessive bit and stabilizer wear due to abrasive formations Warning signs: Sudden set down weight when TIH. Undergauge bits/stabilizers tripped out of hole. Reduction in ROP, increase in torque (from stabilizers). Contributing factor: RIH PDC after roller cone bits. After coring. Slight restriction of circulation (while washing down to bottom). Under gauge Hole

36. Preventive actions: DO NOT JAR DOWN! Always gauge bits etc Trip cautiously Ream suspected under gauge sections Run gauge protected bits and stabilizers Consider using a roller reamer Jar upwards to free if stuck (with maximum trip load) Consider applying torque at last resort. Undergauge Hole

37. Causes: Hard/Soft interbedded formations. Frequent or sudden changes in hole angle or direction. Wellbore Geometry • Warning signs: • Prognosed hard/soft interbedded formations. • Frequent angle/direction changes. • Drilling/sliding with downhole motors. • Erratic torque and drag on connections. • Circulation not restricted. • Problems are located at fixed depths. • Overpull at regular intervals while POOH.

38. Preventive actions: Minimise direction changes in wellbore. Minimise BHA changes and configuration. Consider reaming trips (ream with caution). Slow trip speed before BHA enters suspected zone. Avoid prolonged circulation across soft formations. Frequent surveys. Clear instructions with first actions (Max overpull). Wellbore Geometry

39. Causes: Grooves in the borehole wall cut by rotating drill pipe. Abrupt changes in angle or direction in medium or soft formation High string tension and pipe rotation wears a slot into the formation -Can also occur at the casing shoe if a groove is worn into the casing. Key Seating

40. Warning signs: High angle doglegs in upper hole section Long drilling hours w/o wiper trip through doglegs Cyclic Overpull at tool joint intervals when POOH. Free string movement below keyseat depth is possible. Preventive actions: Minimize dogleg severity to 3 Deg/100’ Limit Overpull through suspected zones. Plan reaming or wiper trip if dogleg present. Run string reamer if suspected. Key Seating

41. Causes: Formation forces exceed casing collapse pressure Casing is too light duty. Casing is old. Casing is landed with too much tension or compaction reducing its collapse rating. Casing shoe is poorly cemented and damaged during trips. Casing joints come undone due to poor make up and/or poor cement Collapsed Casing or Tubing

42. Warning signs: Verify casing wear (ditch magnets). Review caliper logs (when applicable) Increase in drag when tripping in casing. Preventive actions: Use good cementing practices (up to surface or as high as possible). Review well programs for re entry. Use corrosion inhibitors in drilling fluids. Restricted tripping speed first time thru casing. Collapsed Casing or Tubing

43. Causes: Parts of downhole equipment More common inside casing Equipment poorly maintained Poor drilling practices (hole left open, no pipe wiper…) Green crews Warning signs: Metal shavings back at shakers Sudden and/or erratic torque Inability to drill, ROP restricted Junk

44. Preventive actions: Train crews Inspect all tools Keep hole covered Drill pipe wipers Good housekeeping standards. Junk

45. Causes: Cement-related sticking occurs when blocks of cement fall into the wellbore from casing rat holes or cement plugs, jamming the drillstring. It also occurs when the drillstring becomes planted in soft or "green" cement that flash sets when pressure is applied. Warning signs: Increase in Pump pressure leading to inability to circulate when planting string into “ratty” cement. Sudden change in torque Possible visual of cement back at surface (mud discoloration), cement blocks back at shakers. Cement Blocks and Green Cement

46. Preventive actions: Know the Estimated TOC, wash down the last 2 stands. Establish light parameters to start drilling cement. Work string back in casing before Drilling ahead Bleed off any trapped pump pressure (green cement) Jar up with maximum trip load. Cement Blocks and Green Cement

47. Differential sticking

48. A permeable formation is exposed to the wellbore fluid The pressure of the wellbore fluid exceeds the pressure of the formation fluid The drillstring, BHA component, casing or logging tool contacts the permeable formation Mud pressure holds the object against the formation Filter cake builds around the stuck object, holding it firmly in place Origins of Differential Sticking Differential sticking occurs when the drill string is held against the well bore by a force. This force is created by the imbalance of the hydrostatic pressure in the well bore and the pore pressure of a permeable formation. When the hydrostatic pressure is greater than the pore pressure the difference is called the overbalance. The resultant force of the overbalance acting on an area of drill string is the force that sticks the string.

49. Causes: Permeable formations Thick filter cake High overbalance between Hydrostatic pressure and Formation pressure. Differential Sticking • Warning signs: • Overpull on connections and after surveys. • No string movement but full unrestricted circulation • Seepage losses. • High overbalance • Mud logger to inform of permeable formation.

50. Preventive actions: Plan ahead Contingency planning Select BHA’s with minimum wall contact Minimise mud weight (if practical). Have pit space available for mixing and treating Keep pipe moving and circulate whenever possible Continuously monitor pore pressure Minimize pipe static time (brainstorm with Driller for operation at hand). Mud management is a key (plug permeable zones, limit penetration and allow sealing time). Hand over information (monitor, record and handover key hole info's). Be prepared, have spotting agents on board, know how to quickly apply freeing forces to stuck point. Design BHA’s to counter differential. Differential Sticking- Avoidance Filtercake Overbalancepressure Mud Drillstring