MUD LOSS OR LOST CIRCULATION OR LOST RETURN

1Drilling Fluid-Complication Liquidation

2STUCK PIPEIn drilling operations the drill pipe is considered stuck when it cannot be raised , lowered or rotated Hole Pack offHole geometryStuck pipe TypesDifferential stuck upMechanical stuck up3Mechanical stuck caused by a physical obstruction or restriction.usually occurs when the drill string is moving. indicated by obstructed circulation. Occasionally , however, a limited amount of up/down mobility or rotary freedom is evident , even when the pipe is mechanically stuck.Differential Stuck1 caused by differential pressure forces from an overbalanced mud column acting on the drill string against a filter cake depositedon a permeable formation.2. usually occurs while pipe is stationary, such as when connections are being made or when a survey is being taken.3. indicated by full circulation and no up/down mobility or rotary freedom other than pipe stretch and torque.4Mechanical sticking A. HOLE PACKOFF AND BRIDGESSettled cuttings. encountered often in overgauge sections, where annular velocities are reduced. Causes Excessive ROP for a given circulation rate. Inadequate annular hydraulics. Failure to suspend and carry cuttings to the surface -inadequate mud rheology. Highly deviated well paths. High angle wells are more difficult to clean, Formation sloughing and packing off around the drillstring. Not circulating enough to clean the hole before tripping out or making connections.

5major warning signs and indications of cuttings settling are: Fill on bottom after connections and tripping. Few cuttings returning at the shakers relative to the drill rate and hole size. Increase in torque, drag and pump pressure. Over pull on connections and while tripping out. Increase in Low-Gravity Solids (LGS) and possible mud weight and/orviscosity increases.6Preventive measures Maintain proper mud rheology in accordance with hole size, ROP and hole inclination. In near-vertical wells, sweep the hole with high-viscosity mud. In highly deviated wells, sweep with low-viscosity/high-viscosity pills. Always circulate until the sweeps have returned to the surface and the shakers are clean. Use optimized hydraulics compatible with the respective hole size, inclination and ROP. Higher circulation rates always provide improved hole cleaning. Control drilling in high ROP or marginal hole-cleaning situations. Use aggressive drill string rotation for improved hole cleaning. Make a wiper trip after all long motor runs. Use drill string motion (rotate & reciprocate), while circulating at max rate to disturb cuttings beds & reincorporate them into flow stream.7B.Shale instability. Unstable shales can cause packing off and sticking whenthey fall into the wellbore. They may be classified as follows:C.Reactive shales. These are water sensitive shales drilled with insufficientinhibition. Shales absorb water, become stressed and spall into theWellbore.The main indication that reactive shale has been drilled are increases in the funnel viscosity, yield point, gel strengths, Methylene Blue Test (MBT) and, possibly, the mud weight. This will be reflected by increases in torque,drag and pump pressure.8D. Pressured shales. These shales are pressured and mechanically stressedby several different factors - the weight of overburden, in-situstresses, angle of bedding planes and tectonic stresses. When drilled with insufficient mud weight, these shales will slough into the well boreE. Fractured and faulted formations. These are fragile formations whichare mechanically incompetent. They are particularly unstable when thebedding planes dip at high angles9Large quantities of splintery or blocky shale will be encountered whenpressured shales are drilled underbalanced or when fractured formationsslough. Pump pressure, torque and drag will increase when the hole becomesoverloaded with caving shale.Control of formation instability should start during the planning phase of the well. An inhibited mud system, matched to the formation with the proper mud weight, will minimize shale instability. To balance mechanical stresses, highly deviated wells require higher mud weights than vertical wells.Although the first priority of a casing design is to ensure that the well can be drilled safely, casing points may have to be adjusted so that troublesome formations can be cased off.10Needless to say, suitable mud properties must be maintained to ensure goodhole cleaning. If formation caving is detected, respond immediately:1. Stop drilling.2. Sweep the hole with viscous mud.3. Increase the viscosity to improve the carrying capacity.4. Increase the mud weight, when applicable.5. Implement drilling practices to improve cuttings transport and to reduce the possibility of pipe sticking.11F. Unconsolidated formations. These formations cant be supported by hydrostatic overbalance alone.Problems also occur if insufficient filter cake is deposited on loose, unconsolidated sand to prevent it from flowing into the wellbore and packing off the string. Usually encountered at shallow depths or drilling production zones. common indicators are Torque, drag & fill on connections.To drill these formations, the mud should provide a good-quality filter cake to help consolidate the formation so that hydrostatic pressure can push against & stabilize formation. Treatments with seepage-loss material will help seal these formations avoid excessive flow rates & avoid any unnecessary reaming or circulating with BHA opposite unconsolidated formations to minimize erosion. hole should be swept with viscous gel sweeps to ensure good hole-cleaning, and filter-cake building12G. Mobile formation. The overburden weight or tectonic forces can squeeze plastic salt or soft shale into the wellbore, sticking or jamming the BHA in the undergauge hole. The magnitude of the stresses and hence the rate ofmovement will vary from region to region, but generally is greater for formations below 6,500 ft (2,000 m) and for salt formations with temperatures above 250F (121C)H. Ledges and micro-doglegs. These are formed when successive hard/soft interbedded formations are encountered. The soft formations become washed out for various reasons (i.e. excessive hydraulics, lack of inhibition),while the hard rocks remain in gauge. This situation is aggravated by dipping formations and frequent changes in angle and direction. The stabilizer blades may become stuck under the ledges during tripping or picking up for connections13Differentially Stuck PipeFor differential sticking to occur, two conditions must exist:1) Hydrostatic pr of mud must exceed pr of adjacent formation.2) A porous, permeable formation must exist.

CAUSESWhen the pipe becomes differentially stuck, the following conditions exist: The hydrostatic pressure of the mud exceeds the adjacent formation pressure. The formation is permeable (usually sandstone) at the point where the pipe is stuck. Excessive drill solids and high fluid loss increase filter-cake thickness and the coefficient of friction, making it more difficult to pullor jar the drill pipe free.14Mechanics of Differential StickingWhen drilling a well bore with permeable exposed formations, generally well bore pressure is greater than formation pressureDrilling fluid enters formation and deposit a cake on hole wallAs filter cakes are permeable, most of the solids are filtered out at the cake and only clear filtrate passes through the cakeFilter cake grows in thickness as new solids deposited until rate of deposition equals the rate of erosion.15PREVENTIVE MEASURES Reduce the overbalance pressure by keeping the mud weight as low asgood drilling practices allow. Reduce the area of contact between the wellbore and the pipe by using the minimum length of drill collars needed for the required bit weight. Reduce filter-cake thickness. Filter-cake thickness canbe reduced by lowering filtration rate & drill solids content. Maintain a low filtration rate. Control excessive ROP Minimize the muds coefficient of friction Keep the pipe moving when possible Run drilling jars when possible.

16PREVENTIVE MEASURES Watch for depleted pressure zones, where differential sticking occurs frequently. Seepage-loss materials such as asphalt, gilsonite , M-I-X II fiber and bridging agents such as sized-calcium carbonate have been used with success to drill depleted zones with high differential pressures . Depleted zones should be isolated with casing whenever possible.

17FREEING STUCK PIPE WITH SPOTTING FLUIDSCarry Surveys to determine the free point accurately, but running such surveys often takes a significant amount of time. A pipe-stretch method is a quick way to estimate the depth of the stuck zone.the spotting fluid should be applied as soon as possible.18The following procedure is recommended to free stuck drill collars:1. Determine volume of soak solution required to fill annular space around the collars. Annular volume opposite collars can be calculated by multiplying annular volume (bbl/ft) by length of collars (ft).Example:500 ft of 6-in. Collars in 978-in. hole (0.06 bbl./Ft.)(500 ft) = 30 bbl2. This volume should be increased enough to compensate for hole enlargement and leave enough solution in the pipe so additional volume can be pumped periodically to compensate for migration of the spotted fluid. The extra volume usually ranges from 50 to 200% of the annular displacement volume, depending on hole conditions.3. PIPE-LAX/oil solution is mixed by adding 1 gal of PIPE-LAX per barrel of oil in the spot. The solution should be mixed thoroughly before spotting.194. Determine the pump strokes and barrels of spotting fluid and mud to be pumped to displace the entire drill collar annulus with soak solution, leaving the reserve volume inside the pipe. Spot the slurry, then shut the pump down.5. After the PIPE-LAX/oil solution is spotted, the pipe should be worked by putting it in compression. Slack off 10,000 lb below the weight of the pipe and take 12 round of torque per 1,000 ft with tongs or the rotary table. Release the torque and pick up the 10,000 lb of weight. Repeat this cycle about once every five minutes. The pipe usually will come free onthe compression cycle. It should be noted that working the pipe in tension or pulling 10,000 to 50,000 lb over the indicated weight of the drill string could cause the pipe to become stuck further up the hole in a key-seat or dogleg. These hole conditions are common at shallow depths.6. Periodically, pump 1 to 2 bbl of soak solution to keep the collarscovered. Continue to work the pipe as outlined above.20Mud Loss Prevent Early identificationCure Knowing and understanding why a loss has occurred helps in determining and selecting the:Best suited LCM to useThe probable position of the loss zone Whether any changes to mud weight, mud properties or drilling practices are necessary.

21PreventionAnalyzing offset well data - Discussed beforeMud policyMud parametersWell planningFormation strengtheningGood drilling practices22Solid ControlChoosing the correct weighting material

Mechanical treatment

Gravity treatment

Chemical treatment

Dilution23FILTER LOSSBridging particles availabilityBase Particulate sizes (1/3 to largest pore size)Colloidal particulate size - to plug small pore openings and interstitial spacesAPI filter loss all the time may not be correct if particulate size do not match pore openingsDynamic filter loss will be higher than static filter loss24INHIBITIONPotassiums based salts Salts dosage are optimized throughLSM , CST AND CORE FLOW APPARATUS25Control mud properties( MW ,Viscosity,Gel strength) in the proper ranges. Many times mud properties can not be kept at a level which will provide adequate hole cleaning due to other operational considerations. Higher flow rates and aggressive drill pipe rotation are the best methods to improve hole cleaning. High viscosity sweeps are recommended in such cases where good hole cleaning is questionablefluid loss and filter-cake thickness should always be controlled in the proper range.Drill with minimum mud density. This not only enhances the ROP but also diminishes other mud-related effects.v. A good selection of the proper size of bridging materials helps reduce and eliminate whole mud losses into porous formations. 26FORMATION STRENGTHING Two pre-requisites for formation strengthening concept are knowledge of

Fracturing strength lot or pit.The cause of low fracture gradient may be either presence of Microfractures ,Or poor cementing materialOr rock fluid interaction

2.Pore pressure27The formation strength can be increased byUse of micro fractures sealing materialsUse of system loss controlling materialUse of non invasive fluidsChemical treatment

How To Increase Formation StrengthLoss Prevention28Formation Sealing MaterialBituminous Material- generic term for a group of substances composed of mixture of hydrocarbons , commonly solids that are soluble in CS2. Sulfonated asphalt- Asphalt is found in native form but most is produced as residue in petroleum refining. Hard granular Asphalt is used in water base muds for hole stabilization .Air blown asphalt in which asphaltene content increases is used in oil base muds for providing sealing and suspending property. Sulfonated Asphalt is produced by treating it with sulfuric acid and SO3 and neutralization with alkali.Gilsonite -It is a mineral; a natural bitumen . Supposedly originated from oil shales .It is also effective in hole stabilization when drilling steeply dipping shales. Graded according to MP , screen size , fracture size . Its Softening point is 132-190 deg C.29Both work by sealing micro-fracture.They plasters the borehole wall .Both strengthens weak formations and prevents losses in such formations and thus stabilizes boreholeAppropriate dosages for Sulphoated Asphalt are 2% to 3% and for Gilsonite 2-6 lbs/barrel30System Loss MaterialAdded to a drilling fluid while drilling through a known or potential loss zoneSpecially selected sized particulate matter.Particle size distribution is based on expected width of largest fracture. The largest size of particle present in mud must be 1/3 rd of the pore openings size.Generally, particles that are one-third to one-half the square root of the permeability in millidarcies (md) should be able to bridge such formations.Forms an internal bridge in the natural micro-fractures.31BenefitsMaterial is available in the fluid When fractures are initiated When borehole breathing is initiated Where seepage losses is possible Where natural fractures are encountered32System LCM MaterialsSized Calcium CarbonateGraphite PowderSized DolomiteProprietary Products33System LCMNever Use LCM Particles Of Maen Size Greater Than 1/3 Of The Smallest Bit Nozzle SizeNozzle Size Maximum LCM Diameter12 3.17mm14 3.70mm16 4.23mm18 4.76mm34STEELSEAL (Baroid) STEELSEAL is a resilient, angular, dual-composition carbon-based material It is insoluble in waterIt can be compressed, tightly packed in pores and small fracturesIt can expand or contract without being dislodged or collapsed due to changes in differential pressures.It can be used with WBM as well as SOBM as lost control material It acts as solid lubricant for torque and drag reduction Proprietary Products35Hollow Glass Sphere (HGS)Hollow spheres of borosilicate glass. Varying particle size distribution. Low bulk density high strength material. Inert and compatible with different types of mud and mud additives.Easy to prepare and maintain drilling fluid with HGSNo adverse effect on mud properties

36No special infrastructure required for its applicationEasy handling and storageNon abrasive Non corrosiveThe designed drilling fluids, of density as low as 7.5 ppg showed good rheological and filtration properties.Shown retention of specific gravity even after application of 4000 psi pressure at 90 deg C for 8 hours.

37The sub-hydrostatic work over fluid up to S.G.= .065 ( 5.4 ppg) was also designed using hollow glass spheres.These fluids are also expected to minimize formation damage and shall enhance productivity of the reservoir.The sub hydrostatic work over fluids shall prevent losses during well completions and work over operations.

38Application In ONGCFirst field trial in drilling fluid is expected in western offshoreThree types of sub-hydrostatic drilling fluids designed by IDT using HGS vis a vis NDDF system, gel polymer system and KCl-PHPA-glycol system for offshoreInitially it shall be used in non damaging drilling fluid (NDDF) for drilling through limestone reservoir

391.Pull out and waitP/o string to point of safety if well condition permitsWait for 4-8 hoursIf loss stops, continue drilling. If loss does not stop then check for available lcm available at site and identify the best suited

Loss Control40Use Of LCM To Seal Loss ZoneType of sealFracture seal at the face of boreholeFracture seal within well bore More effective bridge is formed within formation LCM does not dislodge easily as a result of pipe movement and not eroded due to fluid movement

41

A- SEAL AT FACEB- SEAL WITHIN FORMATION

SMALL LCM FAIL

LARGE LCM FORM INITIAL BRIDGE

42Types Of LCMFibrous materialRelatively little rigidityTend to be forced inside the large openingsIf opening are small external bulky filter cake formsCan cause serious damage to formationCotton fiber, bagasse, saw dust , leather ,mineral fiber(asbestos), glass fiber, shredded automobile tyre.

43Flaky materialFlat and tend to lie flat across the face of formationIf strong make external cake otherwise may be forced into the openingMica flakes, rice husk, plastic laminates, wood chipsGranular materialMarble chips, ground plastic, nut shell hull

44Use Of Plugging/Bridging MaterialShould be used against partial or seeping lossesUse open ended drill pipe for placement of plug if practical or use watercourse bit or jet bits with nozzle removedIf jet are to be used or MWD/LWD tool is in use medium to fine sized material shall be usedA blend of flaky , fibrous and granular bridging material is recommended for unconsolidated formations.A blend of flaky and fibrous bridging material is recommended for highly permeable formations45A blend of fibrous and granular bridging material is recommended for mud loss in fracturesProper size and types should be mixed in drilling fluid for squeezing into the loss zone. The total amount should be between 20 to 50 lbs./Bbl .If the severity of loss zone increases only the size of LCM shall be increased not the concentration46Preparation Of PillAdd 10-20 lb/bbl of clay in 80 bbl waterTreat with Soda ash and Caustic soda to remove calcium and magnesiumPrepare 100-250 bbl pill depending on hole size .Add different size LCM to obtain 10-20 lb/bbl concentration. Usually add 15 lb/bbl coarse nut plug,5lb/bbl of fine to coarse to medium fiber and 5lb/bbl of fine inch cellophane flakeMix47SqueezeSet the bit/open end at top of loss zonePump lcm slurry and displace to top of string at slow rateRepeat once more if hole is not fullIn case of seepage loss -if hole is full close ram and gently squeeze(50 psig) at 1bbl/min and hold pressure for 4-8 hour or till dissipate and if hole is not full 48Squeeze PressuresTo avoid fracturing maintain safe squeeze pressures in excess of hydrostatic pressures

Surface pressure plus mud column pressure should never exceed 1 psi /ft (overburden pressure)

DEPTH FEETSQUEEZE PRESSURE0-10000-200 PSI1000-5000200-500 PSI> 5000500 PSI