Published on March 8, 2014
LOST CIRCULATION – THE BASICS MOHAN DOSHI
WHAT IS LOST CIRCULATION LOSS OF AN APPRECIABLE PART OR ENTIRE VOLUME OF DRILLING FLUID THROUGH BOREHOLE INTO CAVERNOUS, VUGGY AND / OR HIGHLY POROUS FORMATION
·ASSOCIATED DOWNHOLE COMPLICATION: INFLUX KICK BLOW OUT UNDERGROUND BLOWOUT
WHY IS IT IMPORTANT COST: NOT THE COST OF MUD LOST OR LCM BUT - RIG TIME LOST - COMPLICATION COST
SEVERITY OF LOST CIRCULATION •SEEPAGE LOSS : 0.16 TO 1.6 M3 / HR •PARTIAL LOSS : •COMPLETE LOSS: 1.6 TO 80.0 M3 /HR 80.0 M3 / HR
TYPES OF LOST ZONES • UNCONSOLIDATED OR HIGHLY PERMEABLE FORMATIONS ( LOOSE SAND AND GRAVELS) • HORIZONTAL NATURAL FRACTURES • HORIZONTAL INDUCED FRACTURES
TYPES OF LOST ZONES • VERTICAL NATURAL FRACTURES • VERTICAL INDUCED FRACTURES • CAVERNOUS OR VUGULAR FORMATIONS 2500 FT HORIZONTAL LOSS 2500 FT VERTICAL LOSS
MUD LOSS OCCURS WHEN TOTAL PRESSURE AGAINST FORMATION TOTAL FORMATION PRESSURE OPENINGS IN FORMATIONS ARE ABOUT THREE TIMES AS LARGE AS THE LARGEST PARTICLE OCCURING IN MUD
FORCES REQUIRED FOR FRACTURING FORMATION MATTHEWS AND KELLY(1967) F Pp/ D + Ki / D F = Fracture gradient (psi/ft) Pp = Pore pressure at “D” depth (psi) = Matrix stress at depth “D” (psi) Ki = Dimensionless matrix coefficient for depth at which ““ would be normal matrix stress Pre existing fractures widened if they form an angle of 45 or less with vertical
LOSS CIRCULATION PREVENTION (A)MINIMISING DOWNHOLE FORMATION PRESSURE: 1. MAINTAIN LOWEST SAFE MUD WEIGHT FORMATION PRESSURE FRACTURE PRESSURE PROPER USE OF SOLID CONTROL EQUIPMENT
LOSS CIRCULATION PREVENTION 2. MINIMISE ECD • • • • • OPTIMISATION BETWEEN HOLE GEOMETRY, DRILLING FLUID PROPERTY AND HOLE CLEANING SLOW RUNNING IN OF STANDS BREAK CIRCULATION GRADUALLY AND IN STEPS IN LONG AND OPEN HOLE SECTIONS OR AFTER LONG PERIOD OF CIRCULATION BREAKS MUD WITH LOWER AND FLATTER GEL PROFILE SLOWING OF PUMPS AS MUCH AS PRACTICAL
LOSS CIRCULATION PREVENTION (B) AVOID RESTRICTIONS IN ANNULUS • LIKE BIT/ DC/ STABILISER BALLING • THICK FILTER CAKE • TOO FAST DRILLING • MAINTAINING PROPER HYDRAULICS • USE OF INHIBITIVE MUDS TO CONTROL SLOUGHING/ HEAVING SHALES
LOSS CIRCULATION PREVENTION (C) OTHER PRECAUTIONS • USING SUITABLE LCM IN ZONES OF KNOWN TENDENCY • SETTING INTERMEDIATE (PROTECTIVE) CASING INTO TRANSITION ZONES • KEEP ADEQUATE RECORDS OF PREVENTION AND CURE
LOSS CIRCULATION PREVENTION IDENTIFYING TRANSITION ZONES • • • • • • • • DOWNHOLE LOGGING ROP GAS CUT MUD FORMATION SLOUGHING SHALE DENSITY D-EXPONENT FLOW LINE TEMPERATURE SEISMIC DATA
LOSS CIRCULATION PREVENTION LOSS CIRCULATION MATERIALS LCM MUST SATISFY FOLLOWING REQUIREMENTS • CAPABLE OF FORMING A MUD TIGHT SEAL FOR REMAINING DRILLING • SEAL MUST BE STRONG AND NOT EASILY BROKEN OR REMOVED • MATERIAL SHOULD NOT CAUSE PIPE STICKING • IT SHOULD BE NON DAMAGING TO PAY ZONE
LOSS CIRCULATION PREVENTION TYPE OF SEAL • • FRACTURE SEAL AT THE FACE OF BOREHOLE FRACTURE 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
LOCATING LOSS ZONES 1. SPINNER SURVEY • • • • Made by running a small spinner attachment on a single conductor cable Rotor will spin or turn if there is any horizontal motion of mud The motion of rotor is recorded on film as a series of dashes There is a definite speed up of rotor at the point of loss DISADVANTAGES • • Requires deliberate loss of large volume of mud Not effective where sealing material is already present in mud
LOCATING LOSS ZONES 2. TEMPERATURE SURVEY • Depends on subsurface thermometer for measuring difference in mud temperature and formation temperature • Recorded by running a sensitive element in hole, observing resistance change with respect to temperature • Two surveys are run. One for temperature gradient of well. Other, after adding cool mud. Sharp temperature change will occur at loss point
LOCATING LOSS ZONES 3. RADIOACTIVE SURVEY • Two gamma ray survey • Base log is run before radioactive material • Slug of mud containing radioactive material is then pumped down the hole • A new log is run and high conc. of radioactive material will be located at loss point
LOCATING LOSS ZONES 4. HOT WIRE SURVEY • Hot wire tool is a calibrated resistance wire that is sensitive to temperature change • Run to desired point in the hole and resistance is noted • Mud is pumped into the hole • If tool is above the point of loss, mud will not flow showing change of resistance • If resistance does not change, tool is below the point of loss
LOCATING LOSS ZONES 5. PRESSURE TRANSDUCER SURVEY • Instrument composed of hollow cylinder with an entrance at the top, larger in cross section than the exit at the bottom • The geometry of instrument restricts the flow of mud through the cylinder • A window fitted with a neoprene diaphragm on one side of the cylinder
LOCATING LOSS ZONES 5. PRESSURE TRANSDUCER SURVEY • A movable electrode on the diaphragm moves back and forth between two fixed electrode • The potential difference, indicative of rate of flow of mud, between movable and fixed electrode is measured at the surface • Above point of loss, the readings recorded are normal • Below point of loss, no signal is generated as fluid does not flow through
LOCATING LOSS ZONES 5. PRESSURE TRANSDUCER SURVEY ADAVNTAGES • It is simple in construction and operation • It is not easily clogged by lost circulation material • It is workable in almost any type of mud • It can be used to locate a hole inside the casing DISADVANTAGES • Considerable mud flow is required • The equipment may not be readily available
RESTORING LOST CIRCULATION 1. PULL OUT AND WAIT • P/O STRING TO POINT OF SAFETY • WAIT FOR 4-8 HOURS • MEANWHILE PREPARE LCM PILL ASSUMING CIRCULATION SHALL NOT BE REGAINED
RESTORING LOST CIRCULATION 2. SQUEEZING TECHNIQUES • LOCATE THEIF ZONE • SELECT PROPER LCM • RUN IN OPEN ENDED D/P JUST ABOVE THEIF ZONE • CLOSE PIPE RAMS AND SQUEEZE SLURRY INTO THE ZONE BY PUMPING IT SLOWLY BRIDGING AGENTS IN MUD HIGH F/L SLURRY DOWNHOLE MIXED SOFT PLUG DOB(DIESEL OIL+BENTONITE) PLUGS
RESTORING LOST CIRCULATION 3. CEMENTING TECHNIQUES • • LOT/PIT: ZONE BELOW CASING SEAT IS VERY WEAK CAUSING LOSSES ALSO USED WHEN NATURAL FRACTURES OR CAVERN EXCEEDS 1/4” IN WIDTH 4. OTHER TECHNIQUES • • • BLIND DRILLING, UBD (AERATED/FOAM MUD) BARYTES PLUG
SYMPTOMS OF LOSS ZONES UNCONSOLIDATED FORMATION NATURAL FRACTURED FORMATION GRADUAL FALL IN MUD TANKS THIS CAN OCCUR IN ANY FORMATION, MOSTLY FOUND IN LIMESTONES LOSS MAY BECOME TOTAL IF DRILLING IS CONTINUED AT FIRST THE LOSS IS GRADUAL AND THEN CAN BECOME TOTAL LOSS AS MORE FRACTURES ARE CREATED FOUND IN FORMATIONS THAT CAN BE EASILY FRACTURED FORMATIONS ARE GENERALLY IMPERMEABLE. LOSS IS DUE TO WEAKENING OF THE FORMATION.
SYMPTOMS OF LOSS ZONES Cavernous zone • Confined to limestone • Loss is mostly sudden and complete Drilling may be rough before loss • Bit may drop few cm to several 10’s of cm Induced fracture * In any formation along weak planes * Loss is sudden and complete * Loss may follow after running in
THE BASICS OF LOST CIRCULATION DURING DRILLING ... LOST CIRCULATION - THE BASICS May 06, 2015 Technology mohan-doshi
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The online version of Lost Circulation by Alexandre Lavrov on ScienceDirect.com, the world's leading platform for high quality peer-reviewed full-text books.