lost circulation - the basics

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 : 1.6 TO 80.0 M3 /HR

•COMPLETE LOSS: 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 TOTAL FORMATION

AGAINST PRESSURE

FORMATION

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


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


(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


(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


IDENTIFYING TRANSITION ZONES

• DOWNHOLE LOGGING

• ROP

• GAS CUT MUD

• FORMATION SLOUGHING

• SHALE DENSITY

• D-EXPONENT

• FLOW LINE TEMPERATURE

• SEISMIC DATA


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


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


• 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


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


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


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 Induced fracture

• Confined to limestone * In any formation

along weak planes

• Loss is mostly sudden * Loss is sudden

and complete and complete

Drilling may be rough * Loss may follow

before loss after running in

• Bit may drop few cm

to several 10’s of cm

lost circulation - the basics

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