This document provides an overview of lost circulation, which occurs when drilling fluid is lost into porous or fractured formations. It discusses the types and severity of lost circulation, as well as methods for preventing, locating, and treating lost circulation zones. Key points include that lost circulation can lead to blowouts if not addressed, and that preventing excessive downhole pressure and identifying weak formations are important. Locating lost zones involves surveys to detect where fluid flows into formations, while treatments require sealing fractures or pores with lost circulation materials.

1. LOST CIRCULATION –
THE BASICS
MOHAN DOSHI

2. 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

3. ·ASSOCIATED DOWNHOLE
COMPLICATION:
INFLUX  KICK  BLOW OUT
UNDERGROUND BLOWOUT

4. WHY IS IT IMPORTANT
COST: NOT THE COST OF
MUD
LOST OR LCM
BUT
- RIG TIME LOST
- COMPLICATION COST

5. 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

6. TYPES OF LOST ZONES
• UNCONSOLIDATED OR HIGHLY
PERMEABLE FORMATIONS ( LOOSE SAND
AND GRAVELS)
• HORIZONTAL NATURAL FRACTURES
• HORIZONTAL INDUCED FRACTURES

7. TYPES OF LOST ZONES
• VERTICAL NATURAL FRACTURES
• VERTICAL INDUCED FRACTURES
• CAVERNOUS OR VUGULAR FORMATIONS
 2500 FT  HORIZONTAL LOSS
 2500 FT  VERTICAL LOSS

8. 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

9. 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

10. LOSS CIRCULATION PREVENTION
(A)MINIMISING DOWNHOLE FORMATION
PRESSURE:
1. MAINTAIN LOWEST SAFE MUD WEIGHT
FORMATION PRESSURE
FRACTURE PRESSURE
PROPER USE OF SOLID CONTROL EQUIPMENT

11. 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

12. 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

13. 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

14. LOSS CIRCULATION PREVENTION
IDENTIFYING TRANSITION ZONES
•
•
•
•
•
•
•
•
DOWNHOLE LOGGING
ROP
GAS CUT MUD
FORMATION SLOUGHING
SHALE DENSITY
D-EXPONENT
FLOW LINE TEMPERATURE
SEISMIC DATA

15. 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

16. 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

17. 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

18. 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

19. 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

20. 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

21. 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

22. 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

23. 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

24. 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

25. 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

26. 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

27. 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.

28. 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