This document discusses lost circulation, which occurs when drilling fluid is lost to the formation instead of returning to the surface. It defines lost circulation zones and classifications ranging from seepage to total losses. Causes include fractured formations and exceeding the fracture gradient. Prevention methods are outlined such as using proper mud weight and lost circulation materials. Numerical examples are provided to calculate formation pressure from lost circulation incidents. Detection and remediation techniques include waiting, squeezing lost circulation materials into the zone, and surveys to locate the lost circulation zone.

1. By
Sr. Syed Nawaz
Delta Studies Institute
Andhra University

2. Content…
 Intro
 Indication the lost circulation zone
 Why lost Circulation?
 Classification of Loss Zone
 Quant classification of lost circulation
 Preventions…
 Loss
 Numerical approach
 Restoring of loss zone
 Locating Loss Zone

3. Intro

4. Hydrostatic pressure > Formation pressure
 Respectable amount of drilling fluid loss in
subsurface.
 Important pressures:
 Fracture pressure
 Formation pressure
 Hydrostatic pressure
 Bottom hole pressure

5. Indication of Lost circulation
zone

6. Indications of loss circulation
 Flow back is questionable
 Increased the weight of drill string
 Pump speed increases
 Bottom hole or vertical pressure head reduces
 Pit volume variation

7. Why loss circulation?

8. Reasons behind Lost Circulation
 Annular circulation friction:
 Fracture gradient drilling with heavy fluid causes friction (pressure increased)
 Decrease Pumping pressure
 Entering the hole too quickly:
 Lower of tool increases the pressure
 Decrease the pump pressure
 Excessive mud weight

9. Loss Zone Classification

10. Lost zone classification
 Extremely permeable formation
 Horizontal and vertical natural fractures
 Vertical and horizontal induced fracture

11. Quant classification of lost
circulation

12. Classes of Lost Circulation
 Seepage losses: From 1-10 bbl/hr and lost while circulating at the
normal drilling circulating rate
 Partial losses: From 10-50bbl/hr and lost while circulating at the
normal drilling circulating rate
 Severe losses: Greater than 50 bbl/hr and lost while circulating at
the normal drilling circulating rate
 Total losses: When the mud level in the annulus cannot be seen or
the hole cannot be filled through the annulus. Total losses usually
occur in cavernous formations

13. Preventions…

14. Prevention of lost circulation
 Adequate Hole cleaning
 Avoiding restrictions in the annular space
 Setting casing to protect upper weaker formations within a transition
zone (100% or irreducible water saturation)
 Updating formation pore pressure and fracture gradients (log and
drilling data)
 Maintain proper mud weight
 Treating mud with lost circulation materials
 Leak-off test and Formation Integrity test

15. Loss

16. Economic loss
 Rig time lost (NPT)
 Complication cost

17. Numerical approach

18. Numerical Question?
 During drilling of an 8.5 inch hole at 8000ft , a complete loss of
circulation was observed. Drilling was stopped and the mud level in
the annulus was observed to fall rapidly. The well was filled with
water of 8.3 ppg until the annular level remained stationary. If the
volume of water used was 65.7 bbl and mud density was 10 ppg,
determine the formation pressure and the new mud weight required
to balance the formation pressure. Assume the intermediate casing
to be 9.625 in, 40# set at 6000ft. Drill pipe is grade E, 5 inch OD?

22. Restoring of Lost Zone

23. Restoring of Lost Circulation
 Trip out and wait
 Identify the point of safety and trip out the drill pipe
 Wait for 4-8 hours standard time and selection of LCM
 Squeezing technique
 Identify the thief zone and design LCM
 Locate the pipe above the zone and squeeze the fluid blended
with LCM

24. Continue…
 Blind drilling: fluid does not return to the surface
 In order to identify the lost circulation…


25. Locating Loss Zone

26. Locating loss zones
 Spinner survey
 Temperature survey
 Radioactive survey
 Hot wire survey
 Pressure transducer survey

27. Any Queries?

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