Drilling operations can encounter various problems related to geological uncertainties, wellbore stability issues, and depletion effects. Some key risks include uncertainties in pore pressure-fracture gradient measurements, mud volcanoes causing landslides or weak formations, fault zones providing pathways for fluid flow, and maintaining wellbore integrity in low-pressure depleted zones. Operators address these challenges through careful planning, identifying potential hazard areas using seismic data, selecting appropriate drilling fluid properties, and employing wellbore strengthening techniques and lost circulation materials when needed to prevent fluid losses and wellbore collapse.

1. Drilling
Problems
Farida Ismayilova
Drilling Geohazards Specialist

2. Why we might have problems:
•Uncertainty in PPFG
•Mud volcanoes/Mud flows
•Depletion
•Wellbore stability
•Geological properties of rocks
•Potential water and gas flow
•Operational issues
•Integrity issues
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3. ACG field
• Estimated oil in place: 5,000
•million barrels
• Structure: Anticlines
• Formation: Sandstone
• Main shareholders: BP, SOCAR,
Chevron, Inpex
• Operated since 1997 by BP
• The peak of oil production, 835,000
bpd in 2010
• Current production: 631,000 bpd
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4. Drilling problems solving
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Prevention with
proper planning
Remediation

5. Pore Pressure-Fracture Gradient (PPFG) plot
PPFG uncertainties due to the
uncertainty and quality of:
• MDT(Modular formation
Dynamic Tester)
•Logs
• Seismic velocities
• LOT/FIT measurements
•And etc.
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6. 3 main geohazards
•Mud volcanoes
•Slopes
•Faults
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7. Mud volcanos
• The world's greatest
concentration of mud volcanoes
is found in Azerbaijan.
• 220 out of a global total of
350.
• There are over 140 offshore
mud volcanoes within the
Caspian Sea.
• 3 mud volcanos in ACG(Azeri
Chirag Guneshli) field
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8. Problems associated with mud volcanos:
• The overlying sediments are lightweight.
• Not enough resistance to the upwelling of diapirs underneath.
• The result - a diatreme* - can generate a very high velocity gas plume up to
800 meters high, which will flame and burn people 1 km away.
• Landslides on seabed, dangerous for putting subsea equipment.
• Drilling through buried mud volcano is a threat to wellbore stability as they are
soft.
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*Diatreme- volcanic pipe formed by a gaseous explosion

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Some mud volcanos in the Capian Basin

10. What can be done to identify or mitigate risks:
Using regional geophysical survey to evaluate
the extent of mud volcanos
Determination of geotechnical properties of mud
volcano deposits using geotechnical boreholes
Mapping of mud volcanoes, their activity and
using already existing databases
Study of geotechnical properties, physical
processes, relation of diapirs to faulting, hazards
relating to mudflows, ground disruption and gas
emissions
Setting a casing shoe there should be avoided.
Usually it is placed above buried mud flows.
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11. Faults
Faulting is prevalent along large parts of the
Apsheron Ridge.
5 fault types in the region:
• tectonic faults
• gravity failures
• faults associated with mud volcanoes
• growth faults
•constant offset faults.
Possible origins:
• tectonic in origin
• others are caused by near-surface and deep-
seated gravity failures
• uncertain, because faults of different types can
occur in the same area (for instance, tectonic
faults acting as planes of weakness along which
subsequent gravitational failures occur).
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12. Problems associated with faults
• Can cause massive losses as the fracture is already in place
• Small induced fractures can lower the Fracture Gradient leading to losses
• A dangerous place to set the shoe due to instability and losses
• Possible conduit for gas or water flow from deeper sections causing
overpressure, thus flow or kick
•P.S. ACG has numerous faults in the hinge area due to its anticlinal structure. 12

13. Drilling depleted intervals:
• New zones in mature fields
continue to be actively
developed as operators
strive to maintain depleting
reserves.
• Many of the world’s new
reserves are discoveries
made below these existing,
mature reservoirs
• PS. ACG is also entering
its mature phase while
drilling activities continue.
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Depletion

14. At discovery there will be no pressure breaks within a reservoir. . In this
example, a large pressure break is revealed at the top of the D subunit
early in field life, but there is little hint of the intra-subunit pressure breaks
seen in later wells. 14

15. As production proceeds, differential off-take and injection above and
below laterally extensive thin mudstones typically results in lower
pressures, more and larger pressure breaks, and a wider spread of
pressures
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16. The late life well shows how a laterally extensive thin mudstone near the
base of the B subunit (dashed line) indicated in the mid-life well can
control fluid flow with, in this example, injected water running over the
mudstone, leaving unswept dry oil below. 16

17. Problem with drilling depleted intervals
If we use conventional
drilling techniques are used,
then the higher mud weight
used to hold back the target
interval may result in:
• massive losses (lost
circulation),
• differential sticking,
• sloughing, or collapsing
formations in the lower-
pressure zone.
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Depletion

18. Drilling depleted intervals:
Differential sticking is a
problem that occurs when
drilling a well with a
greater well bore pressure
than formation pressure,
as is usually the case.
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19. Wellbore stability
Maintaining a stable wellbore is of primary importance
during both drilling and production:
• The shape and direction of the hole must be controlled
during drilling
•Hole collapse and solid particle influx must be prevented
during production.
Wellbore stability requires:
• a proper balance between pressure while drilling and
pore/fracture pressure.
•A proper balance between the uncontrollable factors of
earth stresses, rock strength
•Mud chemical composition. – inhibition, overgauge,
undergauge
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20. MW vs. Wellbore stability:
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21. Wellbore stability
Maintaining a stable wellbore is of primary importance
during both drilling and production:
• The shape and direction of the hole must be controlled
during drilling
•Hole collapse and solid particle influx must be prevented
during production.
Wellbore stability requires:
• a proper balance between pressure while drilling and
pore/fracture pressure.
•A proper balance between the uncontrollable factors of
earth stresses, rock strength
•Mud chemical composition. – inhibition, overgauge,
undergauge
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22. Gumbo
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Inhibition helps slowing the hydration ,
swelling and disintegration of clays and
shales.
Shale inhibitive agents: polymer
encapsulator, Inorganic inhibitors or
electrolytes, asphaltic products and so on.

23. Wellbore Strengthening (WS)
Using cage stress (particle bridging) or WS to drill at higher mud weights
without losing fluid. Stress Cage concept below:
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24. Wellbore Strengthening (WS)
• Using cage stress (particle
bridging) or WS to drill at higher
mud weights without losing fluid.
Lost Circulation Material (LCM)
• Added to drilling fluids due to
losses
• Or as a pill treatment to seal
fractures while significant losses
have already occurred
Forms:
• Flake (mika)
• Granular CaCO3
• Chemical (Polymer thickening
agents)
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25. LCM
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LCM is defined by its size and hardness. Grinding cuttings downhole to
generate LCM can immediately act upon fractures to cure lost circulation before
it becomes evident at surface. Oilfield Innovations have a patented downhole
lost circulation material generator that can save you expensive rig time by
preventing lost circulation before it becomes a problem.

26. Downhole LCM generator
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Non-rotating stabilisers create the housing
of a downhole lost circulation material
(LCM) generator with the drill string turning
impellers within the housing that grind rock
cuttings to LCM sized material. As shown
above various configurations of LCM
generators can be constructed to suck in
cutting and grind them into sand size
particles that enter fractures to allow the
mud filter cake to bridge and seal the
fracture to, thus, prevent pressure from
reaching the point of fracture propagation
to inhibit or prevent lost circulation.

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