Lost Circulation

Lost Circulation

• Definition: the significant and continuing

loss of whole mud or cement slurry to a
formation
• Effect: If the wellbore-fluid level drops far
enough and fast enough, the drop can
allow fluid to enter the wellbore from a
higher-pressure formation.
• When this influx or kick does occur, it
makes well control all the more difficult
because of the inability to circulate kill
fluid (Ivan et al. 2003).
Causes of Lost Circulation.
CAUSES
• (1) a formation with flow • (2) an overbalance or positive
channels that allow passage of pressure differential between
hole fluid from the wellbore and the wellbore and the formation.
CAUSES/MECHANISM

• Permeable Zones
• Natural Fractures zones
• Induced Fractures
• Cavernous/Vugular zones
Permeable Zones.
• Some types of rocks, because of their high
primary porosity and permeability, almost seem
to be designed to cause lost-circulation problems.
• Unconsolidated formations, gravel beds, loose
conglomerates, and shallow or highly depleted
sandstones have long been recognized as having
natural lost-circulation tendencies.
• The pore size needs to be larger than about 3
times the solid particle diameter in order for the
mud to be able to enter the pore space
Permeable Zones.
• Some types of rocks, because of their high
primary porosity and permeability, almost seem
to be designed to cause lost-circulation problems.
• Unconsolidated formations, gravel beds, loose
conglomerates, and shallow or highly depleted
sandstones have long been recognized as having
natural lost-circulation tendencies.
• The pore size needs to be larger than about 3
times the solid particle diameter in order for the
mud to be able to enter the pore space
Permeable Zones.

Permeable Zones.
• Losses into porous matrix occur when a high-
permeability rock becomes exposed to the
drilling fluid.
• Their onset is gradual, and the loss rate increases
as more rock is exposed at the borehole wall as
drilling proceeds.
Permeable Zones.
• Gradually, filter cake builds up on the borehole
wall and the loss rate starts to decrease.
• Losses continue at the drill bit until the high-
permeability zone has been passed.
Natural Fractures.
Occur in :
• Natural fractures, fractures that exist before the
well is drilleddmay provide pathways for the
drilling fluid.
• According to one study, natural fractures were
responsible for 76% of losses at one major
operator
• naturally fractured sandstones, shales, and
carbonates—are also conducive to lost circulation
Natural fractures may be either horizontal or
vertical depending on a rock’s depth, mechanical
characteristics, and stress environment.
Natural
Fractures.
Natural Fractures.
• Mud losses into a natural fracture typically
start with a sudden drop in the flow rate out
of the well
• The mud loss flow rate versus time curve
shows a sudden increase and gradual
decrease in the differential flow rate
Natural
Fractures. • Some lost circulation materials (LCMs)
successfully used to treat losses caused by
induced fractures are ineffective in
naturally fractured rocks, because the
permeability and volume of natural fracture
networks may be much larger.
Cavernous/Vugular
• The most severe lost-circulation problems
occur in cavernous or extremely vugular
formations These are typically limestones,
limestone, dolomite, and rock salt that have
been leached by water.
• The void spaces in these formations can be
large enough that when they are
encountered, the drillstring may actually
drop by as much as several feet preceding a
sudden, complete loss of returns.
 Cavernous/Vugular
Cavernous/Vugular • Losses start suddenly when the drill bit hits
the vug.
• The cumulative volume of the lost fluid can
be quite large, especially when several vugs
are connected into one large system.
• Total losses may occur in such formations.

Cavernous/Vugular
Induced Fractures.
• If lost returns occur in an area where
offset wells have not experienced lost
circulation, then the problem is likely
induced fracture
Most induced fractures are related to :
• drilling-fluid or cementing programs
• well architecture: surface or intermediate
casing string is set too high.
• Tripping speed
SUMMARY
SUMMARY
CURING LOSSES
 PRACTICAL GUIDELINES TO COMBAT LOST
CIRCULATION WHILE DRILLING
LOSS SEVERITY LOSS MECHANISM

• Seepage LOSS
• Permeable Zones
• Partial MECHANISM
• Natural Fractures
• Severe zones
• Total • Induced Fractures
• Cavernous/Vugular
zones LOSS SEVERITY
• Information about the loss mechanism is often unavailable when the losses occur.
• The treatment must then be based solely on the severity of losses; ie, the number of barrels lost per hour.
• If both types of information, the mechanism and the flow rate are available, both should be analyzed and used when choosing and designing the treatment.
 DEFINITION:
LOSS SEVERITY:
• The rate of loss 1-10 bbl/hr.
OCCUR IN:
SEEPAGE • any type of formation.
LOSSES ACTION:
• Ignore the Problem and Drill Ahead
• Pull up and Wait
• LCM
 REMEDIAL ACTION:
• Ignore the Problem and Drill Ahead:
LOSS SEVERITY: • when the drilling operation is good and close to a
casing setting depth with an in-expensive drilling
mud
• drill ahead with the intention that the accumulated
SEEPAGE solids would seal the loss zone and stop the
seepage loss
LOSSES • Pull up and Wait
• pulling the pipe into a protective casing or a
secure portion of open hole,
• shutting down the mud pumps for a minimum of
six to eight hours,
• attempting to fill the hole with water,
• gradually resuming circulation in stages.
• Pretreat the Active Mud System with LCM
 DEFINITION
LOSS SEVERITY:
• Rate of loss: 10-500 bbl/hr.
Occur in:
PARTIAL • gravels;
LOSSES • small, natural horizontal fractures;
• barely opened induced vertical
fractures
REMEDIAL ACTION:
• Drill ahead
• LCM, settable systems
 DEFINTION
LOSS SEVERITY: • Severe losses: the rate of loss >500 bbl/hr.
OCCUR IN:
• natural fractures,
SEVERE • induced fractures,
LOSSES • vugs,
• high-permeability matrix
ACTION:
• LCM, settable systems
• Mud Cap Drilling
• Blind Drilling
 DEFINTION
• Rate of losses : no fluid returns
LOSS SEVERITY: OCCUR IN:
• vugular rocks,
• naturally fractured carbonates,
TOTAL • geothermal drilling
LOSSES • Unconsolidated high-permeability
formations
ACTION:
• LCM, settable systems
• Mud Cap Drilling
• Blind Drilling
 PRACTICAL GUIDELINES TO COMBAT LOST
CIRCULATION WHILE DRILLING
LOSS SEVERITY LOSS MECHANISM

• Seepage LOSS
• Permeable Zones
• Partial MECHANISM
• Natural Fractures
• Severe zones
• Total • Induced Fractures
• Cavernous/Vugular
zones LOSS SEVERITY
• Information about the loss mechanism is often unavailable when the losses occur.
• The treatment must then be based solely on the severity of losses; ie, the number of barrels lost per hour.
• If both types of information, the mechanism and the flow rate are available, both should be analyzed and used when choosing and designing the treatment.
 OCCUR IN:
LOSS MECHANISM: • unconsolidated sands
• gravels at shallow depth
POROUS ACTION:
MATRIX • LCM: Fiber-based LCM, Calcium carbonate
and synthetic graphite (depends the pore
throat size)
• Drill Ahead
 OCCUR IN:
• unconsolidated sands
LOSS MECHANISM:
• gravels at shallow depth
ACTION:
CAVERNOUS/ • Blind Drilling
VUGULAR • Underbalanced Drilling
• Casing While Drilling
• Mud Cap
• Crossed linked pill
 SEVERITY
• seepage to total losses
LOSS MECHANISM: OCCUR IN:
• carbonate formations,
• gas-bearing shales,
NATURAL • geothermal wells
FRACTURES ACTION:
• LCM, sinthetyc graphite
• Cross Linking Polymers
• Blind Drilling
• Underbalanced Drilling
• Casing While Drilling
• Mud Cap
 OCCUR IN:
• Any type of formation
LOSS MECHANISM:
ACTION:
• Change drilling parameter
INDUCED • Pull up and wait
FRACTURES • LCM
• Cross Linked Systems
LOST
CIRCULATION
CONTROL
SUMMARY
SUMMARY
SUMMARY
LOSS PREVENTION
LOSS PREVENTION

• Mud System.
• Equivalent Circulating
Density (ECD).
• Casing Setting Depth.
• Using Aerated Mud
• Casing While Drilling
Mud System.
• Keep filtrate losses to a workable minimum
and to maintain a thin, firm, impermeable
filter cake along the borehole wall.
• The mud specific density should be as low as
possible, but high enough to control the
formation pressure
• Pretreat the mud with solid LCM. In an area
where porous, permeable zones are a known
problem, and a low-weight, low-solids mud is
being used,
Equivalent Circulating Density (ECD).
Lost circulation can still result from a high ECD
caused by excessive pump pressure and poor
hydraulics practices.
High surge pressure is a major contributor to
lost circulation. Surge effects can be minimized
by:
• avoiding excessive speed when tripping in the
hole,
• breaking circulation gradually, and
• maintaining circulation at the minimum pump
rate needed to ensure adequate hole
cleaning.
Casing Setting Depth.
• Selection of casing setting depths is
crucial to preventing lost circulation and
is closely related to the design of the
mud program.
• In many wells, it is necessary to set one
or more strings of intermediate casing
to protect low-pressure zones from the
higher mud weights required for deeper
intervals.
• In selecting these casing points, the well
planner should ensure that they are not
themselves located in potential loss
zones (Moore 1986; Devereaux 1998).
Using Aerated Mud
• Aerated mud is defined as a fluid
(in the form of mists and foams)
consisting of liquid (usually
water), air, and drill cuttings
(Guo and Rajtar, 1995).
• Aerated muds are low density
fluids that can be used to
maintain a minimum
overbalance while drilling
probable loss zones such as
depleted formations that are
competent and low-pressured.
Casing While Drilling
• Developments in new drilling technology such
as expandable tubulars and casing-
whiledrilling (CwD) can serve as long term
methods that will mitigate the costly effects of
lost circulation while drilling (Davison et al.
2004).
• The casing is rotated from the surface with a
top drive.
• Drilling fluid is circulated down the casing
internal diameter (ID) and up the annulus
between the casing the wellbore.
CLASSIFICATION OF
TREATMENTS MATERIALS
TREATMENTS MATERIALS
• settable systems;
• lost circulation materials,
commonly known as
LCMs
• Systems based on 2
fluids
LOST CIRCULATION MATERIALS
FUNCTION:
• To bridge across the face of fractures and vugs that
already exist.
• To prevent the growth of any fractures that may be
induced while drilling.
The lifecycle of an LCM:
• Dispersion: LCM should, firstly, be delivered to the (B) Coarse LCM particles bridge the fracture.
place where it is intended to be deposited
• Bridging: mechanical bridge is created across the
fracture on which a low-permeability seal can then be
built.
• Sealing: creating a low-permeability flow barrier (seal)
by depositing fine particles on the bridge.
• Sustaining: ability of the seal to perform its functions
for the time sufficient to drill through the lost (C) Fine particles (LCM, barite) are deposited
circulation zone and cement the well
on the bridge and seal the fracture.
Conventional LCM - Fibrous
• Fibrous: are used in drilling muds to lessen mud
loss in fractures and vugular formations.
• Can be forced into large openings, where they
bridge over and form a mat or base that acts to
• Wood fiber (shredded
seal off the formation when solids from the
wood, sawdust), drilling fluid deposit on it.
• paper pulp,
• glass fiber,
• If the openings are too small for the fibers to
• cotton fiber, enter, a bulky, easily removable external cake
• animal hair, may form on the walls of the hole.
• leather fiber,
• straw, and • Not recommended for oil-based muds.
• shredded tires
Conventional LCM - Flakes
• Flakes: are used to plug and bridge many types of
porous formations to stop the mud loss or to
establish an effective seal over many permeable
formations.
• Sealing action similar to that of fibrous materials.
• Cellophane products are not recommended for
• Cellophane, use in oil-based muds.
• mica (fine and coarse),
• plastic laminate,
• Not normally used in cement because :
• they tend to plug surface and downhole cementing
• wood chips. equipment.
• Also may contain organic chemicals that can seriously
extend cement-thickening time.
 Conventional LCM - Granular
• Granular: form bridges at the formation face
and within the formation matrix, thus
providing an effective seal which depends on
the particle size distribution (PSD).
• Tend to form a bridge just inside the
opening of the pore.
• Nut shells (fine, medium, • Must contain particles that approximate the
coarse, and very coarse), size of the opening, as well as a gradation of
• ground plastics,
• seed grains,
smaller particles to form a seal.
• coarsely ground rock • Granular materials may be used in oil-base
materials (e.g., bentonite,
asphalt, limestone).
muds.
 CONVENTIONAL LCM - MIXTURES
• Mixtures: these are combinations of granular, flaky and
fibrous materials that will penetrate fractures, vugs, or
extremely permeable formations and seal them off
effectively.
• Blended products containing cellophane flakes are not
recommended for use in oil-based muds.
SETTABLE MATERIALS
DEFINITION: A settable material is a material that is pumped in liquid state
and solidifies downhole, sealing the thief zone.
HOW IT WORKS
• Before setting, settable materials should have sufficiently low apparent
viscosity in order to be easily pumpable.
• Upon setting, the material should develop sufficient strength to be able to
withstand pressure variations in the wellbore
EXAMPLES:
• cement,
• cross-linked systems
• Combination (cement & crosslinked systems)
SETTABLE MATERIALS - CEMENT
• Sealing with cement can be effective in those zones where other
treatments would fail.
• Cement’s compressive strength is higher than that of other settable
system , such as gunk, which improves the quality of the seal
• Cement was recommended as a cure against severe losses in
permeable sandstones
• Cement is one of the few treatments that are reportedly effective
against losses in vugular formations
SETTABLE MATERIALS - CROSS-LINKED SYSTEMS

• Crosslinking is the linking of two polymer Polymers Cross Linking LCM

chains by a cross-linking agent. Agents
• The cross-linking agent is activated by
time and temperature or by shearing at
the drill bit.
• After setting, the pill produces a rubbery, Time / Temperature / Shear
ductile substance sealing the fracture and
preventing further losses.
• A typical cross-linked pill is a blend of
polymers, cross-linking agents, and LCMs.
• effective against losses in depleted sands
and unconsolidated formations
Rubbery Ductile Subtance
SETTABLE PILLS BASED ON TWO FLUIDS
• Two-fluid pills consist of two fluids, fluid FLUID 1 FLUID 2
No.1 and fluid No. 2, pumped separately.
• The two fluids set and build a seal after
making contact with each other downhole.
• Up until the fluids reach the thief zone,
they are kept separated from each other. Making Contact in downhole (requires
flow rate)
• To this end, a spacer can be used, or the
two fluids can be pumped through different
pathways (one through the drillstring, the
other one through the annulus) [5].
• The downhole mixing and activation
require controlled flow rates. Seal
SETTABLE MATERIALS - SETTABLE PILLS BASED
ON TWO FLUIDS
No.1. fluid consists of oil (diesel, mineral, or FLUID 1:
synthetic), bentonite, and, possibly, cement • Cement
• Bentonite
An example composition of the bentonite • cement
oil pill is given in Ref. [18]:
• bentonite: 300 - 400 lb (136 - 181 kg);
• diesel oil: 1 bbl (0.16 m3)
FLUID 2
• optional: LCM at 10 - 12 lb/bbl (28.5-34.2 • Water
kg/m3); • WBM

No. 2 fluid: water or WBM

LCM
Location of the Loss Zone
LOCATING LOSS
CIRCULATION ZONE
• Deep and shallow
resistivity logs in the
presence of a short
fracture. Wellbore is
drilled in shale with
synthetic-base mud.
Separation of the two
curves indicates the
fracture or a fractured
zone filled with high-
resistivity mud.
LOCATING LOSS CIRCULATION ZONE
Losses are believed to originate at the drill bit in the following situations :
• if they are observed when drilling ahead;
• if they are accompanied with a significant change in the rate of
penetration, torque, or vibration;
• if the loss occurs while entering a fractured, vugular, or high-permeability
zone known from geological data.
Losses are believed to occur not necessarily at the drill bit under the
following circumstances [46]:
• l losses are observed while tripping or increasing the mud weight;
• losses are observed in a shut-in or killed well.