Drilling School for IPM Well Site Supervisors
Drilling Problems
& Solutions
Section – 4
Lost Circulation
Objectives
On completion of this module you will be able to:
• Understand what is Lost Circulation and it’s effect on
drilling operations.
• Be able to indentify different types of loss circulation.
• Describe methods of preventing loss circulation.
• Be able to recommend the best remedy that corresponds
to particular loss circulation type.
Problems Derived from Loss Circulation
Conditions of Lost Circulation
According to the amount of mud lost to the formation, the lost
can be:
Partial (seepage, reduced return to surface)
Total (no returns seen at surface)
Even in an area with lots of information / experience it’s difficult
to make a valid recommendation
Should use a systematic approach
– Preventive
– Corrective
Classification of the Severity of Losses
Type Typical Loss Rate Typical Formation
Dynamic Static
Seepage < 10% < 10 bbl/hr Sands and Sandstones
Partial 10 % - 50 % 10 bbl/hr - Unconsolidated sand and gravel,
50 bbl/hr small natural or induced fractures
Severe 10 % - 50 % 50 bbl/hr - Long sections of unconsolidated
100 bbl/hr sand and gravel, larger natural or
induced fractures
Total 100 % > 100 bbl/hr Cavernous formations, large and/or
numerous natural or induced
fractures
Causes & Potential Lost-Circulation Zones
Lost circulation is caused by one of the two following mechanisms:
1. Natural losses: where invasion or whole fluid is lost to
formations that are
a. highly permeable
b. unconsolidated
c. fractured
d. cavernous / vugular
2. Induced losses (Fracturing): where the drilling fluid is lost due
to excessive pressure that hydraulically breaks the formation
Natural Losses
Unconsolidated Formations
• Shallow sands or gravel or shell bed (reef formations).
• High matrix permeability (10…100 Darcies)
• It may cause formation to wash out, that could cave in more easily
from overburden and rig weight.
Natural Fractures
• Mud loss also occurs to fissures or fractures on wells where no
coarsely permeable or cavernous formations exist.
• Natural fractures exist in many cases, which may be impermeable
under balance pressure conditions.
• Losses may also occur at unsealed fault boundaries.
• Sub-salt rubble zone: formation is immediately below the salt are
either mechanical weaker or highly fractured (usually shale).
Natural Losses
High Permeable / Low Pressure Formations
• Depleted formations (usually sands). Subnormal formation pressure
due to the extraction of the formation fluids.
Cavernous and Vugular Formations
• Usually associated with low-pressure carbonate (limestone and
dolomite) or volcanic formations.
• When vugular formations are drilled, the drillstring may fall freely
through the void zone and rapid loss of mud is usually experienced.
• The volume and persistence of this kind of loss depends on the
degree to which the vugs are interconnected.
Natural Losses
Induced Losses
MECHANICAL FORCES
Improper hydraulics
Excessive flow rates and fluid rheological properties resulting in
high Equivalent Circulating Density (ECD)
Drilling practices
Pump surging caused by increasing the pump rate too rapidly after
connections and trips
Raising and lowering the pipe too quickly (surge/swab)
Excessive Rate of Penetration
Excessive cuttings in the annular flow stream will result in high ECD
Once a fracture is created, it may be difficult to repair and it may
never regain the original formation strength. Lost circulation may
persist even though the pressure is later reduced.
Induced Losses
Hole Conditions
• Sloughing or caving shales: increased solids loading in the annulus
resulting in high ECD.
• Wellbore washouts: cuttings accumulated in enlarged hole sections
can fall back into the hole, leading to packing off /bridges.
• Cutting bed or Barite sag: forming on the low side of a directional
well. Localized density increase.
• Kick and well control procedures.
Induced Losses
Drilling fluid properties that have an effect on the pressure
losses on the annulus.
Drilling fluids properties
• Excessive drilling fluid density or increasing mud density too fast.
• Excessive viscosities and gel strengths.
• Buildup of drilled solid: low-Gravity Solids (LGS) and high
Methylene Blue Test (MBT) values.
• Thick filter cakes that reduces the hydraulic diameter of the
wellbore.
• Barite sag
Induced Losses
Identify the Type of Loss Zone
Shallow Unconsolidated Natural Fractures Induce Fractures Cavernous Zones
Formations (limestone and some (normally limestone)
hard shales)
Offset records that Offset records and Offset records that Normally confined to
identify the zone and its geological markers include excessive annular limestone and dolomite
characteristics hydraulics
Gradual lowering of mud May occur in any type of Could occur in any type Loss of returns is usually
level in pits hard, brittle rock of rock, but would be sudden and complete
expected in formations
with weak planes, like
soft shales
Loss may become Loss is evidence by Loss is usually sudden Bit may drop from few
complete if drilling is gradual lowering of mud and complete inches to a few feet just
continued in pits preceding loss
Loss may become Loss may follow any Excessive torque may be
complete if drilling is increase in mud weight experience before loss
continued and more or sudden surge in
fractures are exposed pressure
Can be in competent or
incompetent formations
Loss of Mud Volume at Surface
Pit Level
Pores/Perm
Matrix
Loss of Mud Volume at Surface
Pit Level
Natural
Fractures
Loss of Mud Volume at Surface
Pit Level
Induced
Fractures
Loss of Mud Volume at Surface
Pit Level
Cavernous
Preventive Measures
• Casing setting.
• Do not exceed critical tripping speeds (surge pressure).
• Monitor effect of high ROP (annular loading and ECD).
• Caution when starting pumps – break gels mechanically.
• Optimize hydraulics in sensitive areas.
• Wash and ream cautiously through bridges.
• Early kick detection –lower the pressure in the annulus.
• Proper drilling fluids properties: density, viscosity, gel strength, fluid loss
(filter cake), bridging material size.
Anything that reduces the annular clearance
causes a pressure increase
Classification of Lost-Circulation Materials
Lost-Circulation Materials can be classified into six types:
Fibrous
Granular
Flaked or platelet
Mixed
High fluid-loss squeezes
Reinforcing plugs
Classification of Lost-Circulation Materials
Lost-Circulation Materials are supplied in three grades:
Fine materials
under most circumstances will pass through the shaker
screens and stay in the system
Medium materials
tend to be screened out, but most likely will not plug
jets or MWD tools
Coarse materials
can plug off everything except open-ended drill pipe
LCM
Fibers Granular Flakes Blends
Brush Shingle
FedSealTM
Heap Bridging Like
M-I SealTM
Effect Effect
Wood Fiber
Calcium
Drilling Paper Cellophane TigerBulletsTM
Carbonate
Mineral fiber
Cottonseed
Hulls Walnut Mica
Sawdust
Lost Circulation Control and Remedial Options
Sealing Materials to Combat Naturally Occurring Lost Circulation:
Prevention and Control of Lost Circulation
Running LCM in the drilling fluid
• 15 - 20 lb/bbl LCM
• Problems!!!…might require bypassing the shakers
Maintaining good drilling fluid properties
• Density, YP, PV and gel strengths.
• Low MBT levels.
• Solids control.
Keep ECD to a minimum
• Use Hydraulic software to estimate ECD.
• Downhole annular pressure measurement.
• Avoid excessive rate of penetration (ROP).
Prevention and Control of Lost Circulation
Minimize Surge & Swab Pressures
• Use hydraulics software determining trip velocity and acceleration
schedule.
• Break circulation while tripping in.
• Rotate pipe before turning on the pumps.
• Run casing /liner slowly to avoid surge pressures.
Downhole equipment
• Remove bit nozzles if large losses are expected.
• Minimize the BHA (i.e., no stabilizers, minimum DC & HWDP).
Always have a contingency plan to deal with fluid loss
Corrective Measures
Seeping losses Partial Losses Complete Losses Partial or Complete Severe Complete
(bridging agents do (gravel, small (long section of Losses Losses
not form a seal) natural fractures, gravel, long interval (induces fractures) (large open natural
barely open induced of small fractures, fractures, caverns
fractures) large natural and open induced
fractures or open fractures)
induce fractures)
Mixing LCM slurry Mixing LCM slurry High filter loss slurry Soft plug squeeze Squeeze with either
containing fine to containing medium squeeze a high-filter-loss
medium bridging to large bridging slurry squeeze or
agents or utilizing a agents or utilizing a large amounts of
high filter loss slurry high filter loss slurry diesel-oil-bentonite-
squeeze squeeze cement slurries
Hard plug such as Mixing LCM slurry Drilling blind or with
cement, cement- containing large aerated mud. Setting
bentonite, cement- bridging agents or casing should be
gilsonite or diesel - utilizing a high filter considered
oil-bentonite- loss slurry squeeze
cement
Reduce mud weight Reduce mud weight Reduce mud weight
if possible if possible if possible
Lost Circulation Treatments
Loss Severity LCM size Shape
Medium - coarse Granular
Severe
Medium - coarse Fibre
Medium - coarse Flake
Sodium silicate & Cement
Total Gunk treatments
Polymer treatments
MWD LCM Operational Specification
Schlumberger Sugar-Land Product Center (SPC) carries out specification LCM
qualification test on the MWD tools. The LCM operational and environmental
specifications for the MWD tools are as follows:
PowerPulse*
Maximum Lost Circulation Material Size: Medium NUT PLUG
Maximum concentration: 50 lb/bbl
IMPulse*
Maximum Lost Circulation Material Size: Medium NUT PLUG
Maximum concentration: 50 lb/bbl
SlimPulse*
Maximum Lost Circulation Material Size: Medium NUT PLUG
Maximum concentration:
C3 to C8 Version “C” and version “G”
modulators: 40 lb/bbl
C1 and C2 Version “C” modulators: 2 – 3 lb/bbl medium nut plug or
20 – 30 lb/bbl CaCO3 or similar material
Above these limits is no guarantee of good MWD operations.
Reinforcing Plugs
Water-based squeeze
• High-filter-loss squeeze (Salt gel – diatomaceous earth).
• Diesel-Oil Bentonite (soft plug).
• Crosslinked Polymer (soft plug).
• Diesel-Oil / Bentonite / Cement (hard plug).
• Cement Slurry (hard plug).
Oil-based squeeze
• Diatomaceous earth.
• Calcium carbonate.
• Gunk squeeze for oil muds.
Lost Circulation Control and Remedial Options
Plugs Available for Sealing Loss Circulation Zones:
Lost Circulation Control and Remedial Options
Recommended Formulations for Sealing Plugs:
concentrations vary from 200 to 400 lbs of bentonite
per barrel of diesel (2 to 4 Sacs per barrel)
concentrations vary from 300 to 500 lbs of 1:1
bentonite/cement blend per barrel of diesel (about 3 to
5 sacs of cement and 3 to 5 sacs of bentonite mixed
per barrel of diesel)
Lost Circulation Control and Remedial Options
Soft Plug Squeezing Procedure:
Lost Circulation Control and Remedial Options
Summary
Any mud system can be used to drill in lost circulation
zones:
• Materials and Procedures developed to minimize mud losses.
Good well planning including lost circulation contingency
plans need to be in place
• Use best available technology on critical wells.
• Research the well design.
• Observe good drilling practices.
