Principles of Drilling Fluids
钻井液工艺原理
Chapter 8
PROBLEMS RELATED TO DRILLING FLUIDS
钻井液相关问题
Prof. Dr. Xiuhua Zheng
E-mail: Xiuhuazh@cugb.edu.cn
Exploration Dept. School of Engineering and Technology, China University of Geosciences(Beijing)
中国地质大学(北京)工程技术学院勘查教研室
Test for §7
1. Water base muds
2. Subsurface formation pressures
3. suspending agent
4. weighting materials
5. Thinners
6. Fluid loss control
7. Dispersed
8. Non-Inhibited
9. Inhibited
10. Non-dispersed
1. 水基钻井液
2. 地层压力
3. 悬浮剂
4. 加重剂
5. 稀释剂
6. 滤失控制
7. 分散
8. 非抑制
9. 抑制
10. 不分散
Glossary of §8
1. Diagenesis
2. Water sensitive
3. Sloughing/collapse
4. Cation Exchange Capacity
5. Encapsulator
6. Lubricants
7. Penetration rate
8. Loss Circulation
9. Sticking
10. Borehole stability
Drilling Fluids
§8
1. 成岩作用
2. 水敏性
3. 坍塌
4. 阳离子交换容量
5. 包被剂
6. 润滑剂
7. 机械钻速
8. 井漏
9. 卡钻
10. 井壁稳定
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Contents
1. Borehole stability
井壁稳定
2. Loss Circulation
井漏
3. Drilling String Sticking
卡钻
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1. Borehole stability
1.1 Cause of Borehole Instability
Borehole instability is a result of complexity of actions of
varied factors. Unstable formations are predominately
shale formations therefore the problem of borehole
instability is essentially the problem of shale.
1.1.1 Inherent Mechanical Instable Formations
Some formations themselves are mechanically instable
formations because the characteristics of diagenesis(成岩
作 用 ) and geological-structural movements in their
sedimentation process manifest as sloughing, falling,
collapsing and creeping when they are exposed in drilling
process.
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1. Borehole stability
1.1.2 Water Sensitive Chemical-Physical Instable Formations (理化敏感
地层)
Water sensitive chemical-physical instable formations are basically shale
formations. The instability of these formations derives from hydration and
followed swelling, dispersion and disintegration of shale when it is in contact
with water. five categories of shale are classified as shown in the following
Table (Table 1-1). Table 1-1 Classification of Shale
Type
Hardness
MBT
Meq/
100g
Type
Water
%
(w)
%
(w)
Clay content, %
Clay type
S
I
S-I
C
ρ
g/cm3
Character
1.2-1.5
H.D
1
S
20-40
F&B
25-70
20-30
40.4
5.5
2
H
10-20
B
15-25
20-30
25.4
42.0
0.7
1.5-2.2
L.H.D
3
VH
3-10
B
5-15
20-30
38.3
13.0
2.2-2.5
M.D,T.O.S
4
EH
10-20
B
2-10
20-30
18.1
8.3
2.3-2.7
E.H.&B,T.O.D&C
5
B*
0-3
B
2-5
5-30
15.0
15.0
2.5-2.7
H,L.D,T.O.S
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1. Borehole stability
• Where:
• Clay type：S- Smectite, I-Illite, S-I- Smectite, I-Illite, C-Clorite
• Hardness: S-Soft, H-Hard, VH-very hard, EX-Extreme hard, B*Brittle
• Water type: F&B-Free & Bounded, B-Bounded
• Character: H.D.-High dispersable, L.H.D-Less high dispersable,
M.D-Medium disperable, T.O.S-Tendency of sloughing, E.H.BExtreme hard & brittle, T.O.D&C-Tendency of dispersion &collapse,
L.D-Less disperable
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1.1.3 Mechanically Induced Borehole
Instability(力学原因诱发的井壁不稳定)
Improper drilling technical-engineering measures very
often provoke borehole instability such as:
A. Lower than required mud density can not create an
adequate hydrostatic pressure to hold varied down-hole
pressures in balance as before the formations are not
drilled out.
B. Reduction of mud column height by pipe pulling out.
C. Surge or swab resulted from excessively fast pulling or
lowering of drill string may fracture or break down
formations and result in loss of circulation and collapse.
D. Collapse as consequences of uncontrolled loss of
circulation, kicks or blowout.
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1.1.3 Mechanically Induced Borehole
Instability(力学原因诱发的井壁不稳定)
E. Washout and erosion of borehole wall caused by
turbulent flow or long time circulation against an interval of
formations.
F. Collapse caused by collision of drill pipe on "dog leg" or
on segments of formations with sudden change of
inclination or orientation.
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1.2 Indications and Judgement of Borehold
Instability（井壁不稳定的显示和判断)
A. Excessive cuttings on shale shakers and detritus（碎石）
of sloughing or caving shale.
B. Borehole packing-off and bottom filled up and abnormal
amount of cuttings, pump burst at starting or failure of pump
start after a trip in.
C. Build-up of massive cutting beds manifested by trip lags
in defined intervals, difficulty, abnormal pressure or pump
burst at pump starting or sudden drill pipe reversion in drill
pipe running or reaming operations.
D. Stuffed lower portion of dill collars and bit nuzzles by
cuttings.
E. Excessively enlarged hole determined by caliper log.
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1.3 Obtaining stabilized Borehole and
Prevention of Instability
1.3.1 Get Knowledge on Instable Formations(认识不稳定地层)
Collect shale samples of varied intervals and conduct the
following tests:
•
•
•
•
•
•
•
•
X-ray diffraction for petrographical(岩石) and mineralogical analysis.
Cation Exchange Capacity test.
Water content.
Expansion test.
Dispersion and recovery test.
3-dimentional stress test(三轴应力测试).
Capillary Suction Time (CST) test（毛细管吸入时间测试）.
Shale Stability Index or SSI test.
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1.3.2 Properly Determine and Adjust Mud
Density(确定和调整钻井液密度)
According to a field statistics, 80-90% of cases of
borehole instability were provoked directly by loss of
mechanical balance of borehole pressures. so do not raise
mud density too fast and over the formation fracturing limit
in order to avoid irritation of loss of circulation and
formation break down.
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1.3.3 Selection of Inhibitive Mud System and
Addition of Shale Inhibitive Agents
1.3.3.1 Shale inhibitive agents(页岩稳定剂)
There are: Polymer encapsulator(包被剂)，Inorganic
（无机盐） inhibitors or electrolytes，Asphaltic products，
Cationic polymers，and so on.
1.3.3.2 Inhibitive drilling fluid systems(抑制性钻井液体系)
Calcium base mud (lime mud, gypsum mud).
Salt water mud.
KC1-PHPA mud.
Silicate mud or organosilicon mud.
Glycol-polyglycol mud（聚合醇钻井液）.
Formate（甲酸盐）mud.
Oil base mud and W/O invert emulsion drilling fluid.
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1.3.3 Selection of Inhibitive Mud System and
Addition of Shale Inhibitive Agents
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1.3.4 Proper Drilling Engineering Measures（合
适的钻井工艺）
1. Control drill pipe pulling and running speed to avoid
excessive surge and swab caused by pipe movement.
2. Apply adequate pump rate and adjust mud rheological
properties to ensure laminar or transitional flow
pattern（过渡流型） and reduce borehole mechanical
erosion.
3. Maintain a proper gel strength and start pump gently to
avoid excessive surge and swab pressures.
4. Control pipe rotation speed to reduce drill pipe collision
onto borehole wall.
5. Keep a full borehole by pumping mud in annulus during
drill pipe pulling process.
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1.4 Borehole Instability Remedial Procedure
(井塌事故的处理)
1.4.1 Un-aggravated Cases of Borehole Instability（一般井塌)
Abnormal amount of sloughing and caving shale on
shakers ， excessive torque and drag on trips or
connections.
1.4.2 Severe Cases of Borehole Instability（严重井塌）
When severe cases of borehole instability occur, the
phenomena as aggravated torque and drag or sudden
reverse on connections and trips, abnormal difficulty of
pump starting or pump burst, no progress of reaming,
stuffing of bit nozzles or lower portion of drill collars by
cuttings, sudden abnormal pressure build up or sudden
stuck drill pipe may be encountered.
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2. Loss Circulation（井漏）
2.1 Causes and Types of Loss of Circulation(井漏的原因和类型)
There are: Seepage Loss（渗透性漏失）， Natural Fissure（裂缝）
and Cavern Loss（空洞性漏失）， Induced Fracture Loss。
2.1.1 Seepage Loss（渗透性漏失）
A Causes: Seepage loss occurs naturally under normal drilling
conditions in formations with permeability higher than 14 D such as
unconsolidated sands, massive coarse sandstones, gravels or reef
deposits（礁石沉积层）
B indications: Seepage loss appears generally as repeated or
successive losses with a relatively low rate in range of tens of barrels
per hour and in most cases no evident pump pressure drop shows.
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2.1 Causes and Types of Loss of
Circulation(井漏的原因和类型)
2.1.2 Natural Fissure（裂缝）and Cavern Loss（空洞性漏失）
A Causes: This kind of loss of circulation occurs in carbonate（石灰
岩 ） , dolomite and chalk （ 白 云 岩 ） formations with fissures and
caverns, faulted formations, discordant formation faces, shatter belts,
fractured zones and eruptive cavernous and vugular formations.
B Indications: Sudden and severe loss of circulation without return
and loss rate may reach couple to hundreds of barrels per hour very
often accompanied by sudden erratic rates of penetration or drilling
break.
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2.1 Causes and Types of Loss of
Circulation(井漏的原因和类型)
2.1.3 Induced Fracture Loss
A. Causes: This kind of loss of circulation occurs when formations
are fractured by improper engineering operations such as overweighted
mud introduction, excessively fast lowering of drill string or brute pump
starting.
B. Indications: Depending on the magnitude of fracture induction
pressure and strength of formations, the rate of loss is quite different
and some time, loss rate can be hundreds of barrels per hour or even
greater.
C. When pressure in the borehole is raised to a certain value, it may
cause the formation to be fractured and begin to absorb a great mass
of drilling fluid from well bore. The hydrostatic pressure in borehole of
this case is right equal to the formation fracture pressure. The
procedure is as follows fig 2-1
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2.1 Causes and Types of Loss of
Circulation(井漏的原因和类型)
Fig. 2-1. Fracturing test of curve
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2.1 Causes and Types of Loss of
Circulation(井漏的原因和类型)
2.1.4 Hydrostatic Pressure of Drilling Fluid Column
The hydrostatic pressure of drilling fluid is the pressure of drilling
fluid column in static state exerted on the bottom of the well.
  0.052   
2-1
Where :
P --Hydrostatic pressure, psi,
 --Drilling fluid density in well bore, lb/gal,
H--True vertical depth of the well, ft.
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2.2 Prevention of Loss of Circulation
(井漏的预防)
The following measures can be taken for prevention of loss
of circulation:
1.Carefully collect and analyze the regional geological information
and properly design casing program and mud density in different
intervals of a well;
2.Reduce surge and swab pressures;
3. Lower and pull drill string in a gentle way, and so on.
4.Add a certain amount and proper type of LCM according to the
formation nature and mud properties.
5. Weight mud to the required density in several circulating circles
and conduct pressure control procedure as required right away when
abnormal pressure formations are encountered. And so on
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2.3 Remedial Measures for Loss of
Circulation（井漏的处理）
2.3.1 Seepage Loss
If pump pressure decreases, and reduced flow rate in
flow-line and drop of level in mud tanks are observed
during drilling process, it means seepage loss of circulation
occurs. We must take measure as follows:
1. Stop pump for observation
2. Add some viscosifiers such as lime, CMC, PAC, MMH,
XC, and so on.
3. reduced pump rate and lowered penetration rate
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2.3.2 Partial Loss
One of the following measures can be taken based on
the specific conditions:
1. Add some viscosifiers and LCM of different shapes and
sizes.
2. Pump a pill of thick mud mixed with 30-40 lb/bbl LCM of
varied shapes and sizes against the loss interval.
3. Squeeze a high filtration barite-diatomite slurry into the
loss zone at a lowered rate. The formulation of baritediatomite slurry is shown in the following table (Table 2-2).
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2.3.2 Partial Loss
Table 2-2 Formulation of P reparation of 1 bbl Bentonite-Diatomite Slurry
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2.3.3 Loss of Circulation without Return
A. Squeeze and set cement or soft plug slurries.
Extensively used plug slurries are quick setting bentonite-cement,
diesel-bentonite, lime-bentonite plug and quick setting cement slurries(
纯水泥浆).
Table 2-3 Formulation of Quick Setting Bentonite-Cement Slurry
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2.3.3 Loss of Circulation without Return
Table 2-4 Formulation of Diesel-Bentonite Slurry
Table 2-5 Formulation of Diesel-Bentonite Slurry
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2.3.3 Loss of Circulation without Return
B. Drill blind without return and attempt to cure the loss by plugging
effect of cuttings.
C. Change to drilling with foam, mist or air.
D. Introduce casing to seal the loss zone, this is the most safe and
certain measure.
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3. Drilling String Sticking（卡钻)
Drill string sticking can be divided into the following
types: differential pressure sticking, cutting precipitation
sticking, cutting bridge sticking, formation collapse sticking,
tight hole sticking, key-seat sticking and falling object
sticking.
3.1 Differential Pressure Sticking
When a section of drill string stays in contact with borehole wall of a
permeable formation for a interval of time, the string may be pressed
tightly into the wall and the driving power on the string can not
overcome the friction and adhesion of the string on the wall surface and
the string can't be moved (pulled up, lowered down or rotated) under
the differential pressure between the mud hydrostatic pressure and the
formation pressure--a differential pressure sticking occurs
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Fig 3-1 Differential pressure
sticking mechanism
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3.1.2 Prevention Measures
1. Apply a reasonably lower mud density.
2. Select adequate drilling fluid system.
3. Move drill string accordingly in process of mud
circulation and equipment repairs
4. Add some mud lubricants to improve lubrication
character of mud and mud cake. The lubricity of different
lubricants and drilling fluid systems are listed in the
following tables (Table 3-2, Table 3-3).
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3.1.2 Prevention Measures
Table 3-2 Comparison of Various Mud Lubricants
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3.1.2 Prevention Measures
Table 3-3 Lubrication Coefficient of Different Types of Drilling
Fluids
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3.1.3 Spotting for Stuck Pipe Release
The effective procedure for releasing the stuck pipe is submersing
the stuck interval of the drill string by spotting fluid. Formulation of oil
base spotting fluid can be seen in the following table (Table 3-4)
Table 3-4 Formulations of Oil Bade Spotting Fluids
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3.2 Cutting Precipitation Sticking and Cutting
Bridge Sticking(沉砂卡钻和砂桥卡钻)
3.2.1 Causes and Indications
1. Cutting precipitation sticking
Precipitation of abundance of cuttings onto bottom may cause stuck
pipe when pump is suddenly stopped since low mud viscosity and gel
strength and severe accumulation of cuttings in annulus resulted from
excessively high penetration rate and poor mud suspension capacity.
On the other hand, the bit may intrude into cuttings precipitated on
bottom and stuck pipe may occur at pipe connections.
2.Cutting bridge sticking
Cutting bridge may be built up in borehole steps formed by presence
of a series of alternations of soft swelling shale formations overlapped
by sloughing shale formations. If pipe lowering is too fast, the bit may
intrude into the cutting bridge and it results in cutting bridge sticking.
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3.2.2 Prevention Measures
• 1. Maintain good mud rheological properties
• 2. Control penetration rate in soft formations,
• 3. Remove drill cuttings on time and maintain borehole
and bottom clean by application of proper annular
hydraulics and running solid control equipment.
• 4. Gently lower the drill string while vigilantly watch pump
pressure gauge and weight indicator.
• 5. Avoid long-term circulation with bit unmoved against
an interval of hole in order to eliminate borehole erosion.
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3.3 Formation Collapse Sticking(缩径卡钻)
• 3.3.1 Causes and Indications
Formation collapse sticking is caused mainly by sudden
formation collapses that result from surge or swab
provoked by rude pipe pulling, lowering or collision of drill
string on borehole wall or improper starting of pump.
• 3.3.2 Prevention and Remedy
The principal manners for prevention of formation
collapse sticking are enhancing borehole stability by raising
mud inhibition and avoiding surge and swab caused by
pump starting and pipe movement.
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3.4 Salt Creeping and Tight Hole Sticking
（岩盐层塑性蠕动缩径卡钻）
• 3.4.1 Causes and Indications
When a rock salt formation is drilled out, it will expand or
creep continuously into borehole as a plastic object under the
over-burden pressure of the formations above and cause trip
difficulty, or even worse, it may result in sticking。
• 3.4.2 Prevention and Remedy
The creeping of rock salt and the related down hole troubles
can be resolved only by raising mud density and borehole
hydrostatic pressure to balance the overburden pressure,
usually the mud density must reach 2.40 g/cm3 or more.
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3.5 Key Seating Sticking（键槽卡钻）
•The key seating sticking is originated from inserting of drill
string into a key seat in an interval of formation. It is not
related to drilling fluid and is characterized by sudden
occurrence with normal circulation pressure as before and
without an abnormal amount of sloughed or collapsed
shale on shakers.
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3.6 Falling Object Sticking(落物卡钻)
•Failing object sticking is provoked by falling objects such
as bit cones or some pieces of manual tools or other
equipment into borehole and it is characterized by no
observation of rising of pump pressure and absence of
excessive cuttings on shakers.
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Discussion
 The concepts of hole stability, lost
circulation, Sticking pipe and the
Effects of drilling fluids them.
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