PROBLEMS RELATED TO DRILLING FLUIDS 钻井液相关问题 Chapter 8 Principles of Drilling Fluids...

PROBLEMS RELATED TO DRILLING FLUIDS

钻井液相关问题

Chapter 8

Principles of Drilling Fluids钻井液工艺原理

Prof. Dr. Xiuhua Zheng E-mail: [email protected] 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

mailto:[email protected]

Test for §7

1. Water base muds2. Subsurface formation pressures3. suspending agent4. weighting materials5. Thinners6. Fluid loss control7. Dispersed8. Non-Inhibited9. 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

钻井液 Drilling Fluids 2010中国地质大学 ( 北京 ) page 3

China University of Geosciences (Beijing)§8

Problems related to the drilling fluids

Glossary of §8

1. Diagenesis2. Water sensitive 3. Sloughing/collapse4. Cation Exchange Capacity5. Encapsulator6. Lubricants7. Penetration rate 8. Loss Circulation9. Sticking10.Borehole stability

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




Contents

1. Borehole stability 井壁稳定

2. Loss Circulation 井漏

3. Drilling String Sticking 卡钻




1. Borehole stability

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 Cause of Borehole Instability

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.




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 Hard-ness

MBTMeq/100g

Water Clay content, %

Type %(w)

%(w)

Clay type ρg/cm3

Character

S I S-I C

1 S 20-40 F&B 25-70 20-30 40.4 5.5 1.2-1.5 H.D

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 35.0 15.0 15.0 2.5-2.7 H,L.D,T.O.S





• 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.B-Extreme hard & brittle, T.O.D&C-Tendency of dispersion &collapse, L.D-Less disperable




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.




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.




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.




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.




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.




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.




1.3.3 Selection of Inhibitive Mud System and Addition of Shale Inhibitive Agents




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.




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.




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.




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.





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





Fig. 2-1. Fracturing test of curve





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. 2-1 Where : P --Hydrostatic pressure, psi, --Drilling fluid density in well bore, lb/gal, H--True vertical depth of the well, ft.

052.0




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




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




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 barite-diatomite slurry is shown in the following table (Table 2-2).




2.3.2 Partial Loss

Table 2-2 Formulation of P reparation of 1 bbl Bentonite-Diatomite Slurry




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





Table 2-4 Formulation of Diesel-Bentonite Slurry

Table 2-5 Formulation of Diesel-Bentonite Slurry





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.




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




Fig 3-1 Differential pressure sticking mechanism




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).





Table 3-2 Comparison of Various Mud Lubricants





Table 3-3 Lubrication Coefficient of Different Types of Drilling Fluids




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




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.





• 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.




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.




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.




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.




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.




Discussion

The concepts of hole stability, lost circulation, Sticking pipe and the Effects of drilling fluids them.

PROBLEMS RELATED TO DRILLING FLUIDS 钻井液相关问题 Chapter 8 Principles of Drilling Fluids...

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