Oil Base Muds Drilling Fluid Engineering Part IV By Rahman Ashena

1

Definition  The drilling fluids in which the continuous phase is

composed of a liquid hydrocarbon usually Diesel or Gas2oil is an Oil Mud or Oil Base Mud.  Number 2 diesel is usually used.

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R. Ashena

Oil Muds  The top sections are usually drilled by water base muds.  Then oil base muds are drilled at depth.  When Asmari Reservoir is finished drilling, oil muds are

used.

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R. Ashena

Oil Muds/Formations  Pabdeh, the source rock of Asmari and Gurpei

Formations are drilled by Oil Muds as shale inhibitors.  Ilam and Sarvak Reservoirs are then drilled by Oil

Muds.  Kajdomi Formation, the shaly formation, could be drilled by oil muds saturated by KCl as inhibitors.

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R. Ashena

Emulsion-Suspension  Emulsion: The mixture of liquid in liquid.  Suspension: The mixture of solid in liquid.

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R. Ashena

6

No .

Additives of 59 pcf Oil Base Mud

Value in 100 bbl mud

Value in 150 bbl mud

Oil Base Mud in Lab

1

Gasoil (bbl)

73

110

0.4 liter

2

Fluid Loss Control (sacks)

18-20

27-30

0.3 g

3

Primary EmulsifierD.Vert (drum) ‫اﯾﺠﺎد ﮐﻨﻨﺪه اﻣﻮﻟﺴﯿﻮن‬

2

3

6-7 ml

4

Lime (sacks)

18-20

27-30

0.3 g

5

Saturated CaCl2 (bbl)

19

28.5

4-5 cc

6

Secondary EmulsifierMul (drum) ‫ﺛﺎﺑﺖ ﮐﻨﻨﺪه اﻣﻮﻟﺴﯿﻮن‬

0.8

1.2

3-4 ml

7

D.Gel(sacks)

3-4

5-6

0.3 g

R. Ashena

Making Oil Muds in Lab jjMixing time/min

1

2

3

4

187.5

181.5

187.5

181.5

10.5

10.5

10.5

10.5

few

Diesel oil

10

Primary emulsifier

10

Lime hydrated

(gr)

12

8

12

8

15

f.l.c

(gr)

13

10

13

10

20

Salt saturated water

140

57

-

-

20

Cacl2 saturated water (ml)

-

-

140

57

15

Second emulsifier

(ml)

3.5

3.5

3.5

3.5

15

Viscosifier

(gr)

0.5

0.5

0.5

0.5

15

Limestone powder

-

245

-

238

64

90

64

90

60/40

80/20

-

7

composition

R. Ashena

Mud Weight (PCF) O/W

(ml) (ml)

(ml)

(gr)

60/40 80/20

Diesel/Gasoil  CaCl2 is added to ensure that no caving would take

place when drilling formation containing CaCl2.  Diesel or Gasoil are both true.  Since, Gasoil is used in diesel machines, it’s called diesel

too.

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R. Ashena

Diesel Types Diesel Type or No.

Description

1

similar to Kerosene that boil off right after Gasoline or road diesel which is the diesel that trucks and some cars run on is a distillate fuel oil and rarely used. a blend of distillate and residual fuel oil which is a heavy distillate

2 3 4

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Why Diesel No.2 in Oil Muds?  Viscosity Characteristics  Low flammability  Low solvency for rubber (low aromatics)

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Oil Phase Properties  Flash Point: min T @ which vapors above oil can be ignited

by a flame.  Fire point: min T @ which sustanied combustion of vapors above oil is maintained  Oil phase fire point>200°F (safety)

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R. Ashena

Oil Phase Properties  Aromatic HC causes rubber softening (in BOP, etc)

less aromatics  Oil must have acceptable viscosity over a range of P & T.  As T increases, viscosity decreases.

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R. Ashena

Chemical Emulsifier  Is added to inhibit water droplets from coalescing

and settling out of the emulsion.  Water existing in Oil Muds is in the form of an

emulsion.  It also helps the water existing in the rock to emulsify easily.

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R. Ashena

Wetting Agent  ‫ﺗﺸﮑﯿﻞ اﻣﻮﻟﺴﯿﻮن ﺟﺎﻣﺪ در ﮔﺎزوﯾﯿﻞ‬  ‫ﺗﺸﮑﯿﻞ اﻣﻮﻟﺴﯿﻮن آب در ﮔﺎزوﯾﯿﻞ‬  Chemical wettability reversal agent: makes solids wet

by oil rather than water.  Otherwise: solids will be absorbed by the water droplets & cause high viscosities Sag

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Advantages  Good rheology at high temperature  Inhibitive against shale  Less corrosion  Good lubricating  Mud density as low as 7.5 ppg

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disadvantages  Higher initial cost  Pollution concerns  Ineffective logging  Gas is dissolved in liquid

hard to detect gas kicks

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Oil mud frequency  Much less frequent  Reasons:  Higher initial cost  Pollution problems

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R. Ashena

Where oil muds  Deep hot formations (T>300°F)  Drilling salt, Anhydrite, active shale, reservoirs.  Directional drilling when high torque is a problem  Prevention of freeing stuck pipe  Drilling subnormal formations  Corrosion control

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Oil Mud Cost  Initial high cost  Reduce overall drilling costs to offset initial cost

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R. Ashena

(Emulsified) Water phase  Increases mud viscosity like inert solids  Slight increase in mud density  Water is less expensive

less cost of oil mud  Can be as high as 50% of mud volume  Decrease water content to prevent excessive mud viscosity [with density increase] a highly weighted mud has a water content of 12%

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R. Ashena

Chemical composition of water phase  Inhibitive properties of oil muds  In non-shale, sea or fresh water  In shale, saturated CaCl2 or NaCl water

[[chemical potential of water in mud=chemical potential of water in shale]]  NaCl & CaCl2 alter mud activity  [[balanced activity oil mud]]

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‫‪Emulsifier‬‬ ‫‪ Ca/Mg Fatty acid Soap‬‬ ‫ﺷﺎﯾﻊ ﺗﺮﯾﻦ ﻧﻮع اﻣﻮﻟﺴﯿﻔﺎﯾﺮ در ﮔﻞ ھﺎی ﭘﺎﯾﮫ روﻏﻨﯽ ﻧﻮع ﺻﺎﺑﻮن ‪‬‬

‫ﺣﺎﺻﻞ از اﺳﯿﺪ ﭼﺮب ﻣﯽ ﺑﺎﺷﺪ‬ ‫ﻟﮑﻦ ھﺮ ﮔﻮﻧﮫ ﺻﺎﺑﻮن ﻗﺎﺑﻞ ﺣﻞ در روﻏﻦ ﻣﯽ ﺗﻮاﻧﺪ اﺳﺘﻔﺎده ﺷﻮد‪ .‬‬

‫‪R. Ashena‬‬

‫‪22‬‬

Formation of Fatty Soap Emulsifer 12, 14, 16 or 18 Carbons OH

CH 3  CH 2  (CH 2 ) n  C  O  NaOH  CH 3  CH 2  (CH 2 ) n  C  O  H 2O ONa+ Long HC Chain Portion: Soluble in oil

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Ionic Portion: soluble in water

Emulsifier Mechanism  Accumulates at oil/water interface ends & forms a

stable emulsion  This reduces IFT (surface energy of the interface)

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Emulsifier Types  With monovalent cation (like Na+)

has a single

HC chain  With divalent cation (like Ca2+ or Mg2+) has 2 HC chains convex oil surface water in oil emulsion (invert emulsion)  ‫ﯾﻌﻨﯽ آب رﻓﺘﮫ در ﻧﻔﺖ‬  Relative oil/water amounts are important too. ‫ ﭼﯿﺴﺖ؟‬deemulsifer ‫ و‬emulsifier ‫ ﺳﻮال( ﻓﺮق‬ ‫ در ﻣﺮاﮐﺰ ﻧﻤﮏ زداﯾﯽ ﺟﮭﺖ ﺟﺪاﯾﯽ آب و ﻧﻔﺖ‬deemulsifer (‫ ﺟﻮاب‬ ‫از ﯾﮑﺪﯾﮕﺮ ﺟﮭﺖ ارﺳﺎل ﻧﻔﺖ در ﮐﻨﺎر روش ھﺎی ﺣﺮارﺗﯽ و ﻣﯿﺎدﯾﻦ‬ .‫اﻟﮑﺘﺮﯾﮑﯽ ﺑﮑﺎر ﻣﯽ رود‬ 25

R. Ashena

Oil Mud

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R. Ashena

Other Emulsifiers  Organic Acid Type Soap  Cacium Naphtenic Acid Soaps

aromatic structure  Soaps made from Rosins (Pine tree soap) Branched chains & aromatic structures  Soaps from organic amines instead of organic fatty acids

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Solids of oil muds  When water wet solids are introduced to the emulsion, solids

accumulate in water Sag

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R. Ashena

high viscosity of water

Water wet solids  They tend to cause formation of an oil-in-water

emulsion rather water-in-oil.

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R. Ashena

Wettability control agents  Wettability control agents are added to diesel.  Perform like surfactants.  Similar to emulsifiers  One end(s): soluble in oil  The other end: soluble in water

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R. Ashena

Emulsifiers are wetting agents?  They are  They are not fast enough to handle a large influx of water

wet solids during fast drilling or mud weighting operations Special surfactants for oil wetting

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R. Ashena

Emulsion stability  Loose emulsion: Presence of water wet solids  Emulsion stability is assessed by electrical stability tests  As we drill further, emulsion stability requires more

emulsifer.

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R. Ashena

Loose Emulsion Physical Signs  Less shiny surface  Cuttings adhere to each other or to shale shaker (gummy)

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R. Ashena

Viscosity Control  Emulsified water  Viscosity increase  Less total cost

 Soap  Viscosity increase

 Asphalts  Some heavy HC go into solution  Some are carried as colloids.

 Amine Treated Bentonite

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R. Ashena

Viscosity Control  Dispersed in oil mud  Form colloid

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R. Ashena

Filtration Control  Excellent filtration properties  Rarely require FLC  Filtrate is diesel (continuous phase)

*no hazard to reservoir.

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R. Ashena

FLC  Polymer  Asphalt  MnO  Amine Treated Lignite

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R. Ashena

Density Control  Barite: most common  Barite Sag: very probable  Reason: oil muds have low gel strength.

 CaCO3: relatively low MW

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R. Ashena

Alkalinity Control  Lime is used to maintain oil mud alkalinity.  8.5
control corrosion & get best performance of emulsifiers  0.5
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R. Ashena

Superiority of Oil Muds to Water Muds  Has large reserve of undissolved lime when drilling

H2S or CO2 bearing zones

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R. Ashena

Solid Removal  Hydrocyclones & Centrifuges are not economical  Reason: they discard the expensive liquid phase.

 Dilusion is expensive (‫ﻣﮕﺮ اﯾﻨﮑﮫ ﺑﺎ اﺳﮑﺮﯾﻦ ﻧﺘﻮاﻧﯿﻢ ﺟﺪا ﮐﻨﯿﻢ‬  Only screening: screen as fine as 200 mesh  Screening is effective in oil muds.  Reason: cutting disintegration does not usually happen (oil

muds are inhibitive).

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R. Ashena

Adding water with Time in Depth  High Temperature

water evaporation add water to prevent salinity & activity change of oil muds

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R. Ashena

Oil Base Muds

Additives of 59 pcf Oil. Base Mud. Value in. 100 bbl mud. Value in 150 bbl mud. Oil Base. Mud in Lab. 1. Gasoil (bbl). 73. 110. 0.4 liter. 2. Fluid Loss Control (sacks). 18-20. 27-30. 0.3 g. 3 Primary EmulsifierD.Vert. (drum) نﻮﯿﺴﻟﻮﻣا هﺪﻨﻨﮐ دﺎﺠﯾا. 2. 3. 6-7 ml. (drum) نﻮﯿﺴﻟﻮﻣا هﺪﻨﻨﮐ دﺎﺠﯾا. 4. Lime (sacks). 18-20. 27-30. 0.3 g. 5. Saturated ...

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