Oil Base Muds Drilling Fluid Engineering Part IV By Rahman Ashena

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

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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

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Primary EmulsifierD.Vert (drum) ‫اﯾﺠﺎد ﮐﻨﻨﺪه اﻣﻮﻟﺴﯿﻮن‬

2

3

6-7 ml

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Lime (sacks)

18-20

27-30

0.3 g

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Saturated CaCl2 (bbl)

19

28.5

4-5 cc

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Secondary EmulsifierMul (drum) ‫ﺛﺎﺑﺖ ﮐﻨﻨﺪه اﻣﻮﻟﺴﯿﻮن‬

0.8

1.2

3-4 ml

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D.Gel(sacks)

3-4

5-6

0.3 g

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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

-

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composition

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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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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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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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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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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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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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(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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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

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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

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Oil Mud

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

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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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Viscosity Control  Dispersed in oil mud  Form colloid

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

*no hazard to reservoir.

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FLC  Polymer  Asphalt  MnO  Amine Treated Lignite

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

 CaCO3: relatively low MW

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

H2S or CO2 bearing zones

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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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Adding water with Time in Depth  High Temperature

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

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