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
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Gasoil (bbl)
73
110
0.4 liter
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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)
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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
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2
3
4
187.5
181.5
187.5
181.5
10.5
10.5
10.5
10.5
few
Diesel oil
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Primary emulsifier
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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
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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 .
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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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