•Oil based mud is used for the following applications:

• To drill highly reactive clay .

• In drilling deviated or horizontal wells to reduce torque and drag and avoid stuck pipe.

• Drilling formations containing H2S, CO2 and salt producing formations.

• Drilling high temperature formations.

•Ava’s policy on oil based is to use low aromatic content oil whenever possible to reduce the environmental impact.

OIL BASED MUDOIL BASED MUD

•Direct Emulsion

The oil is in emulsion with water, the continuous phase is water and the oil phase is dispersed.

OIL BASE MUD IS DIVIDED

•Inverted Emulsion

Mud type with water in oil, oil is the continuous phase and water is the dispersed phase.

TYPE OF MUDTYPE OF MUD

Water Oil

30 - 10 % Oil

70 - 90 % Water

Continuous Phase

Min.

Water Oil

70 - 90 % Oil30 - 10 %

Water

Dispersed Phase

Max.

DIRECT EMULSIONDIRECT EMULSION

(OIL IN WATER)(OIL IN WATER)

Water Oil

70 - 90 % Oil30 - 10 %

Water

Continuous Phase

Max 30 - 10 %

Oil70 - 90 % Water

Dispersed Phase

Water Oil

Min.

INVERTED EMULSION INVERTED EMULSION

(Water in Oil)(Water in Oil)

Emulsified Brine

The most frequently used base for oil based muds are:

Diesel, LT mineral, Alternative Oil ( Ester oil)• Diesel :• With respect to the environment, AVA uses only LT oil. Only upon special request from the customer is Diesel used in this system.

• Oil LT :•Is an oil with a low aromatic content. The paraffin content is (< 1 %) with respect to Diesel (~ 30 %), due to the lower toxicity the environmental impact is reduced. The products therein are :Lamium 11 C (< 1 %) ; Lamix 30 (< 1 %) ; XP 07 (< 0,1 %).

• Ester :• Is a synthetic product with no aromatic content and is biodegradable. It is produced by a chemical reaction between alcohol and acid.

Bases for Oil based MudBases for Oil based Mud

Inverted emulsion mud low toxicity (LT)

• As opposed to DS IE, LT IE has the additional advantage of being environmentally friendly. It is highly recommended for drilling the following types of wells:

• Drilling reactive clays• Deviated and horizontal wells• Salt domes

• The system is also resistant to carbonates, hydrogen sulfide, anhydrite, salt and cement contamination.

Advantages Limitations•Utilisation of this type of mud could be a problem if:

• Drilling through a potential high loss zone and losses are encountered.

• More difficult to identify a gas kick due to the hydrocarbon nature of the system.

LT IELT IE

MUD Ester Based I.E. Limitations

• Running this type of system could lead to problems if:

• Drilling through a zone where the potential for losses are high and losses are encountered with high to total losses.

• The system is more expensive to run then conventional systems.

• This system is Ester based and contains no aromatics and is biodegradable. Also highly recommended for the following types of wells:

• Drilling reactive clays.• Deviated and horizontal wells.• Salt domes • Can be ran in areas where zero OBM discharge is allowed and the cost of transporting back to shore is excessive.

•The system can be ran with temperatures up to ~ 150 °C / Density max. ~ 1,8 Kg/l.

Advantages

EB IE EB IE

Emulsifiers• Preparation of a stable water-in-oil emulsion is dependent

upon two factors: the size of the brine droplets and the efficiency of emulsifiers that produce and maintain the emulsion.

• A primary and secondary emulsifiers are required to produce a stable invert emulsion for invert drilling fluids.

• Smaller water droplets are produced at higher rates of mixing or shearing, tighter emulsion resulting.

• Emulsifiers are also important in ensuring that solids in the invert emulsion are preferentially wetted by the continuous oil phase.

Control Viscosity

• Organophilic Clay (Avabentoil HY or SA)• Avoil VS

Organophilic Clay• The viscosity properties have to be developped by the dispersion of

the stacks of clay platelets. This is acheived to some extent by mechanical factors such as shear intensity, shear time and temperature.

• Absorption of oil or water molecules opens up the sheets and aids the dispersion process.

• AVABENTOIL HY is a high performance viscosifying clay. It yields rapidly, even under low shear conditions and provides superior rheologies with low plastic viscosity.

• AVABENTOIL SA is an oil miscible viscosifying treated organophilic clay.

Avoil VS

• AVOIL VS is a polymeric material used as a rheology modifier in the AVOIL system or in other invert emulsion systems.

• AVOIL VS is used to raise the low shear rheology without increasing the plastic viscosity of AVOIL and other invert emulsion mud.

Fluid Loss Control- Invert emultion drilling fluids typically have small fluid loss values under high temperature-high pressure test conditions.- When the invert fluids contacts the new formation drilled wall there is a small initial loss of oil to the formation and the brine phase then acts as an impermeable membrane to retard the mouvement of oil into formation.- In addition to the filtration control imparted by the oil and brine phases of invert emultions’ invert systems employ supplemental fluid loss control materials which are high temperature stable and oil dispersible as Avoil FC, Avoil FR-HT..

Mud LT IE- H2O- Lamium 11 510 Kg/m³- Emulsifier 15-18 “- Organophilic Clay 20 “- Filtrate reducer 15 “- Viscosifier 2 “- Wetting Agent 2 “- CaCl2 12 “- Barite 1300 “

density = 1,80 Kg/l

Formulation for IE Formulation for IE

oil base mud conc./m³oil base mud conc./m³

End End

Oil base MudOil base Mud