1. Overview of Drilling Fluids

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Advanced Drilling FluidsAdvanced Drilling Fluids

PE 7123 Fall/2005

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OverviewOverview

Advanced Drilling Fluids PE 7123 Page3

Schematic of Example Rig Circulating Schematic of Example Rig Circulating System for System for Liquid Liquid Drilling FluidsDrilling Fluids


Drilling Fluids Drilling Fluids

API defines a drilling fluid as:– A circulating fluid used in rotary drilling to

perform any or all of the various functions required in a drilling operation

This implies that rotary drilling is impossible without a circulating fluid

Fails to consider the five major mud functions


Drilling FluidsDrilling Fluids

A better definition– An optimum drilling fluid is one in which the

flow rate necessary to clean the hole results in the proper hydraulic horsepower to clean the bit for the weight and rotary speed imposed to give the lowest cost, provided this combination of variables results in a stable borehole that meets formation evaluation criteria and penetrates the desired target.


Drilling Fluid FunctionsDrilling Fluid Functions

Cooling and lubricating the bitCleaning the bottom of the borehole of

drilled cuttingTransporting cuttings to the surfaceStabilizing the wellboreAllowing adequate formation evaluation


And more…And more…

Exert sufficient hydrostatic pressure against productive formation to prevent them from flowing into the wellbore

Keep the wellbore open until steel casing can be run

Seal off the permeable formations with a thin filter cake

Assist in the collection of information from the well in the form of cuttings, cores, and well logs

Support part of the drillstring through buoyancy Control drilling rates


Drilling Fluids Should NOTDrilling Fluids Should NOT

Be harmful to personnel nor the environment

Interfere with formation evaluationDamage the production rate from the

formationsCause corrosion of the drilling equipment

and subsurface tubulars


Why Are We Concerned over Why Are We Concerned over Drilling FluidsDrilling Fluids

All drilling problems are related to drilling fluids

Many wells are abandoned because of poor drilling fluids

Drilling fluid costs can be excessive (over $1,000,000 on some wells)


Drilling Fluids Are Selected on Drilling Fluids Are Selected on the Basis ofthe Basis of

The types of formations (shaleyness) to be drilled The range of temperature and pressure

encountered The type of formation evaluation needed The water quality available Ecological and environmental considerations And, $$$$$$


Types of Drilling FluidsTypes of Drilling FluidsAir-Gas

– Dry air or gas– Foam muds– Aerated muds

Oil-Base Muds– True oil-base muds– Invert-emulsion

Water-Base Muds– Bentonite– Phosphates– A gel-chemical mud– Calcium muds– Low solids/nondispersed

polymer muds– Salt-mud


LIQUIDS

GAS-LIQUID MIXTURES

GAS

WATER_BASE MUD

OIL_BASE MUD

NATURAL GAS AIR

AERATED WATER FOAM


Water Base Mud CompositionsWater Base Mud Compositions


Water Base MudWater Base Mud

Water phase can contain many different dissolved chemicals

Oil is seldom used today, because of ecological considerations

Active solids (clays) are affected by the water present

Inactive solids(both low and high gravity) increased the viscosity of the mud


Oil Base Mud CompositionsOil Base Mud Compositions


Oil Base MudOil Base Mud

Diesel or Mineral Oils are usedThe emulsified water phase contains salts

for osmotic controlAll solids affect the viscosity of the mud


Gas Base MudGas Base Mud

Used when the low hydrostatic pressures are possible

Under-Balanced Drilling

Documents

1. Overview of Drilling Fluids