Perdida De Circulacion De Lodo De Perforacion

Drilling Fluids and Mud losses
.A drilling fluid may be any of number of liquid and gaseous fluids and mixtures of fluids and solids - as solid suspensions, mixtures and emulsion of liquids, gases and solids - used in operations to drill boreholes into the earth.

.A drilling fluid is also frequently called a "drilling mud" or, simply, a "mud"
.Drilling fluid si a term that encompasses mostfluids used in hydrocarbon drilling operations. Drilling fluid can be water-base, oil-base or synthetic-base fluids.

Water based mud (WBM):
Consist of a mixture of solids, liquids, and chemical, with water being the continuous phase.

.Some of the solids in the mud, such as hydratable clays that will be incorporate while drilling, react with water and the chemical additives and are calledactive solids.
.Other solids, such as non-clay drilled solids and weighting materials do no react with water, and are called inactive solids.

Due to their generally low cost, and environmentally friendly composition, water based mud are still the most commonly used drilling fluid.

Oil based mud (OBM) and synthetic based mud (SBM):
Consist of a mixture of solid, liquid, and chemical, with oilor synthetic fluid the continuous phase.
OBM and SBM are usually more expensive, and require more stringed pollution control. Therefore, in most cases their use is limited to challenging drilling conditions, such as HPHT, unstable clay formation, etc...

Advantages and Disadvantages of OBM and SBM over WBM
Advantages:
il.Stable proprieties at temperatures as high as 500 °F
.More inhibitivethan water based mud
.Effective against all types of corrosion
.Superior lubricating characteristics
.Permit mud densities as low as 7.5 ppg

Disadvantages
.Higher initial cost
.Requires more stringent pollution control procedures
.Reduced effectiveness of some logging tools
.Remedial treatment for lost circulation is more difficult
.Detection of gas kicks when drilling conventionally ismore difficult because of gas solubility in oil.

Gases and Gas - liquid mixture:
Gases and gas-liquid mixture are normally used when very low fluids required-either because of low pore pressure or because the decision has been made to drill underbalanced (bottom hole pressure lower than pore pressure).

Drilling Fluids Selection
There are several factors that govern the selection of adrilling fluid.
These factors include:

.Types of formations to be drilled
.Range of formation properties such as temperature, pore pressure, strength and permeability
.Formation evaluation procedure
.Water quality available for mud mixing
.Ecological and environmental concerns and regulations
.Potential problems to be encountered during drilling

Cost is also an important consideration whendesigning a drilling fluid that meets at least functional requirements for effective and safe drilling

Drilling Fluids Functions
A drilling fluid used in drilling process is responsible to providing the function listed below, among others:
Well Control: Provide sufficient hydrostatic pressure against subsurface formation to prevent formation fluids flowing into the well
Well Cleaning/Cuttingtransport: Clean the rock fragments from beneath the bit and carry them to the surface.
Wellbore Stability: Keep the newly drilled borehole open until the next casing can be run and cemented in the hole.
Cooling and Lubrication: Cool the bit and lubricate the rotating drill string

In addition, the drilling fluid must be designed:
.To allow logs for formation evaluation to be run,
.tominimize formation damage in productive zones, and
.to minimizes corrosion of the drill string and of any subsurface equipment.

Drilling Fluids Proprieties
The main functional proprieties of a drilling fluid may be listed as:
1. Density
2. Rheology
3. API Fluid Loss

Drilling Fluids Properties - Rheology
Viscosity: It is a property of fluids and slurries that indicates their resistance to...