SELECTING THE BEST RHEOLOGICAL

MODEL

The importance of drilling fluids in drilling :

The drilling fluid system commonly known as the (mud system) is the single component of the well construction process that remains in contact with the well bore throw the entire drilling operation.

Drilling – fluid –systems are designed and formulated to perform efficiently under expected well bore

conditions .

Advances in drilling – fluid technology have made it possible to implement a cast .effective fit for purpose system for each interval in the well construction process .

Drilling fluid is used to aid the drilling of boreholes into the earth. Often used while drilling oil and natural gas wells and on exploration drilling rigs drilling fluid are also

used for much simpler boreholes such as water wells .

Liquid drilling fluid is often called (drilling mud).

1 .Water – based mud : which can be dispersed and non dispersed .

2 .Non – aqueous muds : usually called oil – based mud and gaseous drilling fluid in which a wide range of

gases can be used .

The three main categories of drilling fluids are:

The main functions of drilling fluid include providing hydrostatic pressure to prevent formation fluid from entering into the well bore, keeping the drill bit cool and clean during drilling, carrying out drill cuttings, suspending the drill cuttings while drilling is paused and when the drilling assembly is brought in and out of the hole. The drilling fluid used for particular job is selected to avoid formation damage and to

limit corrosion .

the active drilling – fluid system comprises a volume of a fluid that’s pumped with specially designed mud pumps from the surface pits, through the drilling strain exiting at the bit up the annular space in the well pore, and back to the surface for solids removal and maintenance

treatments as needed .

The capacity of the surface system usually is determined by the rig size and rig selection is determined by the well design for example, the active drilling- fluid volume on a deepwater well might

be several thousand barrels .

Much of that volume is required to fill the long drilling riser that connect the rig floor to the sea floor .

By contrast , a shallow well on land might only require a few hundred barrels of fluid to reach its objective .

Fluid behavior is divided according to the observed behavior between the shear stress (Ʈ) and shear rate (ƴ) with the temperature and

pressure into two types :

1 .Newtonian fluid 2 .Non-newtonian fluid

Types of Fluid

1 .Newtonian fluid:

This type of fluid exhibit a linear relationship between shear stress (Ʈ) and shear rate (ƴ) (i.e the viscosity is constant).

Example : water and oil

2 .Non _ Newtonian fluid :

A non-Newtonian fluid is defined as a fluid does not have a constant viscosity (i.e the relationship between Ʈ and ƴ is not linear )

Example : drilling mud and cement slurries

Can be classified into two general types:

1 .Time – independent fluid .

2 .Time – dependent fluids .

Non _ Newtonian fluid

In this type of fluid the magnitude of viscosity is not effected by the duration of shear (i.e the shear- stress at constant temperature is solely dependent on the rate of the shear of this temperature ) this type of fluid can be

classified into three types :

A . Bingham – plastic fluids.

B . Pseudo – plastic fluids .

C . Dilatant fluids .

1 .Time – independent fluid :

Types of Flow : Generally, two types of flow can recognized.

1 .Laminar Flow. 2 .Turbulent Flow

THE RHEOLOGY:The rheology is defined as the

study of deformation and flow of matter.

THE PURPOSE OF RHEOLOGY: 1 .Calculating friction in pipe or annulus .

2 .Calculating surge pressure when running or pulling pipe .3 .Estimating hole-cleaning efficiency .

4 .Determining the jet nozzle velocity and friction loss at bit .

5 .Determining the equivalent circulating density of the drilling fluid .

Selecting the best rheological model:

The best method to select the best rheological model which fits the actual rheogram of fluid , which depends on the absolute average percentage error (AAPE) between the measured and calculated values of shear – stress . They considered that the model which gives the lowest

(AAPE) as the best rheological model .

Is an instrument used to measure viscosity and gel strength of drilling mud .

Fann vg meter

This device consist of a rotational cylinder and bob instrument .

Six speeds of rotation (3,6,100,200,300 and 600 rpm) are available in all instruments (some devices have 12 speeds).

Fann vg meter is called (Direct indicating viscometer) because at a given speed, the dial reading is a true

centipoise viscosity .

For example at 300 rpm, the dial reading (511sec - 1) is a true viscosity

Fann vg meter

NAZ AZADZAID HAYDER

MOHAMMED JAMALMOHAMMED AMMAR

Supervised by:

prepared by:

Mr. GHASSAN H. ALI