Drilling Engineering 1 Course3rd Ed. , 3rd Experience

1. Rotary Drilling Systems2. Power System

A. equipmentB. calculations

rig systemsFor all rigs, the depth of

the planned well determines basic rig requirements. The most important rig systems are:Power system,Hoisting system,Drilling fluid circulation

system,Rotary system,Derrick and substructure,Well control system,Well monitoring system

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Typical rig components

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power supply The power system of a rotary drilling rig has to

supply power to all the other systems. the system must provide power for pumps in general, rig light, air compressors, etc.

Since the largest power consumers on a rotary drilling rig are the hoisting, the circulation system, and the rotary

system, these components determine mainly the total power

requirements.

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Power consumptionThe actual power required will depend on

the drilling job being carried out. During typical drilling operations,

the hoisting and the rotary systems are not operated at the same time. Therefore the same engines

can be used to perform both functions.The maximum power used is during hoisting and circulation.

The least power used is during wireline operations.

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power systemDrilling rig power systems are classified as direct drive type (internal combustion engines supply

mechanical power to the rig ) and electric type.

In both cases, the sources of energy are diesel fueled engines.

Most rigs use 1 to 3 engines to power the drawworks and rotary table.

The engines are usually rated between 400 and 800 hp. As guideline, power requirements for most onshore rigs are between 1,000 to 3,000 hp. Offshore rigs in general use much more power.

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Sample of a land rig power supply

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SCR UnitThe power on modern rigs is most

commonly generated by diesel-electric power units. The power produced is AC current

which is then converted to DC current by the use of SCR (Silicon Controlled Rectifier). The current is delivered by cables to electric motors attached directly

to the equipment involved such as mud pumps,

rotary table, Drawworks etc.

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power system performanceThe performance of a

rig power system is characterized by the output horsepower, torque, and fuel consumption

for various engine speeds.

These three parameters are related by the efficiency of each system.

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energy consumption by the engines

Heating values of fuels

The energy consumed by the engines comes from burning fuels.

The engine transforms the chemical energy of the fuel into work. No engine can transform totally the chemical

energy into work. Most of the energy that enters the engine is

lost as heat. The thermal efficiency Et of a machine is

defined as the ratio of the work W generated to the chemical energy consumed

to perform this calculation, we must use the same units both to the work and to the chemical energy. 1 BTU = 778.17 lbf*ft,

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Fuel TypeHeating

Value(BTU/lbm)

Density(lbm/gal)

Diesel 19000 7.2Gasoline 20000 6.6Butane (liquid) 21000 4.7

Methane (gas) 24000 –

thermal efficiencyEngines are normally rated by the power P

they can deliver at a given working regime. Power if defined as the rate work is performed,

that is work per unit of time. If ˙Q is the rate of chemical energy consumed by the machine

(chemical energy per unit of time), we can rewrite the expression for the thermal efficiency as:

To calculate ˙Q we need to know the type of fuel and the rate of fuel consumption in mass per unit time.Consumption of gaseous fuels is given in mass per unit time.consumption for liquid fuels is given in volume per unit time.

we need to know the density of the fluid.

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output powerA system produces mechanical work when the sole

result of the process could be the raising of a weight (most time limited by its efficiency).

P is power, and v the velocity (assuming F constant).

When a rotating machine is operating (for example,an internal combustion engine or an electrical motor), we cannot measure its power, but we can measure its rotating speed (normally in RPM) and

the torque at the shaft. This is normally performed in a machine called dynamometer.

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output powerThe expression relating power to angular velocity

and torque is:ω is the angular velocity (in radians per unit of time)T is the torque.

A common unit of power is the hp (horse power). One hp is the power required

to raise a weight of 33,000 lbf by one foot in one minute:

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output powerFor T in ft lbf and N in RPM we have:

that is

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mechanical horsepower CorrectionWhen the rig is operated

at environments with non–standard temperatures (85F=29C) or at high altitudes, the mechanical horsepower requirements have to be corrected. The correction should follow

the American Petroleum Institute (API) standard 7B-llC:Deduction of 3% of the standard brake horsepower for each

1000 ft of altitude above mean sea level.Deduction of 1% of the standard brake horsepower for each

10F rise or fall in temperature above or below 85F.

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Calculation of the output power and the overall efficiency

A diesel engine gives an output torque of 1740 ft lbf at an engine speed of 1200 RPM. If the fuel consumption rate was 31.5 gal/hr, what is the output power and the overall efficiency of the engine?

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the output power and the overall efficiency

The power delivered at the given regime is:

Diesel is consumed at 31.5 gal/hr. From Table we have:

Converting to hp, results in:

The thermal efficiency is:

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1. (CDF) Jorge H.B. Sampaio Jr. “Drilling Engineering Fundamentals.” Master of Petroleum Engineering. Curtin University of Technology, 2007. Chapter 2

2. (WEC) Rabia, Hussain. Well Engineering & Construction. Entrac Consulting Limited, 2002.Chapter 16