Power System

Drilling Engineering 1 Course
3rd Ed. , 3rd Experience

1.
Rotary Drilling Systems
2.
Power System
A.
equipment
B.
calculations

rig systems

For 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
Fall 14 H. AlamiNia Drilling Engineering 1 Course (3rd Ed.) 4

Typical rig components

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. Fall 14 H. AlamiNia Drilling Engineering 1 Course (3rd Ed.) 7

Power consumption

The 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.

power system

Drilling 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.

Sample of a land rig power supply

SCR Unit

The 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.

power system performance

The 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.

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,
Fuel Type
Heating Value(BTU/lbm)
Density(lbm/gal)
Diesel
19000
7.2
Gasoline
20000
6.6
Butane (liquid)
21000
4.7
Methane (gas)
24000
–

thermal efficiency

Engines 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.

output power

A 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. Fall 14 H. AlamiNia Drilling Engineering 1 Course (3rd Ed.) 16

output power

The 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:

output power

For T in ft lbf and N in RPM we have:

that is

mechanical horsepower Correction

When 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.

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?

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:

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

Power System

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