Petroleum simply means rock oil which is mainly the compound of hydrogen and carbon.
It had been discovered by people long times ago and today it has become the dominant
energy resource to operate the world working. First of all to understand this issue is to
truly learn the underground condition of oil reservoir. There are four main factors
involved in to form a recoverable hydrocarbon formation, sources rock, reservoir rock,
trap and cap. Oil expelled from source rocks, which were mainly shale, and transported
by gravity or pressure to those rocks having pore space, then those rocks confronted
faults or other impermeable barriers to get trapped, finally they were stored and formed a
recoverable oil formation.
Two rock properties should be stated here because they are the essential elements to do
everything about petroleum issues, they are Porosity and permeability. Porosity defined
as the ratio between pore space and rock bulk volume. Higher porosity indicates a great
storage potential of a rock. Permeability simply indicates how efficient fluid can pass
through those rocks. High porosity sometimes can’t guarantee an optimum prospect.
Because those pore spaces are not fully communicated with each other, only when those
pores are efficiently connected, then the oil can be recovered from the formation.
There are three structures can indicate oil reservoir potentials, they are anticline, faults
and stratigraphic trap.
Before the introduction of drilling engineering, several terms will be stated below:
Drilling rig: the working platform above the well, where contains main components for
drilling activity
Drilling pipe: steel made pipe used to do the drilling work
Casing: steel made pipe used to isolate the well from communicating with down hole
rocks
Tubing: small size pipe used as production pipe
BOP: blowout preventer, multi-valve equipment used to prevent the blow out of
formation fluid
Bit:
Cuttings: rock fragments need to be circulated to the surface
Drilling fluid: man-made mud used to circulating cuttings to the surface
After determining to explore an oil field, drilling engineers will start to plan drilling test
wells, which are called the wildcat. If wildcat wells provide a good oil distinction, further
test wells could be drilled to determine the area of this field, these wells are called step
out. After the area being determined, massive production wells can be drilled.
There are several preparations should be done before drilling:
1.
2.
3.
4.
Obtain drilling permission from local government
Building roads to the well location
Transporting drilling equipments and crews
Prepare materials required to drilling program
After these preparations, a brand new well can be drilled. The overall scenario of this job
can be simply described as three main parts. Drilling, circulating, and completing.
It is easy to understand the drilling part which drill pipe is lowered from the drilling rig
into the well to penetrate rock formations. As the drilling progressed, cut rock fragments
need to be brought to the surface, this is the so-called cuttings. It is very important to
circulate these cuttings out of the well, otherwise the further drilling process will be
hindered by those fillings. A common oil production well will have a depth about 1000020000 feet, and this length will be finished in separate sections. After finishing each
section, casing will be lowered and cemented, therefore the hole could be protected from
well wall collapse. After the casing being fixed, another hole section with small hole size
could be drilled.
When the whole length finished, another job will be carried out, which is called
perforation. A special gun will be lowered to the objective section where has oil and gas
indications. Bullets projected from the gun will penetrate the pipe wall, then the
formation and well bore are communicated. Oil and gas can be produced now.
The working platform for drilling work is called drilling rig. It holds the most
components required for the drilling work. Main components comprise the drilling rig are:
1.
2.
3.
4.
5.
Power system
Hoisting system
Rotary system
Circulating system
Well control &monitoring system
For the power system, it basically provides all the necessary power supply to carry out
the drilling work. Normally this power is generated from local combustion generators. A
common drilling rig requires approximately 1000-3000 horse power to maintain the
operation. However, the power efficiency can be varied from place to place. Generally,
the mechanical efficiency of the generator is favorable to work in low altitude and
medium temperature environment.
Hoisting system is one of the main parts to actually doing the drilling job. Either drill
pipe or casing will be lifted and lowered to drill and complete the well. It mainly
composes of the derrick, tackle &block system and dead line anchor system. Tackles and
block do the vertical movement to the pipe. People working on the derrick can help to
safely place these pipes in the right position. The dead line anchor mainly helps the
replacement of the drilling line when it has been subjected wears.
Wells are drilled by the pipe &bit rotation, therefore it is very important to have an
efficient rotation system. This system includes swivel, Kelly, rotary drive and rotary table.
The working principle of rotation system is the Kelly, which is connected to the drill pipe
drove by the rotary table and then the whole drilling string can be rotated for drilling.
In order to keep the drilling operation without big troubles, proper circulation system
should be built to fulfill the requirement. Working scenario of circulating system is the
drilling mud will be pumped into the drill pipe from the mud reservoir, we called it mud
pit. After mud reached the bottom the well, it brings rock cuttings to the surface through
the annulus between drill pipe and well wall. The mud with rock cuttings will be
separated through surface solid control system, such as screens, desanders or centrifuges.
After these, clean drilling mud will be retreated with certain chemicals and again pumped
into the wellbore.
Drill a well is very dangerous, because the pressure in the reservoir could be significant
high, which normally about couple thousands psi. Therefore, in order to guarantee the
drilling operation safe and prevent undesirable accident, well control system must be
installed. The main part of this system is the blowout preventer (BOP). This equipment is
set on the top of the well bore. If there is a sudden pressure change in the well which push
the formation fluid up to the surface, BOP will be closed the seal the well from blowout.
Drilling fluid is an essential material to drill a well. The main functions of it are to
circulating the rock fragments and exerting enough pressure to the formation. In order to
lift those rock fragments up to the surface, special properties should be met to achieve a
successful circulating job.
Some important the fluid properties are list below:
1.
2.
3.
4.
5.
Fluid viscosity
Density
Gel strength
Yield point
pH value
Density:
The density of fluid is primarily related to the hydrostatic pressure it can provide to
stabilize the wellbore. Either over or less mud density will result to problems. If the mud
density is low, then it can’t overcome the formation pressure, blowout may happen.
However if the mud density is weight out according to the pressure requirement, then
drilling mud will invade into the reservoir, which is called the fluid loss. Therefore, it is
crucial to make mud with proper density.
Viscosity:
Viscosity has many types. In this case we only focus on the dynamic viscosity, which
means we only concern the fluid when it is flowing.
In simple words, the dynamic viscosity is the property of fluid which indicates its flowing
behavior. Generally, in daily life, those liquids we call them thick normally have high
viscosity, and oppositely liquid like water which is very easy to flow, normally have low
viscosity. The easiest method to measure the viscosity is using the funnel, fully fill the
funnel with drilling mud, count the time after it entirely leave it. Then a rational viscosity
evaluation could be made. Obviously, liquid use longer time shows a higher viscosity
comparing to those who leave very quickly. The rule unit for viscosity is called poises,
which is the product of pascal and seconds.
Gel strength & Yield point:
Gel strength measures the required stress to initiate the liquid flow from sedate condition.
Yield point indicates the capability of a fluid to suspend the cuttings.
pH:
A pH value range from 8-12 is normally required to allow some mud additives can work.