Once the site has been selected, it must be surveyed to determine its boundaries, and environmental impact studies may need to be performed.
Lease agreements, titles, and right-of way
accesses for the land must be obtained and evaluated legally. For offshore
sites, legal jurisdiction must be determined.
Once the legal issues have been settled, the
crew goes about preparing the land; preparation is essential and involves the
following steps:
1. Land is
cleared and leveled, and access roads may be built.
2. Because
water is used in drilling, there must be a source of water nearby. If there is
no natural source, a water well is necessary.
3. Reserve pit,
which is used to dispose of rock cuttings and drilling mud during the drilling
process and which is lined with plastic to protect the environment, is created.
If the site is
an ecologically sensitive area, such as a marsh or wilderness, then the
cuttings and mud must be disposed offsite, it may have to be trucked away
instead of being placed in a pit.
Once the land
has been prepared, several holes must be dug to make way for the rig and the
main hole. A rectangular pit is dug around the location of the actual drilling
hole.
The cellar
provides a workspace around the hole for the workers and drilling accessories. The
crew then begins drilling the main hole, often with a small drill truck rather
than the main rig.
The first part
of the hole is larger and shallower than the main portion and is lined with a
large-diameter conductor pipe.
Additional holes are dug off to the side to
temporarily store equipment, after which the rig equipment can be brought in
and set up.
Well
drilling has gone through major developments of drilling methods to reach the
modern method of rotary drilling. In this method, a drilling bit is attached to
the bottom end of a string of pipe joints known as the drilling string.
The drilling string is rotated at the surface,
causing rotation of the drilling bit. The rotation of the bit and the weight
applied on it through the drilling string causes the crushing and cutting of
the rock into small pieces.
To remove the cuttings from the hole, a special
fluid, called the drilling fluid or the drilling mud, is pumped down through
the drilling string, where it exists through nozzles in the bit as jets of
fluid.
This fluid cleans the bit from the cuttings
and carries the cuttings to the surface through the annular space between the drilling string and the
wall of the hole.
At
the surface, the mud is screened to remove the cuttings and is circulated back
into the drilling string.The drilling operation is performed using huge and
complex equipment known as the drilling rig.
During a well
test, a transient pressure response is created by a temporary change in
production rate.
The well response is usually monitored during
a relatively short period of time compared to the life of the reservoir, depending upon the
test objectives.
For well evaluation, tests are frequently
achieved in less than two days. In the case of reservoir limit testing, several
months of pressure data may be needed.
In most cases,
the flow rate is measured at surface while the pressure is recorded downhole. Before opening, the initial pressure Pi is constant
and uniform in the reservoir.
During the flowing period, the drawdown pressure response Δp is defined as follows:
When the well
is shut-in, the build-up pressure change Δp is estimated from the last flowing
pressure p(Δt=O):
The pressure
response is analyzed versus the elapsed time Δt since the start of the period
(time of opening or shut-in).
Well test
analysis provides information on the reservoir and on the well.
Geological, geophysical and petrophysical information is used where
possible in conjunction with the well test information to build a reservoir
model for prediction of the field behavior and fluid recovery for different
operating scenarios.
The quality of
the communication between the well and the reservoir indicates the possibility
to improve the well productivity.
Usually, the test objectives can be summarized
as follows:
Exploration
well: On initial wells, well testing is used to confirm the exploration
hypothesis and to establish a first production forecast:
nature and rate of produced fluids, initial
pressure and well and reservoir properties.Tests may be limited to drill stem
testing only.
Appraisal well:
The previous well and reservoir description can be refined by testing appraisal
wells to confirm well productivity, reservoir heterogeneities and boundaries, drive mechanisms etc.
Bottom hole
fluid samples are taken for PVT laboratory analysis. Longer
duration testing (production testing) is usually carried out.
Development
well: On producing wells, periodic tests are made to adjust the reservoir
description and to evaluate the need for well treatment, such as work-over,
perforation strategy or completion design, to maximize the well's production
life.
Communication between wells (interference
testing), monitoring of the average reservoir pressure are some usual
objectives of development well testing.
If you want
to learn more about preparing to drill you could do so in my book, economic
study of oil and gas well drilling.
which is
published on amazon, check it out at the link below.
https://www.amazon.com/dp/B07BST8YCC
تعليقات
إرسال تعليق