For many decades the only way we could extract natural
gas was to drill a well straight down into the ground.
However, in many instances, this is not possible, not
economically feasible, or simply not efficient. Technological
advances now allow us to efficiently deviate from 'straight
line' drilling, and steer the drilling equipment to
reach a point that is not directly underneath the point
of entry. While what is known as 'slant drilling', where
the well is drilled at an angle instead of directly
vertical, has been around for years, new technology
is allowing for the drilling of tightly curved well
holes, and even wells that can take a 90 degree turn
Directional drilling is the process of drilling a curved
well, in order to reach a target that is not directly
beneath the drill site. This is useful in many circumstances
where the area above the targeted deposit is inaccessible.
For example, to reach reservoirs that exist under shallow
lakes, protected areas, railroads, or any other area
on which the rig cannot be set up, directional drilling
is employed. It is also useful for long, thin reservoirs.
These types of reservoirs are not efficiently mined
with a vertical completion. However, horizontal entry
into the reservoir allows it to be drained more efficiently.
To learn more about well completion and production,
click here. Directional
drilling is especially useful for offshore locations.
The cost of offshore drilling rigs can make it uneconomical
to drill a single well. With directional drilling, the
offshore rig can gain access to deposits that are not
directly beneath the rig, meaning that 20 or more wells
can be drilled from a single rig, making it much more
cost effective to drill offshore.
The difference between traditional directional or slant
drilling and modern day horizontal drilling, is that
with directional drilling it can take up to 2,000 feet
for the well to bend from drilling at a vertical to
drilling horizontally. Modern horizontal drilling, however,
can make a 90 degree turn in only a few feet! The concept
of horizontal drilling is not new. In fact, the first
patent for horizontal drilling was issued in 1891 to
Robert E. Lee, for drilling a horizontal drainhole for
a vertical well. The advances in technology and the
increasing focus on accessing less accessible reservoirs
to meet rising demand have allowed for a proliferation
of horizontal drilling.
Horizontal drilling technologies have been heralded
by many as the greatest advances since the conception
of the rotary drilling bit. Horizontal drilling now
accounts for 5 to 8 percent of active onshore wells
in the U.S., and seems to be increasing every year.
The ability of horizontal drilling to reach and extract
petroleum from formations that are not accessible with
vertical drilling has made it an invaluable technology.
Horizontal drilling allows for an increase in the recoverable
petroleum in a given formation, and even increases the
production in fields previously thought of as marginal
or mature. Horizontal drilling also allows for more
economical drilling, and less impact on environmentally
sensitive areas. In fact, in some areas in which drilling
is not allowed for environmental reasons, it is possible
to drill horizontal wells to the targeted deposit without
harming the environment above. To learn more about the
environmental effects of drilling for natural gas, click
addition, with this technology, fewer wells are needed
to produce the same amount of hydrocarbons.
|Slant and Horizontal Drilling
A number of advances were crucial to the progression
of horizontal drilling. Measurement-while-drilling technology
(or 'borehole telemetry') has allowed engineers and
geologists to gain up-to-the-minute subsurface information,
even while the well is being drilled. This avoids some
of the complications of normal logging practices, and
greatly increases the drilling engineer's knowledge
of the well characteristics. Steerable downhole motor
assemblies have also allowed for advances in horizontal
drilling. While conventional drilling occasionally employs
the use of downhole motors just above the drill bit
to penetrate hard formations, steerable drilling motors
allow the actual path of the well to be controlled while
There are three main types of horizontal wells; short-radius,
medium-radius, and long-radius. Short-radius wells typically
have a curvature radius of 20 to 45 feet, being the
'sharpest turning' of the three types. These wells,
which can be easily dug outwards from a previously drilled
vertical well, are ideal for increasing the recovery
of natural gas or oil from an already developed well.
They can also be used to drill non-conventional formations,
including coalbed methane and tight sand reservoirs.
Medium-radius wells typically have a curvature radius
of 300 to 700 feet, with the horizontal portion of the
well measuring up to 3,500 feet. These wells are useful
when the drilling target is a long distance away from
the drillsite, or where reservoirs are spaced apart
underground. Multiple completions may be used to gain
access to numerous deposits at the same time.
Long-radius wells typically have a curvature radius
of 1,000 to 4,500 feet, and can extend a great distance
horizontally. These wells are typically used to reach
deposits offshore, where it is economical to drill outwards
from a single platform to reach reservoirs inaccessible
with vertical drilling.
To give an idea of the effectiveness of horizontal
drilling, the U.S. Department of Energy indicates that
using horizontal drilling can lead to an increase in
reserves in place by 2% of the original oil in place.
The production ratio for horizontal wells versus vertical
wells is 3.2 to 1, while the cost ratio of horizontal
versus vertical wells is only 2 to 1. In carbonate formations,
where 90 percent of horizontal drilling is done, productivity
of horizontal wells is almost 400 percent higher than
vertical wells, while they cost only 80 percent more!
To learn more about the number of horizontal and vertical
wells, and their productivity, click here.
Horizontal drilling is an important innovation that
will likely find countless new applications as the technology
is developed. With increasing demand for natural gas,
innovations like these will be invaluable to securing
and bringing to surface these much needed hydrocarbons.
To learn more about horizontal drilling and its applications,
to see a report published by the Energy Information