Summary
The main subject of this paper will be to outline the field experience
achieved with a new type of well profile and directional drilling system.
Reducing the cost of well construction has been a driver for many new
technologies. The lean casing profile introduced by Eni SpA, the major Italian
oil and gas company, about a decade ago was a successful step towards lowering
the drilling and completion cost in the vertical, top-hole section. Automated
vertical-drilling tools have been the technical enabler of such a concept.
Recently, this oil company has moved further towards an even more radical
"extreme-lean well profile." This paper gives a brief insight into the
well-design concept and the enabling technology behind it. The drilling
technology is based on the well-known automated vertical-drilling system, which
has been enhanced by the capability to drill an enlarged hole size below a
casing without compromising the verticality and hole quality. In the main part
of the paper, two field applications, in the Mediterannean Sea and offshore
Egypt, are described. The paper will also cover the lessons learned especially
from the second of the first two field applications. The extreme-lean well
profile and automated vertical-reaming technology can provide value to several
drilling campaigns not only through the reduction of well-construction cost.
Another major benefit is the ability to run an intermediate casing string, if
required because of difficult well conditions, and still arrive at the same
diameter of casing in the reservoir. The completion concept and the enabling
tool technology are very unique and have not been available to the industry
until recently.
Introduction
It is the ultimate purpose of any oil and gas well to help develop a
reservoir as soon as possible and with the maximum rate and volume of
hydrocarbon recovery. Reaching the reservoir horizon quickly and safely
requires, in many cases, the application of some smart well-construction
techniques. This is true even in the upper sections of the hole. A straight and
smooth borehole curvature reduces the inherent risks of running casing strings.
In addition, such geometry provides the optimum conditions for being able to
drill the horizontal section to the maximum reach (Calderoni et al. 1998). At
the same time, when the trajectory is of a "gun-hole" shape and quality, less
annular space has to be reserved for the casing string running operation. If
this concept is realized through all or most of the hole sections, the well
will be less cascaded than with the conventional approach. This type of "lean
casing profile" allows for faster well construction, fewer consumables and an
increased operational efficiency. The lean-casing-profile concept was first
introduced to the oil field in the early 1990s. Based on the economic success
achieved, the operating company has recently decided to drive this concept even
further. The new extreme-lean casing profile reduces the annular gap even
further than with the previous method. In a way, the extreme-lean shape is an
important step towards the visionary monobore hole, yet much more realistic to
do as of today. As with the previous method, this new well construction scheme
is based heavily on the application of an enabling downhole technology that
guarantees the required straightness and precision. This can be accomplished by
means of an automated rib-steering directional-drilling device that is fully
operated in the sliding mode. In a hole’s vertical section, eliminating
drillstring rotation improves borehole stability. To facilitate the
extreme-lean casing well construction, some new downhole directional-drilling
systems had to be created, such as an automated steering system with an
integrated reamer and an automated rib-steering device with a special diameter.
The new well construction process and made-for-purpose tools have been field
tested in a series of wells in the Egyptian Sea where operating conditions were
critical because of hole-stability problems.
© 2009. Society of Petroleum Engineers
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History
- Original manuscript received:
3 January 2008
- Meeting paper published:
12 March 2008
- Revised manuscript received:
2 February 2009
- Manuscript approved:
10 February 2009
- Published online:
12 November 2009
- Version of record:
11 March 2010
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