Ingenieria

Using Casing to Drill Directional Wells

Drilling with large-diameter tubulars eliminates the need to run conventional
drillpipe, which then must be pulled to install permanent casing. It can mitigate lost
circulation, enhance well control and reduce nonproductive rig time, and also
decrease the risk of unintentional sidetracks or stuck pipe. Fewer trips into and out
of a well, improvedwellsite safety, increased efficiency and lower cost have led to
an expanding range of applications that now includes casing directional drilling.

Kyle R. Fontenot
ConocoPhillips
Puerto La Cruz, Venezuela
Bill Lesso
Houston, Texas, USA
R. D. (Bob) Strickler
ConocoPhillips
Houston, Texas
Tommy M. Warren
Tesco Corporation
Houston, Texas
For help in preparation of this article, thanks toLee Conn,
M-I SWACO, Houston; and Mike Williams, Sugar Land, Texas.
ABC (Analysis Behind Casing), PowerDrive, PowerDrive
Xceed and PowerDrive Xtra are marks of Schlumberger.
Casing Drilling, Casing Drive System and Drill Lock
Assembly (DLA) are marks of Tesco Corporation.
DrillShoe is a mark of Weatherford.
EZ Case is a mark of Hughes Christensen, a division of
Baker Hughes, Inc.

44The use of casing for drilling is an emerging
technology that can reduce well-construction
costs, improve operational efficiency and
safety, and minimize environmental impact.
Fundamentally simple in principle, this drilling
technique uses the large-diameter tubulars that
will be permanently installed in a wellbore in
place of conventional drillpipe. The economic
demands of complex geologicsettings, smaller
reservoirs with limited recoverable reserves, and
the need to optimize development and
exploitation of mature fields make drilling
operations with casing increasingly attractive to
operating companies.
A conventional rotary drill bit or a special
drilling shoe can be attached to the end of a
casing string to drill vertical wells. For additional
flexibility and for thoseapplications that require
directional control, a retrievable bottomhole
assembly (BHA) for drilling can be deployed,
locked in place and then retrieved by wireline
cable. Running and retrieving this BHA through
casing eliminate tripping of drillpipe into and
out of a wellbore and provide added protection
for the advanced systems used in downhole
measurements and directional-drillingapplications.

Minimizing the number of pipe trips during
drilling operations reduces incidents of hole
collapse from swabbing and surging, decreases
the chance of an unintentional sidetrack and
minimizes wear inside previously installed
surface or intermediate casing strings. After
reaching total depth (TD), the casing is already
in place, eliminating the need to pull drillpipe
and then runpermanent casing.
This reduction in pipe handling improves
wellsite safety and allows drillers to use standardsize rigs or smaller rigs built specifically to drill
with casing. New compact rigs for drilling
operations with casing require lower horsepower,
use less fuel, produce fewer emissions, operate
from smaller surface locations, and can be moved
more quickly and easily than largerconventional
rigs (next page).
Compared with traditional drilling operations,
casing while drilling minimizes rig downtime
resulting from unexpected occurrences, such as
stuck pipe or loss of well control from an influx,
or kick, of formation fluid. Anecdotal evidence
indicates that drilling with larger diameter
tubular connections reduces lost circulation by
mechanically plastering cuttings anddrilled
solids into the borehole wall.

Oilfield Review

It is possible that this “smearing” effect
builds an impermeable filtercake or creates a
solid surface finish that may allow weak, lowpressure and depleted intervals to be drilled
without significant loss of drilling fluid.
Casing strings have longer joints than
standard drillpipe, which means that drillers
make about 25% fewer...