Critique of Drilling Research Page: 4 of 5
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cRXTIQIu O1 DRILLI.G RESEARCN
JERRY EINDLIN
UNOCAL GEOTREREL DIVISIONSummary
For a number of years the Department of
Energy has been funding research to reduce
the cost of drilling geothermal wells.
Generally that research has been effective
and helped to make geothermal energy
economically attractive to developers.
With the increased competition for the
electrical market, geothermal energy needs
every advantage it can acquire to allow it
to continue as a viable force in the
marketplace. In drilling related re-
search, there is essentially continuous
dialogue between industry and the national
laboratories. Therefore, the projects
presented in the Program Review are fo-
cused on subjects that were previously
recommended or approved by industry.
Drilling Research Projects Presented
Drilling research projects currently
ongoing were discussed at the Program
Review by representatives of two different
sections--Hard Rock Penetration and Hydro-
thermal Energy Conversion. Topics dis-
cussed included "Acoustic Telemetry in
Drillstrings", "Lost Circulation Control",
"Downhole Memory Logging Tools" and "Mate-
rials for Geothermal Production". There
was also an overview of work being done by
the Hard Rock Penetration Group that
proposed some future projects. Of major
interest in the overview was proposed
research into the reduction of exploration
well drilling costs by combining slim hole
drilling with wireline coring technology
common in the mining industry.
Slim Hole Exploration
If hybrid slim holes--a combination of a
rotary drilled surface interval with
cemented casing and a wireline cored
reservoir interval--can provide adequate
reservoir parameters for resource evalua-
tion, exploration well drilling costs
could be reduced to an extent that would
make geothermal exploration much more at-
tractive to industry. It has long been
recognized that a significant deterrent to
geothermal development is the time lost
between successful exploration and cash
flow from the ensuing development project.
The cost of the capital expended for
exploration can double due to interest
charges by the time production begins.
Reducing exploration costs would therefore
have an even larger effect on improvinggeothermal economics than reducing devel-
opment costs by an equivalent dollar
amount.
The critical factor to remember in consid-
ering slim holes for exploration drilling
is that the well must still yield suffi-
cient information to determine reservoir
parameters.
Acoustic Telemetry in Drillstrings
The desire to transmit data more effec-
tively from downhole to the surface has
been the subject of a large volume of
research by industry for years. Acoustic
telemetry would not only improve the speed
of data transmission over mud-pulse tech-
nology, but could also result in lower
cost for the in-hole tool package. Due to
the large market for this technology,
industry has already signed a license
agreement.
Lost Circulation
Lost circulation treatment has been the
focus of more DOE funded research than any
other subject area. This was very appro-
priate since lost circulation is widely
acknowledged to be the single most costly
problem associated with geothermal drill-
ing. Recently an improved flow line meter
has been developed to replace the tradi-
tional paddle meter that lacked the accu-
racy necessary to be an effective instru-
ment. The rolling float meter is quicker
to indicate lost circulation, and should
work equally well to provide advance
notice of fluids entering the wellbore.
This could be especially advantageous in
slim hole drilling where early kick detec-
tion is an essential part of well control.
Development is continuing on a straddle
packer for isolating lost circulation
zones for treatment with cement or similar
slurries. The system being developed is
based on fiberglass bags that inflate to
provide zone isolation. An upcoming field
test should be especially interesting to
show the practicality of the system.
Investigation is continuing with a bore-
hole televiewer with a long term goal of
characterizing lost circulation zones or
fractures. Intuitively, it seems obvious
that lost circulation could be more easily
treated with a picture of the loss zone.203
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Hamblin, Jerry. Critique of Drilling Research, article, March 24, 1992; United States. (https://digital.library.unt.edu/ark:/67531/metadc883314/m1/4/: accessed April 19, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.