Using Tracers for
Monitoring and Diagnosing Horizontal Well Stimulations, David Holcomb,
Robert A. Woodroof, World Oil Horizontal Well Completions Symposium, 1996.
ABSTRACT
Using Tracers for
Monitoring and Diagnosing Horizontal Well Stimulations
The application of multiple
radioactive tracers (Zero Wash®) and spectral gamma ray imaging has allowed
for improved diagnostics of stimulation treatment distribution. Whether
acidizing and diverting or fracturing and proppant placement, multiple
tracers (i.e.; Iridium-192, Scandium-46, Antimony-124) have allowed
operators to better analyze proppant entry with respect to stage, volume,
and/or type placed across lateral intervals, as well as acid entry and
distribution in order to better understand and optimize treatment techniques
such as diverting, rates, stage sizes, etc.
Holcomb and Read demonstrated
that tracers were useful in evaluating Austin Chalk and Bakken Shale
completions in South Texas and North Dakota respectively. Qualitative
comparisons helped operators understand stimulation coverage and diversion
effectiveness.
Problems still plague the use
of tracers in horizontal wells and usually center around uncemented or
poorly cemented casing. Tracer materials can accumulate behind pipe in
depressions or washed out sections even if acid or slickwater treatments are
overflushed. While this may make tracer images more difficult to interpret,
it does not rule out their usefulness for identifying potential problem
areas. Open hole horizontal completions have also posed problems for tracers
due to wash-off of tracer materials and adsorption onto rock, not
necessarily associated with fracture entry. Improvements made in horizontal
well drilling and completions have been aided by the reliability of improved
Zero Wash® tracer carriers and spectral imaging tools to provide a more
quantitative look at stimulation treatment placement across horizontal well
sections without the problems associated with wash-off and subsequent
adsorption onto rock, casin, liners, etc.
One particular application
has been noted with tracers used to confirm the success or failure of
various diverting techniques to allow lateral zones to be completely
acidized. Different Zero Wash® tracers are placed in different stages of
acid separated by various diverter stages using such materials as oil
soluble resins, gel pills, ball sealers, benzoic acid, rock salt, crushed
Unibeads®:, or foams. Three tracers are usually used in a variety of
carrier sizes, densities, and non-wash/crush/abrasion-loss formats. They
include Iridium-192, Scandium-46, and Antimony-124, with half-lives varying
from sixty to eighty-four days.