Summary
This paper presents technology for water-based drilling fluid that is
weighted with calcium carbonate particles. This technology has functions of
both drilling and completion, and can reach the total depth of
maximum-reservoir-contact (MRC) wells. It creates a filter cake that prevents
fluid leakoff during the drilling process, but readily cleans up the filter
cake over time. This technology is based on the use of an ester, in a solid
form, which hydrolyzes and produces an organic acid. The latter will dissolve
calcium carbonate particles that are used as a weighting material in
water-based drilling fluids. Polylactic acid (PLA) particles were used in this
study to generate lactic acid.
Experiments were conducted to find an optimum particle size of the solid
ester and calcium carbonate particles that should be selected as a compromise
between those that are optimal for fluid-loss control or filter-cake formation
and those that are optimal for self-destruction at the desired time and rate.
Other sets of experiments were conducted to determine the optimal temperature
and soaking time required for the solid ester to hydrolyze and for the
resulting acid to dissolve calcium carbonate particles.
All experiments showed that in controllable conditions of temperature, acid
concentration, and particle size, the cleanup efficiency exceeded 70%. The
optimum particle size was found to be 50 μm for calcium carbonate and 150 μm
for PLA. The optimum temperature was 230°F. These conditions will ensure high
filter-cake-removal efficiency, low filtrate volume, and no
returned-drilling-fluid or high-viscosity problems. Ample soaking time is
needed for PLA to hydrolyze and for the generated acid to remove the filter
cake (i.e., 20 hours).
© 2012. Society of Petroleum Engineers
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History
- Original manuscript received:
21 August 2010
- Meeting paper published:
13 October 2010
- Revised manuscript received:
15 May 2012
- Manuscript approved:
5 June 2012
- Published online:
29 August 2012
- Version of record:
18 September 2012
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