Summary
Two gas fields offshore Sarawak, Malaysia, are characterized by heavily
karstified carbonate reservoirs. These reservoirs are typified by significant
porosity and permeability heterogeneities such that large fluid-loss zones are
commonly encountered while drilling the reservoir section. The drilling
strategy for the subsea development wells called for the use of a solid
drill-in liner as a contingency should major losses be encountered while
drilling the reservoir section. This strategy stands opposed to using a
predrilled liner. The use of a drill-in liner, however, necessitates
perforating.
Typically, completions in such reservoirs are acid stimulated to maximize
productivity. Complete stimulation of the reservoir section is very difficult
to achieve using acid-diversion techniques in a karstic environment because of
the large variability in the permeability. Propellant-assisted perforating was
considered because it achieves effective stimulation diversion, equally across
the entire perforated interval. Modeling work indicated that fracture lengths
of 5 ft or longer would propagate from each perforation tunnel. Such large
propagation lengths greatly increased the probability of connecting the
completion directly to karstic features in the reservoir, to provide enhanced
inflow performance. Another significant benefit was that perforation and
stimulation would take place in a single operation, thereby reducing the
health, safety, and environment (HSE) risk associated with handling acid, while
saving rig time.
Two successful field trials, totaling three wells, will be presented in
detail to illustrate this application for propellant-assisted perforating. The
data presented include prejob planning, execution, and post-job
inflow-performance analysis. The result was three world-class, low-drawdown
wells, each capable of delivering 200 MMscf/D, providing well capacity that met
or exceeded expectations.
Applying the propellant-assisted perforating technique in three subsea wells
in heavily karstified carbonate reservoirs has proved that this technique can
offer a highly effective stimulation method across the entire perforated
interval in such an environment. Additionally, its usage eliminates the need
for conventional, separate acid stimulation, saving rig time and costs while
reducing HSE risks.
© 2009. Society of Petroleum Engineers
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History
- Original manuscript received:
29 August 2008
- Meeting paper published:
3 December 2008
- Revised manuscript received:
5 February 2009
- Manuscript approved:
16 February 2009
- Published online:
29 October 2009
- Version of record:
23 December 2009
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