Acid matrix treatments in carbonate reservoirs create a network of passages in the near-wellbore zone. The acid volume is a key variable that determines the effectiveness of acid treatment. For matrix treatments, the acid volume ranges from 20 to 100 gal/ft. Acid concentration ranges from 15 to 20 wt%. Selection of acid volume and concentration varies based on engineering experience and judgment.

This paper presents an analytical model for calculating time-lapsed injectivity index (II) in order to verify the impact of acid volume with all other contributing variables being fixed. The model integrated matrix acid treatments; injection profile surveys, injection data, completion configurations, and reservoir parameters. The model has been applied on six stimulation treatments where all contributing variables varied, except the acid volume. A normalized performance indicator was characterized based on the II's initial improvement, decline rate, and cumulative improvement.

The calculated IIs by the model successfully matched the measured IIs by the fall-off tests. The model evaluated the treatments contributing variables and established clear correlations between acid volume and the post stimulation performance.

Keywords:
acidizing, complex reservoir, drillstem/well testing, carbonate reservoir, stimulation treatment, cumulative ii gain, Drillstem Testing, Upstream Oil & Gas, completion, enhanced recovery
Subjects:
Improved and Enhanced Recovery, Formation Evaluation & Management, Unconventional and Complex Reservoirs, Acidizing, Waterflooding, Drillstem/well testing, Carbonate reservoirs, Well Operations, Optimization and Stimulation
Copyright 2007, Society of Petroleum Engineers
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