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.

You can access this article if you purchase or spend a download.