Assessment of Matrix Acidizing Treatment Responses in Gulf of Mexico Wells

Abstract

A coherent approach for evaluating matrix stimulation consists of a series of steps. First, pre-treatment well performance data needs to be collected to estimate how severe the well is damaged, and based on the initial information, a treatment can be designed. Then during treatment, skin response should be monitored through pressure and flow rate measurement, to: 1) insure the treatment is performing as desired, and 2) collect data for post-treatment study. From this step, the design and the information about the reservoir used in the design can be confirmed. Generally, a matrix stimulation consists of more than one stage, especially when diversion is required. Posttreatment review and interpretation of skin evolution during each stage provides valuable information regarding causes of the skin responses. And finally, the post-treatment well performance data can be used to confirm the skin estimate obtained during the treatment.We studied the effectiveness of seventeen matrix acidizing treatments in Gulf of Mexico sandstone reservoirs by evaluating the skin factor evolution during the treatments from the rate/pressure responses and by examining production performances after stimulation. For these wells, the skin factors at the end of the acid treatment derived from analysis of the rate and pressure during the treatment were compared with skins obtained from post-treatment production. The study showed that the combination of these methods of evaluation provided additional information about the success of the treatments. Characteristic examples presented in the paper illustrate such behavior as effective stimulation, efficient diversion, acid over-treatment, and proper (or inappropriate) acid selection.