Field results demonstrate enhanced matrix acidizing through real-time monitoring

The use of an inverse injectivity vs. superposition time plot to diagnose t he changing skin factor in a matrix acidizing treatment has been presented previously by Hill and Zhu.(1) The model has been extended to calculate ski n factor as a function of injection time or injected volume to help the ope rator monitor and optimize the treatment. A Windows program based on the th eory has been developed to provide a pretreatment test to evaluate permeabi lity and initial skin factor of the formation when they are not available b efore the acid treatment, to calculate and plot the evolving skin during th e treatment in real time, and to evaluate treatments afterward. It converts surface pressure, when measured, to the bottomhole pressure for the calcul ation, and handles fluid density and viscosity changes in real time. Severa l field examples showed that the technique can be used conveniently to moni tor skin changes and diversion effects during matrix acidizing treatments. The program is reliable and flexible in acquiring and processing data, calc ulating skin, and diagnosing matrix acidizing treatments.