Stimulation of carbonate reservoirs is often considered a routine operation. When the reservoirs are thick (more than 200 m) the stimulation process is much more complex because factors such as reservoir heterogeneity, damage to each zone, matrix mineralogical composition, and pressure regimes of each zone need to be taken into consideration. The presence of natural fractures makes the entire treatment more complex.

Acid placement and diversion need to be carefully designed and optimized to effectively stimulate the wells by reducing the skin factor to the lowest possible value in each zone. At the same time, the selected optimum acid system, placement, and diversion techniques need to be applicable in the field in a simple manner without impacting the overall treatment logistics.

The use of a hydrochloric acid system containing a viscoelastic surfactant system that allows, upon acid spending, the development of viscosity in situ, has shown that significant skin reductions can be obtained provided the proper placement techniques are used. However, in certain cases where natural fractures are dominant, diversion effects can be noticed but are not optimal. An enhanced system that contains temperature-degradable fibers has been used in Kazakhstan. Such systems are shown to successfully divert and stimulate effectively even when natural fractures are dominant.

This paper presents experiences with different types of acid placements and diversion techniques in the thick carbonate reservoirs of western Kazakhstan. Pretreatment and post-treatment production data have been analyzed to evaluate the effectiveness of the treatments in terms of skin reduction or productivity index increase.

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