http://www.onepetro.org/mslib/servlet/onepetropreview?id=SPE-1124...

http://www.onepetro.org/mslib/servlet/onepetropreview?id=SPE-112419-MS&soc=SPE


"Hydrocarbon wells producing from carbonate reservoirs are often stimulated with small quantities of hydrochloric acid, and in most of the cases relevant increases in hydrocarbon production are obtained. Because the chemical reactions involved are simple, the results are almost guaranteed even when using acid systems with a minimal amount of additives. The main question that needs to be answered is if the well was properly stimulated. After the stimulation treatment has the well reached the ideal producing conditions and has the skin been reduced to the minimum possible compatible with the type of reservoir from which hydrocarbons are being produced.
Because almost all the carbonate reservoirs in Kazakhstan have more-or-less thick sections with natural fractures, the hydrocarbon production occurs with a dual-porosity mechanism through the sections with natural fractures and with a matrix flow where no natural fractures are present. These natural fractures create a network, and, as a result of the wellbore intersecting the natural fracture network (either with perforations or through possible fractures induced during the drilling phases), it is not rare to see a well producing with skin as low as ?4 or ?5. When stimulating one of these wells, the question that needs to be answered after a stimulation treatment, once the production data are obtained, is have such skin values have been achieved or not.

In this paper several stimulation treatments performed in thick carbonate reservoirs in Kazakhstan have been analyzed with all relevant available data. The data include the hydrochloric acid systems selected, the additives included in the fluid package, the use and the type of diverting agents, the placement techniques adopted, and the pre-treatment and post-treatment production logs, where available. The treatments have been evaluated to measure the gains resulting from each treatment, and some common trends have been established in terms of skin reduction, or more specifically, productivity index increases for certain types of designs and placements."