Most of the failures of matrix stimulation treatments can be imputed to incorrect field procedures. To improve the success ratio of the jobs, the tailoring of field stimulation procedures must be strictly linked with the clear identification of the target and with the optimization of the design. Objectives are set to meet different well situations, and require specific design and field procedures. Maximizing the injection pressure and rate during matrix stimulations has proven to be a very successful technique, particularly effective over extensive pay zones.
Many interesting theoretical and laboratory studies aimed at optimizing the matrix stimulation treatments and their success ratio have been carried out in the past. Deep consideration has been given to the knowledge of the chemical reactions between the numerous components of the involved systems, and the various types of formation damage which may occur. Also close attention has been paid to optimizing the composition of the stimulation fluids with respect to the reservoir rock lithology, by means of proper selection of additives and by considering the effects of temperature and other important chemical and physical parameters.
Such studies have resulted in a great benefit to the potential of matrix stimulation treatments. However, inadequate field procedures may frustrate the technical and economical efforts of the engineers, geologists, lab researchers involved in the optimization of the design phase. Field experience combined with an accurate post-job evaluation of more than 500 jobs performed over the past 8 years, has shown that out of 53 well documented failures, 41 were due to incorrect field stimulation procedures (Tables 1, 2).
Often in the field the program of a stimulation job is handled as a recipe, the job itself is performed with lack of motivation. This is probably due to a misunderstanding of the ultimate goal; thus, some important items requiring additional rig time (such as wellbore preparation, tubing cleaning, availability of a coiled tubing unit at the well site, proper placement of the acid, use of correct injection procedures, quality control) are neglected because of "short term" economic considerations. Unfortunately, "long term" economics are often adversely affected by this type of philosophy.