Formation damage of near wellbore zone, which occurs during different well operations (drilling, workover), has dramatic influence on well productivity. To improve well performance the removal of damage or creation of new channels, which bypass damage zone, is necessary. For solving this issue, the acid matrix stimulation is widely used in carbonate reservoirs. In order to design and optimize stimulation treatments the simulation modeling is widely used nowadays. One of the critical issues, which influence the stimulation efficiency, is estimation of near wellbore damage zone parameters and taking them into account during stimulation design preparation. Usually this zone is described as the uniform zone with permeability, which is different from reservoir permeability. However, in reality its structure is complex and contains at least two damage subzones with significantly different parameters. Moreover, in case of perforation the created channels can have a positive as well as a negative effect on near well bore zone. The influence of these subzones is also not taken into account in used in practice models for calculation of skin factor due to presence of perforation. These factors influence the efficiency of acidizing stimulation and should be taken into account in modeling process. In this paper, we present details of the approach, which takes into account the complexity of near well bore damage zone and its modification during acid stimulation. For this purpose the combined skin factor is introduced that takes into account the present damage subzones with different permeabilities, perforation channels, wormholes, relative permeabilities and viscosities of pumped fluids and their changes during acidizing process. The combined skin factor approach was implemented into created simulator for matrix acid stimulation, which is used successfully in designing and optimization of stimulation operations on the Company's carbonate fields. The paper, in the example of one of the green oil fields, describes the evolution of well completion and stimulation technologies based on acid matrix stimulation modeling and integration of laboratory and field data. The proposed recommendations allowed to reach the values of skin factor up to −5 and involve into production up to 95% of reservoir thickness.

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Enhanced oil recovery methods, i.e. acid stimulation, are widely used to increase well productivity in oilfield development. The necessity for reservoir stimulation is linked with negative processes related to well drilling and perforation. The correct estimation of damaged zone parameters is the key problem for acid stimulation planning. The proposed petrophysical methodology is based on available data integration: core data, drilling data, well logging, well testing etc. Modern well logging suite allows to solve following task with high accuracy. Sonic radial profiling based on compressional and shear waves registration and multisonde resistivity logging are the key methods to prognose wellbore damaged zone radius and parameters. The methodology based on integration of both these logging data is proposed in this paper. Currently, fullwave acoustic logging provides comprehensive data to estimate drilling mud penetration zone and character of the damage. The approach is based on alteration of sonic waves – compressional and shear waves. But not all the wells logged with sophisticated modern acoustic log tools. Therefore, estimation of mud filtrate penetration and damaged zone is possible based on multiarray resistivity measurements which are primary methods in all well logging suites. At least three different sondes with different radius of investigation are run in a well. These data are enough to use for accurate damaged wellbore zone radius estimation. Calculated results were supported by other available information and verified by data from modern sonic tools. Thus, allows to improve the methodology and use it widely in all wells in a field. Modern fullwave acoustic logging was performed by Schlumberger in few wells of carbonate field of the Company. In rest of the wells wellbore damaged zone estimation based on proposed integrated approach applied for multiarray resistivity interpretation. This workflow allowed to optimize acid near wellbore zone stimulation for the oil recovery enhancement.

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