The first objective of this paper is to present some correlations between formation acid response with stimulation type, reservoir quality, post stimulation injectivity index, productivity index and production logging flow contribution from each of the stimulated zones of wells in the Karachaganak field. The second objective is to provide recommendations on acid stimulation based on geological settings, lithology, petrophysical properties and presence of natural fractures in order to optimize hydrocarbon recovery in carbonate reservoirs in a cost effective manner.

An evaluation of the technical assessment of multistage stimulation based on lithology, porosity, natural fractures, stimulation type, injectivity and the production logging data flow contribution of each zone is the methodology for acid effectiveness measurement. The zonal injectivity of each well generated in Excel describes the pre- and post-stimulation injectivity relative to the stimulation type (acid wash, high rate matrix and acid fracturing). Utilization of Python's matlab to read Excel injectivity analyses data for all the wells further enabled generation of plots for multivariable analyses of the impact of various parameters on productivity. This paper presents the cost effectiveness of stimulation treatment types.

The observation and results of stimulation carried out in many wells shows that porosity, as a petrophysical parameter is not the sole driver of stimulation effectiveness as low porosity zones particularly limestone dominated can have enhanced natural permeability (vugs, fractures) and may have a chance to flow. The high rate matrix technique especially in high dolomitic formation showed better performance when compared to acid frac in the same formation type. Good porosity lithology zones with evidence of natural fractures and/or those that experienced significant mud losses treated with gentle acid wash or high rate matrix showed great productivity with production logging results. The zones close to the toe and the oil water contact treated with acid wash gave good productivity compared to acid frac that tend to intersect natural fractures and connect to the underlying aquifer.

The holistic approach to stimulation results evaluation in carbonate reservoirs is new and will add to the body of knowledge on the most optimal and cost effective acid stimulation type for carbonate reservoirs.

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