Experimental study of the influence of the content of calcite and dolomite in the rock on the efficiency of acid treatment

Injection of acidic formulations into a carbonate reservoir is commonly used in the oil industry to enhance or restore well productivity. The purpose of this method is to create empty channels, the so-called wormholes, which pass deeper into the formation further than the perforated area in the near-wellbore zone of the formation. During the oil production, wormholes become pathways for crude oil to flow into wells. Most of the experimental and numerical studies carried out on this issue are limited in their observations, because they think the issue of wormhole formation only depending on the technological parameters of acidizing (speed and volume of injection). Our study aimed at investigating the effect of the material composition (content of calcite and dolomite) of carbonate rocks on the efficiency of acid treatments. We focus on investigating the effect of the percentage of calcite and dolomite fractions in a carbonate rock on acidizing efficiency, and try to elaborate the influence caused by the percentage of calcite and dolomite associated with the carbonate samples. Note that not all carbonate rocks need to use the same technological parameters for acidizing. However, it is necessary to individually select a few critical technological parameters based on the holding time of the composition in the reservoir as well as on the volume of the composition. In conclusion, the authors have developed recommendations for the application of acid treatment of oil fields in the Perm Krai (Russia), which differ in the material composition of the rock. At one of the oil fields, the authors have conducted pilot tests considering the developed recommendations and received a significant increase in oil recovery (on average, an increase of 1.5–2.0 times) compared to the previous acidizing measures. The results obtained have scientific and practical significance and prospects for further improvement of acid action in carbonate reservoirs.