Yuri Korchagin field, located in the Russian sector of the Caspian Sea, is one of the largest field on the Caspian shelf with proven reserves stand at 29 million tons of oil and 63 billion cubic meters of gas. Since the beginning of commercial operation, in the spring 2010, the field production passed eight million tons of oil. The operator company conducts development of Yu. Korchagin field by a system of horizontal wells with a length up to 8000 m, from a fixed offshore ice-resistant platform, installed in the dome area of the structure. The main challenges in the field development are associated with premature water and gas breakthroughs at high permeability intervals of horizontal wells. Currently, as a result of the sharp increase in the field water cut, the oil production is constrained due to the existing limitations on volume of produced water that can be utilized in the conditions of the offshore field. Two water-injection wells were drilled and commissioned to utilize produced formation water into the aquiferous zone of the carbonate reservoir. In order to restore and increase the injectivity factor, small-volume acid treatments are carried out yearly on the carbonate reservoirs in the lower horizontal sections of the water-injection wells. Since 2014, more than 20 matrix and hydrochloric acid treatments were performed with application of acid systems of different compositions and volumes. In some cases, the wells injectivity increase after matrix acidizing treatments with traditional acid systems was below expectation, demonstrating limited and short-term effect. Therefore, with constantly increasing volume of produced water at the field, it was required to increase the frequency of acid treatments to maintain the appropriate level of injectivity of the water-injection wells. The additional treatments are associated with significant time and financial costs because of the offshore platform standby and production suspension. The need exists to improve efficiency of acid stimulation treatments performed in the field to achieve sustainable increase in injectivity index of existing wells.
The purpose of this study is to analyze acid stimulation treatments carried out on carbonate reservoirs of the horizontal water-injection wells in 2014-2017, evaluate the efficiency of the treatments with different acid systems to change the injectivity factor, discuss the prospects for their application in Yu. Korchagin field and formulate recommendations for further efficiency improvements of acid stimulation treatments in the field.
