From Laboratory Research to Successful Practice: A Case Study of Carbonate Formation Emulsified Acid Treatments

Abstract

Abstract After laboratory research the pilot treatment has been done. After obtaining positive results from this treatment, BMB oil field operator begun to use emulsified acid for small scale acidizing treatment on production wells. Six acidizing treatments have been performed using emulsified acid. Oil and gas production increase was achieved after each treatment. Significant oil and gas production increase and decrease of near wellbore pressure drop was noticed during the production process. After positive results of emulsified acid treatment have been achieved on BMB oil field, this technology was successfully introduced in wells on another oil field located on the same carbonate formation Introduction At the end of the 20'th century one of the biggest oil and gas field was discovered on the West - North part of Poland. This reservoir called BMB is located in carbonate formation at average depth about 3000 m. Commercial oil production from this field started in March 2000. Testing and commercial production confirms existence of near wellbore damage. Significant production restriction and pressure drop in near wellbore area is caused by skin effect in production wells. During the testing stage of the wells, solution of hydrochloric and acetic acid was used for cleaning of the perforations and removing near wellbore damage. High reservoir temperature and rather small volumes of acid were the main reasons for poor results of this treatment. After that, a company operating on this field asked our Stimulation Laboratory for selecting the best fluid for acidizing and formation damage removing. Laboratory research confirmed poor results obtained with use of hydrochloric and acetic acid solutions for this type of formation and reservoir conditions. Main reason for unsuccessful treatments was the high reaction rate between hydrochloric and acetic acid solution and reservoir rock caused by high reservoir temperature (120oC). After laboratory tests and many core flow experiments have been made, an optimal fluid composition was designed. The best solution seems to be an emulsified acid. Water phase of this fluid was 15% of hydrochloric acid solution with corrosion inhibitor. The organic phase was an oil from BMB field with addition of emulsifier. Both fluids were emulsified at volume ratio 1:1.