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

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.

Acid Treatments in High Temperature Dolomitic Carbonate Reservoirs Using Emulsified Acids: A Coreflood Study

“…Acids are widely used to stimulate oil and gas wells to improve the rate of hydrocarbon production (Al-Anzi et al 1998;Kasza et al 2006), and to stimulate disposal wells and water injection wells (Mohammed et al 1999;Nasr El Din et al 2000). HCl was used to be pumped as the main stimulation fluid in carbonate stimulation treatments.…”

“…Micro emulsions utilize the use of large amounts of emulsifier, while macro emulsions have larger droplet sizes and use smaller amounts of emulsifier. Macro emulsions are the most widely used type in the field (Al-Anazi et al 1998;Mohamed et al 1999;Nasr-El-Din et al 2000;Kasza et al 2006). The rheology of emulsified acid is a key parameter in evaluating the performance during well stimulation treatments.…”

“…. Kasza et al (2006) mentioned that stimulation of high temperature dolomite formation, using straight HCl was not effective. Emulsified acid was selected to be an alternative to regular HCl.…”

Effect of Presence of Crude Oil on the Performance of Emulsified Acids

“…Acids are widely used to stimulate oil and gas wells to improve the rate of hydrocarbon production (Al-Anzi et al 1998;Kasza et al 2006), and to stimulate disposal wells and water injection wells (Mohammed et al 1999;Nasr El Din et al 2000). HCl is pumped as the main stimulation fluid in carbonate stimulation treatments, but the reaction between regular HCl and clacite is very fast, and it becomes higher at higher downhole temperatures.…”

“…Based on the droplet size of the acid, emulsified acid systems can be classified as micro (Hoefner and Fogler 1985) or macro-emulsion (Al-Anazi et al 1998). Macro emulsions have larger droplet sizes, use smaller amounts of emulsifier, and are the most widely used type in the field (Al-Anazi et al 1998;Mohamed et al 1999;Nasr-El-Din et al 2000;Kasza et al 2006).…”