Novel Acid Stimulation Technique for Production Improvement – Austrian Eocene Case Study

A new approach to acidizing is presented where an inert dry chemical is hermetically sealed inside a metal carrier and deployed downhole via E-line or slickline. The tool is spotted in front of the zone of interest and an exothermic reaction is initiated generating hot acid vapour. A depleted Eocene sandstone reservoir with a 2 7/8″ tubing inside 6 5/8″ casing was successfully treated leading to sustained production enhancement in addition to significant carbon footprint reduction when compared to a conventional treatment. The treatment approach, production results and description of the CO2 reduction is presented. A rigorous well candidate selection process was done as part of the treatment design which analyzed information including damage mechanism, well completion architecture, mineralogy, well deviation, formation type and compatibility. Based on this analysis, the tool type and tool placement sequence were determined to optimize the stimulation. For this well, two 2″ HCl and two 2″ 12:3 HCl/HF tools were used to treat a 5.5 m perforated interval. The HCl tools served as pre-flush treatment and removed any scale. This was followed by 12:3 HCl/HF tools which stimulated the near wellbore matrix and ultimately improved the reservoir fluid influx. After each tool was ignited, a drop in the fluid level was observed. This was positive indication that the acid vapour was enhancing connectivity to the reservoir. When pulled to surface, it was observed that all four tools had ignited and had undergone a complete chemical burn. The well had several tubing and pump changes throughout its long production history. More recently, the well was treated by bullheading EDTA and solvent to re-establish the oil production rate with unsatisfactory long-term production results. Prior to the novel treatment, the well had been producing at 9 – 11 m3/d (gross rate) and 1.8 m3/d of oil. After the application of the novel technique, the production results showed a return to the historical rate of 1.8 m3/d of oil (100% increase). Eighteen months post-treatment, the oil production is sustained and producing between 1.5 - 1.6 m3/d. Flow-back equipment was eliminated from the operation since the highly reactive hot acid is fully spent and dissipated. The operation was rigless and the only equipment required was a wireline unit, a crane, and a small fluid truck. The entire stimulation was completed in less than one day and the well could be put immediately back on production. A secondary benefit was a notable reduction in CO2 associated with this treatment method versus a conventional acid treatment. This was achieved by reducing the heavy equipment requirements and the associated diesel consumption.