Targeted Acid Stimulation Technique for Production Enhancement – A Montney Case Study

A safe and cost-effective method of stimulating a multi-zone hydrocarbon producing well is presented whereby a tool containing dry chemical is deployed downhole via wireline. An extended exothermic reaction is initiated downhole which generates acid vapour at a target depth in front of the perforated interval. This method allows for each interval to be uniquely treated with specific acid blends and order of operations. A typical well in the field is characterized as a vertical oil producing well with two existing perforated intervals. The top interval is a 3½ foot perforated interval in the Worsley Dolomite with a permeability of 500 - 1000 mD and 40 - 45% porosity. Approximately 50 feet below is a 3 ½ foot perforated Worsley Siltstone interval with 18-20% porosity and permeability of 5 - 10 mD. The 5 ½" 14 lbs/ft cemented production casing is set at approximately 3000 ft. Prior to acidizing, a workover operation was completed where the 2 7/8" tubing was pulled. The order of operations was to first perforate a new 20-foot interval in the Montney that was 70 feet below the Worsley Siltstone. Subsequently, the tightest interval – the Worsley Siltstone – was then treated using an HCl tool deployed via wireline which acted as a pre-flush treatment. This removed any existing scale and provided an HCl rich environment to minimize the risk or precipitation of CaF2 when later acidizing with Mud Acid. After the HCl pre-flush, an HCl/HF tool was then deployed. The next interval was the Worsley Dolomite which was treated with HCl followed by the newly perforated 20-foot Montney interval which was also treated with HCl. This entire operation is completed in 8 hours. Prior to treatment, the candidate wells were producing on average 6 bbl/day and had shown a declining trend over a period of several years. Prior treatments were to bullhead 15% HCl acid and it was believed that the acid was not all going to the desired zone. Using the new method, a total of 7 wells were treated - one well per day - and the average increase in production increase was 342% approximately 60 days post-treatment. The production increase was sustained with wells maintaining an average increase in production of 183% approximately 9 months post-treatment. This method of acidizing has supplanted the previous acidizing method - bullheading of 15% HCl - due to its sustained production enhancement and cost-effectiveness.