An Exhaustive Study of Scaling in the Canadian Bakken: Failure Mechanisms and Innovative Mitigation Strategies From Over 400 Wells

Abstract

The Canadian Bakken has been produced for over 40 years but with advances in fracturing technology during the last 10 years, there has been an exponential increase in Bakken activity. Concurrent with this, there has been a step-change in frequency and severity of scale formation from high value, high productivity wells. This paper summarizes the scaling observations made over the producing life of this high producing formation drawn from treating and servicing over 400 wells through Southern Manitoba and Saskatchewan.The most common scale types are calcite and anhydrite, although there is also evidence of siderite and iron sulfide. Formation of scale in Bakken wells is seen from the bottom of the tubing and open-hole sections up through the casing and rods. Formation water salinity can reach over 250,000 mg/L with up to 20,000 mg/L calcium. When combined with the high down-hole temperature, this brine causes a significant challenge for selection and application of scale inhibitor chemistries.A typical scaling life cycle is given for a Bakken extended reach horizontal well. With production reaching maturity, the severity of scaling in this formation has been found to increase. The influence of fracturing and frequent well interventions has been discussed in terms of the profound effect these activities have on the onset of scale formation.The experiences and strategies of over a dozen different operators have been combined, and the lessons learned from these activities used to determine a common approach in the management of scale in these challenging wells.The paper concludes with several detailed case histories. These show how the development of an innovative scale management philosophy has been successfully put to the test in proactively preventing scale, thereby reducing the overall failure rate for the Bakken operating companies.

Evaluation of formation water chemistry and scale prediction: Bakken Shale

“…The calculations show that calcite scale forms in response to the pH change triggered by the decrease in pressure, and could be as much as 0.045 grams per liter, while the precipitation of halite and anhydrite did not occur except from the most saline samples. This means early flowback will produce little or no halite or anhydrite, but later produced water may generate these other scales as TDS approaches the highly saline formation water levels, consistent with observations (Wylde et al 2012). Table 1 shows an example of calculated scale volume for the selected ten brines.…”

“…Bakken wells produce significant amounts of scale, mostly calcite with minor anhydrite and halite (Cenergy et al 2011, Wylde et al 2012. The severity of scaling is related to time of production with relatively early (Cenergy et al 2011) and later periods (Wylde et al 2012) being the most difficult. The average water volume used in the Bakken is about 900,000 gallons/well (LaFollette et al 2012).…”