Identification of Alkalinity Transfer from Produced to Condensed Brine in Severe Bakken Brine Incompatibility
Authors: Spicka Kevin , Harbert Andrew , Longie Chris , Koerner Alex 
Published: June 2023

Abstract
It has been discovered that condensed brines from wet gas produced up the annulus of Bakken wells can contain up to 30,000 mg/L bicarbonate. When commingling with high calcium-containing produced brine on surface, the incompatibility has led to surface line plugging with calcium carbonate. Previous theories evaluated the possibility of corrosion contributing to the elevated bicarbonate concentrations. Subsequent work discovered that distillation of produced water was able to isolate distillate containing high concentrations of bicarbonate. This paper summarizes the laboratory work conducted to understand the ability of bicarbonate to transfer from distilled produced brine to the collected condensed water as well as field work to confirm suitable mitigative strategies.
Produced brine from different production basins was heated to 250 °F in an oil bath under an inert atmosphere using a distillation apparatus. Alkalinity and pH of the starting produced brine and collected distillate were measured in the lab using phenolphthalein and methyl purple indicators, and a pH probe, respectively. Alkalinity concentrations were also measured via non-dispersive infrared (NDIR) analysis to eliminate interference from other titratable species. Field work consisted of selecting 30 trial wells for batch applications consisting of diluted corrosion inhibitors in addition to only produced water. Wells were tracked for extension of mean time between failure to evaluate program effectiveness. The return on investment was calculated in terms of avoided deferred production.
Surprisingly, it was discovered that simple distillation of produced brine could result in transfer of alkalinity to the collected distillate. NDIR analyses confirmed that minimal alkalinity remained in some samples while the bulk of alkalinity (as bicarbonate) was found in the collected distillate. This discovery has significant implications for the ultimate prevention of buildup of bicarbonate in the condensed brine on surface as well as strategies to mitigate the ensuing brine incompatibility. Produced brines from other production basins were also distilled to see if alkalinity transfer could be observed, or if this phenomenon appears unique to Bakken produced brines. It was found that this alkalinity transfer can be observed in distillation experiments using produced brines from other basins.
The discovery of this alkalinity transfer has implication for the oilfield where condensed brine collects. While currently observed in the Bakken, it is of interest whether other basins could see a similar concentration of alkalinity in condensed brines, resulting in instances of calcium carbonate deposition of varying degree. The ability to identify alkalinity transfer into condensed brines may help identify root causes of incompatibility and subsequent suitable strategies for mitigation in other regions. This phenomenon of measured alkalinity transfer also represents a unique scenario as distilled water is assumed to contain minimal dissolved ions.