It has been proven that scale squeezes can be conducted effectively in the unconventional, horizontal fractured wells in the shale reservoir of the Bakken when using an optimal scale squeeze chemistry. Previous work has discussed inhibitor selection and performance testing along with early case histories and modeling work. This paper discusses new case histories and Place-iT modeling results based on several procedural variations including a range of overflush volumes in the squeeze treatment procedure and the inclusion of acid cleanouts.
Novel, reduced-volume squeeze designs have successfully protected wells from scale deposition while limiting the direct and indirect costs associated with extra placement water. For unconventional shale wells in the Bakken, where produced water is typically very high in TDS and TSS, fresh water is most commonly used to execute squeezes. Reducing the total water volume reduces the costs of purchasing, transporting and storing fresh water. The amount of time and cost to pump the job is decreased. Less time and money is spent lifting the placement water, and consequently, there is less deferred production. In addition, in unconventional production acid treatments are commonly carried out in isolation to maintain production. In this work, applying acidizing stages at the front of the squeeze procedures, provides a novel "squimulation" process to fractured reservoir scale control treatments.
For these unconventional horizontal wells, the use of larger water volumes—either several times full wellbore volume and/or several times daily water production—has not been shown to improve the longevity or cost-effectiveness of squeeze jobs. Contrary to conventional well applications modeled with Darcy flow, it appears diffusion is the more applicable mechanism for scale inhibitor transport in fractured shale wells. This mechanism is consistent with a reduced dependence on water volume deployed in the treatments.
The lessons learned from the unconventional horizontal scale squeezes conducted in the Bakken have resulted in enhanced production and cost savings. There are significant implications for the industry as other key unconventional regions in the U.S. and around the world are looking into scale squeezes as an option for scale control.