Heidrun is recognised as a challenging field for scale management due to the combination of water injection, high barium and clay content, and unconsolidated sandstone formations. A selection and qualification process for scale inhibitor squeeze in this field followed the standard laboratory testing protocols. A novel scale inhibitor chemistry was qualified and field trialled; however, introducing the new scale inhibitor chemistry to the field was more challenging than anticipated.
The technical qualification was successful but the field trial resulted in lost productivity, halting field-wide implementation. The field trial started in Well I and indicated good scale protection but gave considerable loss of productivity. This paper presents the lessons learned through an extensive laboratory investigation to identify specific factors influencing the issues observed with the field trial. Furthermore, work completed to qualify a solution for iron-rich formations is described.
It was determined that the inhibitor was leaching iron from minerals in the reservoir and forming an insoluble complex with the metal, particularly at mildly acidic pH. While elevated iron concentrations were seen in flow-back samples from other wells across the field, these did not approach the levels observed for Well I which was producing from a geological formation rich in iron-bearing minerals. The field trial was successful in less iron-rich formations and the product was implemented field-wide for such reservoir zones. The scale inhibitor was designed to offer strong chelation, a property suited to scale inhibition and reservoir retention, but this was also a significant factor in the productivity loss. This important finding dictated that Product A should be regarded as unsuitable for reservoir zones containing iron-rich minerals. Subsequently, an alternative scale inhibitor was technically qualified and has since been successfully field trialled and implemented in the iron-rich formation.
This selection exercise for Heidrun posed challenges in terms of reservoir retention and iron compatibility for field-wide implementation of new chemistry. Overcoming these issues gave valuable insights for future qualifications of the novel scale inhibitor chemistry.