Identification and modeling of geochemical reactions occurring within the sandstone reservoir flooded by seawater

Abstract

Field X has one of the harshest oilfield scaling regimes in the North Sea and frequent squeeze treatments were implemented, so it will be beneficial to study and identify reservoir interactions among formation water, injected seawater, and reservoir rock, and even predict or evaluate scale problems in the field. For this field, produced water is sampled repeatedly during production and observation and analyses of variations in produced water chemical composition could reveal the extent of brine mixing in the field and enables an in-depth understanding of the fluid-fluid/fluid-rock interactions occurring in the reservoir during water injection. Produced water chemical compositional data from one well have been presented to provide a basic understanding of what geochemical reactions were possibly occurring in the reservoir, which could be then verified through developing a one-dimensional reactive transport model. Any possible occurring reactions among minerals, mixture of formation water and seawater, and CO₂ gas phase would be included in this model to study their effects on variation in produced water chemical composition. A fairly good match between modelled and observed produced water chemical composition has been achieved through varying solubility products and the initial amount of some minerals, ion exchange capacity, and CO₂ partial pressure, which indicates that the final achieved model, could, to some extent, reveal the physical, chemical, and thermodynamic responses of this reservoir system to injected seawater.

KEYWORDS:

• Calcite dissolution
• geochemical reactions
• ion exchange
• reactive transport mode
• sulphate mineral reactions