Characterization of Phosphonate Scale Inhibitors Retention using a Mini Core-flood

Scale inhibitor squeeze treatment is a widely used technique for the prevention of inorganic scale deposition in oil and gas production operations, it consists of the bull-heading of a scale inhibitor (SI) pill, followed by an overflush stage to push the SI deeper into the formation, then the well is shut-in for some time to allow the inhibitor to further retain in the formation. Finally, the well is put back in production, and the SI is slowly released in the production brine, the well will be protected if the produced SI concentration is above a certain concentration, known as MIC (Minimum Inhibitor Concentration), normally few ppm.

The retention level is crucial to determine the squeeze treatment lifetime, particularly at low concentrations. It is generally accepted that the retention is governed by two main two mechanisms, namely, adsorption and precipitation, which depend on pH, divalent ions concentration, such as Ca and Mg, and temperature. Based on recent experiments, adsorption is more dominant than precipitation at low concentrations.

Traditionally adsorption/precipitation experiments have been performed at macroscale using bottle test. The SI concentration in the supernatant after filtering is analyzed by ICP (inductively coupled plasma) and applying scanning electron microscopy (SEM) imaging to analyse the SI retention on particulates. Although, these techniques provide very valuable information, they are not capable to detect the in-situ surface deposits occurring when the SI retention is governed by an adsorption and adsorption /precipitation regime. High-resolution X-ray CT scanning in a mini coreflood, and advanced imaging processing is used to analyse the surface deposits morphology to differentiate between pure adsorption and adsorption/precipitation, to quantify the retention level, and the release rate.