A New Squeeze Scale Inhibitor for a Sandstone Reservoir with a Stimulation Effect

Abstract

Tannic acid, a nontoxic, easily biodegradable compound, is evaluated for scale inhibitor squeeze application in a sandstone reservoir. For this purpose, we designed a new inhibitor squeeze evaluation system, a combined core flood–tube blocking apparatus with appropriate pressure–temperature and data logging arrangement, that can simulate the near-wellbore reservoir as well as downhole locations. Berea sandstone core plugs represented the formation rock and the extended flow tube represented the wellbore. Backflow tests were conducted to measure scale precipitation within the core plug and wellbore flow restriction. A 10 pore volume (PV) tannic acid solution was squeezed through the core plug and after a 14-hr adsorption period, anion and cation brines were squeezed separately through the core plug followed by the tube. The tests were compared with a control and a commonly used phosphonate scale inhibitor. The results showed that a fast rate of permeability reduction due to scale deposition took place in the control experiment starting at the initial brine injection stage and, in the case of the phosphonate scale inhibitor squeeze, there was significant reduction in permeability due to the squeeze itself. There was also progressive reduction of permeability due to less control of scaling phenomena. However, the tannic acid–treated core showed a slight improvement in core permeability and no scale deposition took place up to 250 PV of brine injection. Scanning electron microscopy and inductively coupled plasma (ICP) studies explain the formation stimulating mechanism of this new scale inhibitor.

Keywords:

• core flood study
• scale inhibitor squeeze
• tannic acid
• tube block study