A Single-Stage Acid Treatment to Remove and Mitigate Calcium Carbonate Scale in Sandstone and Carbonate Reservoirs

Abstract

Combining scale inhibition with matrix stimulation in a single treatment has always been a challenge due to potential formation damage. This concern has been historically prominent in carbonate reservoirs, due to the accelerated precipitation of the scale inhibitor at very low pH values. Earlier experience in combining acid stimulation with scale inhibition in carbonate reservoirs has been reported with limited success.This paper presents recent development in combining acid stimulation and scale inhibition treatments in sandstone and carbonate reservoirs. The combined treatment utilizes a newly developed scale inhibitor (a polymer-based inhibitor) that offers full compatibility with a wide range of the commercially available acidizing systems, including hydrochloric acid, mud acids and chelating agents.This treatment minimizes the number of well interventions, significantly reduces well maintenance cost and improves the work-over efficiency. At least one scale inhibitor squeeze treatment is eliminated with every acid stimulation treatment. In addition, there are other inherent advantages including: effective inhibitor placement and better coverage of the target zone.

Effectiveness of Calcium Sulfate Scale Inhibitors in Spent Hydrochloric Acid/Seawater System

“…The use of scale inhibitors may act either as chelating agents to form a soluble complex [17][18][19], or as threshold inhibitors, which block the development of the supercritical nuclei [20,21], or as retarders of the growth of the calcium sulfate crystals [22][23][24]. By simply adding an acid-soluble and effective scale inhibitor into the acid system, mineral scale formation can be prevented during the process of acid stimulation [25][26][27]. In addition, combining scale inhibition and acid stimulation into a single package inherently reduces well intervention costs and well downtime, and therefore achieves significant economic benefits [28].…”