Abstract

Conventional matrix acidizing treatments rely on hydrochloric acid to stimulate carbonate formations. However, the success of these treatments is often limited because of rapid acid spending at low injection rates and asphaltic sludge precipitation. This study investigated ethylenediaminetetraacetic acid (EDTA) as an alternative stimulation fluid. Results show that EDTA can effectively wormhole in limestone, even when injected at moderate or non-acidic pH values (4 to 13) and at low flow rates where only face dissolution would occur with HCl. Stimulation with EDTA at low injection rates is consistent with the dependence of the wormhole structure on the Damkohler number for flow and reaction. Sludge tests show that EDTA does not induce the precipitation of asphaltic sludge from crude oil, even in the presence of 3000 ppm of ferric iron. This result is attributed to EDTA being able to form stable chelates with ferric and ferrous iron.

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