With the onset of water production, fines are usually mobilized to the wellbore, resulting in screen plugging. Fines-plugged screens and/or gravel pack can then accelerate scale precipitation, especially in high-temperature formations. Due to the type of metallurgy, long acid contact times and high acid sensitivity of the formations, removal of the scale with HCl acids has been largely unsuccessful. In high-temperature wells, the choice of acid must be done such that the formation and the completion are not damaged, but the scale and the fines are removed. A series of tests conducted on screens and clay-rich cores show that a new organic acid system, which is highly biodegradable, can successfully remove the calcium carbonate scale and fines to stimulate production. Core flood testing demonstrates that this organic acid system can effectively remove calcium carbonate scales and fines at temperatures up to 204°C(400°F). In addition to its reactivity, the acid system, when combined with corrosion inhibitor, exhibits very low corrosion at high temperatures. Corrosion tests show that at 177°C (350°F), the corrosion rate caused by this organic acid is 0.00049 g/cm2 (0.001 lb/ft2) on 22-Cr for 16 hours. Acid soaking to completely remove scale prior to removal of fines is now possible at temperatures in excess of 121°C (250°F). Successive removal of plugging fines from screens can then proceed without further damage to the integrity of the screen.

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