Acid stimulation is one of the production enhancement methodologies applicable in both development and exploration fields. Sandstone acidizing requires a sophisticated and well-studied approach to avoid formation damage caused by acid precipitation. Although the industry has made significant technical advancements in treatment fluids over the past decades, high bottomhole temperature still presents one of the biggest challenges.

A new chelant-based fluid system was tailored to stimulate sandstone formation effectively under ultrahigh-temperature conditions. The new system has been evaluated extensively in the laboratory.

Laboratory work included sequential dissolution, chemical analysis, and core flow tests. Both dissolution and core flow tests were conducted up to 400°F with reservoir core samples to simulate the actual reservoir condition and treatment design.

Sequential dissolution results indicated that the new chelant-based system dissolved clay minerals in each sequence without causing silica precipitation due to secondary and tertiary reactions. The increase in the permeability of the reservoir core after core flow tests further demonstrated that the new fluid system is indeed highly effective in removing the damaging clay particles. The major advantage of the new chelant-based system is that it can be pumped in a single stage, which has greatly simplified the field operation and diversion requirement. In addition, because of its mild pH, the new system has low corrosion rate and less tendency to emulsion and sludge formation. This new system is HCl acid free, and therefore it eliminates the high risk of silica precipitation due to reaction with sensitive clays at high temperature. Last, but not least, the chelant fluid is consists of a retarded HF system which enables deeper radial penetration with less near-wellbore deconsolidation and which doubles the effect of clay dissolution and stabilization.

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