Abstract

Carbonate minerals are present in sandstone formations. These minerals are either introduced to the formation during drilling/completion operations or naturally present in the rock. There is a need to remove these carbonates to enhance well performance. This especially true if there is a need to use HF-based fluids to prevent the precipitation of calcium and magnesium fluorides.

In this study, we introduced GLDA (L-glutamic acid-N,N-diaceticacid) a new environmentally friendly chelate to remove carbonate minerals from sandstone formations. We also compared its performance with available chelates like EDTA (ethylenediaminetetraaceticacid) and HEDTA (hydroxyethylenediaminetriaceticacid). Berea (5 wt% clays) and Bandera (11 wt% clays) sandstone cores were used in the coreflood experiments. The concentration of the chelates used was 0.6M at pH values of 11 and 4. The coreflood experiments were run at a flow rate of 5 cm3/min and 300°F.

Coreflood experiments showed that at high pH values (pH =11) GLDA, HEDTA, and EDTA were almost the same in increasing the permeability of both Berea and Bandera sandstone cores. GLDA, HEDTA, and EDTA were compatible with Bandera sandstone cores. The weight loss from the core was highest in case of HEDTA and lowest in case of GLDA at pH 11. At pH 4, 0.6M-GLDA performed better than 0.6M HEDTA in the coreflood experiments. The permeability ratio (final/initial) for Bandera sandstone cores was 2 in the case of GLDA and 1.2 in the case of HEDTA at pH of 4, and 300°F. At pH 11, HEDTA, EDTA, and GLDA almost were the same in enhancing the permeability of the Bandera sandstone cores. At pH value of 4, GLDA gave the best results in Berea and Bandera sandstone cores.

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