Influence of corn starch acid hydrolysate on reservoir damage: The key role of molecular structure

Starch has been widely used in water-based drilling fluids (WBDFs). However, potential reservoir damage to starch-based WBDFs has not attracted much attention. To analyze the potential reservoir damage caused by starch, waxy corn starch (WCS) and normal corn starch (NCS) were selected to focus on their acid hydrolysis behavior, the structure of hydrolysates. The reservoir damage performance also was analyzed. The chemical structure was found to play a key role to reservoir damage. After 6 h of acid hydrolysis, WCS achieved 100 % acid hydrolysis rate with low solution turbidity, resulting in near-zero reservoir damage. In contrast, NCS exhibited incomplete acid hydrolysis (<80 %) under similar conditions. The residue led to turbidity in the acid hydrolysis solution and severe reservoir damage (>21.7 %). The main reason was that the acid hydrolysis of WCS forms highly water-soluble oligomers and glucose, leaving no residue and avoiding reservoir damage. In contrast, NCS, which contains over 20 % amylose, generated residual amylose and formed amylose-lipid complexes after acid hydrolysis. These aggregates caused pore blockage, representing the primary mechanism of reservoir damage. This study presents a potential approach for achieving zero reservoir damage in WBDFs applications, while it also provides new insights into the acid hydrolysis mechanism of starch.