New Findings on Damage Potential, Geochemical Reaction Mechanisms, and Production Enhancement Applications for Citric Acid

摘要

Application of citric acid for damage removal in both clasticrnand carbonate rocks has historically not received widespreadrnacceptance due to formation damage concerns regardingrnprecipitation of calcium citrate. In addition, usage of citricrnacid in place of hydrochloric acid has been avoided due tornlower bulk carbonate dissolving power relative to hydrochloricrnacid. However, environmental, safety, and corrosion concernsrnwith using hydrochloric acid have sparked renewed interest inrncitric acid for stimulation.rnThis paper reconsiders the use of citric acid as both anrnadditive to conventional hydrochloric acid systems and as arnstand-alone acidizing fluid. The paper reviews extensivernlaboratory work focused on understanding reaction pathwaysrnand geochemical precipitation issues, and takes a new look atrnparadigms related to the calcium citrate issue.rnLaboratory studies performed independently by twornresearch laboratories address two main areas of investigation:rn(1) Evaluation of potential geochemical reaction paths andrnprecipitation of calcium citrate and (2) mechanisms forrngeneration of differential etching in two carbonate rockrnlithotypes. The described mechanism for etching enhancesrnconductivity in a contrasting mode compared tornhydrochloric acid.rnFindings based on this work provide new insights into thernapplications, usage and potential limitations of citric acid. Arnnewly proposed process for downhole reaction is presented.rnThis process differs greatly from long-held paradigms built onrna foundation of bench-top experimentation. Factors controllingrndownhole reactions are disclosed and the results of corerntesting and fracture conductivity are presented.