Evaluation of preservative chemistries to control microbial activity during well completion

摘要

Microbiologically-influenced corrosion (MIC) poses a serious concern to the production and the integrity of pipelines, vessels and tanks. High water content directly increases the risk for MIC as it results in an increase of the microbial load in the system. Compared to conventional production systems, unconventional fields are at a higher risk for premature MIC due to large volumes of water used to initially fracture the formation. Thus, microbial control during hydraulic fracturing is a critical step to prevent corrosion and maintain the integrity of the well. The use of traditional oilfield biocides in the hydraulic fracturing process commonly represents a challenge. This is mainly due to the high temperatures of the reservoirs, high solid contents, low persistence of the chemistry and incompatibility with friction reducers and gel frac packages. To qualify alternative chemistries for use during fracing, we evaluated a number of preservative chemistries in conditions mimicking a hydraulic fracturing application. Preservatives are slow-acting, highly persistent molecules that are used to provide long-term microbial control. The efficiency of 5 preservatives was tested, at 3 equivalent dosages, against a field microbial population at elevated temperatures for a period of 28 days. Microbial activity was followed by ATP and dormancy index (AMPi) measurements. The results indicated that at low dosages, all chemistries induced the population to a dormancy state that was able to recover after 28 days when fresh sterile medium was added. At a higher dosage, several of the preservatives provided adequate control even after the addition of sterile medium to stimulate hew growth. At a highest dosage evaluated, all chemistries tested provided good control and no recovery of survival organisms was observed. Moreover, the efficiency of the two top performing preservatives was tested in combination with increasing dosages of commonly used biocides and synergistic effects were assessed. Our results indicate that thetise of preservatives with or without biocides may provide a long-lasting control of microbial activity downhole during well completion and prevent early contamination and premature MIC risks in the system.