The Impact of Re-Injecting Flowback Fluids on Formation Damage. Case Study: Marcellus Shale

Abstract

Reuse of flowback water in hydraulic fracturing is usually used by industry to reduce consumption, transportation and disposal cost of water. But because of complex interactions between injected water and reservoir rocks, induced fractures may be blocked by impurities carried by flowback and mineral precipitation by water-rock interactions, which causes formation damage. Therefore, knowledge of flowback water-rock interactions is important to understand the changes within the formation and effects on hydraulic fracturing performance. This study focuses on investigating flowback water-rock interactions during hydraulic fracturing in Marcellus Shale Formation. Simple deionized water-rock interactions and complicated flowback water-rock interactions were studied under static and dynamic conditions. In static experiments, crushed reservoir rock samples were exposed to water for three weeks at room condition. In the dynamic experiment, continuous water flow interacted with rock samples through the core-flooding experimental system for three hours at reservoir condition. Before and after experiments, rock samples were characterized to determine the change on the rock surfaces. Water samples were analyzed to estimate the particle precipitation tendency and potential to modify flow pathway. Surface elemental concentrations, mineralogy and SEM images of rock samples were characterized. Ion contents, particle size, TDS and Zeta potential in the water samples were analyzed. In both static and dynamic experiments, compared with deionized water-rock interaction, rock samples after being exposed to flowback water show change in the elemental compositions, more fine particles attachment and new minerals detected on rock surface due to effect of flowback water. In produced water, Na, Sr and Cl are extremely high after flowback water-rock interactions because of flowback water contamination. Water parameter analysis indicates after flowback water-rock interactions, suspensions in produced water have highest precipitation tendency because of extremely highest TDS, largest particle size and lowest absolute Zeta potential relative to all water samples. Therefore, according to rock and water characterization, if flowback water without any treatment would be reused in the field hydraulic fracturing operation, created flow pathways and pores are more likely to be blocked and formation damage will be caused. This study provides information on comparison between deionized water-rock interaction and flowback water interaction. The information enhances the understanding of basic water-rock interaction mechanisms and evaluates formation damage caused by reuse of flowback water.