Abstract

Ferrous sulfide (FeS) precipitation is a severe problem and the significance of this problem is increased in the shale gas and oil production due to the potentially increasing biologically and thermally induced sulfide production. Although FeS scale is ubiquitous, little is understood about its precipitation and inhibition properties due to experimental difficulties. In conventional research, we used a batch reactor to study the precipitation kinetics and inhibition of FeS formation. In order to assess scaling risk in pipes, a new plug flow reactor was developed under anoxic condition at different ionic strength (IS), pH and temperature to enable more reliable study of FeS precipitation kinetics at high surface to solution ratio. The precipitation kinetics of FeS is successfully fitted by a second/pseudo-first order rate equations for batch/plug flow systems. The rate of precipitation increases with increasing pH and temperature, and decreases with increasing IS. Commercial scale inhibitors, citrate, EDTA and other chelating agents have been tested for their inhibition effects on FeS precipitation. The new plug flow apparatus not only adds reliable data to the limited database of scaling kinetics in realistic flowing pipes, but also supplies a new method to study the effect of inhibitors in oil production systems. The research outcomes will contribute to the prediction of FeS scaling risk under different brine composition and well conditions.

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