Design, testing, and implementation of a real-time system for monitoring flow in horizontal wells

The Horizontal Reactive Media Treatment Well (HRX Well®) is a technology capable of collecting and treating groundwater passively. To monitor the internal flow rate, ensuring it remains at an acceptable level and maintains the desired capture zone size in the aquifer, Point Velocity Probes (PVPs) were adapted for the task. The modified PVP was assessed for its performance in a mock-HRX Well setting, which consisted of a laboratory sand column, similar in diameter to the HRX Well cartridges that would house the PVP in the field, with flow directed along the longitudinal axis of the probe. Experiments were conducted to assess 1) the effects of friction between the fluid and the probe surface, which could bias a velocity measurement low, and 2) the effect of gas in the porous medium, potentially generated by some reactive media, on PVP signals and measurements of velocity. It was determined that PVP length exerted no discernable effect on the quality of the PVP performance. However, the effects of gas in the porous medium were varied. Compared to velocity estimates assuming a fully saturated porous medium, the bias to velocity measurements was negative if gas was limited to locations near a PVP's injection-detection array, such as might occur by inadvertent bubble injection during the tracer pulses. The bias was positive if the gas was generated uniformly throughout the porous medium, such as might occur in a reactive porous medium like granular iron, or one featuring vigorous biological activity. A field trial of the HRX Well was subsequently undertaken with internal PVPs. The PVPs identified a missing seal that was later retrofit, and documented flow in the HRX Well at velocities in the range of 1.3 to 4.0 m/d, which compared well with expectations based on a site model that predicted velocities of 1.3 to 2.3 m/d. The results of this study demonstrate that HRX Wells perform hydraulically as designed, and that PVPs are effective devices for tracking flow rates within them in near real-time.