Performance assessment of the water curtain system: a monitoring system in an underground water-sealed oil reservoir in China

The water curtain system is a vital part of an underground water-sealed oil reservoir. It is significant to evaluate the performance of the water curtain system. A field monitoring system was designed for realizing the performance assessment in the first underground water-sealed oil reservoir in Huangdao city, China. The system could monitor the operating water level of the water curtain system, groundwater level around the reservoir, and pore pressure between the caverns. This study systematically analysed the complete monitoring data of 2015. During the trial production operation, the operating water level of the water curtain system was above the 38 m minimum hydraulic boundary. Without considering other water replenishment, the ratio of the water inflow to the replenishment of the water curtain system was about 84.86%. Due to the effect of construction, the groundwater level of some wells was decreased. After starting the operation of artificial water replenishment, the water curtain system was able to supply a sufficient amount of water to these wells (OH-2, OH-4, OH-7, and OH-10) and recover the groundwater level. Most of the pore pressures at − 15 m and − 25 m were higher than or equal to the medium pressure; thus, the effective recharge depth of the water curtain system was between − 15 m and − 25 m, which encompassed the elevation of the cavern vault (− 20 m). Therefore, when the operating water level was between 38 and 40 m, the performance of the water curtain system could guarantee the project safety based on the analysis of water inflow, the groundwater, and the effective recharge depth of the water curtain system. These data could be used to check the effect of the cavern design and the employed construction method, which could further guide development and inventions related to the water-sealed technology.