Downhole Oil-Water Interface Wireless Monitoring by Considering Steady-State Inductance Variations

In the oil and gas production, the oil-water interface should be monitored to warn risks and to optimize the efficiency. The conventional buoyancy method could only be conducted when the production is stopped, not being able to support the production. Thus, many studies have been made to achieve real-time monitoring. Nevertheless, almost none of the published techniques could juggle a large range and a high accuracy within the confines of limited space. To address such an issue, a wireless monitoring method is proposed based on the idea that the oil-water interface’s variation could be reflected by the stray inductance of the tubing-interface-cubing circuit. The oil-water interface’s variation is firstly related with the gas segment inductance. Then, a monitoring device is developed to measure the voltage and the current, which are used to calculated the aforementioned inductance and further the interface’s variation. Afterwards, comprehensive numerical analyses are made to figure out influences of several factors, e.g. the system frequency, which could collectively induce a deviation of 2.87% in the extreme situation. At last, an on-site experiment is conducted, and the maximum absolute deviation is smaller than ±0.5 m, indicating the validity.