Monitoring the Liquid Level of Shale Oil Well Through EM Telemetry, a Case Study

Abstract Shale oil had been invested heavily in China, as exampled by Daqing oil field, Xinjiang oilfield and so on. The liquid level of shale oil well was generally tested through acoustic means at the wellhead. This method was not accurate due to factors such as the wax, dead oil and well deviation, incorrect data led to the wrong development strategy or even downhole pump damage. In this paper, downhole telemetry was raised based on EM transmission, its working principle was discussed. Relevant tools were manufactured based the principle, field trial was also completed in the oilfield. EM had been familiar to us for the purpose of communication, but its application downhole was a complete different scenario due complex electric conductivity environment. We explored the downhole EM transmission mechanism and developed the tubing-casing-subsurface channel model, low frequency EM source at the tubing could pass through casing to enter the reservoir and be detected on the ground. To turn the theory into reality, we designed the telemetry system including the modules of electric circuit, coil, metal centralizer and receiving device. Electric circuit could modulate the pressure data into low frequency alternative current and pass it to the coil module. Under the effect of alternative current, the coil module would induce magnetic field on the tubing with the pressure date. EM signal could flow along the path of metal centralizer and penetrate the casing to enter the subsurface, the receiving device could detected the voltage potential between wellhead and ground, its precision was microvolt level. Downhole liquid pressure monitoring gauge was manufactured and tripped into shale oil well up to 1466m to gain the knowledge of liquid level. The signal attenuated as the gauge went deeper but was still 1.5 times of noise at the bottom of well. The gauge helped the operator monitor the change of liquid level and took relevant measures accordingly if the change was abrupt. This paper prescribed the application of EM into downhole liquid level monitoring. We shared the experience with our counterparts and helped the expansion of downhole telemetry technology.