This paper summarizes the results of an eight well field trial that utilized a wireless surveillance technique to measure real-time wellbore fluid interface depths. The measurement of fluid depth in oil and gas wells is widely used for calculating reservoir pressure in the absence of downhole gauges and for other well information requirements. As this innovative technology does not require well entry it reduces operational costs and exposure to HSE risks. Furthermore, this technique overcomes issues inherent in acoustic measurement, related to low-pressure environments and short distance measurement.
The novel Frequency and Time Domain Reflectometry (FDR/TDR) technique described in this paper utilizes Microwave (MW) and Radio Frequency (RF) to scan the inside of the tubing string from the wellhead to a subsurface feature. The scanning operation consists of injecting pulses of MW/RF frequencies through the wellhead via an antenna installed in a Tree Cap or the annulus. The core advantages of the technique are:
Low energy MW/RF pulses
Well pressure control and well entry tooling requirements are minimized
Pre-determined MW/RF frequencies for tubing scans are harmonized with completion geometry to optimize measurement efficiency
The scanning process takes approximately one minute
Data processing of the scan information identifies single and multiple fluid level interfaces in addition to other well features.
The data is available immediately and displayed on a surface readout unit (SRU).
The average rig up to rig down time taken for each well was approximately forty minutes. The position and movement of the well bore fluid levels and other well features such as tubing joint identification were successfully measured providing data for the analysis of the well fluid inventory. The identification of individual casing and tubing joints allowed depth correlation to be verified to previously measured depths and provided a simple method of calibration. The technique provided accurate measurements over short and long distances.
The trial provides evidence of the successful development and implementation of a wireless field deployable subsurface well surveillance sensor. The sensor technology is designed for deployment in single and multiple well applications used for continuous monitoring of well integrity and for production optimization purposes.
Further development of the sensor has advanced by focusing on the introduction of the technology to multiple wells and remote surveillance real-time monitoring operations for both tubing and annulus fluid level measurements.