Advanced Downhole Flow Detection through Acoustic and Temperature Sensing in Combination with Geochemical Testing; A holistic Approach

Abstract As the need for energy increases, drilling and completion of new deep natural gas wells is also increasing. Commonly, gas wells are monitored through real-time surface readings. Government regulations and environmental considerations mandate the safe operation of all producing assets. A measure of well health is the annuli readings. Normally, each outer casing annulus should read zero pressure. However, due to a number of factors, the annuli can sometimes exhibit positive pressure. Once a well exhibits abnormal annuli pressures, it must be investigated and actioned accordingly. As the casings can cover a long section of footage, it is necessary to run a downhole detection tool to identify the fluid flow. This paper describes the best practices to detect fluid outflow through temperature and acoustic logging in combination with geochemical laboratory testing and provides field applications. Conventional bleed-off/build-up cycles are used to check the sustainability of the pressure build-up in the annuli. Once that pressure is confirmed to be sustainable, a slim downhole tool conveying high-definition spectral noise and temperature sensors is run to determine the fluid flow location. The high-definition acoustic survey is conducted on the stations using a wide frequency range acoustic sensing platform that can record within a 15 ft radius of investigation. The acoustic survey produces a high-definition power spectrum that can reveal and characterize flow activity within the well system, including the tiniest of noises generated by fluid movement. This was combined with high-precision temperature surveys and analysis. To identify the feeding zone, fluid is sampled via pressurized cylinders at the surface and dispatched to a laboratory for geochemical isotopic fingerprinting analysis. Carbon isotopes were measured using gas chromatography connected to an isotope ratio mass spectrometer. Downhole logging composed of High Precision Temperature and High-definition Spectral Noise Logging was combined with surface pressure reading analysis to provide a complete assessment of the casing fluid outflow. Logging showed clear signs of downhole fluid movement while gas isotope analysis identified sample origin. Carbon isotope compositions were compared to other endmembers. Carbon isotopic profile plots were used to fingerprint the origin of the moving fluid. The novel suggested methodology and procedure of downhole fluid movement detection in combination with geochemical testing provides comprehensive and highly accurate analysis that helps to reveal the truth of fluid movement and enables for fit for purpose preventative workover operation.