Evolution of Casedhole Nuclear Surveillance Logging Through Time

Abstract

Nuclear logging techniques have played a critical role in the evaluation and surveillance of hydrocarbon reservoirs since the introduction of the gamma ray log in 1939. This paper reviews the history of key developments in nuclear logging that led to improved methods to identify gas-oil (GOC), gas-water (GWC), and oil-water (OWC) contacts in steel-cased wells, as well as methods to identify gas, steam, and waterflood front encroachment, calculate their saturations, and recognize problems in efficient reservoir depletion. This paper will focus solely on nuclear methods used to directly identify fluids behind pipe using natural gamma radiation, neutron-induced gamma radiation, and neutron flux measurements. This includes gamma ray, spectral gamma ray, single- and dual-detector neutron measurements, pulsed-neutron capture, (), and pulsed-neutron spectroscopy (carbon/oxygen or C/O) methods. It will not cover other methods of identifying fluids behind pipe, such as borehole gravity and deep electromagnetic (EM) methods using wired pipe. It also will not cover indirect methods to infer fluid types in reservoirs, such as nuclear production logging using gamma density and pulsed-neutron measurements.