Well Logging Using Radioactive Sources
D.D. Brown (Halliburton Energy Services)
In petroleum exploration well logging operations are conducted in an effort to predict the ability of an oil or gas well to produce the specific hydrocarbon (oil or gas). This prediction is based on the evaluation of the geological formation and the formation parameters such as density, porosity, permeability and the presence and type of hydrocarbon. Two primary tools are utilized in these evaluations which require the use of radioactive sources. These sources may be a 4, 8, or 19 Curie Am241Be sources or a 1.5 or 2 Curies Cs-137 source depending on the specific tool function and design. Additional sources of the same isotopes but of lesser activities are used for shop and pre- and post-job tool calibrations. The tools are used in sets and the collected data are compared by computer algorithms to determine the conditions of the specific well and geological formation. The density tool utilizes a 1.5 or 2 Curie Cs-137 source depending on the design of the specific tool to measure the formation density as well as a related evaluation of the formation porosity. The neutron tool may utilize either a 4, 8, or 19 Curie Am241Be source depending on the specific tool design to identify porous formations and for an estimate of the actual porosity of the formation. It is also possible to use the data from these tools to distinguish between oil, gas, or water zones within the formation by comparison to other log data.
