METHOD FOR INVESTIGATING A FLOOD FRONT PROFILE DURING FLOODING OF FORMATIONS

摘要

A method of determining the flood front profile created during the production flooding of an oil-bearing formation utilizes cased observation boreholes located between the injection wells and the producing wells. The time and depth of arrival of the flood front at an observation borehole are detected by gamma ray spectroscopy examination of the formation. Tracer elements having characteristic gamma ray emission energies are employed to facilitate detection of the flood front and its direction of travel. The tracer elements may be naturally radioactive substances or they may be normally stable elements which are rendered radioactive by neutronbombardment. Elements having interfering spectral lines may be separated on the basis of half-life measurements, selective detection periods or the response of the elements to different energy neutrons. By repeating the detection process at different depths and times, the profile of the flood front as it approaches the producing wells may be developed. This information may be used to control the flooding operating to prevent or localize premature breakthrough to the producing wells.