Empty-Hole Logging Programs For Reservoir Evaluation
New logging programs have been designed for use in holes drilled with cable tools or air-drilled with rotary rigs. The Gamma-Ray Log is generally very useful for correlation. Gamma-Gamma Density, Induction, and Neutron Logs provide basic information to permit evaluation of the gas or oil in place. The techniques for quantitative interpretation involve new ways of interrelating data from the basic logs, taking into account the response of each to hydrocarbons. The specific logging program, and its accompanying interpretation scheme, is based upon the type of hydrocarbon present. When only gas is present, the porosity and gas saturation are obtained by one of the following programs: 1) Induction plus Gamma-Gamma logs when the formation is of moderate resistivity; 2) Neutron plus Gamma-Gamma Logs when the true resistivity (Rt) is high. When oil is the principal hydrocarbon, a resistivity measurement is essential for saturation determination; porosity is preferably obtained from the Gamma-Gamma Density Log. When gas, oil, and water coexist, all three basic tools are required. The Gamma-Ray and Caliper curves, normally available with the above services, are essential for proper interpretation. The addition of the Temperature Survey to the logging program provides a means of locating permeable gas horizons and assists in validating the application of the basic logs.
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