Study of influence factor for dual-detector C/O logging in slim holes
小井径双源距碳氧比C/O测井的影响因素及处理

It helps to design scale schemes and interpretation model to study the influence of borehole and formation environments in C/O logging on two detectors. The paper investigates the rules of C/O values changing with borehole diameter, cement thickness, case size, formation porosity , oil saturation, formation lithology and oil density. The results indicate that when a borehole is full of oil, C/O values increase with increasing borehole diameter or case size, and the influence of borehole increases. When a borehole is full of water, C/O values decrease with increasing borehole diameter or case size. C/O values decrease with increasing cement thickness. The higher porosity and water saturation, the higher C/O values when borehole condition is invariable, which is useful for C/O logging. Contrarily, the less porosity and water saturation, the less C/O values, and which is bad for C/O logging. Formation lithology influences seriously C/O values, limestone has higher C/O value than that of sand when other conditions are the same. The higher oil density, the higher C/O value. The paper also introduces a data-processing method that can remove the influence of borehole and formation environment on the two detectors.