碳氧比测井曲线水流影响校正

脉冲中子全谱测井资料显示,当测井仪附近出现向上水流时,随着连续氧活化指数(Oxygen Activation Index,IOA)曲线升高,碳氧比测井的碳氧比和硅钙比曲线会相应降低,需要校正水流对这些曲线的影响。产生这种水流影响的原因是,氧活化伽马射线被计入非弹性散射净谱和俘获谱,导致非弹性散射氧产额和俘获钙产额增大。由于这两个谱中的氧活化伽马射线计数都与IOA值呈正比,在资料处理解释环节可利用IOA曲线剔除氧活化伽马射线计数的贡献。应用提出的新校正公式,能彻底消除水流对碳氧比和硅钙比曲线的影响。实测资料处理结果表明,脉冲中子全谱测井的IOA曲线可用于指示主要的产水层和管外窜槽,校正水流对碳氧比和硅钙比曲线的影响,提高含油饱和度解释精度,对综合评价地层水淹等级起到关键的作用。

Correction of Water Flow Effect on Carbon/Oxygen Logging Curves

It is needed to correct the effect on the carbon/oxygen logging curves caused by upward water flow around a pulsed neutron spectral tool,when the oxygen activation index (IOA) curve increases,and the carbon/oxygen ratio (C/O) curve and the capture silicon/calcium ratio (Si/Ca)curve decrease correspondingly.This effect arises from counts of oxygen activation gamma-ray caused by water flow provide certain contributions in the net inelastic spectrum and the capture spectrum,which lead to increases of inelastic oxygen yield and capture calcium yield.As the contributions of oxygen activation gamma-rays in these spectra are all proportional to the value of IOA,the IOA curve is employed in data processing and interpreting to correct water flow effects on the C/O curve and Si/Ca curve.By using the proposed correction formulas,water flow effects on the corrected logging curves can be completely removed.Results of processing field logging data demonstrate that the IOA curve in a pulsed neutron spectral log not only plays an assistant role in indicating the main water-producing layers and channeling behind casing,but al plays a key role in improving the interpretation accuracy of reservoir oil saturation and the comprehensive evaluation of formation water-flooded level through its function in correcting the main carbon/oxygen logging curves which are affected by water flow.