三探测器密度测井的薄层影响及校正

THIN BED INFLUENCES AND CORRECTING OF THREE-DETECTORS DENSITY LOGGING

薄层是影响岩性密度测井的重要因素 ,而双源距岩性密度测井无法对薄层进行校正。于是 ,出现了一种三探测器岩性密度测井仪器 ,这种仪器可以对薄层进行校正并能更准确地求取地层的光电吸收截面系数。研究薄层对密度测井的影响 ,可以方便确定仪器的记录点 ,并为后期的数据处理方法研究提供理论基础。文章利用MonteCarlo方法 ,计算了不同厚度薄层 ,在纵向位置的变化和不变时 ,对三个探测器计数的影响 ,得到了随着低密度薄层位置的移动 ,探测器计数逐渐增大 ,达到极大值后又逐渐减小 ,曲线形状对称 ;随着高密度薄层位置的移动 ,探测器计数逐渐减小 ,达到极小值后又逐渐增大 ,曲线形状对称 ;极大值和极小值均出现在源与探测器之间的中点位置 ;在一定厚度范围内 ,探测器计数随薄层厚度的增加而增加 ;当薄层厚度增加到一定程度 ,探测器计数将不再变化 ,趋于一个恒定的值。

Thin bed is one of important influencing factors of litho logy density logging, bur dual-spacing litho logy density logging can't correct the influence of thin beds. A new three-detector litho logy density tool appears. It can correct the influence of thin beds and obtain photoelectric absorption coefficient of formations more exactly. After understanding thin bed influences on density logging, it is convenient to determine the record points of the tool, and provide theoretical basis for data processing method. Using Monte Carlo method, the article calculates the influence of thin beds with different thickness on the readings of the 3 detectors while they move or immobilize. Calculated results show that moving along the bed with low density, the detector readings increase gradually up to the maximum, then decrease. Its curve is symmetrical. While moving along the bed with high density, the detector readings decrease gradually down to the minimum, then increase. Its curve is symmetrical. The maximums and minimums both happen to the midpoints between the detector and the source. Within a certain thickness scope, the detector readings will increase as the bed thickness increasing. When the thickness increases to above the scope, the readings will keep a constant. Also, the article discusses the correcting methods under the influence of both mud-cake and thin beds.