сгдт水泥密度-套管壁厚测井解释新模型

Interpretating Responses of сгдт Casedhole Gamma-Density-Thickness Tool Using Numerical Modeling Techniques.

俄罗斯 сгдт测井仪使用 1 37Cs伽马源及一个短源距探测器和多个周向排列的长源距探测器来测量水泥环密度和套管壁厚 ,适合在外径 146 mm或 16 8mm的套管中应用。1996年以来 ,用这种仪器已在大庆油田测井数百井次。因该地区油水井套管外径多为 140 mm,故有必要对仪器重新进行刻度。为此 ,按照仪器在该地井中的实际情况建立计算模型 ,进行蒙特卡罗模拟 ;研究了仪器在不同套管内液体密度、套管壁厚、水泥环密度、裸眼井径和地层密度条件下的响应。模拟结果显示 ,长短源距处射线计数率的数值均随套管内液体密度、套管壁厚或套管外流体密度的增加而线性下降。用线性回归的方法得到了相对计数率的对数值随不同参数变化而变化的斜率。通过分析仪器响应规律 ,建立了一套改进的解释模型 ,给出了一个测井解释实例。

With a 137 Cs gamma ray source, a short spaced NaI detector (SD) and six long spaced NaI detectors (LD), the сгдт HB tool was originally designed to determine cement density and casing thickness in 146 mm or 168 mm outer diameter (OD) casing. From 1996, hundreds of wells in Daqing oilfield have been measured with this kind of tool. As the local wells are usually cased with 140 mm OD casing, it is necessary to recalibrate the logging tools. For this purpose, Monte Carlo simulations are performed with models set up according to a virtual downhole tool under local well conditions. Responses of the tool to different conditions of fluid density in the casing, casing thickness, cement density, openhole diameter and formation density are studied. Simulation results show that both SD count rate and LD count rate decrease logarthmically with the increase of fluid density in the casing, casing thickness or density of media behind casing. Slopes of thel ogarithm of relative count rate against each above mentioned factor are obtained by means of linear regression. Through analyzing responses of the tool, a set of innovated interpretation model is achieved. An interpretation example is presented.