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首页> 外文期刊>Applied radiation and isotopes: including data, instrumentation and methods for use in agriculture, industry and medicine >Characterizing, Simulating, and Eliminating Vibration-induced Counts in Measurement-while-drilling Gamma Ray Detectors
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Characterizing, Simulating, and Eliminating Vibration-induced Counts in Measurement-while-drilling Gamma Ray Detectors

机译：在随钻测量伽马射线探测器中表征，模拟和消除振动引起的计数

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摘要

A measurement-while-drilling (MWD) gamma ray tool will report a higher than actual count rate if its scintillation crystal package produces vibration-induced light pulses. The scintillation crystal is used as a transducer that measures the count rate of gamma rays coming from naturally occurring radioisotopes in downhole shales. Each gamma ray causes the crystal to emit a number of visible light photons that are converted into an electrical pulse by a photomultiplier tube. The pulse is shaped and digitized by tool electronics and registers as a count if it is above some threshold energy. The harsh shock and vibration conditions MWD gamma detectors experience can cause a crystal package to emit spurious light pulses which typical tool electronics cannot distinguish from genuine gamma counts, so the detector will report a higher than actual count rate. For ‘geosteering' applications a higher count rate typically will indicate that the drill string trajectory must be changed to remain within a reservoir because such a response is indicative of a shale reservoir boundary; therefore vibration-induced counts will provide a false control input, making it difficult to steer correctly. This could cause the trajectory of the drill string to exit the reservoir, Measurements of vibration-induced counts from MWD scintillation packages were made using an electrodynamic vibration table, gamma ray spectroscopy electronics, and a digitizing oscilloscope. It was found that a scintillation package will produce counts as a function of the input g-level if the Rigid body resonant frequency of the crystal in its support structure is within the bandwidth of the operational vibration environment. These measurements provided the basis for computer simulations of MWD gamma ray logging that showed the detrimental effect of vibration-induced counts on log accuracy. It was concluded that stiffening the scintillation crystal mechanical support and, therefore, moving the rigid body resonant frequencies of the system outside the operational vibration bandwidth ensures the scintillation package will not produce vibration-induced counts in a specified bandwidth. # 1997 Elsevier Science Ltd. All rights reserved
机译：如果随钻测量（MWD）伽马射线仪的闪烁晶体组件产生振动引起的光脉冲，则报告的计数率将高于实际计数率。闪烁晶体用作测量井下页岩中天然存在的放射性同位素的伽玛射线计数率的换能器。每种伽马射线使晶体发出大量可见光光子，这些光子被光电倍增管转换为电脉冲。脉冲由工具电子设备整形和数字化，如果超过某个阈值能量，则将其记录为计数。 MWD伽马探测器在恶劣的冲击和振动条件下可能会导致晶体包装发出伪造的光脉冲，这是典型的工具电子设备无法与真正的伽马计数区分开的，因此探测器报告的计数率会高于实际计数率。对于“地质导向”应用，较高的计数率通常将指示必须更改钻柱轨迹以保留在储层内，因为这样的响应表示页岩储层边界。因此，由振动引起的计数将提供错误的控制输入，从而难以正确操纵。这可能导致钻柱的轨迹离开油藏。使用电动振动台，伽马射线光谱学电子设备和数字化示波器对MWD闪烁组件的振动感应计数进行测量。已经发现，如果晶体在其支撑结构中的刚体共振频率在工作振动环境的带宽之内，则闪烁封装将根据输入的g电平产生计数。这些测量为MWD伽马射线测井的计算机模拟提供了基础，该模拟显示了振动引起的计数对测井精度的有害影响。结论是，加强闪烁晶体的机械支撑，并因此将系统的刚体共振频率移至工作振动带宽之外，可以确保闪烁包在指定的带宽内不会产生由振动引起的计数。 ＃1997 Elsevier Science Ltd.保留所有权利

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