利用PNST测井评价示踪陶粒压裂裂缝Ⅱ:时间谱

Applications of Pulsed Neutron Log to Evaluate Fracture Intervals Packed with Detectable Proppants Ⅱ:Time Spectroscopy

为满足水力压裂支撑缝高评价需要,针对含高热中子俘获截面材料氧化钆的非放射性示踪陶粒的辨识问题,研究了PNST俘获时间谱测井资料处理与解释方法。从预处理2个伽马探头和热中子探头的俘获时间谱出发,研究了示踪陶粒沾污套管内壁、进入水泥环窜槽和支撑地层裂缝等几种典型情况的时间谱特征,以及反映时间谱特征的地层与井眼俘获截面、非弹与俘获计数率、井眼与地层成分俘获计数率等测井曲线的提取方法,并展示了测井曲线在示踪陶粒压裂井的应用。通过比较压裂前后PNST各探头的这些测井曲线,能直观、清晰地辨识示踪陶粒;仅利用压裂后近伽马计数率和近/远伽马计数率比值交会解释,能定性辨识示踪陶粒支撑的裂缝。

To meet the needs of proppant placement evaluation of hydraulic fractures packed with non-radioactive detectable ceramic proppants that contain a high thermal neutron capture cross- section compound, gadolinium oxide, data processing and interpretation of decay curve in time spectrum logged with the PNST （pulsed neutron spectral tool）are studied. Firstly, time spectra recorded with the two gamma-ray and one thermal neutron detectors in the PNST are pre- processed. Then, time spectrum characteristics under several typical conditions, such as the detectable proppants in the borehole, cement channeling, and induced fractures of formation are determined. Corresponding logs from each detector, including borehole and formation capture cross-sections, inelastic and capture count rates, and capture count rates of borehole and formation components are extracted. Field example illustrates that fracture intervals packed with detectable proppants can be recognized directly and clearly by comparing these before-frac and after-frac logs, and can be qualitatively recognized by using a cross-plot of the near/far count ratios and near count rates both only from the after-frac logs.