利用PNST测井资料评价示踪陶粒压裂裂缝Ⅰ:能谱

Using the Pulsed Neutron Log to Evaluate Fracture Intervals Packed with Detectable Proppants Ⅰ:Energy Spectroscopy

为满足水力压裂支撑缝高度评价需要,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俘获伽马能谱测井资料处理与解释方法。经预处理实测俘获能谱和元素标准谱、解谱确定元素产额、校正井眼元素产额、运用相对灵敏度因子和氧化物闭合模型等数据处理与解释步骤,获得了地层元素干重与矿物组分。为反映地层的可压裂性,进一步计算了岩石脆性指数。测井实例表明,通过比较压裂前后地层钆元素干重的差异,能辨识示踪陶粒铺置位置。该方法的解释结论与测量热中子俘获截面的解释结论相符,且该方法具有特异性和更高的灵敏度。

To meet the needs of proppant placement evaluation of hydraulically induced 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 capture gamma-ray energy spectrum logged with the PNST pulsed neutron spectral tool are studied.Dry weight concentrations of formation element and mineral component are obtained through several data processing and interpretation steps,which involves pre-processing the measured capture spectrum and standard spectra;Analyzed is the measured spectrum to determine element yields;subtracted are baseline yields of borehole element with applying relative sensitivity factors and the oxide-closure model.The rock brittleness index is further calculated for formation fracability evaluation.Fracture intervals packed with detectable proppants can be identified from overlapping the after-frac and before-frac logs of gadolinium concentration.The interpretation results by this method and the method of thermal neutron capture cross section are consistent with each other.However,this method has specificity and higher sensitivity,and is more reliable.