论文详情
A group of organic-rich shale has been discovered in the Niutitang Formation in northwestern Hunan Province,but there are few studies on the petrophysical characteristics of the Lower Cambrian shale in the area.Using the shale samples of the HY1 well and CY1 well as the research objects in this study,the pore characteristics and rock electrical characteristics of the Lower Cambrian shale were investigated using low-frequency nuclear magnetic resonance (NMR),spectrum induced polarization (SIP) experiments,mineral analysis,scanning electron microscope observation,etc.The results showed that various pore types are developed in the Lower Cambrian shale,mainly micropores and mesopores and also macropores and micro-fractures.The distribution of T2 shale in HY1 well is discontinuous and multi peaked with obvious trough,mainly microporous and mesoporous,and poor connectivity.There is a discontinuity between the peaks,indicating that the shale of HY1 well has mainly micropores and mesopores,and macropores are less developed with poor connectivity.The T2 distribution of CY1 well shale shows a bimodal distribution;the left peak distribution is dispersed,and the peaks are continuous.There is no obvious boundary,indicating that the CY1 well shale has various pore types;macropores are well developed and with good pore connectivity.Combined NMR and SIP tests showed no obvious phase shift spectrum peak in the Lower Cambrian shale.The real part of the conductivity and NMR porosity and permeability show relatively discrete distribution characteristics.The imaginary part of the conductivity in the shale samples of the well HY1 showed a more concentrated distribution,whereas the imaginary part of the conductivity of the CY1 well shale sample showed a more dispersed distribution,indicating that the pore structure of HY1 well is similar to that of CY1 well,but the pore complexity is different.The result between SIP and NMR response parameters revealed no significant correlation between the imaginary part of the conductivity and the specific surface area calculated by T2ML,and the product of the imaginary part of the conductivity and the formation resistivity factor showed a good correlation with the specific surface area.This suggests that the shale has complex pore characteristics and strong anisotropy;however,in the Lower Cambrian strata,the formation resistivity factor plays a crucial role in regulating the shale conductivity.