Shale Nuclear Magnetic Resonance Petrophysics Methodological And Experimental Study Based On Two Dimensional Relaxation Spectra

With the deepening of oil and gas exploration,unconventional reservoirs,which are represented by shale,tight sandstone,gradually become the research object.As a powerful tool for petrophysical study,nuclear magnetic resonance?NMR?can provide reservoir physical parameters such as porosity,permeability,pore size distribution,surface relaxivity and so on.Nowadays,shale NMR studies are mainly faced with challenges of short relaxation component detection,component identification of hydrogen nuclei in solid and liquid,viscosity prediction,etc.On account of the issues above,BE-CPMG pulse sequence is utilized firstly.Numerical simulation is performed to optimize experimental parameters.T₂ spectra with and without hydrogen nuclei in solid component is rapidly obtain by the contrast of CPMG and BE-CPMG experiments,respectively.The difference of hydrogen nuclei in solid and liquid is observed in one dimensional experiments.Then,a rapid,high contrast two-dimensional T₁-T₂ correlation pulse sequence based on partial inversion recovery of T₁ encoding is proposed.The kernel function is derived according to Bloch equation.Numerical simulations for forward modeling and inversion are performed to verify the feasibility of this method and the stability of the inversion algorithm.Experimental verification of the feasibility of the pulse sequence is conducted through the experiments on copper sulfate solution,artificial sandstone and shale samples.Compared with T₁-T₂ correlation based on inversion recovery and saturation recovery method,two dimensional T₁-T₂ correlation based on partial inversion recovery has the advantages of speediness and high contrast.Based on NMR relaxation theory,the inversed T₁-T₂ spectrum is projected to T₂sec-T₂ spectra for component identification and viscosity prediction.The experimental approaches have instructive impacts on both NMR well logging and petrophysics.