NMR Logging Fluid Identification Method Based On DE Pulse Sequence

Resistivity logging data encounter great difficulties in low resistivity reservoir, water flooded layer, complex lithology and complex reservoir space, recognizing fluid type accurately and calculating quantitatively fluid saturation. NMR logging can measure NMR characteristic of hydrogen atomics and has more advantages in explaining bound and movable fluid porosity, permeability, saturation and studying reservoir pore structure character, etc. But now many fluid identification methods such as difference spectrum method(DSM), shifted spectrum method(SSM), time domain analysis(TDA), diffusion analysis(DIFAN) can not reach satisfactory level to fluid identification in complex reservoir.A method of NMR logging two-dimensional spectrum fluid identification is proposed based on CPMG pulse sequence and Difussion Editing (DE) pulse sequence. It spurn traditional method which use single echo spacing to measure echos. Firstly it uses many echo spacing and windows to form a new CPMG and DE pulse sequence, and then builds up two-dimensional relaxation model of them. Finally two-dimensional spectrum are inversed by measured echoes which come from CPMG and DE pulse sequence using the inversion technique of conjugate gradient. Consequently it is able to calculating reservoir parameter and evaluating fluid type. Forward and inverse numerical experiment from different saturation in Oil-Water and Gas-Water phase shows that the inversion of two-dimensional Oil-Water spectrum and two-dimensional Gas-Water spectrum fit each other well. So this method is so feasible theoretically that it can be used in laboratory and work which identificates and evaluates reservoir fluid.