Study On Fluid Identification Based On Nmr CPMG And 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 new method of quantitative fluid characterization 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 multi-fluid relaxation model of Oil-Water and Gas-Water. Finally non-difussion water T₂ spectrum (surface relaxation spectrum), non-difussion oil T₂ (bulk relaxation spectrum) spectrum and gas T₂ spectrum (difussion relaxation spectrum) are inversed by measured echos which come from CPMG and DE pulse sequence. Consequently it is able to use separating oil, gas and water spectrum to calculating reservoir parameter and evaluating fluid type. By this method conincidence T₂ spectrum of oil, gas and water can be separated from each one. It overcomes the defect of conventional fluid identification methods (TDA and DIFAN), which aim at spectrum to explain and calculate. Forward and inverse numerical experiment from different saturation in Oil-Water and Gas-Water phase shows that the inversion of non-difussion water T₂ spectrum (surface relaxation spectrum), non-difussion oil T₂ spectrum (bulk relaxation spectrum) and gas T₂ spectrum (difussion relaxation spectrum) fit each other well. So this method is so feasible theoretically that it can be used in laboratory and work which identificates and evaluate reservoir fluid.