Abstract:

The movable fluid evaluation was conducted based on a total of 277 matrix block samples from three typical domestic lowpermeability reservoirs of different lithologies, mainly using nuclear magnetic resonance(NMR) core analysis technique of low magnetic field and supplemented by other routine test means including rock thin section, environment scanning electron microscopy(ESEM), high-resolution computed tomography(CT) and imaging logging. The distribution law and influencing factors of reservoir movable fluid were analyzed, and the cutoff value for T₂ and porethroat radius of movable fluid were calculated. The results show that the movable fluid parameters of low permeability reservoirs have wide range. The relation of the movable fluid parameters and the permeability gets better with the increase of permeability. The correlation among percentage of movable fluid, porosity, permeability is better in sandstone reservoirs. The values calculated by nonlinear optimization method well agreed with the measured values. Micropore structures, such as development degree of micro-fracture, pore size distribution, clay mineral and the filling degree, determine the distribution of movable fluids in low permeability reservoirs.

Key words: low permeability reservoir, nuclear magnetic resonance(NMR), T₂ spectrum, movable fluid, pore type, relaxation time