Irreducible water distribution from nuclear magnetic resonance and constant-rate mercury injection methods in tight oil reservoirs

Fifteen tight cores from Chinese Ordos basin were selected to obtain the irreducible water from fully-saturated by centrifuging with rotational speeds increased from 0 to 10,000 r/min, T2 spectra were measured by a low-field NMR core analysis unit concurrently. The fully-saturated T2 spectra showed a tri-modal pattern and ranged in 0 similar to 6, 6 similar to 100 and 100 similar to 1000 ms, which corresponded to micro-, meso- and macro-pore spaces, respectively. The irreducible water reached at the speed of 10,000 r/min with water saturation varied in 38.695 similar to 55.728%. Pore distributions by constant-rate mercury injection were adopted to get the transform coefficients between T2 time and pore-throat radius. SEM and thin sections were also introduced to support an intuitive understanding. It was found that irreducible water mainly remained in pores and throats ranged in 0.01 similar to 2 and 10 similar to 100 mu m. The micro-pore spaces dominated by clay minerals, irregular microstructure and rough particles surface were considered to be dominantly effect factors.