A Nuclear Magnetic Resonance Cryoporometry Study On The Pore Size Characterization Of Unconventional Oil And Gas Reservoir Rocks

The accurate characterization of micro-nanoscale pore structure of unconventional oil and gas reservoirs is extremely significant and act as important basis of unconventional oil and gas research.In this paper,typical unconventional oil and gas reservoir rocks,such as shale,tight sandstone,and coal,are selected as research objects.Many techniques are used,such as casting slices,scanning electron microscopy,focused ion beam,X-ray diffraction analysis,mercury intrusion capillary pressure(MICP),low pressure nitrogen adsorption isotherm(N2-LPAI)and nuclear magnetic resonance relaxation.Through analysis and comparative experiments,nuclear magnetic resonance cryoporometry(NMRC)was studied for the adaptability of unconventional oil and gas reservoir rocks.A new probe liquid was used by NMRC.This study provides the theoretical and technical support for improving the application of low-field NMRC in characterization of pore structure of unconventional oil and gas reservoirs rocks.The main results of this study are as follows:(1)Based on the previous studies in the field of NMRC,this paper proposes systematic theory of characterization of pore size distribution of unconventional oil and gas reservoir rocks by NMRC and lays foundation for promoting the development of NMRC in unconventional oil and gas reservoirs.(2)The comparative study of NMRC,MICP and L2-LPAI methods was used to investigate the applicability of NMRC in characterizing pore size distribution of shale,tight sandstone,and coal and clarify the advantages of NMRC;(3)This study developed a new method for characterizing the pore size distribution of tight sandstone using octamethylcyclotetrasiloxane(OMCTS)as an NMRC probe liquid(NMRC-OMCTS).This method can accurately characterize the pore size distribution of tight sandstones with different oil levels;(4)Through comparative experiments,the effects of sample size,the KGT value of probe liquid,freezing and thawing process,and the pyrite content on the accuracy of NMRC were investigated in unconventional oil and gas reservoirs.