Petrophysical properties and fluids transportation in gas shale:A NMR relaxation spectrum analysis method

Gas shale is characterized by well-developed nano-pores,special pore structure,complex organic and inor- ganic compositions,and ultra-low permeability,which brings major challenge for the analyses by the conventional ana- lytical methods. On the basis of nuclear magnetic resonance ( NMR) experimental analyses of the marine Longmaxi formation shales from the Sichuan basin,this study provided a comprehensive methodology for measurement of the po- rosity,permeability,pore type,pore structure,and methane adsorption capacity of shale,and from theoretical and tech- nical perspectives,discussed the NMR applications in the characterization of reservoir physical properties and fluids transportation in shale. Results show that NMR technique can be used to quantitatively identify the clay-bonded fluid,capillary-bonded fluid,and movable fluid in shale,and to calculate their porosities;The dual-T2 cutoff based pore size distribution classification method is effect for evaluation of gas accumulation and gas transportation in shale;The SDR permeability evaluation model deduced from the double-exponential relationship with the T2 geometric mean in the full water-saturated state and in the bound water state,is applicable for shale permeability calculation;NMR technique can be used to quantitatively identify the adsorbed methane,porous-medium-confined methane,and bulk methane in shale, and to obtain isothermal adsorption curve of shale;A real-time NMR-based monitoring of the CO2 -CH4 displacement in shale indicated that additional 25% of adsorbed methane gas can be recovered by the injection of CO2 . It is concluded that the applications of NMR in analyses of the petrophysical properties and fluids transportation,provide a new solu- tion for shale gas reservoir characterization.