An NMR study of porous rock and biochar containing organic material

With traditional sandstone oil reservoirs coming to the end of their useful lives, there is interest in extracting oil and gas from shale and carbonate rocks. Recovered samples often contain hydrocarbon material, sometimes in a fairly mobile form, sometimes in a tarry form. There is also an interest in studying forms of porous carbon, such as biochar, both for their soil-remedial properties, and for carbon sequestration. Biochars, depending on heat-treatment temperature and duration, also frequently contain residual hydrocarbon matter. There are two techniques that will be discussed: Proton NMR Relaxation (NMRR) and NMR Cryoporometry (NMRC) [10.1016/j.physrep.2008.02.001]. This study applies proton NMR Relaxation to characterise the quantity and mobility of hydrocarbon matter in dried shale and carbonate rock and biochar pores. Curve-fitting is applied to the Free Induction Decays (FIDs) and Carr-Purcell-Meiboom-Gill (CPMG) echo trains to quantify the measurements. This study also applies NMR Cryoporometry, to measure structure: pore-size distribution and pore volumes of the rock, and of the stable carbon skeleton. It has the significant advantage of being usable even when there are liquids and volatile components already in the pores. In porous rocks, combining mobility and structural information will provide a measure of the difficulty of removing the tar/oil from the rock. In biochar, combining the mobility of the labile components with the structural information for the stable biochar skeleton will inform calculations of lifetime of the labile components within the biochar. The NMRC data will also inform estimates of the lifetime of the biochar carbon skeleton