| Summary: | Conventional logging tool response is complicated by the presence of shale making it difficult to interpret the log response. Water saturation in shales assumes the shales are filled with brines found in nearby sands. In gas shales where brines cannot be sampled it is impossible to measure shale water saturation. The porosity and water saturation of six unpreserved shale samples and their pulverized equivalents were measured with NMR. The estimated NMR porosity from the cuttings is always lower than plug porosity but within +/- 1.0 p.u. The estimated water saturation from cuttings is about 60% lower than that of plugs and may be a function of cutting size. Ninety percent of the water present in the all the six shale plugs/cuttings is bound to the surface of the core either as hydration water or by capillary forces. An obvious drawback of the study is the use of unpreserved core plugs. Immersion of cuttings in water and oil indicate the estimation of porosity and water saturation by NMR was possible in oil based mud. NMR is used routinely in the oil and gas industry to determine in-situ water saturation and bound or non movable water saturation. It is used for rock typing and to provide estimates of permeabilities. Extending these uses to zones of permafrost and hydrate requires understanding NMR measurements in the presence of cold temperature and ice. The porous media in permafrost region generally contain ice in addition to brine. The presence of ice complicates the fluid dominated NMR response. The main objective of this study is to understand the freeze-thaw behavior of NMR in saturated reservoir rocks using a 2 MHz (oilfield operating frequency) NMR spectrometer and a Carr, Purcell, Meiboom and Gill (CPMG) pulse sequence technique. In this experimental based study, brine saturated reservoir and synthetic core plugs were temperature cycled from 22° C to -12° C. Core porosities ranged from 18% to 37% while Klinkenberg permeabilities ranged from 10 md to 5000 md. Quartz is the dominant mineral present in all ...
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