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Advancement in Source Rock Porosity and Fluid Characterization Using Core NMR


This investigation began as a result of production not matching the in place volumes from core of a Sand Wash basin in the oil window. Initially it was determined that using GRI methodology severely underestimated total porosity and movable hydrocarbon due to cleaning. Conventional core NMR was used to attempt to resolve the core cleaning issue however it was inadequate in determining total porosity as early T2 arrival times are not recorded which is where most unconventional pores exist. To measure these early T2 arrival times, high resolution core NMR was used which captures almost 90% of the T2 signal. The results of the high resolution core NMR was an increase from a GRI based porosity of 6.5% to a NMR measured porosity of 17.1%. This drastically increased the in place volumes and allowed for a more reasonable match of oil recovery. Due to the high change in total porosity a process using high resolution NMR was developed termed Sequential Fluid Characterization (SFC), which allows for the determination of fluid components (movable fluid porosity, capillary bound porosity, clay bound porosity, and bitumen). The high resolution core NMR and SFC were also applied to the Marcellus shale and other dry gas plays. The result was an increase in total porosity with the core NMR which in turn yielded an increase in calculated in place volumes. In addition a bcf/ft was calculated for these plays using the SFC derived porosity and it was noted plays like the Marcellus in WV produce economically at high rates due to more in place volumes that were previously un-recognized. This is an indicator that unconventional plays less than 100 feet can be economic targets if the bcf/ft is high.