Improved oil-in-place determination in very shaly sandstones in the San Jorge Basin Using Total-Porosity NMR logs

摘要

NMR logs run in oil-bearing, shallow sandstones in the Las Heras area of the San Jorge basin indicate that many reservoirs are shalier and have a much lower effective porosity than generally assumed from cores or conventional log evaluation based on density logs. This would imply that oil-in-place determination based on cores or density logs is overestimated, leading to erroneous estimates of recovery factors. Extensive coring in a well with very shaly sands proved the NMR porosity for T sub 2 above 3 ms is effective porosity, as clay content from infrared spectroscopy (FT-IR) measurements metched shaliness derived from NMR's total and effective porosity. As expected, core porosity (which includes clay-bound water) closely matched NMR total porosity.