AAPG Annual Convention and Exhibition

Datapages, Inc.Print this page

The Light and Dark Side of Eagle Ford Shale Oil: Extrapolating Data Rich Wells to a Field Scale Model


Many operators have drilled into the Eagle Ford Shale to exploit the massive amount of oil in place (OIP) that resides within its mixed carbonate organic mudstone facies. However, drilling in non-core areas of the play can be very challenging. The present work focuses on the appraisal of an up-dip, immature acreage position in South Texas, USA. Prediction of well performance from liquid-producing organic shale reservoirs is more challenging than gas producers due to the dual nature of the hydrocarbon pore fluid i.e. bound oil and potentially producible light oil. Differentiation between the fluids is critical in the evaluation of these reservoirs and is challenging when using basic logs. The solution is to separate these fluids using nuclear magnetic resonance (NMR) with the critical part of the analysis being the determination of the NMR T2 cutoff to discriminate bound and light oil. Predictive results are best achieved through core-log integration. Detailed petrophysical evaluations on data rich wells have been extrapolated including interpretations from wells with standard log data sets to determine the reservoir quality and total OIP within the area of interest. NMR log and core data were then used to partition the bound and light oil fractions. The final result is a 3D geocellular model showing where larger amounts of light oil exist and where the highly viscous, largely immobile oil is dominant. The results of this study were used to appraise a marginal acreage position, better understand well performance and allocate production from multiple reservoirs within the subsurface.