Integrated Reservoir Characterization with Spectroscopy,Dielectric and NMR T1-T2 Maps in Freshwater Environment,Case Studies from Alaska

摘要

Hydrocarbon identification and evaluation with conventional triple-combo logs and Archie-based equations in freshwater environments has been a challenge for petrophysicists.In the first case study from Alaska,shallow reservoir information from non-Archie based technologies including total organic carbon(TOC)from spectroscopy measurements,hydrocarbon volume derived from dielectric and NMR logs were used for quick hydrocarbon bearing zones identification,decision making on fluid sampling and early determination of oil properties.The high-resolution NMR T1-T2 maps,derived from the latest inversion,revealed the presence of viscous oil.Another targeted formation is a laminated shaly sand sequence,also in a freshwater environment.The array resistivity logs show a low contrast profile and it is more challenging for fluid identification and evaluation.Relatively high resistivity anisotropy from 3D induction suggest the formation is potentially hydrocarbon bearing.TOC from spectroscopy and water filled porosity from dielectric compared to the total porosity are direct indicators of the presence of hydrocarbons in the formation,but the interpretation is complicated by water-based mud(WBM)filtrate invasion.The stacked T1-T2 maps generated immediately after NMR logging for selected intervals,clearly showed the presence of light oil.This was confirmed by the latest wireline formation testing in the next logging run.Instead of quantitative formation properties evaluation this paper focuses on qualitative fluid identification with non-resistivity-based technologies,particularly with T1-T2 maps.NMR T1-T2 fluid mapping has been traditionally used for unconventional reservoir and is well discussed in various literatures.In our case,this technique has been applied for conventional reservoirs in the freshwater environment.