SUBSURFACE FLUID CHARACTERIZATION USING DOWNHOLE AND CORE NMR T1T2 MAPS COMBINED WITH PORE-SCALE IMAGING TECHNIQUES

摘要

Characterization of the subsurface fluid types,porosity, saturations, and wettability arecritical for understanding the type andvolumes of fluids that will be produced duringprimary completions and secondarywaterflood recovery. The oil reserves withinthe Green River Formation of the Uinta Basin(Utah, USA) in the Greater Monument ButteUnit (GMBU) have variable fluid volumes,saturations, and wettability. Within apotential pay section of over 2000 feet areover twenty defined producing sandstonereservoir intervals within the Green RiverFormation with variable depositionalenvironments, mineralogy, and rock quality.Traditional core analyses for saturations andwettability are time-consuming and expensivebecause of variable reservoir propertieswithin discontinuous sands and highparaffinicoil containing asphaltenes andresins. Similarly, the variable wettabilitycomplicates standard analyses of NMR datafor fluid type and volume estimations.Newfield has approximately a dozen wellswith nuclear magnetic resonance (NMR) T_1,T_2, and diffusion data in the producing sectionof Monument Butte Field. We have identifiedpatterns of NMR, dielectric, and standardtriple-combo log data that are associated withdifferences in estimation of clay-bound watervolumes from NMR and XRD data. Wepresent results from pore-scale imaging, NMRcore-flood experiments, USBM measurementsof wettability, and 2.5D inversion of NMRdata used to characterize the variablewettability of GMBU sandstone reservoirs.We found that the sandstone reservoirs aremixed-wet at the micro- and macro-porescales, including presence of oil-wet clays.Mixed-wettability complicates estimation offluid types and volumes from NMR data usingstandard interpretation techniques. Ananalysis protocol involving pore-scaleimaging, core-flood NMR experiments, and2.5D NMR processing and analysis permitreduction of interpretation ambiguity of theNMR data.