Lab Investigation of EOR Potential for a Stack Pilot

摘要

Laboratory studies of unconventional reservoirs are faced with considerably more challenges than those ofconventional reservoirs.The assessment of Enhanced Oil Recovery potential in unconventional reservoirs(UCR EOR)in particular needs to address the characterization of static and dynamic properties given thetightness of the rocks,available sample size and simulation of EOR under elevated pressure and temperatureconditions.This paper summarizes a laboratory study designed and performed for a potential EOR pilotutilizing cyclic gas injection(Huff-n-Puff)in the Sooner Trend Anadarko Canadian Kingfisher(STACK)shale play in Oklahoma.The lab study focuses on characterizing the rock-fluid interactions as well asupscaling key parameters for the field-scale modeling and simulation.A systematic approach was followed in the design of a laboratory program specific to the characteristics ofrock/fluid interaction and the proposed injection scheme of a cyclic gas injection pilot.Digital Core Analysis(DCA)incorporating micro CT,SEM and FIB-SEM analyses were performed in order to determine basicpetrophysical properties at micro scale,with capillary pressure and relative permeability curves simulateddigitally.Porosity and relative permeability end points were also measured on preserved STACK coreplugs.Minimum miscibility pressure(MMP)measurements of field separator gas and STACK crude oilwas performed with a rising bubble apparatus(RBA).Finally,a huff-n-puff experiment was designed andperformed within a custom pressure cell to study the recovery efficiency at the existing core sample scale.Digital Core Analysis(DCA)has been shown to reliably produce petrophysical properties for tightSTACK cores.Laboratory miscibility pressure measurements were conducted at reservoir conditions(4,500psi and 183 °F)using field crude samples and the associated gas composition.Seven injection/productioncycles were applied to a re-saturated standard core plug with oil production observed and measured inthe effluent.Cyclic injection continued until no further oil could be visually observed in the effluent.Acustomized 2-stage drawdown was incorporated to provide input for the recovery process.The total recoveryafter seven cycles reached 82 %OOIP.This work provides the first rock and fluid analysis integrating digital and traditional approaches forassessment of EOR potential in unconventional reservoirs such as those found in the STACK.Thissystematic approach presents properly designed and executed laboratory experiments without leaving outkey formation and fluid variables.This workflow can be applied in similar UCR EOR studies to lay a solid foundation for appraising UCR EOR potential and providing reliable inputs for upscaling to the field levelstudies.