A Systematic Workflow for Modelling and Upscaling Force Upscaling Workshop 2004 Tor Barkve and Jan C Rivenæs Force Upscaling Workshop 2004 Tor Barkve and Jan C Rivenæs

T&K A modellers eye test W E R E A L Y H A T E LZXUPSCALINGQWS BUTWEHAVETOLIVEWITHIT AHFGRLSXVCPTYUSZØLASSNDFGWAQTSRAYSU

T&K Modelling and data rescaling CORE AND LOG DATA DYNAMIC WELL DATA SEISMIC DATA OUTCROP DATA DATA RESCALING RESERVOIR DESCRIPTION DATA RESCALING FLOW MODELLING ECONOMIC AND STRATEGIC DECISIONS

T&K Building a sand-castle? MODEL UNCERTAINTY MODEL GOAL DATA UNCERTAINTY Where should I focus in the modelling process? How should I treat uncertainty?

T&K The art of planning GEOLOGY PETROPHYSICS GEOPHYSICS RESERVOIR

T&K Establishment of standards 2000 BEST PRACTICE FOR UPSCALING A.GRINDHEIM ROXAR 2001 BEST PRACTICE FOR WATER SATURATION MODELLING 2003 BEST PRACTICE FOR PERMEABILITY MODELLING 2004

T&K The art of planning The main purpose is to establish a common understanding of modelling purpose, modelling challenges and modelling resources. ”The geologist is a working on a scale we cannot use” ” The reservoir engineer is destroying the geo model by upscaling” DISCUSSING THE MODEL PLAN?

T&K What is upscaling? Upscaling is finding a coarse-scale value representing the effect of a fine scale distribution. A cynic would describe upscaling as a process of putting incorrect information into the wrong model to get the right answer. Mike King, BP The answer my friend, is blowing in the wind. Bob Dylan, Not BP.

T&K The upscaling stages DEFINITION OF SCALES SAMPLING METHOD AVERAGING DATA FILTERING

T&K Scale selection DATA AND OBSERVATIONS PHYSICAL MODEL WORK LOAD MODEL PURPOSE

T&K Definition of scales Horizontal length (m) Vertical thickness (m) Laminae Beds Para- sequences Geological model Flow model Core Probe Log Adapted from Pickup and Hern (2002)

T&K Selecting scales: Geological view Important ”upscaling” is taking place already in the core description. The coupling between small-scale properties and fluid flow not well understood. Thief zones Well A Well B Modelling of large scale features below grid resolution is a headache Can we model fault zone properties?

T&K Selecting scales: Geophysical view Impedance log 3D seismic impedance Seismic data resolution is often not good enough to identify flow elements Oseberg Ness Channel Overbank

T&K Selecting scales: Dynamical view Which scales can be detected from dynamic data only? Cost-Efficient Reservoir Characterization: Project at Rogalandsforskning Supported by Eni, Hydro and Statoil

T&K Selecting scales: Mathematical view ALIASING: Modelling errors caused by discrete data representation. NYQUIST SAMPLING THEOREM: To avoid aliasing, the grid cell size should be at least half the characteristic length of the object sampled.

T&K Selecting scales: Purpose NON-FACIES MODEL Three length scales: Trend, correlation length, stochastic variation HORIZONTAL PERMEABILITY Data uncertainty much larger than upscaling uncertainty VERTICAL PERMEABILITY ??? FACIES MODEL Multiple length scales Upscaling uncertainty generally large

T&K The upscaling stages DEFINITION OF SCALES SAMPLING METHOD AVERAGING DATA FILTERING

T&K Data filtering Correct preparation of logs is perhaps more important than selection of upscaling average: Removal of shoulder effects Use of bias logs General recommendations: Avoid use of cut-off in logs Use PHIE and KHE Consider cut-off in geo to sim upscaling

T&K The upscaling stages DEFINITION OF SCALES SAMPLING METHOD AVERAGING DATA FILTERING

T&K Sampling methods: Logs ”Blocking” of wells Problem 1: Slanted well in regular grid Problem 2: Straight well in skewed grid

T&K Sampling methods: Grids Sampling is an major error source. Grid correspondence should be attempted. Geo grid and sim grid should be constructed together. GEOLOGICAL FRAMEWORK SIM.GRID GEO.GRID

T&K Half-cell upscaling DUAL GRID Upscale to dual grid Use Eclipse keyword LINKPERM GEO STREAMLINE COMPARISON SIM BASIC GRID(S) Construct dual grid Transmissibility upscaling

T&K Sampling and geology Grid following lithostratigraphic horizons

T&K The upscaling stages DEFINITION OF SCALES SAMPLING METHOD AVERAGING DATA FILTERING

T&K Selection of averages Use a ”mortar method”: Target Reference: Beckner & Kumar: SPE Res.Eng. August 2001 Create upper bound Create lower bound Create improved upper bound ……

T&K Averages and geology Averages are typically symmetrical: Upwards coarsening sequence or upwards refining sequence is irrelevant. More work needed!

T&K Summary and conclusions Upscaling methods must be evaluated based on their role in the total work process. Upscaling methods are rather coarse but cannot be evaluated independent from other uncertainty. Four aspects of upscaling are generally equally important: Selection of scales Data filtering Sampling Averaging Main challenges for upscaling are Vertical permeability Facies boundaries