HOW USEFUL IS RESERVOIR MODELLING FOR E & P FORECASTING ?

1. HOW USEFUL IS RESERVOIR MODELLING FOR E & P FORECASTING ? Dr. Nazmul Huq Reservoir Engineering Expert ENI UK

2. OUTLINE OF PRESENTATION • INTRODUCTION • RESERVOIR MODELLING AND PRODUCTION FORECASTING • WHAT IS RESERVOIR MODELLING ? • APPROACH & SIGNIFICANCE • DESIGN, CONSTRUCTION AND APPLICATION OF RESERVOIR SIMULATION MODELS • HISTORY MATCH • IMPORTANCE IN APPROXIMATING FIELD DESCRIPTION & PERFORMANCE – HOW & WHY ? • CONDITIONS OF ACCEPTABILITY • PREDICTIVE MODELLING – FORECASTING PERFORMANCE • TRANSITION FROM HISTORY TO FUTURE PERFORMANCE • SENSITIVITY TO VARIATIONS IN RESERVOIR PARAMETRS • CONCLUDING DISCUSSION

3. RESERVOIR MODELLING • KNOWLEDGE OF RESERVOIR HETEROGENEITY WILL ALWAYS BE INCOMPLETE • HETEROGENEITY – IMPACT OF SMALL SCALE VARIATIONS ON PERFORMANCE / PRODUCTION FORECASTING

4. RESERVOIR MODELLING & PRODUCTION FORECASTING • MATERIAL BALANCE • ANALYTICAL CALCULATIONS – WELL TESTS, FIELD OBSERVATIONS, etc. • DECLINE CURVE ANALYSIS • NUMERICAL RESERVOIR MODELLING

5. WHAT IS RESERVOIR MODELLING ? • APPROACH & SIGNIFICANCE • DESIGN, CONSTRUCTION AND APPLICATION OF RESERVOIR SIMULATION MODELS

6. RESERVOIR MODELLING & PRODUCTION FORECASTING • MATHEMATICAL EXPRESSION OF PHYSICAL CONCEPTS • LIKELY OCCURRANCE IN REALITY & CONCLUSIONS DERIVED BY APPROPRIATE MATHEMATICAL TECHNIQUES • RESERVOIR DATA - PROPERTIES DETERMINE BEHAVIOUR • BEST COMBINATION RESULT IN MATCH OF HISTORICAL PERFORMANCE • HISTORY MATCH - NON UNIQUE - SENSITIVITY / LONGER HISTORY – ACCURACY • RESERVOIR DELIVERABILITY - PREDICTION OF PERFORMANCE • BUSINESS APPROACH – MAXIMISE RECOVERY PRODUCTION FORECASTING

7. RESERVOIR MODELLING & PRODUCTION FORECASTING • BUSINESS PERSPECTIVE – ECONOMIC DEVELOPMENT • DEVELOPMENT OF RESERVOIR SIMULATION MODEL • MATCHING FIELD HISTORY – HOW & WHY - IMPROVE RESERVOIR DESCRIPTION • PREDICTIVE MODELLING – PRODUCTION FORECASTING • DEMAND • INVESTMENT STRATEGY & REGULATIONS • OPERATING STARTEGY

8. RESERVOIR MODELLING • DISCRETIZATION • IN SPACE - GRID BLOCKS - RESERVOIR CHARACTERISTICS • RESERVOIR • IN TIME - TIMESTEPS - DELIVERABILITY - PRODUCTION FORECASTING • NUMERICAL SOLUTION OF FLUID FLOW EQUATIONS – DIGITAL COMPUTERS

9. RESERVOIR MODELLING GEOLOGICAL MODEL RESERVOIR CHARACTERISATION MATHEMATICAL MODEL IN-PLACE FLUID VOLUMES WELL DEFINITION HISTORY MATCHING PREDICTIVE MODELLING

10. RESERVOIR MODELLING • DETERMINATION OF IN-PLACE HYDROCARBONS AND RECOVERABLE RESERVES • VARIATIONS IN RESERVOIR AND FLUID PROPERTIES IN SPACE AND TIME • DISCRETIZATION OF RESERVOIR INTO BLOCKS • APPLICATION OF FLUID FLOW EQUATIONS RESULTING FROM PRODUCTION / INJECTION • MATHEMATICAL MODELS SOLVED NUMERICALLY • ‘PREDICT’ HISTORICAL PERFORMANCE • ADJUST RESERVOIR PARAMETERS TO OBTAIN ‘ACCEPTABLE’ HISTORY MATCH • PREDICT FUTURE PERFORMANCE – ‘PRODUCTION FORECASTING’ - OPTIMUM DEVELOPMENT

11. STRATEGIC & TACTICAL ASPECTS OF RESERVOIR MODELLING • STRATEGIC • NATURAL DEPLETION • WATER / GAS INJECTION • WATER ALTERNATE GAS INJECTION (WAG) • ENHANCED / TERTIARY OIL RECOVERY • TACTICAL • DETAILED WELL PLANNING • DRILLING HAZARDS • HIGH PRESSURE ZONES • COMMUNICATION WITH INJECTORS

12. RESERVOIR MODELLINGRESERVOIR DEPTH - AREAL

13. RESERVOIR MODELLINGRESERVOIR DEPTH - VERTICAL GAS OIL WATER

14. RESERVOIR MODELLINGAREAL GRID DISCRETIZATION

15. RESERVOIR MODELLINGVERTICAL GRID DISCRETIZATION

16. RESERVOIR MODELLINGWELL LOCATIONS - VERTICAL Gas Injector Oil Producer Water Injector

17. RESERVOIR MODELLINGWELL LOCATIONS P ---- Producers I ---- Injectors

18. RESERVOIR MODELLINGWELL LOCATIONS Horizontal Producer Horizontal Injector

19. HISTORY MATCH • IMPORTANCE IN APPROXIMATING FIELD DESCRIPTION & FIELD PERFORMANCE – HOW & WHY ? • CONDITIONS OF ACCEPTABILITY

20. HISTORY MATCH • NO UNIVERSAL METHODOLGY • UNCERTAINTY – COMPARISON OF OBSERVED & CALCULATED VALUES • DYNAMIC PROPERTIES • WELL PRODUCTIVITY • SATURATION DEPENDENT VARIABLES – GOR / WOR, etc. • RESERVOIR PRESSURE • ADJUSTMENT TO DATA - FUNCTION OF RELIABILITY • ADJUSTMENT REQUIRES SUBSTANTIATION / PHYSICALLY REALISTIC

21. HISTORY MATCH • VARIABILITY OF APPROACH TOWARDS HISTORY MATCH • DETAILED ANALYSIS OF OBSERVATIONS ESSENTIAL • EXAMPLES • ADJUSTMENTS TO WELL DEFINITION PARAMETERS • ADJUSTMENTS TO RESERVOIR ARCHITECTURE / PROPERTIES • ADJUSTMENTS TO FLUID PROPERTIES • APPLIED METHODOLOGY IMPACTS PREDICTIONS

22. HISTORY MATCH • QUALITY OF HISTORY MATCH DIRECTLY IMPACTS PRODUCTION FORECASTS • HISTORY MATCH - VARIATIONS • PESSIMISTIC RESERVOIR PROPERTIES • OPTIMISTIC RESERVOIR PROPERTIES • MOST LIKELY RESERVOIR PROPERTIES • COMBINATION • QUANTIFYING RANGE IN UNCERTAINTY OF HISTORY MATCH CRITERIA • ACCEPTABILITY OF HISTORY MATCH • FUNCTION OF OBJECTIVE / PROBLEM • QUALITATIVE / QUANTITATIVE

23. __ MODEL DATA + ACTUAL DATA WATER CUT FLOWING BOTTOM HOLE PRESSRE GAS OIL RATIO OIL RATE

24. __ MODEL DATA + ACTUAL DATA WATER CUT FLOWING BOTTOM HOLE PRESSRE OIL RATE GAS OIL RATIO

25. PREDICTIVE MODELLING – FORECASTING PRODUCTION PERFORMANCE • TRANSITION FROM HISTORY TO FUTURE PERFORMANCE • SENSITIVITY TO VARIATIONS IN RESERVOIR PARAMETERS

26. PREDICTIVE MODELLING • PROJECT LIFE – COMMERCIAL / TECHNICAL – OVERALL RESERVOIR MANAGEMENT • EXPLORATION / APPRAISAL STAGE – OPTIMUM DEVELOPMENT PLAN • FIELDS UNDER PRODUCTION – HISTORY MATCH – BASE PREDICTION • ASSESSMENT OF VARIOUS RECOVERY MECHANISMS • PREDICTION SENSITIVITIES

27. RESERVOIR MODELLING - SENSITIVITIES • QUANTIFICATION OF UNCERTAINTY • SENSITIVITIES PROJECT RANGE OF FORECASTS • EQUIPROBABLE RESERVOIR DESCRIPTIONS • VARIOUS OPERATING CONDITIONS • INADEQUATE HISTORY – EXPLORATION / APPRAISAL STAGE • CORPORATE FORECASTS • QUANTIFYING RANGE IN UNCERTAINTY OF PRODUCTION FORECASTS – RISK ANALYSIS • PROVEN / PROBABLE / POSSIBLE • MINIMUM / MOST LIKELY / MAXIMUM

28. RESERVOIR MODELLING PROCESS - HIERARCHY • UNDERSTANDING THE PHYSICS OF FLOW PROCESSES • ANALYTICAL CALCULATIONS • CONCEPTUAL MODELLING • STREAMLINE MODELLING • EXPANSION TO FIELD SCALE

29. RESERVOIR MODELLING – STREAMLINE SIMULATION • COMPLIMENTARY TECHNOLOGY TO CONVENTIONAL MODELLING • STREAMLINES IN TERMS OF TIME OF FLIGHT ( TOF ) • EXTREMELY FAST AND EFFECTIVE • PRELIMINARY INSIGHT INTO RESERVOIR FLOW CHARACTERISTICS

30. S Leverett’s Fractional EquationBuckley-Leverett Frontal Advance TheoryWelge Recovery Technique • Fw = 1 + 1/ (1+ 1/M) • M = Mobility Ratio • (dx/dt) = c. (dfw) / (dSw) Fractional Flow of Water Swbt Swf IMMOBILE WATER REMAINING OIL

31. FLOW STREAMLINES PRODUCER INJECTOR

32. CONCEPTUAL STREAMLINE SIMULATION1 PRODUCER & 2 WATER INJECTORSTIME OF FLIGHT (TOF)

33. RESERVOIR MODELLING PROCESS Reservoir Model Analytical Calculations Conventional Modelling Conceptual Modelling History Match Streamline Sensitivity Detailed circle Modelling Fast circle Predictions Production Forecasts History Match

34. DISCUSSION • RESERVOIR MODELLING & PRODUCTION FORECASTING • UNUSUAL PRODUCTION DOWNTIMES – CATASTROPHY / URGENT WELL REPAIRS, etc. • HETEROGENEITY / RESERVOIR EXTENSION • AQUIFER INFLUX - UNUSUAL WATER BREAKTHROUGH / GAS BREAKTHROUGH • QUANTIFICATION OF UNCERTAINTY – ASSESSMENT OF RISK • TIE-IN WITH CORPORATE FORECASTS – GAS CONTRACTS / BUDGETTED FORECASTS

35. Oil and Gas IQ : • “PRODUCING PRECISE FORCASTS IS CRITICAL TO OPTIMISING YOUR PROFITS” • RESERVOIR MODELLING • UNDERSTAND OIL & GAS RESERVOIR DESCRIPTION • INSIGHT INTO THE PHYSICS OF FLOW PROCESSES • GUIDANCE TOWARDS THE RIGHT STRATEGY • SAVES TIME & ADDS VALUE TO DETERMINE STRATEGY • ALLOWS SCOPE FOR IMPROVEMENT OF RECOVERY • MITIGATES COSTS AND CONSEQUENTLY • RESERVOIR MODELLING GUIDES TOWARDS PRECISE PRODUCTION FORECASTING

36. CONCLUSION RESERVOIR MODELLING IS THEMOST USEFULTECHNIQUE FOR E & P FORECASTING