EVOLUTION OF RESERVOIR MANAGEMENT TECHNIQUES

EVOLUTION OF RESERVOIR MANAGEMENT TECHNIQUES From Independent Methods to an Integrated Methodology Impact on Petroleum Engineering Curriculum, Graduate Teaching and Competitive Advantage of Oil Companies SPE 39713, Kuala Lumpur, Malaysia, 23 24 March 1998. Alain C. Gringarten

CONTENT RESERVOIR MANAGEMENT PROCESS DEFINITION OBJECTIVES METHODOLOGY IMPLEMENTATION IMPACT ON COMPETITIVE ADVANTAGE PETROLEUM ENGINEERING CURRICULUM

RESERVOIR MANAGEMENT APPLICATION OF AVAILABLE TECHNOLOGY AND KNOWLEDGE TO A RESERVOIR SYSTEM WITHIN A GIVEN MANAGEMENT ENVIRONMENT IN ORDER TO CONTROL OPERATIONS AND MAXIMISE ECONOMIC RECOVERY

OBJECTIVES OF RESERVOIR MANAGEMENT DECREASE RISK INCREASE OIL AND GAS PRODUCTION INCREASE OIL AND GAS RESERVES MINIMISE CAPITAL EXPENDITURES MINIMISE OPERATING COSTS MAXIMISE RECOVERY

RESERVOIR MANAGEMENT TOOL: MODELLING THE RESERVOIR BEHAVIOUR TO MAKE DECISIONS ACQUIRE DATA MODEL RESERVOIR BEHAVIOUR PREDICT PRODUCTION & CALCULATE RESERVES

THE MODELLING PROCESS 1 2 3 IDENTIFICATION OF A RESERVOIR MODEL RESERVOIR CHARACTERISATION (INVERSE PROBLEM) CALCULATION OF THE RESERVOIR MODEL BEHAVIOUR UPSCALING AND SIMULATION MATCHING OF RESERVOIR SYSTEM PAST PERFORMANCE HISTORY MATCHING (DIRECT PROBLEM) 4 PREDICTION OF RESERVOIR SYSTEM FUTURE PERFORMANCE (DIRECT PROBLEM)

RESERVOIR MANAGEMENT PROCESS CENTRE FOR PETROLEUM STUDIES Static Information Dynamic Information DATA Geology Geophysics Geochemistry Drilling Petrophysics Geomechanics Fluids Flowmetre Survey Well testing Pressure, Surface Rates, Downhole Rates Tracers Production data INTERPRETATION MODELS Geological Geophysical Geochemical Petrophysical Geomechanical Fluid Production Logging Well Test Tracer Integration Well Flow RESERVOIR MODEL SIMULATION OF RESERVOIR MODEL BEHAVIOUR (Upscaling) Simulation Black Oil/Compositional/Thermal (History Matching) Reservoir Prediction of Well Performance Improvement of Well Performance Completion design Stimulation Artificial lift 1997 by Alain C. Gringarten Development Scenario Pipeline & Facilities Calibrated Simulation Prediction of Reservoir Performance Prediction of Field Performance (Decline Curve Analysis) Economic Production Infrastructure Health, Safety and Environment RESERVOIR MANAGEMENTDECISIONS

THE RESERVOIR MANAGEMENT PROCESS DATA IMPLEMENTATION RESERVOIR CHARACTERISATION PREDICTION OF RESERVOIR PERFORMANCE PREDICTION OF WELL PERFORMANCE INFORMATION KNOWLEDGE FIELD DEVELOPMENT PLAN WISDOM RESERVOIR MANAGEMENT DECISIONS CENTRE FOR PETROLEUM STUDIES 1997 by Alain C. Gringarten

RESERVOIR CHARACTERISATION CENTRE FOR PETROLEUM STUDIES Static Information Dynamic Information DATA Geology Geophysics Geochemistry Drilling Petrophysics Geomechanics Fluids Flowmetre Survey Well testing Pressure, Surface Rates, Downhole Rates Tracers Production data INTERPRETATION MODELS Geological Geophysical Geochemical Petrophysical Geomechanical Fluid Production Logging Well Test Tracer INTEGRATION Well Flow RESERVOIR MODEL SIMULATION OF RESERVOIR MODEL BEHAVIOUR (Upscaling) Simulation Black Oil/Compositional/Thermal (History Matching) Reservoir Prediction of Well Performance Improvement of Well Performance Completion design Stimulation Artificial lift 1997 by Alain C. Gringarten Development Scenario Pipeline & Facilities Calibrated Simulation Prediction of Reservoir Performance Prediction of Field Performance (Decline Curve Analysis) Economic Production Infrastructure Health, Safety and Environment RESERVOIR MANAGEMENT DECISIONS

RESERVOIR CHARACTERISATION INTEPRETATION OF DATA >> STATIC INTERPRETATION MODELS ( DESCRIPTION) GEOPHYSICS, GEOLOGY GEOCHEMISTRY PETROPHYSICS >> DYNAMIC INTERPRETATION MODELS ( BEHAVIOUR) GEOMECHANICS WELL TESTS, TRACERS FLOWMETRE SURVEYS

Data type 1 Data type 3 Data type 3 Identification Identification Identification Consistency Verification NO Consistency Verification NO Consistency Verification NO YES YES YES Interpretation for Data Type 1 Interpretation for Data Type 2 Interpretation for Data Type 3

INTERPRETATION MODELS Petrophysical Data 10 layers Well test Data 2 media 1 Petrophysical Well test 2 Tracer Data Tracer Production Logging Data Flow rate Concentration Time 10 permeabilities Production Logging Identification of producing layers Depth

Geomechanical Data INTEGRATION OF INTERPRETATION MODELS Fluid Data Petrophysical Data Geomechanical Fluid Production Logging Data Petrophysical Production Logging Geochemical Data Geochemical RESERVOIR MODEL Tracer Tracer Data Geophysical Well test Geological Geophysical Data CENTRE FOR PETROLEUM STUDIES Geological Data Well test Data

INTEGRATION OF INTERPRETATION MODELS DETERMINISTIC TECHNIQUES STOCHASTIC TECHNIQUES >> INTERPOLATION BETWEEN SPARSE DATA (WELLS) AND EXTRAPOLATION >> CORRELATION AND ORDERING OF INFORMATION >> INTEGRATION OF INFORMATION (CONDITIONING) FROM DIFFERENT DATA SOURCES WITH DIFFERENT LEVELS OF RELIABILITY >> GENERATION OF MULTIPLE, EQUIPROBABLE REALISATIONS OF THE RESERVOIR (PARAMETER DISTRIBUTIONS) >> QUANTIFICATION OF UNCERTAINTIES

RESERVOIR MODEL VERIFICATION Once the reservoir model is constructed, one must verify that this reservoir model is consistent with all available information and interpretation models. This means that the reservoir model must reproduce all data acquired: the seismic, logs, etc..., well tests.

Data type 1 Data type 3 Data type 3 Identification Identification Identification Consistency Verification NO Consistency Verification NO Consistency Verification NO YES YES YES Interpretation for Data Type 1 Interpretation for Data Type 2 Interpretation for Data Type 3 Integration into Reservoir Simulate Data Type 1 Simulate Data Type 2 Simulate Data Type 3 Match Data Type 1 Match Data Type 2 Match Data Type 3 NO NO NO YES YES YES NO CENTRE FOR PETROLEUM STUDIES RESERVOIR MODEL

VERIFICATION OF RESERVOIR MODEL FLOW BEHAVIOUR Static Information Dynamic Information DATA Geology Geophysics Geochemistry Drilling Petrophysics Geomechanics Fluids Flowmetre Survey Well testing Pressure, Surface Rates, Downhole Rates Tracers Production data INTERPRETATION MODELS Geological Geophysical Geochemical Petrophysical Geomechanical Fluid Production Logging Well Test Tracer Integration Well Flow RESERVOIR MODEL SIMULATION OF RESERVOIR MODEL BEHAVIOUR (Upscaling) Simulation Black Oil/Compositional/Thermal (History Matching) Reservoir Prediction of Well Performance Improvement of Well Performance Completion design Stimulation Artificial lift 1997 by Alain C. Gringarten Development Scenario Pipeline & Facilities Calibrated Simulation Prediction of Reservoir Performance Prediction of Field Performance (Decline Curve Analysis) Economic Production Infrastructure Health, Safety and Environment RESERVOIR MANAGEMENT DECISIONS

RESERVOIR MODEL FLOW BEHAVIOUR USUALLY APPROXIMATED WITH NUMERICAL SIMULATOR DIFFERENT FLOW SIMULATORS MAY BE REQUIRED FOR DIFFERENT FLOW DATA COMPLEXITY OF SIMULATOR FUNCTION OF PERFORMANCE TO BE SIMULATED (Black Oil, Compositional, Thermal, Chemical) WELL TEST DATA REQUIRE HIGH RESOLUTION NEAR WELLS GRIDDING FOR EXISTING NUMERICAL SIMULATORS COARSER THAN FOR RESERVOIR MODEL ( UPSCALING REQUIRED) SIMULATION OF VERY LARGE RESERVOIRS OR OF LOCAL HETEROGENEITIES REQUIRES: Several hundred thousand cells, or New mathematical formulations (Adaptive gridding, Streamline simulators,...)

RESERVOIR MODEL FLOW BEHAVIOUR VERIFICATION RESERVOIR MODEL FLOW BEHAVIOUR CONSISTENCY IS VERIFIED BY COMPARING: OBSERVED DATA FROM WELLS (GOR, WOR,...), and CORRESPONDING RESPONSES FROM NUMERICAL SIMULATOR (HISTORY MATCHING) POSSIBILITY TO MATCH SATURATION FRONT LOCATIONS BETWEEN WELLS OBTAINED FROM REPEATED 3-D SEISMIC SURVEYS (RESERVOIR MONITORING)

HISTORY MATCHING MATCH BETWEEN DATA AND MODEL CALCULATED BEHAVIOR CAN BE REFINED BY ADJUSTING RESERVOIR MODEL PARAMETERS WITHIN LIMITS CONTROLED BY CONDITIONING ADJUSTMENT CAN BE MADE EASIER AND FASTER WITH STATISTICAL OPTIMISATION METHODS (ADAPTIVE HISTORY MATCHING) AND EXPERT SYSTEMS LACK OF SATISFACTORY MATCH WITHIN LIMITS CONTROLED BY CONDITIONING REQUIRES MODIFYING THE RESERVOIR MODEL ( RESERVOIR CHARACTERISATION)

CHARACTERISATION: AN ITERATIVE PROCESS CENTRE FOR PETROLEUM STUDIES Interpretation s Integration into Reservoir Verify Reservoir (Synthetic seismograms, logs, well tests, production...) NO YES RESERVOIR MODEL YES Another? NO END

PRODUCTION PREDICTION FOR PREDICTING PRODUCTION, THE RESERVOIR SIMULATOR MUST BE COUPLED WITH: WELL MODELS AND A SURFACE FACILITIES SIMULATOR

PRODUCTION PREDICTION Static Information Dynamic Information DATA Geology Geophysics Geochemistry Drilling Petrophysics Geomechanics Fluids Flowmetre Survey Well testing Pressure, Surface Rates, Downhole Rates Tracers Production data INTERPRETATION MODELS Geological Geophysical Geochemical Petrophysical Geomechanical Fluid Production Logging Well Test Tracer Integration Well Flow RESERVOIR MODEL SIMULATION OF RESERVOIR MODEL BEHAVIOUR (Upscaling) Simulation Black Oil/Compositional/Thermal (History Matching) Reservoir Prediction of Well Performance Improvement of Well Performance Completion design Stimulation Artificial lift 1997 by Alain C. Gringarten Development Scenario Pipeline & Facilities Calibrated Simulation Prediction of Reservoir Performance Prediction of Field Performance (Decline Curve Analysis) Economic Production Infrastructure Health, Safety and Environment RESERVOIR MANAGEMENT DECISIONS

DECLINE CURVE ANALYSIS Static Information Dynamic Information DATA Geology Geophysics Geochemistry Drilling Petrophysics Geomechanics Fluids Flowmetre Survey Well testing Pressure, Surface Rates, Downhole Rates Tracers Production data INTERPRETATION MODELS Geological Geophysical Geochemical Petrophysical Geomechanical Fluid Production Logging Well Test Tracer Integration Well Flow RESERVOIR MODEL SIMULATION OF RESERVOIR MODEL BEHAVIOUR (Upscaling) Simulation Black Oil/Compositional/Thermal (History Matching) Reservoir Prediction of Well Performance Improvement of Well Performance Completion design Stimulation Artificial lift 1997 by Alain C. Gringarten Development Scenario Pipeline & Facilities Calibrated Simulation Prediction of Reservoir Performance Prediction of Field Performance (Decline Curve Analysis) Economic Production Infrastructure Health, Safety and Environment RESERVOIR MANAGEMENT DECISIONS

RESERVOIR SIMULATION ( 1960 s to 1970 s) Static Information Dynamic Information DATA Geology Geophysics Geochemistry Drilling Petrophysics Geomechanics Fluids Flowmetre Survey Well testing Pressure, Surface Rates, Downhole Rates Tracers Production data INTERPRETATION MODELS Geological Geophysical Geochemical Petrophysical Geomechanical Fluid Production Logging Well Test Tracer Integration Well Flow RESERVOIR MODEL SIMULATION OF RESERVOIR MODEL BEHAVIOUR (Upscaling) Simulation Black Oil/Compositional/Thermal (History Matching) Reservoir Prediction of Well Performance Improvement of Well Performance Completion design Stimulation Artificial lift 1997 by Alain C. Gringarten Development Scenario Pipeline & Facilities Calibrated Simulation Prediction of Reservoir Performance Prediction of Field Performance (Decline Curve Analysis) Economic Production Infrastructure Health, Safety and Environment RESERVOIR MANAGEMENT DECISIONS

RESERVOIR SIMULATION ( 1980 s) Static Information Dynamic Information DATA Geology Geophysics Geochemistry Drilling Petrophysics Geomechanics Fluids Flowmetre Survey Well testing Pressure, Surface Rates, Downhole Rates Tracers Production data INTERPRETATION MODELS Geological Geophysical Geochemical Petrophysical Geomechanical Fluid Production Logging Well Test Tracer Integration Well Flow RESERVOIR MODEL SIMULATION OF RESERVOIR MODEL BEHAVIOUR (Upscaling) Simulation Black Oil/Compositional/Thermal (History Matching) Reservoir Prediction of Well Performance Improvement of Well Performance Completion design Stimulation Artificial lift 1997 by Alain C. Gringarten Development Scenario Pipeline & Facilities Calibrated Simulation Prediction of Reservoir Performance Prediction of Field Performance (Decline Curve Analysis) Economic Production Infrastructure Health, Safety and Environment RESERVOIR MANAGEMENT DECISIONS

FREQUENTLY ASKED QUESTION HOW MUCH OF THIS PROCESS DO WE NEED TO GO THROUGH? Knowledge Risk MANAGEMENT PROCESS NEED TO QUANTIFY THE RISK

IMPLEMENTATION THROUGH NEW TECHNOLOGY STOCHASTIC MODELLING ADAPTIVE HISTORY MATCHING RESERVOIR MONITORING NEW MATHEMATICAL FORMULATIONS FOR SIMULATORS MULTIPHASE PIPELINE SIMULATORS MASSIVE PARALLEL PROCESSING KNOWLEDGE BASE SYSTEMS COMPUTER AIDED PRODUCTION (CAP) TOOLS

COMPUTER AIDED PRODUCTION (CAP) TOOLS THE POWERFUL AND PROVEN COMPUTER TECHNOLOGIES THAT HAVE BEEN USED BY SPECIALISTS BEING MADE AVAILABLE TO AND USABLE BY THE PRACTISING PROFESSIONAL

NEEDS OF THE PRACTISING PROFESSIONAL EASE-OF-USE PRODUCTIVITY TRANSPARENT TECHNOLOGY TASK ORIENTED APPROACH KNOWLEDGE BASED SYSTEMS METHODOLOGY ( HENCE REPEATABILITY)

COMPETITIVE ADVANTAGE IF TOOLS BECOME STANDARD METHODOLOGY SOFTWARE COMPETITIVE ADVANTAGE MUST BE THE UNDERSTANDING OF FUNDAMENTALS KNOW-HOW Example: Well Test Analysis

WELL TEST ANALYSIS BREAKTHROUGH IN THE 1980 S FROM INDIVIDUAL METHODS GIVING DIFFERENT ANSWERS TO AN INTEGRATED METHODOLOGY BASED ON SIGNAL THEORY WELL TEST ANALYSIS SOFTWARE PERSONAL COMPUTERS DIFFERENT INTERPRETERS USING THE SAME METHODOLOGY GET THE SAME ANSWERS SIDE EFFECTS ERRONEOUS ANALYSES, FASTER SOLUTION EDUCATION / TRAINING

NEW CURRICULUM SPECIALISTS THAT KNOW HOW TO WORK EFFECTIVELY IN MULTI-DISCIPLINARY TEAMS Fundamental Understanding of: Reservoir Characterisation, Reservoir ling, Reservoir Simulation, and Field Management The Processes for Integrating and Processing All Available Information in Order to Make Reservoir Management Decisions Work Flow Concepts Links Between the Various Types of Data

MSc Specifications Follow the reservoir management process

EXAMPLE: THE MSc IN PETROLEUM ENGINEERING AT IMPERIAL COLLEGE CENTRE FOR PETROLEUM STUDIES THE RESERVOIR MANAGEMENT PROCESS THE MSc IN PETROLEUM ENGINEERING IMPLEMENTATION DATA RESERVOIR CHARACTERISATION PREDICTION OF RESERVOIR PERFORMANCE FIELD DEVELOPMENT PLAN PREDICTION OF WELL PERFORMANCE INFORMATION KNOWLEDGE WISDOM MODULE 1: FUNDAMENTALS INDUSTRY PRESENTATIONS MODULE 2: RESERVOIR CHARACTERISATION MODULE 4: RESERVOIR PERFORMANCE MODULE 5: FIELD DEVELOPMENT MODULE 3: WELL PERFORMANCE GROUP FIELD PROJECT RESERVOIR MANAGEMENT DECISIONS INDIVIDUAL RESEARCH PROJECT

MSc Specifications Follow the reservoir management process Lectures only by experts in their fields

MSc Specifications Lectures only by experts in their fields Follow the reservoir management process Students with fundamental background

MSc Specifications Follow the reservoir management process Lectures only by experts in their fields Students with fundamental background Fundamental / Application / Support courses

October November December FUNDAMENTALS 103 hrs RESERVOIR CHARACTERIZATION 183 hrs Introduction Basic Petroleum Geology Basic Petroleum Geophysics Rock properties Sub-Surface Mapping Reservoir Fluids Hydrocarbons in-place and Reserves Production Mechanisms Flow In Porous Media Drilling Introduction to petroleum economics Geological, geophysical and geochemical modeling Geomechanics Petrophysics Production logging Fluid sampling and analysis Well Testing Integration into reservoir model Group Project Phase 1: Reservoir Characterization Well completion practices Principles of well production Reservoir Performance prediction Numerical Reservoir Performance predictors Upscaling Practical use of numerical simulators History matching, predictions and optimisation Group Project Phase 2: Predictions and Well Placement Optimization Process engineering/surface facilities Extending field life and improved oil recovery Health, safety and environment Economics Group Project Phase 3: Surface Facilities and Development Plan EXAMS INDIVIDUAL PROJECT WELL 42 RESERVOIR 114 PERFORMANCE FIELD DEVELOPMENT 96 Early May May to September January February March

MSc Specifications Follow the reservoir management process Lectures only by experts in their fields Students with fundamental background Fundamental / Application / Support courses Block teaching

MSc Specifications Follow the reservoir management process Lectures only by experts in their fields Students with fundamental background Fundamental / Application / Support courses Block teaching Lectures/notes coordinated and integrated

MSc Specifications Follow the reservoir management process Lectures only by experts in their fields Students with fundamental background Fundamental / Application / Support courses Block teaching Lectures/notes coordinated and integrated Integration with Petroleum Geoscience

MSc in PETROLEUM ENGINEERING MSc in PETROLEUM GEOSCIENCE TERM 1 TERM 2-4 RESERVOIR CHARACTERISATION FUNDAMENTALS CENTRE FOR PETROLEUM STUDIES Petroleum Geology, Petroleum Geophysics, Rock Properties Geological Field trip Reservoir Fluids Drilling STOOIP & Reserves Flow in Porous Media Production Mechanisms Development Geology and Reservoir ling Petroleum Engineering Reservoir Geology, Geophysics and Geochemistry Petrophysics & Formation Evaluation Fluid Sampling & Analysis Geophysics Production Logging Structural & Stratigraphic Analysis Well Test Analysis of Sedimentary Basins Integration into Reservoir Maureen Group Project (Reservoir Characterisation) Geomechanics Well Performance Reservoir Performance Field Development Maureen Group Project (Colin Wall Award) Individual Research Project Petroleum Economics Basin ling Structures, Fluids & Pressures Geostatistics Sequence statigraphy Group project (Barrel Award) Individual Research Project

MSc Specifications Follow the reservoir management process Lectures only by experts in their fields Students with fundamental background Fundamental / Application / Support courses Block teaching Lectures/notes coordinated and integrated Integration with Petroleum Geoscience Teach prevailing commercial software

MSc Specifications Follow the reservoir management process Lectures only by experts in their fields Students with fundamental background Fundamental / Application / Support courses Block teaching Lectures/notes coordinated and integrated Integration with Petroleum Geoscience Teach prevailing commercial software Use actual field data

Use of field data Tutorials for taught courses Group field project Phase 1: Reservoir characterisation 16 teams (Petroleum Engineering+Geoscience) Phases 2: Production planning 8 teams (Petroleum Engineering) Phase 3: Field development 8 teams (Petroleum Engineering) Individual research projects

Field data: Maureen Field Block 16/29a (UK sector of the North Sea) Phillips UK operator 1983-1999 4 appraisal,12 production and 7 water injection wells seismic traces and interpreted maps; geological maps; core photographs; routine and special core analysis reports; PVT analysis reports; RFT data; DST and production test data; monthly production data

Field data: Maureen Field

Maureen Group Field Project Phase 1: Reservoir characterisation 10 days, December 5-6 wells STOIIP Reserve estimates Preliminary 3D model Permeability, md 10000 1000 100 10 A B C D E F 1 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 Fractional Porosity Depth, ft 13150 13200 13250 13300 13350 13400 13450 13500 13550 RCAL Porosity RCAL Porosity Corrected Log Porosity 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 Fractional Porosity 10 3 500 450 STOIIP Recoverable 490 OWC Layer A Pressure Change, p, and Derivative ( psi) 10 2 10 1 Last test rate only Entire rate history Oil, MMbbl 400 350 300 250 200 150 100 50 0 367 193 324 157 283 123 0 0 313 341 173 191 61 10-1 -3-2 -1 2 10 10 10 1 10 10 Elapsed time, t ( hours) P10 P50 P90 Maximum Most Likely Minimum Probability: Stochastic Deterministic

Maureen Group Field Project Phase 2: Well placement & Production Optimization 6 days, February simulation model optimized well placement plan oil recovery cumulative oil production optimized well design artificial lift options a drilling plan casing design Hole Casing Size Size 36 30 24 20 17 ½ 13 3 / 8 12 ¼ 9 5 / 8 8 ½ 7 Ekofisk Chalk and Sands Maureen 2 FPSO Maureen 1 Drill 17 ½ hole Mio-Oligocene Sand Balder Formation Maureen Pay Drill Drill 24" hole 36"hole Drill 12" hole Drill 8 ½ hole 0 2000 4000 6000 8000 10000 12000 completing 14000 coring plug back 16000 0 20 40 60 80 100 Time (Days) Depth ft MDRKB BHP, psia 4000 3000 THP = 700 psia 600 I.P.R 2000 0 10 4 2 104 Oil Rate, STB/D 500 400 300 Oil rate, stb/d 50000 40000 30000 20000 10000 0 Oil Rate Cum. Oil Production 0 2 4 6 8 10 12 14 16 18 Years 200 180 160 140 120 100 80 60 40 20 0 Cumulative oil production, mmstb

Maureen GroupField Project Phase 3: Development plan 10 days, March improved recovery plan surface production facilities HSE plan economic viability abandonment plan assessment of risks Colin Wall prize GAS FOR Gas Lift Crude Oil From Wells 3 Stage Compressors Oil Gas 1 st Separator Gas water Test Separator Gas water Cooler Oil Compressors 2 nd Separator Water Skimmer Oil water Dehydrator Oil CPI Glycol Dehydrator Glycol Make up water Gas 3 rd Separator water GAS OIL WATER GAS TO SALE Oil OIL TO SALE TO INJECTION WELLS Present Value, million 150 100 50 0-50 -100-150 -200 Excluding Abandonment Including Abandonment 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 NPV, million 600 Discount Factor 500 Critical : 17.4% Lease Rate 400 Oil Price Critical : 3.23/bbl Critical : $12.05 300 Inflation 200 Critical : 6.4% 100-100 -75-50 -25 0 25 50 75 100 % Change from Base Case Values 0 CAPEX -100 Critical : 930million -200 OPEX Critical : 420million -300-400 -250-500

THE ULTIMATE RESERVOIR MANAGEMENT GOAL TO MODEL A PETROLEUM RESERVOIR AND ASSOCIATED WELL AND SURFACE FACILITIES WITH SUCH AN ACCURACY THAT ON-GOING PREDICTIONS CAN BE USED WITH CONFIDENCE TO OPTIMISE PRODUCTION OPERATIONS, INCREASE RECOVERY AND REDUCE OPERATING COSTS THEREBY SUBSTANTIALLY INCREASING ECONOMIC RETURN WITHIN MANAGEMENT GUIDELINES