Reservoir Fluid (PVT) Analysis - Value to Appraisal / Field - PowerPoint PPT Presentation

Reservoir Fluid (PVT) Analysis - Value to Appraisal / Field Development Planning Brian Moffatt t: +44 (0) 7771 881182 e: info@petrophase.com www.petrophase.com

PVT Information PVT Information Key for all areas of Field Development Exploration • Composition for economics Appraisal • Contaminants • Flow Assurance Development • Phase Behaviour for Reservoir Simulation Production • Composition monitoring

How to Maximise the Value of PVT Information?

Introduction - PVT Concerns Issues from Linkedin PVT Forum Questions Value of PVT 0 2 4 6 8 10 12 14 16 18 20 Understanding PVT Data EOS Modelling Methods PVT and Reservoir Behaviour Equipment Sampling QC Methods Training Questions

Introduction – PVT Concerns Forum replies focus on: • Data QC Methods • Sampling 0 2 4 6 8 10 12 14 16 18 20 Understanding PVT Data EOS Modelling Methods PVT and Reservoir Behaviour Equipment Sampling QC Methods Training Questions Replies/Question

This Presentation How to Maximise the Value of PVT Information? • PVT Data QC • Uncertainties from Sampling • Storage Issues • Uncertainties from PVT Lab Measurements • Understand the Data in Context • Modelling Key Information • Focus on Matching Key Data • Correct handling MWs • Poor EOS performance for oil compressibility and viscosity • Mapping reservoir simulation results to a surface model • Which PVT uncertainties can most affect Development?

Maximising the Value of PVT Data PVT Data QC

PVT Data QC PVT DATA QC Traditional Context / QC Application Lab Agreement Sampling Sample Measurements with Field Conditions Quality Consistency Data Well Air /OBM Material Characteristics Contamination Balance Opening Equilibrium Pressures of Field GOR vs Plots Samples Lab data Sample Compositions Equilibrium Plots Data trends

Where do PVT Data Errors Arise ? Sampling • Bottomhole-two phase flow into sampler • Formation tester-OBM Contamination • Separator-Reservoir two phase flow, Recombination GOR, Liquid Carryover Storage • Contaminant absorbtion Measurement Errors • Sample handling-loss of heavy ends from gas samples

Maximising the Value of PVT Information QC for Sampling Errors

QC: Bottomhole Flowing Samples Problem Areas • Bottomhole-two phase flow into sampler • Commingled flow from different intervals

QC: Formation Tester Information Obtained • Formation pressure and pressure gradient (fluid type) • Estimate formation permeability. • Sample compositions Possible Problems • Two phase flow from poor probe contact • OMB contamination

QC FT: OBM Contamination • GC trend analysis: hump in the compositional analysis, especially observed in the carbon number range of the oil based mud components (C15-C20).

QC FT: Poor Compositions Use sample composition in an EOS Analysis to compare predicted and measured values for • Surface GOR • Phase Behaviour Pressure (psia) 5550 5600 5650 5700 9950 10000 Compare PVT Lab Densities with 10050 10100 Densities from Pressure Gradients TVD SS ft 10150 10200 10250 10300 10350 10400 Data PVT Report Oil

QC: Surface Sampling

QC: Surface Sampling Separator bbl/MMscf GOR is highly dependent on 8.0 surface 6.0 conditions. 4.0 30 C 2.0 50 C 0.0 10 20 30 Should not 40 50 60 70 80 90 100 110 120 affect 130 140 150 160 170 180 recombined Pressure, Bar fluid. One lean condensate at different conditions

QC: Surface Sampling What causes CGR scatter? 7,000 Conditions? 6,000 GOR Mscf/bbl 5,000 Wellstream? 4,000 3,000 2,000 1,000 0 0 500 1000 1500 2000 WHP psia CGR vs Sep Press

QC: Surface Sampling Equilibrium Plot Hoffmann-Hocott Equilibrium Plot Between Surface Liquid 4.5 and Gas Compositions. 4 Identifies CO2 3.5 C1 N2 Log 10 (K*P) 3 C2 Trend for Carryover C3 • Liquid Carry-over 2.5 iC4 Data nC4 • Sample Handling 2 Theory iC5 nC5 Trend for Heavy Loss of heavy ends 1.5 C6 Benz end Losses C7 1 • Poor Temperature/ 0.5 C8 Tol Pressure Readings -2 0 2 4 6 Temp Function

Slide 19 QC Data in Context: Strange GC What if after QC of Surface and BH samples, there are no obvious errors but the Compositions Disagree AGAIN! 100 10 1 % MOL 0.1 0.01 0.001 BHS1 BHS2 BHS3 Separator

Slide 20 QC Data in Context: Strange GC 10,000 9,000 8,000 • Initial GOR was steady at 7,000 GOR scf/bbl 6,000 around 8,000 scf/bbl and 5,000 samples gave a typical 4,000 3,000 Gas Condensate 2,000 behaviour 1,000 0 • However recombined 1 2 3 4 5 6 7 8 9 10 Flow Period Separator Sample gives P sat > P res • This was a low Permeability Formation P res with high drawdown

Slide 21 QC Data in Context: Strange GC • At lower rates and lower 10,000 drawdowns the tested GOR reduced 8,000 GOR scf/bbl • The API and Liquid 6,000 colour suggested the fluid maybe a Volatile oil 4,000 • An EOS analysis giving a 2,000 fluid with P sat = P res gas a Volatile Oil with GOR 0 value of 2000 scf/bbl 0 2 4 6 8 Gas Rate mmscf/d • FLUID IS VOLATILE OIL!

Maximise the Value of PVT Information QC for Sample Storage and PVT Measurements

QC:Sample Storage Pressures of Sample Bottles drop during storage due to cooling • Where groups of samples available the highest pressure sample is less likely to have suffered leakage and compositional changes • With pressure drop can get deposition of asphaltenes/ sometimes reversible Contaminant absorbtion a problem in non conditioned bottles

QC:PVT Lab Measurements Consistency Checks used for Common Lab Measurements • CVD/DL Material Balance • EOS Modelling for reality checks Consistency Checks routinely carried out by PVT labs, data quality now generally excellent. However historical data and data from unknown labs can still have errors. AT P=0, Z-factor approaches Unity

Maximising the Value of PVT Information Modelling Key Information

Modelling Key Information Which data do you match to? The “Best Fit” may not match well in the are of interest, e.g. if the reservoir does not drop below the saturation pressure

Modelling Key Information 0.750 0.740 PVT labs measure 0.730 Density g/cc volumetrics well, however 0.720 0.710 EOS can struggle with 0.700 DATA compressibilities. 0.690 SRK 0.680 0.670 0.660 5000 6000 7000 8000 Pressure (psia) EOS models are particularly limited in modelling near critical fluids. Unrealistic Unlikely phase envelopes can arise. Critical Behaviour Beware of using different compositions in a well matched EOS!

Modelling Key Information Conversion difficulties in transferring from reservoir modelling software to processing modelling software! Reservoir Engineer's Process Engineer’s perspective perspective

PVT Modelling Errors -Viscosities Matching viscosity using the LBC correlation is highly dependent on densities. Poor densities gives poor viscosities away from control points, and also for the gas ! 9000 Liquid viscosities are not 8000 7000 Viscosity cp well predicted by EOS and 6000 5000 B&R so often correlations are 4000 Kartoatmodjo 3000 used. For heavy oil the Kartoatmodjo HO 2000 P&F errors can be >100%. 1000 0 0 200 400 600 800 Rs scf/bbl

PVT Modelling Errors - MW • Samples are prepared Oil Gravimetrically • Response of GC Detectors are Proportional to Mass – Internal standards are added by weight Increasing MW 30

PVT Modelling Errors - MW • Average Molecular Weight for a Fraction not Known SCN31 • Each Fraction has Complex Mix of Compounds • Different Service Companies may use Different Sets 280 260 240 220 Fraction MW 200 180 160 140 120 100 C9 C10 C11 C12 C13 C14 C15 C16 C17 C18 C19 Core Labs Petrobras Expro

Which PVT uncertainties data can most affect Development? • Volumetrics for economics • Measured GORs • Phase Behaviour for Reservoir Simulation • Contaminants, Flow Assurance Issues • Viscosities • Compositions

Volumetrics PVT labs measure reservoir condition densities to better than 1%. Insensitive to compositional errors from sampling. Errors small compared to GRV and Sw errors. CGR vs Sep Press However, surface liquid 8.0 6.0 volumes and hence STOIIP 4.0 30 C 2.0 strongly influenced by 50 C 0.0 10 20 30 40 50 Separator Conditions. 60 70 80 90 100 110 120 130 140 150 160 170 180

GOR The GOR is often chosen for modelling from a single recombined sample! Is this sample consistent with the rest of the test data? Often ignore much relevant test data. 7,000 6,000 GOR Mscf/bbl 5,000 4,000 3,000 2,000 1,000 0 0 500 1000 1500 2000 WHP psia

Phase Behaviour for Reservoir Simulation PVT labs measure volumetrics well, however still a need to QC particularly old data Sampling errors can lead to unrepresentative phase behaviour. P res