Application of Equation of State Based Methods to Correct for Oil - PowerPoint PPT Presentation

Application of Equation of State Based Methods to Correct for Oil Based Drilling Fluid Contamination in Condensates and Near Critical Systems John Ratulowski Shell Exploration and Production Technology Company Houston TX

Outline • Sources of Error in Fluid Property Measurement • Development of EOS models for OBM Contaminants • Dead Oil Data • Live Oil Data • A Field Example for a Condensate • Conclusions

Sources of Error from Downhole Samples • Sampling – Phase splits due to drawdown – Contamination • Transfer and Handling – Leaks – Lack of equilibration • Laboratory Analysis – Poor technique – Lack of equilibration – Quantification of contamination

Philosophy of the EOS Approach • The chemistry of the contaminants is better known than that of the oil • Develop contaminant EOS description based on the known structure, physical properties, and available VLE data. – Actual compounds in the contaminant – Model compounds structurally similar – Pseudo-components with fixed properties • Tune oil pseudo-component properties to match measured VLE data of the contaminated system • This approach reduces the number of adjustable parameters

Petrofree (Not Petrofree LE) Five fatty acid esters with carbon numbers 16 to 24 and an ethyl side Ester Boiling Points chain 450 400 Boiling points extrapolated from 350 Normal BP C known values 300 250 Group contribution techniques used to 200 estimate EOS parameters 150 100 Viscosity model fit to data from 10 C 50 4 6 8 10 12 14 16 18 20 22 24 to 65 C Number of Carbons Branched Straight Chain Methane BIP’s fit to gas solubility data

Petrofree EOS Model Results Petrofree Density Petrofree Viscosity Atmospheric Pressure 0.9 12 10 0.85 8 gm/cc Viscosity cp 6 0.8 4 2 0.75 0 2000 4000 6000 8000 10000 0 Pressure psia 0 20 40 60 80 100 T Celcius 75 F 150 F 300 F Model Data Methane Solubility in Petrofree 1500 GOR SCF/BBL 1000 500 0 1000 2000 3000 4000 5000 6000 Pressure psia 100 F 300 F

Escaid Mineral Oil Refined product with low aromatic SimDist of Escaid Mineral Oil content C11 to C15 on SimDist analysis 100 In-house ECHO correlation used to generate pseudo-component properties This was sufficient to match stock tank wt % 10 density Viscosity model to data between 4 C and 38 C 1 5 10 15 20 Methane BIP correlation fit to gas Carbon Number solubility data for mineral oils

EOS Results for Escaid Methane Solubility in Escaid Escaid Viscosity Avg Error 2.6% 2500 3 2000 2.5 SCF/BBL 1500 Viscosity cp 2 1000 500 1.5 0 1 2000 3000 4000 5000 6000 7000 8000 40 50 60 70 80 90 100 Pressure psia Temperature F 100 F 200 F 300 F 250 F EOS Model Measured

Low Molecular Weight Olefins Novaplus, Petrofree LE, IsoTeq, and Ultidrill are all compositionally similar C14, C16, and C18 alpha or internal olefins. They may be branched or linear and may consist of single compounds or groups of isomers C14, C16, C18 alpha olefins are used as model compounds Literature data used to develop EOS description Methane BIP correlation fit to gas solubility data

EOS Results for the Olefins Methane Solubility in Novaplus at 200 F 8000 6000 Pressure psia IsoTeq Viscosity 4000 Avg Error 0.09% Measured 7 2000 6 0 Viscosity cp 5 0 500 1000 1500 2000 2500 3000 GOR SCF/BBL 4 3 Methane Solubility in Novaplus at 250 F 2 40 50 60 70 80 8000 Temperature F EOS Model Measured 6000 Pressure psia 4000 Measured 2000 0 0 500 1000 1500 2000 2500 3000 GOR SCF/BBL

Other Contaminant Models • Aquamul – C20 alkyl ether – Approach similar to Petrofree esters – Limited success matching gas solubility data • Novasol – Alpha-olefin isomers groups one near C20 the other near C30 – Normal paraffins n-C30 and n-C40 – Viscosity, density, and gas solubility matched adequately

Density of Dead Oil Blends IsoTeq/Oil API Gravity 50 •Linear mixing rule for API gravity. 45 API Gravity 40 •Variability in base fluid properties 35 caused some error in the Petrofree trace 30 •Aquamul and Novasol results similar 25 0 20 40 60 80 100 Mass % Contaminant Measured EOS Model Petrofree/Oil API Gravity Escaid/Oil API Gravity 35 50 34 45 API Gravity API Gravity 33 40 32 35 31 30 30 25 0 20 40 60 80 100 0 20 40 60 80 100 Mass % Contaminant Mass % Contaminant Measured EOS Model Measured EOS Model

Viscosity of Dead Oil Blends Petrofree/Oil Viscosity •Two oils of different gravity Avg Error 3.2% All Points 30 •Temperature range from 40 to 100 F 25 Viscosity cp •Contamination range from 5 to 60 wt % 20 15 •Novasol 3.7 % average error 10 0 10 20 30 40 50 60 •Aquamul 2.7 % average error Mass % Contaminant EOS Model Measured IsoTeq/Oil Viscosity Escaid/Oil Viscosity Avg Error 4.1% All Points Avg Error 6.3% All Points 30 30 25 25 20 Viscosity cp Viscosity cp 20 15 15 10 10 5 0 5 0 10 20 30 40 50 60 0 10 20 30 40 50 60 Mass % Contaminant Mass % Contaminant EOS Model Measured EOS Model Measured

GOM Black Oil • The oil was a black oil with a GOR of approximately 1200 SCF/BBL and a stock tank gravity of 27 API Gravity • CCE’s at 130 F and 163 F run with 0, 5, and 10 wt % basis dead oil of three contaminates • Results presented as deviations uncontaminated- contaminated • Poor quality GOR data • In general, model and experiments compared favorably

EOS Results for the Black Oil (Live Oil) Escaid Contaminated Black Oil Escaid Contaminated Black Oil Live Oil Viscosity 7000 psia 162 F 1400 0.03 1200 0.02 1000 Delta Psat psia Delta Viscosity cp 0.01 800 0 600 -0.01 400 -0.02 200 -0.03 0 -0.04 0 2 4 6 8 10 0 2 4 6 8 10 Wt % Escaid Wt % Escaid Measured 163 F EOS Model 163 F Measured EOS Model Measured 130 F EOS Model 130 F Petrofree Contaminated Black Oi Petrofree Contaminated Black Oil Live Oil Viscosity 7000 psia 162 F 1200 0 1000 -0.02 Delta Psat psia Delta Viscosity cp 800 -0.04 600 -0.06 400 -0.08 200 -0.1 0 -0.12 0 2 4 6 8 10 0 2 4 6 8 10 Wt % Escaid Wt % Escaid Measured 163 F EOS Model 163 F Measured EOS Model Measured 130 F EOS Model 130 F

EOS Results for the Black Oil (Flash Data) Petrofre Contaminated Black Oil Black Oil Flash GOR ESCAID 0 1350 -0.2 1300 -0.4 GOR SCF/BBL 1250 Delta API -0.6 1200 -0.8 1150 -1 1100 -1.2 1050 -1.4 0 2 4 6 8 10 0 2 4 6 8 10 Mass % Contaminant Wt % Escaid Measured EOS Model Measured EOS Model Escaid Contaminated Black Oil Black Oil Flash GOR Petrofree 0 1450 1400 -0.5 1350 GOR SCF/BBL Delta API -1 1300 1250 -1.5 1200 -2 1150 1100 -2.5 0 2 4 6 8 10 0 2 4 6 8 10 Wt % Escaid Mass % Contaminant Measured EOS Model Measured EOS Model

• Volatile oil with a 1950 SCF/BBL GOR and 33.8 API tank gravity • Mixture of Novasol contaminated and uncontaminated samples available from several wells and zones • Question: How confident are we in our corrected PVT data from the contaminated samples? • Minimal PVT rum for three contamination levels up to 10 %

EOS Results for a Volatile GOM Oil Oil Formation Volume Factor Flash GOR 1.9 2000 1.85 1900 GOR SCF/BBL Bo RB/STB 1800 1.8 1700 1.75 1600 1500 1.7 0 5 10 15 20 0 5 10 15 20 % NOVSOL % NOVSOL Measured EOS Model Measured EOS Model Saturation Pressure Flash API GRavity 5300 36.5 36 5200 35.5 Psat psia 5100 API 35 5000 34.5 4900 34 4800 33.5 0 5 10 15 20 0 5 10 15 20 % NOVSOL % NOVSOL Measured EOS Model Measured EOS Model

Near Critical Gas Condensate •Near critical gas condensate 2300 Phase Envelope SCF/BBL or 435 BBL/MMSCF 12000 •31 API stock tank oil (condensate) Reservoir 11000 •Retrograde behavior at 130 F and 180 F Pressure psia confirmed in four experiments at two 10000 laboratories 9000 Critical Point •Uncontaminated sample available from 8000 first well drilled in water base mud 7000 0 100 200 300 400 500 600 •Question: Would even small amounts of Temperature F Novaplus contamination effect the phase behavior?

EOS Results for GOM Near Critical Fluid GOM Near Critical Fluid 180 F CCE GOM Near Critical Fluid 130 F CCE Phase Diagram Phase Diagram 1 0.05 1 0.03 0.8 0.04 0.8 Vol Frac Upper Liq Vol Frac Lower Liq Vol Frac Upper Liq Vol Frac Lower Liq 0.02 0.6 0.03 0.6 0.4 0.02 0.4 0.01 0.2 0.01 0.2 0 0 0 0 5000 6000 7000 8000 9000 10000 4000 5000 6000 7000 8000 9000 10000 Pressure psia Pressure psia Expt. Uncontaminated Expt.5 wt % Novaplus Uncontaminated 5 wt % Novaplus EOS Uncontaminated EOS 5 wt% Novaplus

• Single stage flash CGR of 37.8 BBL/MMSCF with a tank gravity of 48.4 API • Same three contaminants as black oil study • Two different EOS characterizations were used. Results of the models are sensitive to the detail of EOS characterization • Reasonably good agreement for flash data between experiment and model • Contaminant-gas binary interaction parameters should be fit in the retrograde region for accurate prediction of saturation pressure