Determination of Minimum Miscibility Pressure Using Vanishing Interfacial Tension (VIT)

in Support of EOR for Alaska North Slope (ANS) Heavy Oil

ABSTRACT

The answer to the growing Petroleum crises is the development and production of heavy oils. The production from light oil fields of Alaska’s North Slope is on the verge of decline. Due to the extremely viscous nature of these oils, it is hard to produce by natural pressure. Miscible gas injection displacement Enhanced Oil Recovery (EOR) can be one of the methods for production of these heavy oils.

Minimum miscibility pressure (MMP) is an important optimization parameter for EOR processes involving CO2 or hydrocarbon gas injection. The MMP for a gas-oil system is directly related to the interfacial tension between the injected gas and the reservoir crude oil. In this study, a new technique called Vanishing Interfacial Tension (VIT) was used to measure MMP at reservoir conditions. Experiments were conducted using various gas-oil systems to determine the MMP. The experimental results were modeled using the Peng–Robinson Equation-of-State (EOS) by CMG simulator. The Peng-Robinson EOS was tuned with experimental data to predict the MMP accurately.

This study has demonstrated the accurateness of the VIT technique in predicting MMP by pendant drop method experiments and simulations using CMG software.

Tathed V S (ftvst@uaf.edu), Dandekar A Y, Patil S L

Department of Petroleum Engineering, University of Alaska Fairbanks, Alaska 99775-5880, USA

OBJECTIVE

•To determine the MMP of different injection gas-oil systems

at reservoir temperature by measuring the gas-oil IFT at

various pressures.

•To quantify the MMP experimentally using the pendant

drop method and by equation of state (EOS) simulations

using a CMG simulator.

•To characterize the mass transfer interactions between

gas-oil systems by carrying out compositional and density

measurements at varying pressures and at reservoir

temperature by tuned EOS simulations using a CMG

simulator.

ACKNOWLEDGMENTS &

DISCLAIMER This material was prepared with support of the US

Department of Energy (US DOE), BPXA and Conoco

Phillips. The opinions, findings and conclusions expressed

herein are solely of those of the authors and do not

necessarily reflect the views of the US Government or any

agency thereof.

EXPERIMENTAL SETUP

TEST MATERIALS

OILS:

• ANS Sample A Dead Oil

• ANS Sample B Dead Oil

• ANS Sample A Live Oil

• ANS Sample B Live Oil

GAS INJECTANTS:

• Carbon Dioxide (CO2)

• Methane (CH4)

• Viscosity Reducing Agent (VRI)

PROCEDURE

Gas at a particular pressure is injected into the cell.

Crude at a pressure slightly higher than that of the injected gas in

allowed to enter the gas phase in the form of drops.

The images of the falling drops are captured and the value of de

and ds are determined.

Density of gas phase and crude oil are determined using Anton

Par Densitometer.

Using the above values interfacial tension is determined by :

where,

σ = interfacial tension, dynes/cm

g = acceleration due to gravity, cm/s2

de = equatorial diameter or the maximum horizontal diameter of the

drop, cm

ds = is the diameter of the drop measured at a distance de above

the tip of the drop, cm

H = is a function of S = (ds/ de), S is the drop shape factor.

Plot a graph of IFT vs P and measure the P where IFT is zero

(straight line plot). This point is the known as the Minimum

Miscibility Pressure (MMP).

The value is then compared with results obtained from CMG.

RESULTS

CONCLUSIONS

• The equilibrium time allowed in the VIT technique

simulates the gas and reservoir oil to continuously

interact and attain equilibrium.

• Miscibility was seen to be achieved by forward contact

process.

• The amount of components extracted by the injection

gases from the reservoir oils depends on the volumetric

ratio between the oil and the gas. Results obtained from

MCM simulations showed that MMP was lower for higher

injection gas to reservoir oil ratios.

• The MMP measurements obtained by MCM simulations

prove that the results obtained by the pendant drop

technique are accurate and reliable.

• The correlations used to measure MMP were based on

parameters, components which may or may not be

present in the gas-oil systems used here. Hence, there

was a vast deviation between experimental results and

those obtained by correlations.

RESULTS contd…

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H

gd gle )(2

Oil Sample CO2 MMP CH4 MMP VRI MMP

Expt. Simulated Expt. Simulated Expt. Simulated

Sample A Dead Oil 2150 2178 6432 6450 2725 2754

Sample B Dead Oil 2215 2243 6618 6645 2884 2900

Sample A Live Oil 2478 2505 6652 6690 3206 3215

Sample B Live Oil 2586 2625 6988 7013 3550 3577

Oil Sample CO2 MMP CH4 MMP VRI MMP

Expt. Simulated Expt. Simulated Expt. Simulated

Sample A Dead Oil 2150 2178 6432 6450 2725 2754

Sample B Dead Oil 2215 2243 6618 6645 2884 2900

Sample A Live Oil 2478 2505 6652 6690 3206 3215

Sample B Live Oil 2586 2625 6988 7013 3550 3577