Research on the physical properties of supercritical CO2 and the log

216903

Research on the physical properties of

supercritical CO 2 and the log evaluation of CO 2 -bearing volcanic reservoirs

Baozhi Pan, Jian Lei, Lihua Zhang

1 and Yuhang Guo College of Geo-Exploration Science and Technology, Jilin University, Changchun, Jilin 130026,

People's Republic of China

E-mail:Zhanglh@jlu.edu.cn

Received 18 December 2016

Accepted for publication 25 April 2017

Published 3 July 2017

Abstract

CO 2 -bearing reservoirs are difficult to distinguish from other natural gas reservoirs during gas explorations. Due to the lack of physical parameters for supercritical CO 2 , particularly neutron porosity, at present a hydrocarbon gas log evaluation method is used to evaluate CO 2 -bearing reservoirs. The differences in the physical properties of hydrocarbon and CO 2 gases have led to serious errors. In this study, the deep volcanic rock of the Songliao Basin was the research area. In accordance with the relationship between the density and acoustic velocity of supercritical CO2 and temperature and pressure, the regularity between the CO 2 density and acoustic velocity, and the depth of the area was established. A neutron logging simulation was completed based on a Monte Carlo method. Through the simulation of the wet limestone neutron logging, the relationship between the count rate ratio of short and long space detectors and the neutron porosity was acquired. Then, the nature of the supercritical CO 2 neutron moderation was obtained. With consideration given to the complexity of the volcanic rock mineral composition, a volcanic rock volume model was established, and the matrix neutron and density parameters were acquired using the ECS log. The properties of CO 2 were applied in the log evaluation of the CO 2 -bearing volcanic reservoirs in the southern Songliao Basin. The porosity and saturation of CO 2 were obtained, and a reasonable application was achieved in the CO 2 -bearing reservoir.

Keywords: supercritical CO

2 , density, acoustic time, neutron porosity, reservoir log evaluation (Somefigures may appear in colour only in the online journal)

1. Introduction

The use of CO2

is extensive in industry,agriculture, medicine, andsoon.TheCO 2 flooding technology which is used to enhance oil and gas recovery started to be used for actual pro- duction internationally in the 1970s, and then application was introduced in China(Chenet al2012). This technology has played an important role in the improvements that have been made in oil and gas production during the last 40 years. How- ever, there are issues such as corroded formations, and pre- cipitation of the solid phase in CO 2 flooding and storage projects (Zhang2011), which takes advantage of the logging data tomonitor CO

2underground occurrence states, and the effects of

CO 2 displacement in oil reservoirs(Zhouet al2009, Guan and Tutuncu2012). Due to these factors, some properties of CO 2 are not clear, and quantitative evaluations have been difficult to achieve. Natural CO 2 -bearing reservoirs are found in many regions around the world. For example, the Bohai Sea, Songliao, and Yinggehai Basins in China,the Val Verde Foreland Basin in Texas, USA, and the Pannontan Basin in Hungary(Houet al

2009).Daiet albelieved that when a reservoir contains more

than 60% CO 2 , it is considered to be an industrial gas reservoir. Based on this standard, the origin of the main industrial CO2 -bearing reservoirs in China are inorganic(Daiet al1994).

Therefore, many of the CO

2 -bearing reservoirs are closely associated with magma activity, and exist in volcanic rocks.Journal of Geophysics and Engineering J. Geophys. Eng.14(2017)1052-1060(9pp)https://doi.org/10.1088/1742-2140/aa6f221

Author to whom any correspondence should be addressed.1742-2132/17/0501052+09$33.00 © 2017 Sinopec Geophysical Research Institute Printed in the UK1052Downloaded from https://academic.oup.com/jge/article/14/5/1052/5107938 by guest on 16 June 2023

CO 2 commonly remains in a supercritical state within a reservoir. Its critical temperature is 31.06°C, and its critical pressure is 7.39 MPa. The supercritical CO 2 with properties between gas and liquid, has the double characteristics of gas and liquid, and has different physical properties when com- pared with conventional natural gas. The research of the physical properties of supercritical CO 2 has important sig- nificance for the accurate evaluations of CO 2 -bearing reser- voirs based on log data. The research methods have included laboratory measurements, andfitting experimental data to empirical formula, or obtained the properties of supercritical CO 2 by deriving formula from the theory of the gas mole- cular. The relationship between the density and acoustic

Research on the physical properties of

supercritical CO 2 and the log evaluation of CO 2 -bearing volcanic reservoirs

Baozhi Pan, Jian Lei, Lihua Zhang

1 and Yuhang Guo College of Geo-Exploration Science and Technology, Jilin University, Changchun, Jilin 130026,

People's Republic of China

E-mail:Zhanglh@jlu.edu.cn

Received 18 December 2016

Accepted for publication 25 April 2017

Published 3 July 2017

Abstract

CO 2 -bearing reservoirs are difficult to distinguish from other natural gas reservoirs during gas explorations. Due to the lack of physical parameters for supercritical CO 2 , particularly neutron porosity, at present a hydrocarbon gas log evaluation method is used to evaluate CO 2 -bearing reservoirs. The differences in the physical properties of hydrocarbon and CO 2 gases have led to serious errors. In this study, the deep volcanic rock of the Songliao Basin was the research area. In accordance with the relationship between the density and acoustic velocity of supercritical CO2 and temperature and pressure, the regularity between the CO 2 density and acoustic velocity, and the depth of the area was established. A neutron logging simulation was completed based on a Monte Carlo method. Through the simulation of the wet limestone neutron logging, the relationship between the count rate ratio of short and long space detectors and the neutron porosity was acquired. Then, the nature of the supercritical CO 2 neutron moderation was obtained. With consideration given to the complexity of the volcanic rock mineral composition, a volcanic rock volume model was established, and the matrix neutron and density parameters were acquired using the ECS log. The properties of CO 2 were applied in the log evaluation of the CO 2 -bearing volcanic reservoirs in the southern Songliao Basin. The porosity and saturation of CO 2 were obtained, and a reasonable application was achieved in the CO 2 -bearing reservoir.

Keywords: supercritical CO

2 , density, acoustic time, neutron porosity, reservoir log evaluation (Somefigures may appear in colour only in the online journal)

1. Introduction

The use of CO2

is extensive in industry,agriculture, medicine, andsoon.TheCO 2 flooding technology which is used to enhance oil and gas recovery started to be used for actual pro- duction internationally in the 1970s, and then application was introduced in China(Chenet al2012). This technology has played an important role in the improvements that have been made in oil and gas production during the last 40 years. How- ever, there are issues such as corroded formations, and pre- cipitation of the solid phase in CO 2 flooding and storage projects (Zhang2011), which takes advantage of the logging data tomonitor CO

2underground occurrence states, and the effects of

CO 2 displacement in oil reservoirs(Zhouet al2009, Guan and Tutuncu2012). Due to these factors, some properties of CO 2 are not clear, and quantitative evaluations have been difficult to achieve. Natural CO 2 -bearing reservoirs are found in many regions around the world. For example, the Bohai Sea, Songliao, and Yinggehai Basins in China,the Val Verde Foreland Basin in Texas, USA, and the Pannontan Basin in Hungary(Houet al

2009).Daiet albelieved that when a reservoir contains more

than 60% CO 2 , it is considered to be an industrial gas reservoir. Based on this standard, the origin of the main industrial CO2 -bearing reservoirs in China are inorganic(Daiet al1994).

Therefore, many of the CO

2 -bearing reservoirs are closely associated with magma activity, and exist in volcanic rocks.Journal of Geophysics and Engineering J. Geophys. Eng.14(2017)1052-1060(9pp)https://doi.org/10.1088/1742-2140/aa6f221

Author to whom any correspondence should be addressed.1742-2132/17/0501052+09$33.00 © 2017 Sinopec Geophysical Research Institute Printed in the UK1052Downloaded from https://academic.oup.com/jge/article/14/5/1052/5107938 by guest on 16 June 2023

CO 2 commonly remains in a supercritical state within a reservoir. Its critical temperature is 31.06°C, and its critical pressure is 7.39 MPa. The supercritical CO 2 with properties between gas and liquid, has the double characteristics of gas and liquid, and has different physical properties when com- pared with conventional natural gas. The research of the physical properties of supercritical CO 2 has important sig- nificance for the accurate evaluations of CO 2 -bearing reser- voirs based on log data. The research methods have included laboratory measurements, andfitting experimental data to empirical formula, or obtained the properties of supercritical CO 2 by deriving formula from the theory of the gas mole- cular. The relationship between the density and acoustic