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PVT properties in exploration
Organic Geochemistry 33 (2002) 611–612 www.elsevier.com/locate/orggeochem
Preface
PVT properties in exploration
This Special Issue of Organic Geochemistry presents selected papers from the American Chemical Society (ACS) Geochemistry Division’s session on ‘‘The Integration of Organic Geochemistry and PVT Studies in Petroleum Exploration and Production’’, convened at the ACS spring 2000 meeting held in San Francisco, California. The session illustrated the growing acceptance of bulk oil analysis and predictions of PVT properties within the exploration community. Bulk oil analysis—the determination of bulk properties such as density and viscosity—has been a standard part of reservoir analysis for many years. These properties, along with certain bulk phase-related properties such as bubble/dew point and amount of solution gas, are loosely grouped under the moniker of ‘‘PVT Properties’’. PVT properties are crucial in determining the optimal production strategy to best exploit a reservoir. Recent work has been aimed at extending the application of these properties beyond resource exploitation towards exploration and production allocation. Bulk-oil analysis utilized in reservoir management has gained acceptance in the organic geochemistry community as an exploration and oil characterization tool that is complementary to existing techniques. Similarly, organic geochemical analysis is gaining acceptance in reservoir management as a means of addressing diverse problems from oil fingerprinting to wax and asphaltene management. In addition to analyzing bulk properties in existing samples, the prediction of bulk properties from estimates of oil composition is a growing and fruitful field of endeavor. The prediction of bulk properties relies on two categories of models. Equations of state (EOS) can be used to predict the relationships among the intrinsic state properties of pressure, density, and temperature. Given a one-phase mixture of known composition, any of these properties can be predicted as a function of the other two properties. These models do NOT predict any phase information, however. Typically, equations of state are semi-empirical relationships that are carefully tuned for specific applications. In order to predict phase behavior of mixtures, further modeling efforts are required. Fluid phase
equilibria models (FPE) are used to predict the number and composition of phases that minimize the Gibbs free energy of a system. FPE models require knowledge of the chemical potential of all species in all possible mixtures. This quantity can be predicted from volumetric data and, in particular, from data generated using equations of state. Thus, together, EOS and FPE models can predict any of the PVT properties utilized in reservoir management and, increasingly, in exploration. This Special Issue of Organic Geochemistry is devoted to methods of calculating and utilizing PVT properties that would be of interest to the practicing organic geochemist. The issue is divided into two logical sections. The first section focuses on development of equations that can be used to estimate bulk properties and phase properties, relying on empirical models, equations of state, and FPE models. To introduce the issue, Meulbroek gives a broad outline of PVT and FPE modeling, and describes the application of equations of state to several exploration problems. Next, Sorensen et al. explore an area of fundamental difficulty: developing an EOS that handles both non-polar species such as hydrocarbons and ionic materials within water. Their solution—to treat ionic species as real components with very large critical properties—allows current EOS applications to model brines with no change in algorithm. Understanding combined hydrocarbon and water PVT is vital for modeling of hydrate production, corrosion potential of produced fluids and modeling aquifer degassing. Aquifer degassing occurs during production depletion and possibly during major uplift events. Therefore, good PVT modeling of subsurface water systems is vital for production and exploration. Aqueous PVT information is also fundamental to the interpretation of fluid inclusion data. The second section focuses on applications of models and data to understanding the relationships among oils. This section consists of three papers. In the first paper, di Primio explores the use of PVT data as a mechanism to compare the relationships between oils of different prospects. Unlike most geochemical analysis which relies on analysis of individual compounds, bulk analysis
0146-6380/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved. PII: S0146-6380(02)00027-X
612
Preface / Organic Geochemistry 33 (2002) 611–612
represents an integration of chemical compositional differences, and can reveal genetic similarities even though moderate alteration. Next, Losh et al. use the results of phase modeling to describe subsurface multi-phase mixing, and show coherent regional patterns of fluid alteration in the Gulf of Mexico. Understanding patterns of alteration can lead to insights on regional fluid flow and timing. Finally, England presents several empirical correlations based on regional PVT databases that allow the explorationist to predict Condensate Gas Ratios, which are crucial for condensate prospect evaluation. An ability to predict CGR in satellite areas allows portfolios to be managed in far more economic way. Due to the difficult nature of obtaining reliable
gas-condensate samples down-hole, it is vital to be able to estimate CGR reliably. The future of the marriage between geochemistry and PVT data and the combination of these data to solve production and exploration problems looks healthy, and with this special issue we hope to have stimulated an interest in the geochemical community.
Peter Meulbroek, Gordon MacLeod Chemistry 139-74, California Institute of Technology Pasadena, CA 91125, USA E-mail address: [email protected] (P. Meulbroek)
Preface
PVT properties in exploration
This Special Issue of Organic Geochemistry presents selected papers from the American Chemical Society (ACS) Geochemistry Division’s session on ‘‘The Integration of Organic Geochemistry and PVT Studies in Petroleum Exploration and Production’’, convened at the ACS spring 2000 meeting held in San Francisco, California. The session illustrated the growing acceptance of bulk oil analysis and predictions of PVT properties within the exploration community. Bulk oil analysis—the determination of bulk properties such as density and viscosity—has been a standard part of reservoir analysis for many years. These properties, along with certain bulk phase-related properties such as bubble/dew point and amount of solution gas, are loosely grouped under the moniker of ‘‘PVT Properties’’. PVT properties are crucial in determining the optimal production strategy to best exploit a reservoir. Recent work has been aimed at extending the application of these properties beyond resource exploitation towards exploration and production allocation. Bulk-oil analysis utilized in reservoir management has gained acceptance in the organic geochemistry community as an exploration and oil characterization tool that is complementary to existing techniques. Similarly, organic geochemical analysis is gaining acceptance in reservoir management as a means of addressing diverse problems from oil fingerprinting to wax and asphaltene management. In addition to analyzing bulk properties in existing samples, the prediction of bulk properties from estimates of oil composition is a growing and fruitful field of endeavor. The prediction of bulk properties relies on two categories of models. Equations of state (EOS) can be used to predict the relationships among the intrinsic state properties of pressure, density, and temperature. Given a one-phase mixture of known composition, any of these properties can be predicted as a function of the other two properties. These models do NOT predict any phase information, however. Typically, equations of state are semi-empirical relationships that are carefully tuned for specific applications. In order to predict phase behavior of mixtures, further modeling efforts are required. Fluid phase
equilibria models (FPE) are used to predict the number and composition of phases that minimize the Gibbs free energy of a system. FPE models require knowledge of the chemical potential of all species in all possible mixtures. This quantity can be predicted from volumetric data and, in particular, from data generated using equations of state. Thus, together, EOS and FPE models can predict any of the PVT properties utilized in reservoir management and, increasingly, in exploration. This Special Issue of Organic Geochemistry is devoted to methods of calculating and utilizing PVT properties that would be of interest to the practicing organic geochemist. The issue is divided into two logical sections. The first section focuses on development of equations that can be used to estimate bulk properties and phase properties, relying on empirical models, equations of state, and FPE models. To introduce the issue, Meulbroek gives a broad outline of PVT and FPE modeling, and describes the application of equations of state to several exploration problems. Next, Sorensen et al. explore an area of fundamental difficulty: developing an EOS that handles both non-polar species such as hydrocarbons and ionic materials within water. Their solution—to treat ionic species as real components with very large critical properties—allows current EOS applications to model brines with no change in algorithm. Understanding combined hydrocarbon and water PVT is vital for modeling of hydrate production, corrosion potential of produced fluids and modeling aquifer degassing. Aquifer degassing occurs during production depletion and possibly during major uplift events. Therefore, good PVT modeling of subsurface water systems is vital for production and exploration. Aqueous PVT information is also fundamental to the interpretation of fluid inclusion data. The second section focuses on applications of models and data to understanding the relationships among oils. This section consists of three papers. In the first paper, di Primio explores the use of PVT data as a mechanism to compare the relationships between oils of different prospects. Unlike most geochemical analysis which relies on analysis of individual compounds, bulk analysis
0146-6380/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved. PII: S0146-6380(02)00027-X
612
Preface / Organic Geochemistry 33 (2002) 611–612
represents an integration of chemical compositional differences, and can reveal genetic similarities even though moderate alteration. Next, Losh et al. use the results of phase modeling to describe subsurface multi-phase mixing, and show coherent regional patterns of fluid alteration in the Gulf of Mexico. Understanding patterns of alteration can lead to insights on regional fluid flow and timing. Finally, England presents several empirical correlations based on regional PVT databases that allow the explorationist to predict Condensate Gas Ratios, which are crucial for condensate prospect evaluation. An ability to predict CGR in satellite areas allows portfolios to be managed in far more economic way. Due to the difficult nature of obtaining reliable
gas-condensate samples down-hole, it is vital to be able to estimate CGR reliably. The future of the marriage between geochemistry and PVT data and the combination of these data to solve production and exploration problems looks healthy, and with this special issue we hope to have stimulated an interest in the geochemical community.
Peter Meulbroek, Gordon MacLeod Chemistry 139-74, California Institute of Technology Pasadena, CA 91125, USA E-mail address: [email protected] (P. Meulbroek)