This work aims to improve the understanding of how fracture zones affect carbonate reservoir properties based on observations of a pre-salt well located in the Santos Basin,Brazil.The identification of fracture zones ...This work aims to improve the understanding of how fracture zones affect carbonate reservoir properties based on observations of a pre-salt well located in the Santos Basin,Brazil.The identification of fracture zones allowed for the observation of a relationship between the occurrence of rock fractures and the silicification,as the latter plays an important role in determining porosity(higher silica content may increase brittleness of the rocks therefore increasing the likelihood of creating fractures zones and fractures may be filled up reducing the total porosity).To support the proposed observation,an integrated study was conducted using borehole imaging,spectroscopy logs,and sidewall core samples.The porosities were defined using nuclear magnetic resonance log analysis,alongside sidewall core samples,and thin sections.The integration of rock samples and well data with seismic analysis was performed to analyze the presence of a regional fault system that could explain high fracture densities as well as observed silica content characteristics.The results show how different types of cement filling up the formation pores affect fracture densities and total porosity.Furthermore,it was possible to infer that the amount of silica content observed in well logs and thin sections relates to hydrothermal fluids reaching out the reservoir through regional fault systems detected in the seismic section.Therefore,this paper supports the comprehension of how diagenetic processes can significantly affect the properties of presalt reservoirs.展开更多
Carbonate rocks exhibit complex and heterogeneous pore structures;such heterogeneity is manifested by the occurrence of a wide variety of pore types with different sizes and geometries as a result of depositional and ...Carbonate rocks exhibit complex and heterogeneous pore structures;such heterogeneity is manifested by the occurrence of a wide variety of pore types with different sizes and geometries as a result of depositional and diagenetic processes.These complications substantially increase the uncertainty of predicted rock hydraulic parameters because samples with comparable porosities might have very different permeability values.In this study,small-scale characterisation of porosity and permeability in heterogeneous Eocene limestone samples from the Bassein Formation of the B-X structure of the MK Field in Mumbai Offshore Basin,India,was carried out,employing an integrated framework that in-corporates thin-section petrography,routine core analysis,mercury injection capillary pressure and nuclear magnetic resonance data.The pore characteristics of these carbonates range from poor to excellent.The studied samples exhibited large ranges of porosity,permeability and other associated petrophysical attributes.The pore types,as well as their orientations and connectivity,are the primary factors causing the heterogeneity.Because of the complexity of the pore networks,a simple lithofacies classification alone would have been insufficient to link porosity and permeability.The reservoir char-acteristics in the study area are strongly linked to the development and/or destruction of reservoir porosity-permeability during different phases of diagenesis.Twenty-four carbonate core samples from the limestone unit were studied and classified into microfacies and pore type classes,producing an accurate assessment of reservoir attributes.The comprehensive workflow incorporates the pore volume distributions and pore throat attributes for each rock type.Three carbonate microfacies were identified by petrographic analysis and their petrophysical characteristics,such as porosity,permeability,pore throat size,pore volume and fluid flow factors,were measured.The study demonstrates how macro-porosity,mesoporosity and microporosity are associated with various rock types and how they affect permeability and cementation exponents.The results of this study provide a comprehensive experi-mental framework for geological and geophysical interpretation that can be applied to identify potential reservoir facies and strengthen our understanding of heterogeneous carbonates.The framework can also be used to guide reservoir evaluation of similar heterogeneous formations in other areas.展开更多
文摘This work aims to improve the understanding of how fracture zones affect carbonate reservoir properties based on observations of a pre-salt well located in the Santos Basin,Brazil.The identification of fracture zones allowed for the observation of a relationship between the occurrence of rock fractures and the silicification,as the latter plays an important role in determining porosity(higher silica content may increase brittleness of the rocks therefore increasing the likelihood of creating fractures zones and fractures may be filled up reducing the total porosity).To support the proposed observation,an integrated study was conducted using borehole imaging,spectroscopy logs,and sidewall core samples.The porosities were defined using nuclear magnetic resonance log analysis,alongside sidewall core samples,and thin sections.The integration of rock samples and well data with seismic analysis was performed to analyze the presence of a regional fault system that could explain high fracture densities as well as observed silica content characteristics.The results show how different types of cement filling up the formation pores affect fracture densities and total porosity.Furthermore,it was possible to infer that the amount of silica content observed in well logs and thin sections relates to hydrothermal fluids reaching out the reservoir through regional fault systems detected in the seismic section.Therefore,this paper supports the comprehension of how diagenetic processes can significantly affect the properties of presalt reservoirs.
文摘Carbonate rocks exhibit complex and heterogeneous pore structures;such heterogeneity is manifested by the occurrence of a wide variety of pore types with different sizes and geometries as a result of depositional and diagenetic processes.These complications substantially increase the uncertainty of predicted rock hydraulic parameters because samples with comparable porosities might have very different permeability values.In this study,small-scale characterisation of porosity and permeability in heterogeneous Eocene limestone samples from the Bassein Formation of the B-X structure of the MK Field in Mumbai Offshore Basin,India,was carried out,employing an integrated framework that in-corporates thin-section petrography,routine core analysis,mercury injection capillary pressure and nuclear magnetic resonance data.The pore characteristics of these carbonates range from poor to excellent.The studied samples exhibited large ranges of porosity,permeability and other associated petrophysical attributes.The pore types,as well as their orientations and connectivity,are the primary factors causing the heterogeneity.Because of the complexity of the pore networks,a simple lithofacies classification alone would have been insufficient to link porosity and permeability.The reservoir char-acteristics in the study area are strongly linked to the development and/or destruction of reservoir porosity-permeability during different phases of diagenesis.Twenty-four carbonate core samples from the limestone unit were studied and classified into microfacies and pore type classes,producing an accurate assessment of reservoir attributes.The comprehensive workflow incorporates the pore volume distributions and pore throat attributes for each rock type.Three carbonate microfacies were identified by petrographic analysis and their petrophysical characteristics,such as porosity,permeability,pore throat size,pore volume and fluid flow factors,were measured.The study demonstrates how macro-porosity,mesoporosity and microporosity are associated with various rock types and how they affect permeability and cementation exponents.The results of this study provide a comprehensive experi-mental framework for geological and geophysical interpretation that can be applied to identify potential reservoir facies and strengthen our understanding of heterogeneous carbonates.The framework can also be used to guide reservoir evaluation of similar heterogeneous formations in other areas.
