Summary A new integrated workflow for generation of AVO feasibility maps to be used in prospect de-risking is presented. We demonstrate the workflow on data from the Barents Sea. The methodology enables rapid extrapolation of expected... more
Summary A new integrated workflow for generation of AVO feasibility maps to be used in prospect de-risking is presented. We demonstrate the workflow on data from the Barents Sea. The methodology enables rapid extrapolation of expected rock physics properties away from well control, along selected horizon, constrained by seismic velocity information, geological inputs (basin modelling, seismic stratigraphy and facies maps) and rock physics depth trend analysis. The workflow should allow for more rapid, seamless and geologically consistent DHI de-risking of prospects in areas with complex geology and tectonic influence. The AVO feasibility maps can furthermore be utilized to generate non-stationary training data for AVO classification.
Research Interests: Geology, Computer Science, Stratigraphy, Workflow, Tectonics, and 3 moreHorizon, Facies, and Extrapolation
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Porosity evaluation in depth is a complex mechanical problem where irreversible mechanical compaction drives the initial consolidation phase of the sediment. The ability to quantitatively model this process has many applications in the... more
Porosity evaluation in depth is a complex mechanical problem where irreversible mechanical compaction drives the initial consolidation phase of the sediment. The ability to quantitatively model this process has many applications in the oil and gas industry, including AVA modeling, pore pressure prediction, and more. We present a method to model compaction in tectonically active basins using large deformation theory. Mechanical compaction is posed as a plastic-poroelastic process and is modelled using natural strain increments. Our method allows us to model porosity evaluation for different pore pressures and lithologies.
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Research Interests: Geology and Statistics
F024 Application of Contact Mechanics to Hydrocarbon Prediction in Shallow Sediments P.A. Avseth* (Rock Physics Technology) R. Bachrach (Western-Geco Schlumberger) A.J. van Wijngaarden (Norsk Hydro Research Center) T. Fristad (Norsk Hydro... more
F024 Application of Contact Mechanics to Hydrocarbon Prediction in Shallow Sediments P.A. Avseth* (Rock Physics Technology) R. Bachrach (Western-Geco Schlumberger) A.J. van Wijngaarden (Norsk Hydro Research Center) T. Fristad (Norsk Hydro Exploration and Production) & E. Odegaard (Norsk Hydro Exploration and Production) SUMMARY Recent efforts in rock physics have included a better understanding of the seismic properties of hydrocarbon reservoirs at shallow depths. Rock physics models based on contact theory have been used successfully to predict lithology and pore fluids from well log and seismic data in poorly consolidated Tertiary sediments (Mavko et al. 1998; Avseth et al. 2005). However
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Summary We integrate basin modeling with rock physics in order to model the seismic velocities of quartz-rich sands/sandstones as a function of burial history. First we show an example from the North Sea, where we demonstrate how the... more
Summary We integrate basin modeling with rock physics in order to model the seismic velocities of quartz-rich sands/sandstones as a function of burial history. First we show an example from the North Sea, where we demonstrate how the different velocities and associated seismic signatures in two nearby wells can be explained by local variability in burial history. A gentle Quarternary uplift due to deglaciation has been larger in the west than in the east, and this difference is enough to explain the different diagenetic history of the two reservoir sandstones. The reservoir in Well 1 has been buried at temperatures just above 70C for a longer time than the stratigraphically timeequivalent reservoir in Well 2; hence the cement volume is predicted to be slightly higher, and the top of the reservoir in Well 1 is stiffer than in Well 2. The combined modeling of chemical compaction and rock physics properties show that the velocities make a drastic jump at the burial depth where the rocks have been buried at higher temperatures than 70C through geologic time. We use the same technique in an inverse manner to estimate maximum burial depth and net uplift for selected wells in the Barents Sea.
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We have demonstrated a new approach to estimate fluid and pressure sensitivity in cemented sandstones. We estimate a weight function, where we assume grain contacts are either uncemented or cemented. We apply a hybrid rock physics model... more
We have demonstrated a new approach to estimate fluid and pressure sensitivity in cemented sandstones. We estimate a weight function, where we assume grain contacts are either uncemented or cemented. We apply a hybrid rock physics model where we combine Hertz-Mindlin contact theory for unconsolidated grain contacts, and Dvorkin-Nur contact cement model for cemented grain contatcs. A weight factor, W, is determined from bulk modulus versus porosity relations, where the two contact theories represent lower and upper bounds, respectively. Using this approach, we are able to quantify expected changes in seismic properties, including acoustic impedance and Vp/Vs, as a function of both saturation and pressure.
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F041 Combined Diagenetic and Rock Physics Modeling for Improved Control on Seismic Depth Trends 1 Hans Martin Helset 1 James C. Matthews 1 Per Avseth 2 and Aart-Jan van Wijngaarden 2 . 1) Geologica P.O.Box 8034 N-4068 Stavanger Norway; 2... more
F041 Combined Diagenetic and Rock Physics Modeling for Improved Control on Seismic Depth Trends 1 Hans Martin Helset 1 James C. Matthews 1 Per Avseth 2 and Aart-Jan van Wijngaarden 2 . 1) Geologica P.O.Box 8034 N-4068 Stavanger Norway; 2 Norsk Hydro P.O. Box 7190 N-5020 Bergen Norway. Abstract Seismic data are inherently non-unique and reservoir characterization based on seismic amplitudes relies on realistic a priori geologic constraints. One of the key issues in seismic data analysis is to understand the expected response of brine saturated sands versus shales (i.e. the background trend) at any given depth before we can
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Quantitative interpretation of seismic data for reservoir rock and fluid properties commonly relies on deterministic rock physics relations and may often neglect statistical variability or spatial correlation. Geostatistical methods, on... more
Quantitative interpretation of seismic data for reservoir rock and fluid properties commonly relies on deterministic rock physics relations and may often neglect statistical variability or spatial correlation. Geostatistical methods, on the other hand, take into account spatial dependence but results are often obtained without properly formalizing rock physics relations between seismic measurements and rock and fluid properties. This paper presents a strategy for integrating deterministic rock physics relations and spatial, statistical representations within a Bayesian framework. Data from the turbidite Glitne Field in the North Sea (Figure 1) provide an example for the approach. Because the reservoir is very heterogeneous, merging statistics with rock physics is particularly worthwhile to improve seismic reservoir prediction. Figure 1. The location of Glitne Field in the North Sea and the top Heimdal horizon as illustrated by reflection times. Available data are AVO seismic attributes, well observations, two-way seismic traveltimes, and cap-rock properties. The focus is on describing the spatial probability distribution of reservoir facies and fluid saturation along the seismic horizon representing the top Heimdal Formation (Figure 1), which is capped by Lista Formation at approximately 2000 m. Available data include AVO attributes (zero-offset reflectivity and AVO gradient) extracted from 3-D prestack seismic data and log-based analysis of facies and fluid saturation in four wells. Figure 2 shows zero-offset reflectivity (top, left) and AVO gradient (bottom, left) along the horizon (with the facies and fluid observations in the four wells indicated), a plot of zero-offset reflectivity versus AVO gradient (top, right), and a well log from the area (bottom, right). Two-way seismic traveltimes to the horizon of interest and cap-rock properties (density, P - and S -wave velocity) from well logs are also available (Figure 1). A 245 × 505 grid, each block being 12.5 × 12.5 m2, covers the domain of interest. This …
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In this study, we suggest an approach to predict stress sensitivity in cemented sandstones using non-uniform contact theory. We assume that the cemented rock will consist of a binary mixture of cemented and uncemented grain contacts. In... more
In this study, we suggest an approach to predict stress sensitivity in cemented sandstones using non-uniform contact theory. We assume that the cemented rock will consist of a binary mixture of cemented and uncemented grain contacts. In this way we are able to predict the pressure sensitivity in cemented rocks. We apply a hybrid rock physics model where we combine Hertz-Mindlin contact theory for unconsolidated grain contacts, and Dvorkin-Nur contact cement model for cemented grain contatcs. A weight factor, W, is determined from bulk modulus – porosity relations, where the two contact theories represent lower and upper bounds, respectively. Using this approach, we are able to quantify expected changes in seismic properties, including acoustic impedance and Vp/Vs, as a function of both saturation and pressure, and hence we can create 4-D rock physics templates of these parameters.
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F011 Z-99 Seismic fluid prediction in poorly consolidated and clay laminated sands Abstract 1 Per Avseth 1 Aart-Jan van Wijngaarden 1 Harald Flesche 1 Torbjorn Fristad 2 Johannes Rykkje 1 and Gary Mavko 3 1) Hydro Research Center Bergen... more
F011 Z-99 Seismic fluid prediction in poorly consolidated and clay laminated sands Abstract 1 Per Avseth 1 Aart-Jan van Wijngaarden 1 Harald Flesche 1 Torbjorn Fristad 2 Johannes Rykkje 1 and Gary Mavko 3 1) Hydro Research Center Bergen Norway; 2) Hydro Exploration Sandvika Norway; 3) Stanford University California USA Rock physics models based on contact theory have been used successfully to predict lithology and pore fluids from well log and seismic data (Mavko et al. 1998; Avseth et al. 2005). However several studies have indicated that shear wave velocities in poorly consolidated sands are often lower than predicted by
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F032 Rock Physics Depth Trend Analysis Based on Stacking Velocity P. Hoang* (Odin Petroleum A.S.) P.A. Avseth (Rock Physics Technology A. S.) B. Ursin (Norwegian University of Science and Technology) & A.J. van Wijngaarden (Norsk... more
F032 Rock Physics Depth Trend Analysis Based on Stacking Velocity P. Hoang* (Odin Petroleum A.S.) P.A. Avseth (Rock Physics Technology A. S.) B. Ursin (Norwegian University of Science and Technology) & A.J. van Wijngaarden (Norsk Hydro) SUMMARY In this paper we present methodologies to obtain rock physics properties as a function of burial depth i.e. rock physics depth trends (RPDTs). Several authors have suggested using rock physics models calibrated to well log data or constrained by diagenetic models to obtain empirical RPDTs. We present an alternative way to extract seismic RPDTs from seismic stacking velocities. At well locations we use
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ABSTRACT We have shown how we can derive attributes similar to elastic impedances, which we refer to as pseudo-elastic impedances, directly from rock physics templates of AI versus Vp/Vs, without knowing the density. This allows us to... more
ABSTRACT We have shown how we can derive attributes similar to elastic impedances, which we refer to as pseudo-elastic impedances, directly from rock physics templates of AI versus Vp/Vs, without knowing the density. This allows us to calibrate the elastic impedances to local rock physics models, and to honour the curvature of rock physics models, normally associated with compaction trends. In areas with large variability in burial depth, it is important to honour the true variability of the background trend. The final regression models are easy to implement in quantitative interpretation workflows, and allow for quick mapping of fluid or lithology anomalies that are consistent with rigorous rock physics models. We have demonstrated the validity of this approach on well log and seismic data from a prospective area in the Norwegian Sea.
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We use combined burial history and rock-physics modeling of sand and shale to predict expected amplitude variation with offset (AVO) signatures and seismic fluid sensitivities for a given burial history. The advantage with this approach... more
We use combined burial history and rock-physics modeling of sand and shale to predict expected amplitude variation with offset (AVO) signatures and seismic fluid sensitivities for a given burial history. The advantage with this approach is that we can extrapolate away from wells in areas with complex tectonics. Furthermore, we can use depth trends derived from local burial history to create AVO probability density functions (PDFs) for calibration and classification of AVO attributes in a given area. We demonstrate the use of these techniques on two hydrocarbon discoveries with different burial histories: the Alvheim Field in the North Sea and the Skalle Field in the Barents Sea.
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When we began to soliciti papers for this special section of The Leading Edge on “Resource plays I: Rock physics,” we debated among ourselves the definition of resource plays and what articles we should be looking for. We also searched... more
When we began to soliciti papers for this special section of The Leading Edge on “Resource plays I: Rock physics,” we debated among ourselves the definition of resource plays and what articles we should be looking for. We also searched for how others define the term resource plays and have come to realize that it is more of an economic term associated with volume and risk rather than its geologic characteristics.
In a proposed methodology for probabilistic calculation of elastic parameters from seismic reflectivities, one can focus on bulk density and VP/VS ratios and how those change at a layer interface. The probabilistic approach helps to model... more
In a proposed methodology for probabilistic calculation of elastic parameters from seismic reflectivities, one can focus on bulk density and VP/VS ratios and how those change at a layer interface. The probabilistic approach helps to model uncertainties in the elastic parameters. Zoeppritz's equation for calculation of PP reflection coefficients (RCs) is used to create 2D conditional probability density functions (CPDFs) of model parameters which are constructed by systematic grid search over the entire space of the model parameters. The method accurately recovers even highly irregular (nonelliptical) PDFs with multiple maxima. Moreover, it finds a global maximum, as opposed to many other techniques in which the algorithms, if supplied by a poor initial set of parameters, can become “stuck” in a local maximum. No empirical relationships are built into the method. The final products include “most probable” as well as uncertainty maps of various rock properties. The methodology was...
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Seismic 3D amplitude variation with offset (AVO) data from the Alvheim field in the North Sea are inverted into lithology/fluid classes, elastic properties, and porosity. Lithology/fluid maps over hydrocarbon prospects provide more... more
Seismic 3D amplitude variation with offset (AVO) data from the Alvheim field in the North Sea are inverted into lithology/fluid classes, elastic properties, and porosity. Lithology/fluid maps over hydrocarbon prospects provide more reliable estimates of gas/oil volumes and improve the decision concerning further reservoir assessments. The Alvheim field is of turbidite origin with complex sand-lobe geometry and appears without clear fluid contacts across the field. The inversion is phrased in a Bayesian setting. The likelihood model contains a convolutional, linearized seismic model and a rock-physics model that capture vertical trends due to increased sand compaction and possible cementation. The likelihood model contains several global model parameters that are considered to be stochastic to adapt the model to the field under study and to include model uncertainty in the uncertainty assessments. The prior model on the lithology/fluid classes is a Markov random field that captures l...
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Rock-physics trends and properties of clay-rich source rocks are investigated in selected wells in the North Sea and Norwegian Sea. Properties can vary significantly because of burial compaction, composition, diagenesis, organic richness,... more
Rock-physics trends and properties of clay-rich source rocks are investigated in selected wells in the North Sea and Norwegian Sea. Properties can vary significantly because of burial compaction, composition, diagenesis, organic richness, and maturation. The many competing effects can be difficult to disentangle in traditional rock-physics crossplots. However, nearly all the source-rock data in the study are bounded nicely by linear trends that are based on rock-physics models, in acoustic-impedance (AI) versus shear-impedance (SI) crossplots. These reference models serve as a nice screening tool for organic richness and/or maturation level (i.e., hydrocarbon generation and expulsion), regardless of burial depth. The use of rock-physics templates for the early mature to mature stage of clay-rich source rocks is demonstrated by combining a simple basin-modeling approach with a rock-physics model using Backus average in which the organic-rich shale is represented by a transverse isotr...
Research Interests: Geology and Geophysics
Research Interests: Geology and Geophysics
A novel inter-disciplinary methodology for the generation of rock property and AVO feasibility maps or cubes to be used in subsurface characterization and prospect de-risking is presented. We demonstrate the workflow for 1D, 2D and 3D... more
A novel inter-disciplinary methodology for the generation of rock property and AVO feasibility maps or cubes to be used in subsurface characterization and prospect de-risking is presented. We demonstrate the workflow for 1D, 2D and 3D cases on data from the North Sea and the Barents Sea, offshore Norway. The methodology enables rapid extrapolation of expected rock physics properties away from well control along selected horizons, constrained by seismic velocity information, geological inputs (basin modeling, seismic stratigraphy and facies maps) and rock physics depth trend analysis. In this way, the expected rock physics properties of a reservoir sandstone (saturated with any pore fluid) can be predicted at any given location between or away from existing wells while honoring rock’s burial and thermal history at this same location. The workflow should allow for more rapid, seamless and geologically consistent subsurface mapping and de-risking of prospects in areas with complex geol...
We develop a new scheme for calculation of density ratio, an attribute that can be directly linked to hydrocarbon saturation, and apply it to seismic AVO data from the Hoop area in the Barents Sea. The approach is based on the inversion... more
We develop a new scheme for calculation of density ratio, an attribute that can be directly linked to hydrocarbon saturation, and apply it to seismic AVO data from the Hoop area in the Barents Sea. The approach is based on the inversion of Zoeppritz’s equation for PP-wave. Furthermore, by utilizing interval velocities, we quantify uplift magnitude for a given interval beneath BCU horizon in the Hoop area. Depending on the temperature gradient, the maximum burial depth can be estimated, a crucial factor affecting the elastic properties of the rocks. Coupling uplift map with temperature history for key stratigraphic units from basin modeling enables us to extend training data away from well control. By doing so, we have created nonstationary amplitude variation with offset (AVO) probability density functions (PDFs) for calibration and classification of seismic attributes in the test area. This decreases the likelihood of misclassification of pore fluid type as opposed to the case wher...
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Quantitative seismic interpretation has become an important and critical technology for improved hydrocarbon exploration and production. However, this is typically a resource-demanding process that requires information from several well... more
Quantitative seismic interpretation has become an important and critical technology for improved hydrocarbon exploration and production. However, this is typically a resource-demanding process that requires information from several well logs, building a representative velocity model, and, of course, high-quality seismic data. Therefore, it is very challenging to perform in an exploration or appraisal phase with limited well control. Conventional seismic interpretation and qualitative analysis of amplitude variations with offset (AVO) are more common tools in these phases. Here, we demonstrate a method for predicting quantitative reservoir properties and facies using AVO data and a rock-physics model calibrated with well-log data. This is achieved using a probabilistic inversion method that combines stochastic inversion with Bayes' theorem. The method honors the nonuniqueness of the problem and calculates probabilities for the various solutions. To evaluate the performance of the...
AVO inversion of prestack seismic data, constrained by geologic knowledge and rock-physics modeling, is an essential technology that can greatly reduce interpretation risk during exploration. However, in spite of its great potentials,... more
AVO inversion of prestack seismic data, constrained by geologic knowledge and rock-physics modeling, is an essential technology that can greatly reduce interpretation risk during exploration. However, in spite of its great potentials, this technology suffers from a wide range of pitfalls and many uncertainties. In this study, we demonstrate the use of simultaneous AVO inversion in an area of the Norwegian Sea where several proven discoveries with strong AVO anomalies are present, all of which are structural traps. The inversion successfully delineated these discoveries, and a pure blind test of a prospect on a structural high correctly predicted the presence of hydrocarbons. The AVO inversion also gave support for a stratigraphic trap in a graben setting between the prolific structural highs. However, this prospect turned out to be a failure, as the observed AVO anomaly was false. Postdrill analysis showed that a thin, very hard, calcareous event right above the target had created a...
Research Interests: Parameter estimation, Risk Analysis, Complex System, Statistical Techniques in Spatial Analysis, North Sea, and 9 morePetroleum Industry, Probability Density Function, Physical Model, Physical Properties, Amplitude versus Offset, Quadratic discriminant analysis, Statistical techniques, Bayesian Classification, and Spatial mapping
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We use combined burial history and rock-physics modeling of sand and shale to predict expected amplitude variation with offset (AVO) signatures and seismic fluid sensitivities for a given burial history. The advantage with this approach... more
We use combined burial history and rock-physics modeling of sand and shale to predict expected amplitude variation with offset (AVO) signatures and seismic fluid sensitivities for a given burial history. The advantage with this approach is that we can extrapolate away from wells in areas with complex tectonics. Furthermore, we can use depth trends derived from local burial history to create AVO probability density functions (PDFs) for calibration and classification of AVO attributes in a given area. We demonstrate the use of these techniques on two hydrocarbon discoveries with different burial histories: the Alvheim Field in the North Sea and the Skalle Field in the Barents Sea.
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... The brown data points represents well 34/6-A-8 (western area) and the blue points represents ... where cl is fractional amount of coated quartz grains, fV is the fractional amount of quartz ... We know the present day temperature, but... more
... The brown data points represents well 34/6-A-8 (western area) and the blue points represents ... where cl is fractional amount of coated quartz grains, fV is the fractional amount of quartz ... We know the present day temperature, but we need to add a number of oC corresponding ...
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The petroleum industry is increasing its focus on the exploration of reservoirs in turbidite systems. However, these sedimentary environments are often characterized by very complex sand distributions. Hence, reservoir description based... more
The petroleum industry is increasing its focus on the exploration of reservoirs in turbidite systems. However, these sedimentary environments are often characterized by very complex sand distributions. Hence, reservoir description based on conventional seismic and well-log interpretation may be very uncertain. There is a need to employ more quantitative seismic techniques to reveal reservoirs units in these complex systems from