72 research outputs found
Erratum
No full text The January 2011 issue featured an article, “Stress and fluid sensitivity in two North Sea oil fields—comparing rock physics models with seismic observations”, written by Kenneth Duffaut, Per Avseth, and Martin Landrø. The article contained errors in the units of density on page 99. </jats:p
Quantitative Seismic Interpretation using Rock Physics Templates - case examples from the Zumba field
No full textA post drill inversion study was done by Avseth et al. (2016) after the dry well result from Zumba prospect. The AVO inversion failed in a graben setting, caused by a hard carbonate layer and associated refraction just above the target prospect. The new AVO inversion results showed a significant improvement both in AI and Vp/Vs predictions.
The objective of this thesis is to improve the understanding of the seismic response for better lithology and fluid prediction and investigate further prospectivity in the Zumba graben with the updated elastic inversion data which are calibrated to the new well.
In this study, we utilized Rock Physics Templates (RPTs) for lithology and pore fluid interpretation of well-log data and elastic inversion results. The main procedure consists of two basic steps: (1) selecting the template that is consistent with the well-log data; and (2) applying the user-defined polygon boundaries in the template to classify elastic inversion results. We also generated rock physics attribute (CPEI and PEIL) from RPT(s) that can be used to screen reservoir zone from seismic inversion.
The results show that we can potentially distinguish between different types of lithology facies in the study area. We are also able to delineate and predict potential hydrocarbon accumulations and possible remaining prospectivity in the Zumba Graben in the Norwegian Sea
AVO classification of facies and fluids constrained by burial history - Demonstrations on real data from Norwegian Shelf
No full textDenne studien har til formål å generere AVO-klassifisering av facies/væsker fra Yttergryta til Natalia, og tar hensyn til begravelseshistorien. For å oppnå målet, følges 3-trinns arbeidsflyt. Studien starter med Hampson Russell AVO, hvor vi fikk avskjæringen og gradienten for Yttergryta og Natalia. Det neste trinnet er å gjøre PeLe-modellering for porøsitetsdybde trender for Yttergryta og Natalia, slik at vi får de elastiske parameterne for begge. Det siste trinnet er DigAVO, hvor vi tar inn sluttresultatene fra Hampson Russell AVO og PeLe-modellering. Slik at vi kunne se forskjellen mellom Natalia og Yttergryta. Dermed demonstrere hvordan sementering påvirket begge og for å de endelige resultatvisualiseringene av Yttergryta og Natalia
Stress and fluid sensitivity in two North Sea oil fields—comparing rock physics models with seismic observations
No full text During 4D seismic reservoir characterization, it is important to have reliable rock physics models for both static (e.g., mineralogy, porosity, cement volume) and dynamic (e.g., saturation, pressure, temperature) reservoir parameters. Without a good understanding of reservoir geology and associated static rock physics properties, it is impossible to interpret time-variant changes in pore pressure and saturation (Andersen et al., 2009). The dry rock properties of the reservoir can be obtained from well-log data combined with geological information about mineral composition and rock texture, and Gassmann theory to estimate the effect of pore fluid changes. Normally, core measurements are undertaken to quantify stress sensitivity, but these are often affected by induced fractures caused by the coring acquisition that will enhance the stress sensitivity of the rock (Holt et al., 2005). Duffaut and Landrø (2007) showed how calibrated Hertz-Mindlin contact theory could be applied to estimate stress sensitivity on [Formula: see text] ratios in two North Sea oil fields (Statfjord and Gullfaks), in order to explain observed AVO signatures during water injection and associated pore-pressure increase. It was found that loose Gullfaks sands yielded high [Formula: see text] ratios (up to about 7) during water injection, whereas slightly quartz-cemented Statfjord sands yielded more moderate changes in [Formula: see text] ratios (approximately 2). The differences were modeled by varying the number of grain-to-grain contacts. In this paper we further investigate the pressure sensitivity of seismic parameters in these two oil fields, applying the rock physics modeling approach presented by Avseth and Skjei (TLE, this issue), and we demonstrate a good match between rock physics modelling results and seismic observations in terms of [Formula: see text]. The stress sensitivity of [Formula: see text] decreases drastically when sands become cemented, as crack-like porosity at grain contacts are eliminated. </jats:p
The effects of seismic anisotropy and upscaling on rock physics interpretation and AVO analysis
No full textIn seismic reservior characterization, it is important that the measured sonic log used is accurate and consistent. Due to anisotropic effects in the reservoir, which is majorly caused as a results of interbedded sequence of sand and shales, sonic log (compressional and shear wave velocities) acquired in vertical wells are different from those acquired in deviated wells. Rock physics models are created for anisotropic heterogeneous sand-shale sequence. These models are varied as a function
of angle, porosity, saturation and net to gross. Variation of Thomsen anisotropic parameters and anelliptic parameters as a function of saturation and net-to-gross are investigated in order to understand the significant of anisotropy on these properties. From the rock physics modelling, anisotropic effect becomes more pronounced at high propagation angle and also the variation of the geologic parameters strongly depends on the propagation angle. Anisotropy effects decreases with increasing net-to-gross and anelliptic parameters are more sensitive to fluid saturation compared to Thomsen anisotropy parameters.
A method is proposed for anisotropy correction of deviated wells using core measurement (model rock properties) of sand and shale from the study area, the inclination angle of the well and the net to gross ratio of the reservoir. The anisotropy corrected logs are then used for improved rock physics interpretation using the rock physics templates(RPT) and AVO analysis. The proposed correction is lithology dependent and the correction is significant in regions with low net-to-gross. Discrimination of lithologies and fluid saturation on the rock physics template is enhanced as a result of the anisotropy correction.
The rock physics templates are constructed for different net to gross and propagation angles for varying fluid saturation in order to account for anisotropic effects. There is better separation of water sands and gas sand on the horizontal RPT(created at 72 deg) compared to vertical RPT(created at 0 deg). Vertical well, deviated well and anisotropy corrected well log data from the North Sea are
superimposed on the rock-physics templates. Poor separation of lithology and saturation is observed on the RPT using the deviated well. It can be observed that the anisotropy corrected deviated well follows similar trends as the vertical well. Anisotropy effect on the reservoir properties that are accounted for using the proposed method are clearly seen on 3D rock physics templates. AVO inversion is also performed on the horizon attribute data from study area. The inverted rock physics
properties are plotted on the created rock physics models for two vertical wells from the study area. The two vertical wells show different AVO class response. The net-to-gross and porosity are different for the two wells and in general, these observations are constrained by local geology
AvO modelling constrained by burial history as an anomaly screening tool in complex geological settings.
No full textAvO-teknologi har blitt anerkjent for å være sterkt påvirket av begravningshistorie. Siden bergartene som bygger opp mediet har registrert de forskjellige hendelsene og prosessene i strukturen sin, blir disse hendelsene registrert i de fysiske egenskapene til bergartene. I det spesifikke tilfellet ved områder med kompleks bassengutvikling, gir kunnskapen om deres begravningshistorie en måte å begrense tolkningen og prediksjonen av AvO-signaturene. Noen nye studier har som mål å integrere den generelle geologiske kunnskapen om begravningshistorien med modellering av formasjonsfysikk for å bedre forståelsen av bergartsegenskaper og deres effekt på bølgeforplantning. I dette arbeidet viser vi hvordan en slik integrering kan resultere i et kraftig verktøy for å utforske de mulige scenariene og tilhørende usikkerhetsmomenter, spesielt i uutforskede områder. Vi viser innflytelsen som begravningshistorien har på sandsteins- og skiferegenskapene; innvirkningen som forskjellig kontekst for konstruksjon av skifertrender har på skiferegenskapsestimering og effekten som landhevings-estimater og tilhørende avvik har på de forventede sandsteinsegenskapene romlig. Vi har vist at en integrert metodikk gjør det mulig for oss å beskrive, utforske og analysere distinkte geologiske scenarier som tar bassengutviklingen i betraktning og gir en følsomhetsanalyse for de kontrollerende faktorene i AvO-respons for et gitt basseng. Vi har brukt denne metodikken i det sørvestlige Barentshavet, og viser potensialet for prediksjon og screening av uutprøvde AvO-signaturer. Videre kan anvendelsen av denne metodikken være fordelaktig under risikovurderingen av petroleumsprospekter
AVO classification of facies and fluids constrained by burial history - Demonstrations on real data from Norwegian Shelf
No full textDenne studien har til formål å generere AVO-klassifisering av facies/væsker fra Yttergryta til Natalia, og tar hensyn til begravelseshistorien. For å oppnå målet, følges 3-trinns arbeidsflyt. Studien starter med Hampson Russell AVO, hvor vi fikk avskjæringen og gradienten for Yttergryta og Natalia. Det neste trinnet er å gjøre PeLe-modellering for porøsitetsdybde trender for Yttergryta og Natalia, slik at vi får de elastiske parameterne for begge. Det siste trinnet er DigAVO, hvor vi tar inn sluttresultatene fra Hampson Russell AVO og PeLe-modellering. Slik at vi kunne se forskjellen mellom Natalia og Yttergryta. Dermed demonstrere hvordan sementering påvirket begge og for å de endelige resultatvisualiseringene av Yttergryta og Natalia.This study is aimed to generate AVO classification of facies/fluids from Yttergryta to Natalia, and taking into account the burial history. To accomplish the objective, 3-stages workflow is followed. The study starts with Hampson Russell AVO, where we got the intercept and gradient for Yttergryta and Natalia. The next step is to do PeLe-modeling for porosity-depth trends for Yttergryta and Natalia, such that we get the elastic parameters for both of them. The last step is DigAVO, where we take in the outputs from Hampson Russell AVO and PeLe-modeling. Such that we could see the difference between Natalia and Yttergryta. Thereby, showcase how cementation affected both of them and to get the finale result visualizations of Natalia and Yttergryta
AvO modelling constrained by burial history as an anomaly screening tool in complex geological settings.
No full textAvO-teknologi har blitt anerkjent for å være sterkt påvirket av begravningshistorie. Siden bergartene som bygger opp mediet har registrert de forskjellige hendelsene og prosessene i strukturen sin, blir disse hendelsene registrert i de fysiske egenskapene til bergartene. I det spesifikke tilfellet ved områder med kompleks bassengutvikling, gir kunnskapen om deres begravningshistorie en måte å begrense tolkningen og prediksjonen av AvO-signaturene. Noen nye studier har som mål å integrere den generelle geologiske kunnskapen om begravningshistorien med modellering av formasjonsfysikk for å bedre forståelsen av bergartsegenskaper og deres effekt på bølgeforplantning. I dette arbeidet viser vi hvordan en slik integrering kan resultere i et kraftig verktøy for å utforske de mulige scenariene og tilhørende usikkerhetsmomenter, spesielt i uutforskede områder. Vi viser innflytelsen som begravningshistorien har på sandsteins- og skiferegenskapene; innvirkningen som forskjellig kontekst for konstruksjon av skifertrender har på skiferegenskapsestimering og effekten som landhevings-estimater og tilhørende avvik har på de forventede sandsteinsegenskapene romlig. Vi har vist at en integrert metodikk gjør det mulig for oss å beskrive, utforske og analysere distinkte geologiske scenarier som tar bassengutviklingen i betraktning og gir en følsomhetsanalyse for de kontrollerende faktorene i AvO-respons for et gitt basseng. Vi har brukt denne metodikken i det sørvestlige Barentshavet, og viser potensialet for prediksjon og screening av uutprøvde AvO-signaturer. Videre kan anvendelsen av denne metodikken være fordelaktig under risikovurderingen av petroleumsprospekter.AvO technology has been recognized to be profoundly affected by burial history because the rocks that composed the medium have recorded the different events and processes in their structure; thus, these events are recorded in the physical properties of the rocks. In the specific case of areas with complex basin development, the knowledge of their burial history provides a way to constrain the interpretation and prediction of the AvO signatures. Recent studies have aimed to integrate the general geological knowledge about the burial history with rock-physics modelling to improve the understanding of the rock properties and their effect on the wave propagation. In this work, we show how such integration can result in a powerful tool to explore the possible scenarios and their associated uncertainties, especially in unexplored areas. We show the influence that the burial history has on the sandstone and shale properties; the impact that different context for constructing shale trends have on shale properties estimation and the effect that the uplift estimation and its deviation have on the expected sandstone properties spatially. We have demonstrated that an integrated methodology allows us to describe, explore and analyze distinct geological scenarios that honour the basin evolution providing sensitivity analysis for the different controlling factors of the AvO responses for a given basin. We have applied this methodology in the southwestern Barents Sea, showing the potential for prediction and screening of untested AvO signatures. Furthermore, the application of this methodology can be beneficial during risk assessments workflows for petroleum prospects
The effects of seismic anisotropy and upscaling on rock physics interpretation and AVO analysis
No full textIn seismic reservior characterization, it is important that the measured sonic log used is accurate and consistent. Due to anisotropic effects in the reservoir, which is majorly caused as a results of interbedded sequence of sand and shales, sonic log (compressional and shear wave velocities) acquired in vertical wells are different from those acquired in deviated wells. Rock physics models are created for anisotropic heterogeneous sand-shale sequence. These models are varied as a function
of angle, porosity, saturation and net to gross. Variation of Thomsen anisotropic parameters and anelliptic parameters as a function of saturation and net-to-gross are investigated in order to understand the significant of anisotropy on these properties. From the rock physics modelling, anisotropic effect becomes more pronounced at high propagation angle and also the variation of the geologic parameters strongly depends on the propagation angle. Anisotropy effects decreases with increasing net-to-gross and anelliptic parameters are more sensitive to fluid saturation compared to Thomsen anisotropy parameters.
A method is proposed for anisotropy correction of deviated wells using core measurement (model rock properties) of sand and shale from the study area, the inclination angle of the well and the net to gross ratio of the reservoir. The anisotropy corrected logs are then used for improved rock physics interpretation using the rock physics templates(RPT) and AVO analysis. The proposed correction is lithology dependent and the correction is significant in regions with low net-to-gross. Discrimination of lithologies and fluid saturation on the rock physics template is enhanced as a result of the anisotropy correction.
The rock physics templates are constructed for different net to gross and propagation angles for varying fluid saturation in order to account for anisotropic effects. There is better separation of water sands and gas sand on the horizontal RPT(created at 72 deg) compared to vertical RPT(created at 0 deg). Vertical well, deviated well and anisotropy corrected well log data from the North Sea are
superimposed on the rock-physics templates. Poor separation of lithology and saturation is observed on the RPT using the deviated well. It can be observed that the anisotropy corrected deviated well follows similar trends as the vertical well. Anisotropy effect on the reservoir properties that are accounted for using the proposed method are clearly seen on 3D rock physics templates. AVO inversion is also performed on the horizon attribute data from study area. The inverted rock physics
properties are plotted on the created rock physics models for two vertical wells from the study area. The two vertical wells show different AVO class response. The net-to-gross and porosity are different for the two wells and in general, these observations are constrained by local geology
Modeling burial induced changes in physical sandstone properties - A case-study of North Sea and Norwegian Sea sandstone formations
No full textThe changes in physical properties of sandstones with burial depth are a result of mechanical and chemical compaction processes. These processes are affected by rock microstructure, pressure regimes and temperature history. Data from 30 wells have been used to investigate and compare the changes in porosity, bulk density, elastic moduli and wave propagation velocities between the mid-Jurassic sandstones of the Etive Fm. in the North Sea and the Garn Fm. in the Norwegian Sea.
At shallow burial depths (less than 2 km) the changes of the physical properties are governed by effective stress. A mechanical compaction model is used to describe the porosity loss and the bulk density increase with depth, whereas the friable-sand theory is used to explain the changes in elastic moduli and wave propagation velocities. For both formations, the under predictions by the models in the porosity, bulk moduli and P-wave velocity values from the data suggest high depositional porosities (0.40) and small amounts of quartz cement at depths of 1.6-2.0 km.
At greater burial depths and temperatures (greater than 2 km, and greater than 75°C) quartz cementation is the main controlling factor in the changes of the physical properties. The porosity loss and the bulk density increase with depth are explained by means of a quartz cement precipitation model, and the contact-cement theory is used to describe the changes in elastic moduli and wave propagation velocities. High porosities (greater than 0.15) at great burial depths (greater than 4 km) suggest the presence of higher amounts of clay coatings in both formations, and they may also be a result of high overpressures. The great variations in porosity and bulk modulus values for Garn sandstones encountered at same depths, indicate that the Garn Fm. is less well sorted and more affected by different types of quartz deposition than the Etive Fm. The contact-cement model main over prediction trend for the bulk modulus of highly overpressured sandstones enlightens the effects of different pressure regimes in the chemical compaction domain
- …
