scholarly journals Origin of Gassmann’s equations

Geophysics ◽  
1999 ◽  
Vol 64 (5) ◽  
pp. 1627-1629 ◽  
Author(s):  
James G. Berryman
Keyword(s):  
Shear Modulus ◽  
Seismic Data ◽  
Fluid Migration ◽  
Fluid Substitution ◽  
Correct Interpretation ◽  
Velocity Data ◽  
Basic Assumptions ◽  
Fluid Properties ◽  
Quantitative Understanding ◽  
Undrained Conditions

Gassmann’s relations are receiving more attention as seismic data are increasingly used for reservoir monitoring. Correct interpretation of underground fluid migration from seismic data requires a quantitative understanding of the relationships among the velocity data and fluid properties in the form of fluid substitution formulas, and these formulas are very commonly based on Gassmann’s equations. Nevertheless, confusion persists about the basic assumptions and the derivation of Gassmann’s (1951) well‐known equation in poroelasticity relating dry or drained bulk elastic constants to those for fluid‐saturated and undrained conditions. It is frequently stated, for example, but quite incorrect to say that Gassmann assumes the shear modulus is constant (i.e., mechanically independent of the presence of the saturating fluid). This note clarifies the situation by presenting an unusually brief derivation of Gassmann’s relations that emphasizes the true origin of the constant shear modulus result, while also clarifying the role played by the shear modulus in the derivation of the better understood result for the bulk modulus.

Implementation Of Interval Velocity Data In The Analysis Of Vertical Fluid Migration Routes And Charging Offshore Qatar

2014 ◽  
Author(s):  
K. J. Andresen ◽  
A. Uldall ◽  
M. Hertle ◽  
L. Madsen ◽  
C. Perrin ◽  
...  
Keyword(s):  
Fluid Migration ◽  
Velocity Data ◽  
Migration Routes ◽  
Interval Velocity

Elastic inverse scattering for fluid variation with time-lapse seismic data

Geophysics ◽  
2015 ◽  
Vol 80 (2) ◽  
pp. WA61-WA67 ◽  
Author(s):  
Zhaoyun Zong ◽  
Xingyao Yin ◽  
Guochen Wu ◽  
Zhiping Wu
Keyword(s):  
Shear Modulus ◽  
Inverse Scattering ◽  
Seismic Data ◽  
Scattering Theory ◽  
Time Lapse ◽  
Monitoring Data ◽  
Prestack Inversion ◽  
Fluid Factor ◽  
Reference Medium ◽  
The Difference

Elastic inverse-scattering theory has been extended for fluid discrimination using the time-lapse seismic data. The fluid factor, shear modulus, and density are used to parameterize the reference medium and the monitoring medium, and the fluid factor works as the hydrocarbon indicator. The baseline medium is, in the conception of elastic scattering theory, the reference medium, and the monitoring medium is corresponding to the perturbed medium. The difference in the earth properties between the monitoring medium and the baseline medium is taken as the variation in the properties between the reference medium and perturbed medium. The baseline and monitoring data correspond to the background wavefields and measured full fields, respectively. And the variation between the baseline data and monitoring data is taken as the scattered wavefields. Under the above hypothesis, we derived a linearized and qualitative approximation of the reflectivity variation in terms of the changes of fluid factor, shear modulus, and density with the perturbation theory. Incorporating the effect of the wavelet into the reflectivity approximation as the forward solver, we determined a practical prestack inversion approach in a Bayesian scheme to estimate the fluid factor, shear modulus, and density changes directly with the time-lapse seismic data. We evaluated the examples revealing that the proposed approach rendered the estimation of the fluid factor, shear modulus, and density changes stably, even with moderate noise.

Exact equations for fluid and solid substitution

Geophysics ◽  
2014 ◽  
Vol 79 (3) ◽  
pp. L21-L32 ◽  
Author(s):  
Nishank Saxena ◽  
Gary Mavko
Keyword(s):  
Shear Stress ◽  
Shear Modulus ◽  
Bulk Modulus ◽  
Fluid Substitution ◽  
Pore Shape ◽  
Effective Shear Modulus ◽  
Stiffness Measurement ◽  
Saturated Rock ◽  
Mean Stresses

We derived exact equations, elastic bulk and shear, for fluid and solid substitution in monomineralic isotropic rocks of arbitrary pore shape and suggested methods to obtain the required substitution parameters. We proved that the classical Gassmann’s bulk modulus equation for fluid-to-fluid substitution is exact for solid-to-solid substitution if compression-induced mean stresses (pressure) in initial and final pore solids are homogeneous and either the shear modulus of the substituted solid does not change or no shear stress is induced in pores. Moreover, when compression-induced mean stresses in initial and final pore solids are homogeneous, we evaluated exact generalizations of Gassmann’s bulk modulus equation, which depend on usually known parameters. For the effective shear modulus, we found general exactness conditions of Gassmann and other approximations. Using the new exact substitution equations, we interpreted that predicting solid-filled rock stiffness from a dry rock stiffness measurement requires more information (i.e., assumptions about the pore shape) compared to predicting the same from a fluid-saturated rock stiffness.

THE INTEGRATED USE OF PETROPHYSICAL, AVO, SEISMIC INVERSION AND 3D VISUALISATION TOOLS FOR RESERVOIR CHARACTERISATION

2001 ◽  
Vol 41 (2) ◽  
pp. 131
Author(s):  
A.G. Sena ◽  
T.M. Smith
Keyword(s):  
Seismic Data ◽  
New Technology ◽  
Seismic Inversion ◽  
Well Log ◽  
Reservoir Properties ◽  
Gas Field ◽  
Geological Interpretation ◽  
3D Visualisation ◽  
Quantitative Understanding ◽  
Inversion Techniques

The successful exploration for new reservoirs in mature areas, as well as the optimal development of existing fields, requires the integration of unconventional geological and geophysical techniques. In particular, the calibration of 3D seismic data to well log information is crucial to obtain a quantitative understanding of reservoir properties. The advent of new technology for prestack seismic data analysis and 3D visualisation has resulted in improved fluid and lithology predictions prior to expensive drilling. Increased reservoir resolution has been achieved by combining seismic inversion with AVO analysis to minimise exploration risk.In this paper we present an integrated and systematic approach to prospect evaluation in an oil/gas field. We will show how petrophysical analysis of well log data can be used as a feasibility tool to determine the fluid and lithology discrimination capabilities of AVO and inversion techniques. Then, a description of effective AVO and prestack inversion tools for reservoir property quantification will be discussed. Finally, the incorporation of the geological interpretation and the use of 3D visualisation will be presented as a key integration tool for the discovery of new plays.

Seafloor pockmarks on the Chatham Rise, New Zealand: Possible causes and links to glacial cycles.

2020 ◽  
Author(s):  
Ingo Pecher ◽  
Bryan Davy ◽  
Jess Hillman ◽  
Lowell Stott ◽  
Richard Coffin ◽  
...  
Keyword(s):  
New Zealand ◽  
Seismic Data ◽  
Fluid Migration ◽  
Glacial Cycles ◽  
Open Questions ◽  
Glacial Stage ◽  
Alternative Hypotheses ◽  
Deep Sources ◽  
Water Depths ◽  
The Last Glacial

<p>An area of the seafloor of >50,000 km<sup>2</sup> on the Chatham Rise and Bounty Trough east of New Zealand’s South Island is covered by seafloor depressions.  Distribution and type of these depressions seem to be bathymetrically controlled, with smaller depressions occurring between ~500-700 m water depth and larger ones in water depths of >800 m.  Formation of these features is enigmatic.  The smaller features display typical features of pockmarks caused by sudden escape of fluids and gas.  Echosounder and seismic data furthermore reveal wide-spread buried pockmarks that appear to have been formed repeatedly near glacial-stage maxima.  Some of the buried pockmarks appear to be stacked, often at a slight offset, underlain by positive-polarity reflections, and aligned with structures that promote fluid escape.  These patterns are compatible with repeated release of fluids from deep sources and precipitation of authigenic material.  Some of the larger seafloor depressions appear to involve interaction with the Southland Current.  These depressions have been interpreted as contouritic mounds although alternative hypotheses have been proposed and they may be linked to deeply rooted fluid migration.</p><p>Pronounced Δ<sup>14</sup>C anomalies during the last glacial termination, around the time of formation of the most recent pockmarks, indicate release of significant amounts of geologic carbon.  The pockmark fields coincide with the extent of the flat-subducted Hikurangi Plateau.  We hypothesize formation of the pockmarks is linked to repeated release of CO<sub>2</sub> that originates from carbonates on top of the Hikurangi Plateau.  We will discuss this hypothesis, open questions in particular related to the “valve” mechanism controlling repeated release and pockmark formation, as well as alternative mechanisms for possible formation of seafloor depressions in the study area.</p>

scholarly journals AVO analysis for high amplitude anomalies using 2D pre-stack seismic data

2022 ◽  
Author(s):  
Lamees N. Abdulkareem ◽  
Keyword(s):  
Seismic Data ◽  
High Amplitude ◽  
Rock Properties ◽  
Fluid Substitution ◽  
Amplitude Variation ◽  
Amplitude Variation With Offset ◽  
The Real ◽  
North West ◽  
Avo Analysis ◽  
Controlling Parameter

Amplitude variation with offset (AVO) analysis is an 1 efficient tool for hydrocarbon detection and identification of elastic rock properties and fluid types. It has been applied in the present study using reprocessed pre-stack 2D seismic data (1992, Caulerpa) from north-west of the Bonaparte Basin, Australia. The AVO response along the 2D pre-stack seismic data in the Laminaria High NW shelf of Australia was also investigated. Three hypotheses were suggested to investigate the AVO behaviour of the amplitude anomalies in which three different factors; fluid substitution, porosity and thickness (Wedge model) were tested. The AVO models with the synthetic gathers were analysed using log information to find which of these is the controlling parameter on the AVO analysis. AVO cross plots from the real pre-stack seismic data reveal AVO class IV (showing a negative intercept decreasing with offset). This result matches our modelled result of fluid substitution for the seismic synthetics. It is concluded that fluid substitution is the controlling parameter on the AVO analysis and therefore, the high amplitude anomaly on the seabed and the target horizon 9 is the result of changing the fluid content and the lithology along the target horizons. While changing the porosity has little effect on the amplitude variation with offset within the AVO cross plot. Finally, results from the wedge models show that a small change of thickness causes a change in the amplitude; however, this change in thickness gives a different AVO characteristic and a mismatch with the AVO result of the real 2D pre-stack seismic data. Therefore, a constant thin layer with changing fluids is more likely to be the cause of the high amplitude anomalies.

scholarly journals Controls of Deep-Seated Faults and Folds on Hydrocarbon Fluid Migration and Accumulation in Sedimentary Basins: A Case Study from the Northwestern Sichuan Basin, China

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-15
Author(s):  
Xi Wang ◽  
Yin Liu ◽  
Jian Cao ◽  
Yiduo Liu ◽  
Bing Luo ◽  
...  
Keyword(s):  
Seismic Data ◽  
Sichuan Basin ◽  
Horizontal Direction ◽  
Late Triassic ◽  
Fluid Migration ◽  
Thrust Faults ◽  
Hydrocarbon Accumulation ◽  
3D Seismic ◽  
Thrust Sheets ◽  
3D Seismic Data

Deep-seated faults and folds of foreland basin systems have become important exploration targets in the recent years because they are crucial in controlling fluid migration and hydrocarbon accumulation. In this study, we analyzed the characteristics and formation history of these structures in the northwestern Sichuan Basin using recently acquired two-dimensional (2D) and three-dimensional (3D) seismic data. The seismic interpretation revealed that the thrust sheets, tectonic wedges, and foredeep were well developed in the northwestern Sichuan Basin from the mountain to the basin. Forward thrusts, fault-bend folds, and wedges are the main types of structures in the thrust sheets and tectonic wedges. The deep-seated faults and folds were easily recognized in the high-resolution 3D seismic data. The imbricate thrust faults that merged into detachment layers of the Lower Cambrian are the main types of structures in the foredeep, and they show a prominent strike-slip influence in the horizontal direction. The formation of these structures in the foredeep in the northwestern Sichuan Basin mainly endured two stages of thrusting, including those during the Middle-to-Late Triassic and Cenozoic. Based on the tectonic evolution and seismic data, we infer that these deep-seated faults and folds in the foredeep may have formed earlier than the northern Longmen Shan fold-and-thrust belts and they may have been initially active in the late of Early Triassic and reactive during the Cenozoic. Furthermore, evaporites in the Lower and Middle Triassic were crucial in forming these structures. The petroleum exploration data suggested that the deep-seated faults can facilitate hydrocarbon accumulation. The thrust faults in the foredeep were more likely to act as migration pathways for fluids instead of sealing barriers along the horizontal direction. The interconnected reservoirs of deep-seated folds possess a great potential to allow large-scale hydrocarbon accumulation. Our study provides a good example for evaluating the hydrocarbon exploration potential in the deeply buried area in the sedimentary basin.

Sign in / Sign up

Export Citation Format

Share Document