scholarly journals Quantitative seismic characterization of CO2 at the Sleipner storage site, North Sea

2017 ◽  
Vol 5 (4) ◽  
pp. SS23-SS42 ◽  
Author(s):  
Bastien Dupuy ◽  
Anouar Romdhane ◽  
Peder Eliasson ◽  
Etor Querendez ◽  
Hong Yan ◽  
...  
Keyword(s):  
High Resolution ◽  
Wave Velocity ◽  
Rock Physics ◽  
Joint Estimation ◽  
P Wave ◽  
Storage Site ◽  
Seismic Waveform ◽  
P Wave Velocity ◽  
Seismic Characterization

Reliable quantification of carbon dioxide ([Formula: see text]) properties and saturation is crucial in the monitoring of [Formula: see text] underground storage projects. We have focused on quantitative seismic characterization of [Formula: see text] at the Sleipner storage pilot site. We evaluate a methodology combining high-resolution seismic waveform tomography, with uncertainty quantification and rock physics inversion. We use full-waveform inversion (FWI) to provide high-resolution estimates of P-wave velocity [Formula: see text] and perform an evaluation of the reliability of the derived model based on posterior covariance matrix analysis. To get realistic estimates of [Formula: see text] saturation, we implement advanced rock physics models taking into account effective fluid phase theory and patchy saturation. We determine through sensitivity tests that the estimation of [Formula: see text] saturation is possible even when using only the P-wave velocity as input. After a characterization of rock frame properties based on log data prior to the [Formula: see text] injection at Sleipner, we apply our two-step methodology. The FWI result provides clear indications of the injected [Formula: see text] plume being observed as low-velocity zones corresponding to thin [Formula: see text] filled layers. Several tests, varying the rock physics model and [Formula: see text] properties, are then performed to estimate [Formula: see text] saturation. The results suggest saturations reaching 30%–35% in the thin sand layers and up to 75% when patchy mixing is considered. We have carried out a joint estimation of saturation with distribution type and, even if the inversion is not well-constrained due to limited input data, we conclude that the [Formula: see text] has an intermediate pattern between uniform and patchy mixing, which leads to saturation levels of approximately [Formula: see text]. It is worth noting that the 2D section used in this work is located 533 m east of the injection point. We also conclude that the joint estimation of [Formula: see text] properties with saturation is not crucial and consequently that knowing the pressure and temperature state of the reservoir does not prevent reliable estimation of [Formula: see text] saturation.

scholarly journals P-wave velocity and density structure beneath Mt. Vesuvius: a magma body in the upper edifice?

2013 ◽  
Vol 56 (4) ◽  
Author(s):  
Paolo Capuano ◽  
Guido Russo ◽  
Roberto Scarpa
Keyword(s):  
High Resolution ◽  
Wave Velocity ◽  
Gravity Data ◽  
High Energy ◽  
P Wave ◽  
Gravity Inversion ◽  
Density Structure ◽  
Resolution Image ◽  
High Resolution Image ◽  
P Wave Velocity

<p>A high-resolution image of the compressional wave velocity and density structure in the shallow edifice of Mount Vesuvius has been derived from simultaneous inversion of travel times and hypocentral parameters of local earthquakes and from gravity inversion. The robustness of the tomography solution has been improved by adding to the earthquake data a set of land based shots, used for constraining the travel time residuals. The results give a high resolution image of the P-wave velocity structure with details down to 300-500 m. The relocated local seismicity appears to extend down to 5 km depth below the central crater, distributed into two clusters, and separated by an anomalously high Vp region positioned at around 1 km depth. A zone with high Vp/Vs ratio in the upper layers is interpreted as produced by the presence of intense fluid circulation alternatively to the interpretation in terms of a small magma chamber inferred by petrologic studies. In this shallower zone the seismicity has the minimum energy, whilst most of the high-energy quakes (up to Magnitude 3.6) occur in the cluster located at greater depth. The seismicity appears to be located along almost vertical cracks, delimited by a high velocity body located along past intrusive body, corresponding to remnants of Mt. Somma. In this framework a gravity data inversion has been performed to study the shallower part of the volcano. Gravity data have been inverted using a method suitable for the application to scattered data in presence of relevant topography based on a discretization of the investigated medium performed by establishing an approximation of the topography by a triangular mesh. The tomography results, the retrieved density distribution, and the pattern of relocated seismicity exclude the presence of significant shallow magma reservoirs close to the central conduit. These should be located at depth higher than that of the base of the hypocenter volume, as evidenced by previous studies.</p>

Elastic reflectivity vectors and the geometry of intercept-gradient crossplots

2019 ◽  
Vol 38 (10) ◽  
pp. 762-769
Author(s):  
Patrick Connolly
Keyword(s):  
Elastic Property ◽  
Elastic Properties ◽  
Wave Velocity ◽  
Seismic Data ◽  
Measurement Errors ◽  
Rock Physics ◽  
P Wave ◽  
S Wave ◽  
P Wave Velocity ◽  
Well Log Analysis

Reflectivities of elastic properties can be expressed as a sum of the reflectivities of P-wave velocity, S-wave velocity, and density, as can the amplitude-variation-with-offset (AVO) parameters, intercept, gradient, and curvature. This common format allows elastic property reflectivities to be expressed as a sum of AVO parameters. Most AVO studies are conducted using a two-term approximation, so it is helpful to reduce the three-term expressions for elastic reflectivities to two by assuming a relationship between P-wave velocity and density. Reduced to two AVO components, elastic property reflectivities can be represented as vectors on intercept-gradient crossplots. Normalizing the lengths of the vectors allows them to serve as basis vectors such that the position of any point in intercept-gradient space can be inferred directly from changes in elastic properties. This provides a direct link between properties commonly used in rock physics and attributes that can be measured from seismic data. The theory is best exploited by constructing new seismic data sets from combinations of intercept and gradient data at various projection angles. Elastic property reflectivity theory can be transferred to the impedance domain to aid in the analysis of well data to help inform the choice of projection angles. Because of the effects of gradient measurement errors, seismic projection angles are unlikely to be the same as theoretical angles or angles derived from well-log analysis, so seismic data will need to be scanned through a range of angles to find the optimum.

High-resolution three-term AVO inversion by means of a Trivariate Cauchy probability distribution

Geophysics ◽  
2011 ◽  
Vol 76 (3) ◽  
pp. R43-R55 ◽  
Author(s):  
Wubshet Alemie ◽  
Mauricio D. Sacchi
Keyword(s):  
High Resolution ◽  
Wave Velocity ◽  
P Wave ◽  
S Wave ◽  
Avo Inversion ◽  
P Wave Velocity ◽  
Multivariate Gaussian ◽  
Density Perturbations ◽  
Gaussian Prior ◽  
Scale Matrix

Three-term AVO inversion can be used to estimate P-wave velocity, S-wave velocity, and density perturbations from reflection seismic data. The density term, however, exhibits little sensitivity to amplitudes and, therefore, its inversion is unstable. One way to stabilize the density term is by including a scale matrix that provides correlation information between the three unknown AVO parameters. We investigate a Bayesian procedure to include sparsity and a scale matrix in the three-term AVO inversion problem. To this end, we model the prior distribution of the AVO parameters via a Trivariate Cauchy distribution. We found an iterative algorithm to solve the Bayesian inversion and, in addition, comparisons are provided with the classical inversion approach that uses a Multivariate Gaussian prior. It is important to point out that the Multivariate Gaussian prior allows us to include the correlation of the AVO parameters in the solution of the inverse problem. The Trivariate Cauchy prior not only permits us to incorporate correlation but also leads to high-resolution (broadband) P-wave velocity, S-wave velocity, and density perturbations.

Petrophysical, mineralogical, and P-wave velocity characterization of Albian carbonates from Campos Basin, Brazil

2013 ◽  
Author(s):  
Nathaly Archilha ◽  
Roseane Missàgia ◽  
Marco de Ceia ◽  
Irineu Lima Neto ◽  
Luan de Castro ◽  
...  
Keyword(s):  
Wave Velocity ◽  
P Wave ◽  
Campos Basin ◽  
P Wave Velocity

Laboratory characterization of coal P-wave velocity variation during adsorption of methane under tri-axial stress condition

Fuel ◽  
2020 ◽  
Vol 272 ◽  
pp. 117698
Author(s):  
Shuangjiang Zhu ◽  
Fubao Zhou ◽  
Jianhong Kang ◽  
Youpai Wang ◽  
Haijian Li ◽  
...  
Keyword(s):  
Wave Velocity ◽  
Stress Condition ◽  
Axial Stress ◽  
P Wave ◽  
Velocity Variation ◽  
Laboratory Characterization ◽  
P Wave Velocity ◽  
Adsorption Of Methane

Pyrolysis-induced P-wave velocity anisotropy in organic-rich shales

Geophysics ◽  
2014 ◽  
Vol 79 (2) ◽  
pp. D41-D53 ◽  
Author(s):  
Adam M. Allan ◽  
Tiziana Vanorio ◽  
Jeremy E. P. Dahl
Keyword(s):  
Wave Velocity ◽  
Elastic Anisotropy ◽  
Rock Physics ◽  
Confining Pressure ◽  
Source Rocks ◽  
Acoustic Properties ◽  
P Wave ◽  
Velocity Anisotropy ◽  
Geochemical Parameters ◽  
P Wave Velocity

The sources of elastic anisotropy in organic-rich shale and their relative contribution therein remain poorly understood in the rock-physics literature. Given the importance of organic-rich shale as source rocks and unconventional reservoirs, it is imperative that a thorough understanding of shale rock physics is developed. We made a first attempt at establishing cause-and-effect relationships between geochemical parameters and microstructure/rock physics as organic-rich shales thermally mature. To minimize auxiliary effects, e.g., mineralogical variations among samples, we studied the induced evolution of three pairs of vertical and horizontal shale plugs through dry pyrolysis experiments in lieu of traditional samples from a range of in situ thermal maturities. The sensitivity of P-wave velocity to pressure showed a significant increase post-pyrolysis indicating the development of considerable soft porosity, e.g., microcracks. Time-lapse, high-resolution backscattered electron-scanning electron microscope images complemented this analysis through the identification of extensive microcracking within and proximally to kerogen bodies. As a result of the extensive microcracking, the P-wave velocity anisotropy, as defined by the Thomsen parameter epsilon, increased by up to 0.60 at low confining pressures. Additionally, the degree of microcracking was shown to increase as a function of the hydrocarbon generative potential of each shale. At 50 MPa confining pressure, P-wave anisotropy values increased by 0.29–0.35 over those measured at the baseline — i.e., the immature window. The increase in anisotropy at high confining pressure may indicate a source of anisotropy in addition to microcracking — potentially clay mineralogical transformation or the development of intrinsic anisotropy in the organic matter through aromatization. Furthermore, the evolution of acoustic properties and microstructure upon further pyrolysis to the dry-gas window was shown to be negligible.

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