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## Publications

Publications (68)

Rock composition can be related to conventional well logs through theoretical equations and petrophysical endpoints. Multimineral analysis is a formation evaluation tool that uses inversions to quantify rock composition from well logs. However, because of data errors and the multivariate selection of petrophysical endpoints, solutions from the mult...

Multimineral log analysis is a quantitative formation evaluation tool for geological and petrophysical reservoir characterization. Rock composition can be estimated by solving equations that relate log measurements to the petrophysical endpoints of minerals and fluids. Due to errors in log data and uncertainties in petrophysical endpoints of consti...

We present a workflow to build permeability models for flow simulation in unconventional naturally fractured reservoirs constrained by 3D seismic, geologic data and concepts, geomechanics observations, and dynamic data. Joints and faults are modeled separately to account for their differences in scale and flow properties. Seismic-derived orientatio...

Modeling of rock types or facies in unconventional reservoirs presents numerous challenges that are not encountered in conventional reservoirs. Because the exploitation of unconventional reservoirs frequently relies on the use of large numbers of long, data-poor horizontal wells, routine tasks in conventional reservoirs, such as petrophysical analy...

We present in this paper a methodology to use prestack seismic inversion results to constrain facies modeling in unconventional reservoirs. The fact that the exploitation of unconventional reservoirs typically relies on the use of large numbers of long, closely spaced, data poor horizontal wells creates challenges in petrophysical analyses, rock ph...

This article describes a statistical methodology to estimate dominant fracture orientation and dispersion from seismically calculated 3D structural attributes. The orientation-dispersion parameter is a modified version of the circular variance that is independent of direction and can be used to compute the Fisher coefficient, a key parameter in the...

URTeC 1581308
This paper describes a statistical methodology to estimate dominant fracture orientation and dispersion from seismically-calculated 3D structural attributes. The dispersion parameter, the circular variance, can be easily associated with the Fisher coefficient, a key parameter in the probability density function used in discrete fractu...

Among all possible rock properties, reservoir engineers reserve the distinguished title of "reservoir properties" to pore volume, fluid type, and connectivity because of their direct impact in the economics of hydrocarbon reservoirs. In some reservoirs, engineers may be able to alter the original in-situ properties by applying additional processes...

The idea of monitoring our reservoirs spatially in three dimensions with discrete snapshots (time-lapse measurements) along the production (or injection) time axis is extremely compelling but of course, as we have found, it is not as straightforward as one might initially anticipate. However, by persevering we have noted a long list of direct and i...

The use of seismic anisotropy is a topic that has evolved dramatically in the last 25 years in the oil and gas industry. Even though physicists who study waves and vibrations in solids have taught us that elastic properties of rocks should be described by a complex set of functions and parameters, many years of seismic data processing were conducte...

Crossplots are commonly used in the geosciences to gain qualitative insight about relationships between different variables, typically three (for two-dimensional colored crossplots). On rare occasions, the relationships among four variables are explored by using three-dimensional colored crossplots. The variable used to color the crossplot is usual...

As geoscientists and engineers started realizing that more oil and gas could be squeezed out of existing reservoirs, awareness about characterizing the reservoirs grew, gradually at first and rapidly later. Apparently, the three main reasons that led to the development of reservoir characterization can be listed as follows:

Reverse time migration (RTM) received its name because its inventors were literally running the time axis of their modeling programs backward and computationally sending waves back into a model of the Earth to make images. By extrapolating waves in time, rather than along the vertical direction, waves could go all directions rather than just within...

Summary Impedance creates a simple quantitative tie between seismic and well log data. Researchers generated some useful models and trends to also qualify these ties. After all, seismic impedance estimation is an interpretation instrument with a wide area of coverage. In this research we investigate one of the methods for impedance estimation. The...

Reservoir modeling is recognized as the construction of a 3D numerical representation of the hydrocarbon reservoir, in depth, comprising the reservoir structure (e.g., as delimited by stratigraphic horizons and faults); internal architecture (e.g., depositional facies); petrophysical properties (e.g., porosity, permeability); and fluid distribution...

A study was conducted to demonstrate the generation of facies probabilities from seismic data. It was demonstrated that crossplotting was a simple and powerful tool to examine the relations between two different variables, data series, logs, or seismic attributes. A colored crossplot helped in deciding whether a particular combination of seismic at...

The Rocky Mountain hydrocarbon province accounts for a large percentage of the natural gas reserves of North America. However, oil and gas exploration and development in this region has been challenging due to high topography and rough terrain for acquiring seismic data combined with structural complexity, which includes large thrust faults and hig...

The reason why acoustic and shear impedances inverted from seismic data have become popular seismic attributes is because, unlike other attributes, they can also be easily estimated at log scale. Log-scale impedances are easier to interpret because at log scale we have additional information that provides more insight about reservoir properties, an...

Oil and gas exploration and production in Latin America has come a long way since Standard Oil initiated operations in Lake Maracaibo, Venezuela, more than 100 years ago. From a few dominant players during most of the first 80 years of activities - mainly Mexico and Venezuela - the last 30 years have witnessed a diversification of producers that ha...

Time-lapse VP/VS volumes have been estimated in order to enhance the dynamic characterization of the tightgas sandstone reservoirs in Rulison Field, Western Colorado. Based on compressional (PP) as well as fast-(S11) and slow (S22) shear datasets from 4D-9C surveys, the Vp/Vs volumes were generated after cross-equalization, post-stack inversion and...

In the regions of complex geology such as Rulison field, Colorado incorporation of additional tools is required for reservoir characterization, monitoring and production enhancement. Such a tool is Vp/Vs extracted directly from seismic. We have developed and tested an algorithm, which will ensure correct and detailed Vp/Vs ratios, extracted from mu...

3D PS-converted waves in land data from a carbonate reservoir southeast of Venezuela were analyzed using examples of geometric attributes. Focus was on seismic coherence and principal component analysis. Coherence results were obtained from semblance and principal component estimates. Analysis of results showed that structural attributes derived fr...

In many practical situations when the objective is to differentiate between high and low gas concentrations, using P-to-P (PP) seismic data alone may not be enough to successfully complete the task. The abrupt reduction in P-wave velocity (V=P) with the first few percent of gas controls the seismic response. Therefore, usually only the presence of...

We consider the problem of characterizing the lithology of a reservoir using gamma ray logs as well as seismic traces around the well. We first calculate the continuous-wavelet transform of the the data and then use the fact that the energy of such transformation is proportional to a power of its scale. The technique consists in estimating the powe...

We consider the problem of characterizing the lithology of a reservoir using gamma ray logs as well as seismic traces around the well. We first calculate the continuous wavelet transform of the the data and then use the fact that the energy of such transformation is proportional to a power of its scale. The technique consists in estimating the powe...

The 2000 SEG/EAGE Summer Research Workshop drew a large proportion of participants from contracting firms (Figure 1a). The affiliation of first authors was also largely from contractors (Figure 1b), with the remainder of participants and first authors being evenly distributed between oil companies and academia. If these statistics can be taken as a...

For eight years now, there has been significant effort in Venezuela to record, process, and interpret multicomponent seismic data. This paper discusses the main results of three projects aimed mainly to help other studies in fracture, lithology, and heavy oil characterization in different types of geologic environments.

Ninety-nine professionals, the majority of whom have significant experience with shear waves, gathered in October 2000 at the SEG-EAGE Summer Research Workshop in Boise, Idaho, U.S. The 63 papers presented raised many hotly debated technical issues. More general issues also emerged during the discussions: What is the application domain of a technol...

We present the problem of tracing rays in 2D and 3D heterogeneous isotropic media as a set of optimization problems. Each optimization problem is obtained by applying Fermat's principle to an approximation of the travel time equation from a fixed source to a fixed receiver. We assume a piecewise linear ray path that simplifies the computations of t...

We present the problem of tracing rays in 2D and 3D heterogeneous isotropic media as a set of optimization problems. Each optimization problem is obtained by applying Fermat's principle to an approximation of the travel time equation from a fixed source to a fixed receiver. We assume a piecewise linear raypath which simplifies the computations of t...

Estimation of petrophysical properties of rocks from seismic attributes plays a very important role in defining reserv oir models for reservoir characterization and simulation. How ever,some degree of uncertainty is alw ays related to such propert yestimates. This w ork presents a nonlinear analysis technique, based on artificial neural netw orks,f...

We combine various methods to estimate fracture orientation in a carbonate reservoir located in southwest Venezuela. The methods we apply include the 2-D rotation analysis of 2-D P-S data along three different azimuths, amplitude-variation-with-offset (AVO) of 2-D P-wave data along the same three azimuths, normal-moveout (NMO) analysis of the same...

An account is given on some of the issues addressed by the Rio '99 Technical Program. The topics covered include the evolution of the Brazilian continental margin, the multidisciplinary approach taken by an oil company in evaluating several offerings for a period of four months, the challenges of seismic acquisition in the extreme conditions of the...

The authors performed extensive modeling studies to evaluate P-S converted waves effectiveness and limitations in the estimation of both cracks orientation and density. The target area is a fractured, carbonate reservoir located in south-west Venezuela. The reservoir depth is on the order of 3000 m, which implies that high quality P-S data are need...

In this paper, we introduce a fast and simple method to estimate petrophysical properties from well information and two dimensional seismic attributes. The method generalizes the well known linear regression techniques where the reservoir properties are obtained as linear combination of seismic attributes. The estimates are obtained after solving a...

A new method to combine information from various seismic attribute maps is presented. It compares the response about some points of interest with attribute response in the rest of the area studied. Method consists of three steps. First, control points are selected and grouped in different classes. Second, similarity maps related to each class are c...

This paper in troduces an ellipsoidal appro ximation of
phase and group velocities of the P-, S1- and S2-w ave
propagation modes in an orthorhombic media and, show
how to estimate elastic constan tsfrom these velocities.
The procedure is basically tw o-fold. First, w e estimate
seven ellipsoidal velocities near the vertical symmetry
axis whic h rep...

This Paper introduces an ellipsoidal approximation of group velocities for -P -S1 and -S2 modes in an elliptical approximation near the vertical axes of symmetry.
Visualization of the three modes are given and compared with the exact 3D modes.
http://www.earthdoc.org/publication/publicationdetails/?publication=61100

Although there is not a unique approach to understand the meaning of seismic attributes, they are becoming a widespread tool in reservoir characterization. In areas where very little petrophysical and production information is available, seismic attributes can play an important role in identifying new prospects and reducing exploratory risks. We pr...

The elastic constants that control the P and SV propagation in trasverse isotropic elastic media are calculated using the Muir-Dellinger approximation whic is a generalization of the Levin elliptic approximation

P-S converted waves are a cost effective alternative in delineating fracture strike, density, and lateral extent. This is because P-S converted waves are: 1) generated with a compressional source, 2) less labor intensive, 3) expected to contain the same information as S-waves, and 4) more practical in 3-D surveys. Through careful survey design/aqui...

The procedure to estimate elastic constants of a transversely isotropic medium from limited-aperture traveltimes has two steps. First, P- and SV-wave traveltimes are fitted with elliptical velocity functions around one of the axes of symmetry. Second, the parameters that describe the elliptical velocity functions are transformed analytically into e...

The elastic constants that control P‐ and SV‐wave propagation in a transversely isotropic media can be estimated by using P‐ and SV‐wave traveltimes from either crosswell or VSP geometries. The procedure consists of two steps. First, elliptical velocity models are used to fit the traveltimes near one axis. The result is four elliptical parameters t...

Singular value decomposition (SVD) is performed on the matrices that result in tomographic velocity estimation from cross-well traveltimes in isotropic and anisotropic media. The slowness model is parameterized in four ways: One-dimensional (1-D) isotropic, 1-D anisotropic, two-dimensional (2-D) isotropic, and 2-D anisotropic. The singular value di...

The inversion proposed in this paper is a simple extension of well-known isotropic schemes and it is conceptually identical for all wave types. Examples are shown to ilustrate the application of the technique to cross-well synthetic and field P-wave data. The examples demonstrate three important points: 1) when velocity anisotropy is estimated by i...

The estimation of velocity anisotropy in heterogeneous media can aid the
solution of imaging and interpretation problems. It can aid imaging
because when anisotropy is properly considered, events can be focused in
the correct place with the correct velocity without the well known
distortions obtained when using isotropic velocities in anisotropic
e...

As discussed in Part I of this paper, we believe it is often useful to model the elastic properties of reservoir and associated rocks as anisotropic, and, in particular, we have argued in favor of a monoclinic model with horizontal symmetry plane. For simplicity, we choose a subset model for this paper, transversely isotropic with vertical symmetry...

Traditionally in the problem of tomographic traveltime inversion, the model is divided into a number of rectangular cells of constant slowness. Inversion consists of finding these constant values using the measured traveltimes. The inversion process can demand a large computational effort if a high‐resolution result is desired. We show how to use a...