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GoNorton, Jeannemarie (Battelle - Oak Ridge Operations) | Beard, Les (Battelle - Oak Ridge Operations) | Gamey, Jeffrey (Battelle - Oak Ridge Operations) | Doll, William (Battelle - Oak Ridge Operations) | Sheehan, Jacob (Battelle - Oak Ridge Operations)

In January 2008, low-altitude (~1-3 meters above ground level) airborne geophysical surveys were carried out at the Marine Corps Air Ground Combat Center (MCAGCC), near Twentynine Palms, California. The primary goal of the surveys was to assess the viability of airborne magnetic or electromagnetic geophysical surveys at MCAGCC for detection and mapping of unexploded munitions. Due to high magnetic content in the rocks and soils at MCAGCC magnetic methods had been shown in the past to have limited usefulness. The background magnetic conditions made this site a good candidate for the use of a new 8- channel Time-domain Electromagnetic system (TEM8) developed by Battelle. The first phase of the project was an assessment of the efficacy of TEM8 and vertical magnetic gradient (VG-22) technologies, based on results from surveys of two 8 hectare areas and a 2 hectare geophysical prove out (GPO) area. This demonstration showed that both VG-22 and TEM8 were useful at this site, but the combination of the two datasets is more effective than either dataset used singularly for target prioritization.

amplitude, anomaly, area, background, dataset, detection, Figure, formation evaluation, Frag, gradient, item, method, pick, positive, Prioritization, reference, seg las vegas, site, survey, system, value

SPE Disciplines:

We present a 2-D frequency-domain elastic full-waveform inversion algorithm based on a forward problem solved with a frequency-domain parsimonious P0 finite-volume method. A preconditioned conjugate gradient method allows the reconstruction of elastic parameters for various acquisition configurations. Solving many times the forward problem is required in the main steps of the inversion algorithm. In the frequency domain, the forward problem reduces to the resolution of a huge and sparse linear system which is efficiently performed with a massively parallel direct solver. The designed algorithm is validated with three simple synthetic examples for the reconstruction of both P and S wave velocities from vertical and horizontal particle velocities in regular equilateral triangular meshes.

Quantitative seismic imaging of elastic parameters is one of the main challenge of geophysical exploration at different scales (subsurface, oil exploration, crustal and lithospheric investigations). Frequency-domain full-waveform inversion (FWI) (Pratt and Worthington, 1990; Pratt et al., 1996, 1998) allows to build accurate velocity models of complex structures from long offset acquisition geometries using only few discrete frequencies thanks to the wavenumber redundancy provided by multi-aperture geometries. Moreover, proceeding sequentially from the low frequencies to the high ones defines a multiresolution imaging strategy which helps to fulfill the assumptions underlying local optimization approaches. Applications to real data using the acoustic approximation for 2D geometries have been performed with success for imaging complex structures (Ravaut et al., 2004; Operto et al., 2006), while the reconstruction of elastic parameters has been found to be a quite challenging problem (Gelis et al., 2007) mainly due to the high numerical cost of the forward problem. Recently, a 2D parsimonious P0 Finite Volume (FV) method has been proposed by Brossier et al. (2007) for accurate and efficient elastic wave modeling on triangular meshes. Accurate modeling of wave propagation for complicated topographies is achieved for a discretization of 15 triangular cells per minimum wavelength which leads to significant memory and CPU-time savings compared to that required by O(?x^2) Finite Difference (FD) methods. In this study, we present a massively parallel frequency-domain FWI algorithm for imaging 2D elastic parameters based on the P0 FV forward problem and solved using a massively parallel direct solver. The algorithm is validated with three simple synthetic examples.

The LU factorization, although memory demanding, allows to solve efficiently thousands of forward problems since the factorization is independent of the right-hand side source terms in the equation 2. In this study, we used the massively parallel direct solver MUMPS which has been developed for distributedmemory platform (Amestoy et al., 2006).

The inverse problem is solved with a standard weighted leastsquares preconditioned conjugate gradient method (Tarantola, 1987) for elastic parameters reconstruction. The Born approxi- mation is used for computing the gradient of the objective function while the full solution of the forward problem is recomputed at each iteration of the inverse problem using the FV method in a way similar to the FD method proposed by Gelis et al. (2007).

SPE Disciplines: Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (1.00)

This paper aims at clarifying the true nature of AVO gradient and the root of its ability as a DHI. It is demonstrated that coefficient B in R(θ)≈A+Bsin2θ may not always be an acceptable approximation to the gradient of amplitude variation with offset (or, in otherwords, with incidence angles). With large offset data being included in AVO inversion, the so-called AVO gradient estimated on basis of the three-term approximation cannot be the coefficient B defined by Shuey in equation (3). Nor can it be the gradient of amplitude versus sin2θ. It is a mixture of coefficient B and the term C(2tg2θ+tg4θ).

The root of ability of the AVO gradient as a DHI might be buried in AVO inversion practice where large offset data are included into the inversion. Such ability and the success of AVO technique might mainly depend upon the degree of approximation of the estimated AVO gradient to the Poisson reflectivity defined by Verm and Hilterman (1995).

amplitude, approximation, AVO, AVO gradient, AVO inversion, AVO technique, coefficient, data, equation, Figure, gradient, incidence angle, inversion, reflection, reflectivity, Shuey, sin, term

SPE Disciplines: Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (0.70)

The accurate delineation of the continental-oceanic boundary (COB) is important for deep-water petroleum exploration at passive continental margins. Integrated analysis of the satellite-derived gravity and airborne magnetic fields reveals distinct anomalous signatures that are characteristic of the oceanic and rifted-continental types of the Earth''s crust. Different signatures of the gravity and magnetic anomalies, displayed as changes in amplitude, wavelength and spatial arrangement, originate from differences in density, magnetization, depth and structural deformation of rock complexes composing these crustal types. Calculation of horizontal gradients of the isostatic gravity and downward-continued aeromagnetic fields provides the most efficient enhancement and visualization of changes in anomalous signatures of the enhanced gravity and magnetic fields on both sides of the COB. Integration of the aeromagnetic and satellite-derived gravity data provides complementary evidences for reliable and accurate interpretation of the COB location.

anomaly, basement, boundary, COB, crust, data, difference, downhole intervention, field, Figure, gradient, gravity, Horizontal Gradient, interpretation, lateral, margin, origin, production enhancement, Signature, West Africa

SPE Disciplines: Reservoir Description and Dynamics > Reservoir Characterization > Exploration, development, structural geology (0.66)

Seismic attributes are derived from seismic records, and many seismic attributes can find counterparts in gravity and magnetic transformations. In this work, I explain some quantities computed from seismic, gravity and magnetic data that use the same mathematics but may bear different names. In particular, I compare the development history and physical meaning of (a) the complex trace attributes of seismic data and the complex analytic signal of gravity and magnetics and (b) the seismic dip and azimuth and the horizontal gravity gradient vector. I also show differences of the curvature attributes in applications to seismic and gravity and magnetic data. Such comparisons may be beneficial to the use and further development of seismic attributes and gravity and magnetic transformations.

Oilfield Places:

- North America > United States > New Mexico > San Juan Basin (0.99)
- North America > United States > Colorado > San Juan Basin (0.99)

SPE Disciplines: Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (1.00)

**Summary**

We investigate optimal sensor configurations of total-field magnetic surveys for near-surface applications such as unexploded ordnance detection. Vertical gradient configurations are often used because they effectively remove longer wavelength cultural or geological features and attenuate coherent noise. However, they also result in additional attenuation from the signals of interest. Using survey design techniques we demonstrate that a vertical gradient configuration is inferior to a configuration with all the sensors at the same level and with half the sensor spacing. This result is consistent with potential field theory where knowledge of the field at one elevation can be used to predict the field anywhere above that layer. The coherent noise suppression advantage of the vertical gradient can be achieved using a reference sensor which is ideally placed closer to the dominant noise source. We demonstrate the survey design techniques and results on low-level unexploded ordnance detection from a helicopter.

configuration, design, dipole, Figure, gradient, helicopter, layer, magnetometer, measurement, model parameter, noise, optimal, parameter, quality, reference, sensor, survey, survey quality, variance

SPE Disciplines: Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (0.56)

This paper investigates the use of spectral decomposition for extracting information on fluid properties. Traditional theory for detecting fluid response is based on the pure elastic Gassman theory, and the resultant seismic effects are frequency-independent. Using dynamic fluid substitution, we demonstrate that the frequency response of seismic reflection and its resultant attenuation and dispersion are directly linked to fluid saturation. To extract this information, we develop an accurate two-stage spectral decomposition method by matching pursuit. This allows us to calculate a range of frequency-dependent attributes, such as, absorption coefficient and amplitude gradient in the frequency domain. Application to real data shows a good link between the anomalies and hydrocarbon saturation. The results highlight that careful data processing and modeling are necessary to understand the complex effect of different fluids on the spectral response and enable robust interpretation.

SPE Disciplines: Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (1.00)

We consider the linearized constant density viscoacoustic wave equation, which involves simultaneous inversion both for velocity and attenuation contrasts or perturbations. The medium parameters can be characterized by a complex-valued velocity that includes wave speed as well as attenuation. The least-squares error measures the squared norm of the difference between modeled and observed data. Its gradient with respect to the medium parameters represents a migration image. We can use a gradient-based minimization algorithm to invert for the model parameters. Convergence rates will improve by using a suitable preconditioner, which usually is some approximation of the Hessian. For the linearized, constant density viscoacoustic wave equation we derive an exact Hessian that differs from the more conventional Hessian by including the complex-valued part. For the inverse problem, we consider a single point scatterer and investigate the one-dimensional vertical line as preconditioner. We observe that this preconditioner improves the convergence and accuracy. However, the question remains if the suggested preconditioner is feasible, since computing and inverting it is computationally costly.

SPE Disciplines: Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (0.70)

Candidate time-lapse down-hole gravity measurands are compared for monitoring water front advancements at the inter-well scale. The ability to sense small temporal changes to already minimal density contrasts presented by typical OWC problems drives performance requirements of new down-hole technology being developed by Lockheed Martin (

The question naturally arises regarding which component of gravity is best observed, as the miniature interferometric device can be configured to sense one of several gravity components. The concept of measuring differential gravity is introduced and simulated data are compared to respective inline and cross gravity gradients.

Distributed density contrasts associated with gradual water saturation changes due to homogeneous sweep show 50 m advancement increments are observable beginning at 200 m proximity to monitoring wells if differential gravity is measured to 1 ?Gal. Likewise, a change from ideal sweep to breakout is observed at 130 m proximity. Corresponding sub-Etövös-level inline and cross gradient signals are deemed unobservable.

The differential gravity measurement is nominally drift-free and immune to invaded zone irregularities, so can be collected as part of a periodic wireline service without undue concern regarding accurate downhole replacement. Permanent emplacement in i-fields is also possible. By virtue of common mode rejection, differential gravity surveys are also free of the multiple environmental corrections typically required of surface micro-gravity acquisitions (

Advancement, change, cross gradient, differential gravity, downhole intervention, Figure, formation evaluation, gradient, gravity, gravity sensor, inline, location, measurement, production control, production enhancement, production monitoring, proximity, reference, reservoir, survey, water, well logging

Oilfield Places:

- Asia > Middle East > Saudi Arabia > Ghawar Oil Field (0.99)
- North America > United States > Alaska > North Slope > Prudhoe Bay Oil Field (0.98)
- Europe > United Kingdom > North Sea (0.98)
- (3 more...)

SPE Disciplines: Reservoir Description and Dynamics > Formation Evaluation & Management > Open hole/cased hole log analysis (1.00)

An inversion methodology for marine controlled-source electromagnetic (MCSEM) data with approximate Hessianbased optimization and a fast finite-difference time-domain forward operator is presented. Using data from a synthetic hydrocarbon reservoir, we demonstrate that models are reproduced with a spatial resolution determined by the skin depth of the frequencies included in the inversion. Both single and multiple resistive bodies can be resolved in the subsurface. Using reciprocal treatment and multiple frequencies at each receiver position, the comprehensive inversion sequence of a typical MCSEM survey, which should match the acquired data to within the measurement error, executes within ~100 iterations, with about 30 iterations per day, requiring at most a few hundred nodes on a parallel cluster.

approximate hessian-based optimization, Artificial Intelligence, fast finite-difference time-domain, finite-difference time-domain forward code, formation evaluation, forward, geophysics, gradient, gradient calculation, inversion, iteration, marine csem, misfit, model, position, receiver, Reservoir Characterization, reservoir description and dynamics, shallow subsurface, source, structural geology, survey, th annual international, Upstream Oil & Gas

SPE Disciplines:

Thank you!