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Downton J.E.,CGG Geosoftware | Roure B.,CGG GeoConsulting
Interpretation | Year: 2015

Amplitude variation with offset and azimuth (AVOAz) analysis can be separated into two separate parts: amplitude variation with offset (AVO) analysis and amplitude variation with azimuth (AVAz) analysis. Useful information about fractures and anisotropy can be obtained just by examining the AVAz. The AVAz can be described as a sum of sinusoids of different periodicities, each characterized by its magnitude and phase. This sum is mathematically equivalent to a Fourier series, and hence the coefficients describing the AVAz response are azimuthal Fourier coefficients (FCs). This FC parameterization is purely descriptive. The aim of this paper is to help the interpreter understand what these coefficients mean in terms of anisotropic and fracture parameters for the case of P-wave reflectivity using a linearized approximation. The FC representation is valid for general anisotropy. However, to gain insight into the significance of FCs, more restrictive assumptions about the anisotropy or facture system must be assumed. In the case of transverse isotropic media with a horizontal axis of symmetry, the P-wave reflectivity linearized approximation may be rewritten in terms of azimuthal FCs with the magnitude and phase of the different FCs corresponding to traditional AVAz attributes. Linear slip theory is used to show that the FCs can be interpreted similarly for the cases of a single set of parallel vertical fractures in isotropic media and in transverse isotropic media with a vertical axis of symmetry (VTI). The magnitude of the FCs depends on the fracture weakness parameters and the background media. For the case of vertical fractures in a VTI background, the AVOAz inverse problem is underdetermined, so extra information must be incorporated to determine how the weights are modified due to this background anisotropy. We evaluated this on a 3D data set from northwest Louisiana for which the main target was the Haynesville shale. © 2015 Society of Exploration Geophysicists and American Association of Petroleum Geologists. Source


Wang H.,CGG GeoConsulting | Titchmarsh H.J.,CGG GeoConsulting | Chesser K.,CGG GeoConsulting | Zawila J.,SM Energy | And 5 more authors.
Society of Petroleum Engineers - Unconventional Resources Technology Conference, URTeC 2015 | Year: 2015

The application of horizontal drilling and multi-stage hydraulic fracturing has boosted economic recoveries from unconventional reservoirs. Applying this technology requires proper placement of horizontal wells combined with hydraulic stimulation to create fractures extending from the horizontal wellbore. The economics of unconventional plays can be improved if horizontal wellbores target facies with favorable reservoir and geomechanical properties. An integrated, multi-disciplinary approach has been developed in order to reduce economic risk, facilitate improved and faster decision making and enable more efficient and effective well placement. Subsurface volumes of lithofacies, reservoir rock properties and geomechanical properties, all of which honor data from multiple disciplines, provided the means to generate lithology and property maps, including Phi-H, together with associated measurements of uncertainty for selected facies and properties. This seismically-constrained geomodeling approach enabled optimum identification of sweet spots for reservoir development and well placement. The methodology demonstrates the value of incorporating stratigraphic, geological, petrophysical, engineering and geophysical data into an integrated subsurface reservoir model. Copyright 2015, Unconventional Resources Technology Conference. Source


Gentilhomme T.,CNRS Georesources lab | Oliver D.S.,University of Bergen | Mannseth T.,University of Bergen | Caumon G.,CNRS Georesources lab | And 2 more authors.
Computational Geosciences | Year: 2015

Ensemble-based optimization methods are of- ten efficiently applied to history-matching problems. Although satisfactory matches can be obtained, the updated realizations, affected by spurious correlations, generally fail to preserve prior information when using a small ensemble, even when localization is applied. In this work, we propose a multi-scale approach based on grid-adaptive second-generation wavelets. These wavelets can be applied on irregular reservoir grids of any dimensions containing dead or flat cells. The proposed method starts by modifying a few low frequency parameters (coarse scales) and then progressively allows more important updates on a limited number of sensitive parameters of higher resolution (fine scales). The Levenberg-Marquardt ensemble randomized maximum likelihood (LM-enRML) is used as optimization method with a new space-frequency distance-based localization of the Kalman gain, specifically designed for the multi-scale scheme. The algorithm is evaluated on two test cases. The first test is a 2D synthetic case in which several inversions are run using independent ensembles. The second test is the Brugge benchmark case with 10 years of history. The efficiency and quality of results of the multi-scale approach are compared with the grid-block-based LM-enRML with distance-based localization. We observe that the final realizations better preserve the spatial contrasts of the prior models and are less noisy than the realizations updated using a standard grid-block method, while matching the production data equally well. © 2015, Springer International Publishing Switzerland. Source

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