Benjamin Roure

Azimuthai simultaneous elastic inversion for fracture detection

Azimuthal AVO has proved to be useful to predict fractures. However, there are a number of limitations with the technique including the fact that only band limited fractional elastic parameters are estimated. Further, the method is derived for the case of an isotropic over HTI anisotropic half-space. It is not theoretically valid for the case of two anisotropic half-spaces. In order to overcome these limitations this paper develops and demonstrates a new (patent pending) azimuthal simultaneous elastic inversion. Azimuthand angle-limited seismic traces are modeled using the anisotropic Zoeppritz equation to generate equivalent reflectivity volumes which are then convolved with appropriate user defined wavelets, generating 3D volumes of the fracture parameters. HTI anisotropy, the lowest symmetry which describes fractures, is used in this implementation. Alternative parameterizations using rock physics models are examined to reduce and constrain the parameterization. The algorithm is demonstrated on both synthetic and real seismic data with good results.

Interpreting azimuthal Fourier coefficients for anisotropic and fracture parameters

AbstractAmplitude 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 m...

Global 4-D Seismic Inversion And Time-lapse Fluid Classification

Independent inversion of base and monitor seismic surveys can yield estimates of elastic properties that are inconsistent with expected production effects. We therefore propose a global time-lapse inversion scheme, involving joint inversion of base and monitor data. All vintages and input angle stacks are combined in a single objective function, which is optimized using simulated annealing to estimate the time-variant distribution of elastic attributes that best matches all available data. The multi-vintage nature of the optimization allows us to incorporate flexible, user-defined rock physics constraints on the evolution of Vp, Vs and density between consecutive surveys. There are no restrictions on the number of input angle stacks or number of monitor surveys. The constrained, global inversion solution can therefore be easily updated as new data become available. We apply the global 4-D inversion with rock physics coupling to data from the Brage Field and compare results with a workflow involving separate inversions of base and monitor data. The global 4-D inversion results are combined with a time-lapse Bayesian fluid classification scheme to map production-induced fluid movements and quantify associated uncertainty.

Fracture Characterization by Seismic Anisotropy Analysis at Awali Anticline Structure Bahrain: Case Study

The Amplitude Versus Azimuthal AVAZ analysis has proved to be an important tool for characterizing fracture distributions and orientations of hydrocarbon reservoirs. This paper is aiming at the application of this tool for characterizing the fractures in Bahrain field reservoirs. Better understanding of faults and fractures distribution is essential to optimize EOR strategy and reservoir management. Regional analysis is possible by looking at faults distribution characterized by structural attributes analysis validated by regional stress and geological information. The investigation at local scale is more cumbersome but an Amplitude Variation with Azimuth (AVAz) method based on azimuthal Fourier Coefficients (FCs) proves to be a simple and powerful tool to characterize fractures distribution validated by FMI data. The anisotropy information was then used to update and improve the reservoir model long production history matching.