Interval Anisotropic Parameter Estimation Using Velocity-independent Layer Stripping
Moveout analysis of long-spread P-wave data is widely used to estimate the key time-processing parameter η in layered VTI media. Inversion for interval η values, however, suffers from instability caused by the tradeoff between the effective moveout parameters and by the subsequent error amplification during Dix-type layer stripping. Here, we propose an alternative approach to interval parameter estimation based on the velocity-independent layer-stripping method of Dewangan & Tsvankin (2006). This method makes it possible to compute the interval moveout in a layer of interest without knowledge of the medium parameters in the overburden. Then the interval traveltimes are inverted for the normal-moveout velocity (Vnmo) and η using the single-layer nonhyperbolic moveout equation. Thus, the layer stripping of η in the conventional method is replaced by the much more stable stripping of reflection traveltimes. We also develop the 3D version of the layer-stripping method and apply it to interval parameter estimation for orthorhombic media using wide-azimuth P-wave data. The superior accuracy and stability of our algorithm is illustrated on ray-traced synthetic data for typical layered VTI and orthorhombic models. Even small correlated noise in reflection traveltimes produces substantial distortions in the effective η, and for some models, even in the effective Vnmo. As a result, the inter val η values estimated by the conventional Dix-type method may be highly inaccurate. In contrast, the output of our layer-stripping algorithm proves to be insensitive to mild correlated traveltime errors. The algorithm is also tested on wide-azimuth P-wave reflection data recorded above a fractured reservoir at Rulison field in Colorado. The interval moveout parameters estimated by the velocity-independent layer stripping in the shale layer above the reservoir are more plausible and stable than those obtained by the Dix-type method.
Velocity analysis using nonhyperbolic moveout in transversely isotropic media
Transversely isotropy(TI) is a general kind of media. When the length of CMP is great larger then the depth of the reflector, the information included in the Time-Distance curve can be used to get the anisotropy parameters of the TI media. Several kinds of velocity with TI media are discussed. An anisotropy media model and an isotropy media model is tested for the double-parameter Velocity analysis.
Inversion of self-potential anomalies caused by 2D inclined sheets using neural networks
The modular neural network (MNN) inversion method has been used for inversion of self-potential (SP) data anomalies caused by 2D inclined sheets of infinite horizontal extent. The analysed parameters are the depth (h), the half-width (a), the inclination (α), the zero distance from the origin (xo) and the polarization amplitude (k). The MNN inversion has been first tested on a synthetic example and then applied to two field examples from the Surda area of Rakha mines, India, and Kalava fault zone, India. The effect of random noise has been studied, and the technique showed satisfactory results. The inversion results show good agreement with the measured field data compared with other inversion techniques in use.