Anisotropic model building with wells and horizons: Gulf of Mexico case study comparing different approaches

Abstract

Anisotropic depth imaging with Vertical Transversely Isotropic (VTI) models has become dominant in the industry.However, anisotropic parameters for these models continue to be derived by very basic practices without use of tomography. Hanging a single profile of Thomsen parameters from the water bottom still remains the most common practice. In a simple structural setting, it is usually possible to focus the data and obtain a good image despite having a simple and unrealistic model for Thomsen parameters. However, depth positioning of such images is usually suboptimal. Better positioning requires more geologically plausible models. In addition, imaging in complex settings may require Tilted Transversely Isotropic (TTI) models. In this case study we construct several anisotropic models using approaches with increasing complexity and evaluate the model impact on image quality and ties to well data. We start with a "new default" model, where a single, smoothed, borehole-calibrated profile is hung from the water bottom, and then we progress to an "intermediate" model where a similar profile with more vertical details is propagated using major geological horizons. We finish with an "elaborate" model, where profiles from several wells are interpolated throughout the model using geologic horizons. We contrast all these models to an "old default" model derived without well calibration. We observe a generally steady improvement in well ties compared to the "old default" model, with the proportionally largest change coming from simple well calibration ("new default" model) and additional uplift coming from incorporating geologic horizons ("intermediate" model). Differences between "intermediate" and "elaborate" models are small, while switching to TTI models clearly helps resolve complex structures in dipping areas. IntroductionIt is well understood that seismic data do not constrain all parameters of an anisotropic velocity field. Therefore, Thomsen parameters are usually estimated from joint inversion of well and seismic data at borehole locations. Profiles derived at wells are extrapolated or interpolated throughout the volume and kept static; whereas, velocity is updated with tomography. It is a general expectation that more accurate and geologically plausible volumes of Thomsen parameters models may lead to better images and improved well ties. We apply different model building practices and quantify their impact on imaging and ties to well data.

Applications of deterministic and stochastic rock physics modelling to anisotropic velocity model building

“…3, we present the location of 18 wells in the Green Canyon (GC) area of the Gulf of Mexico (GoM). We are focusing on a study area that was investigated by Bakulin et al . (2010).…”

“…This method is 1D and assumes a vertical well and flat layers. It is important to note that this process does not provide a unique solution for ε and δ but it can be considered as a 'first look' at the anisotropy before invoking a more complicated tomographic approach such as the one suggested by Bakulin et al (2010b). In Fig.…”

“…Many authors have pointed out that many anisotropic models in depth can generate the same offset time‐domain response that is often used for seismic model analysis (Osypov et al . 2008; Bakulin et al . 2010).…”

Investigation of deep-water Gulf of Mexico subsalt imaging using anisotropic model, data set and RTM — Tempest

“…Using the new Tempest model, a synthetic data set was created to be used for (1) testing of wide-azimuth data processing such as 3D surface related multiple elimination (Dragoset et al, 2008) (2) testing of anisotropic model building techniques (Bakulin et al, 2010), and (3) testing of new depth-imaging techniques such as 3D anisotropic RTM.…”

“…few years. These include the recording of wide-azimuth marine data (Napier et al, 2010), the use of RTM (Baysal et al, 1983) as the leading tool for prestack depth-migration, a move from isotropic toanisotropic model building and depth-imaging (Bakulin et al, 2010), and the development and use of more sophisticated multiple elimination techniques (Dragoset et al, 2008). Today's processing of modern Gulf of Mexico seismic data uses mainly wide-azimuth data compared to processing of narrow-azimuth data in the past.…”