Seminars & Talks | Center for Energy & Geo Processing

Full waveform inversion (FWI) delivers high-resolution images of a subsurface medium model by minimizing iteratively the least-squares misfit between the observed and simulated seismic data. Due to the limited accuracy of the starting model and the inconsistency of the seismic waveform data, the FWI problem is inherently ill-posed, so that regularization techniques are typically applied to obtain better models. FWI is also a computationally expensive problem because modern seismic surveys cover very large areas of interest and collect massive volumes of data. The dimensionality of the problem and the heterogeneity of the medium both stress the need for faster algorithms and sparse regularization techniques to accelerate and improve imaging results.

This talk develops a compressive sensing approach for the FWI problem, where the sparsity of model perturbations is exploited within learned dictionaries. Based on stochastic approximations, the dictionaries are updated iteratively to adapt to dynamic model perturbations. Meanwhile, the dictionaries are kept orthonormal in order to maintain the corresponding transform in a fast and compact manner without introducing extra computational overhead to FWI. Such a sparsity regularization on model perturbations enables us to take randomly subsampled data for computation and thus significantly reduce the cost. Compared with other approaches that employ sparsity constraints in the fixed curvelet transform domain, our approach can achieve more robust inversion results with better model fit and visual quality.

Texture attributes for detecting salt bodies in seismic data

Texture-based methods have proven to be useful in the detection of salt bodies in seismic data. In this abstract, we present three computationally inexpensive texture attributes that strongly differentiate salt bodies from other geological formations. The proposed method combines the three texture attributes along with region boundary smoothing for delineating salt boundaries. Our first proposed attribute is directionality, which differentiates between regions where texture lacks any specific direction (potentially, salt) and areas with directional texture. The second attribute is the smoothness of texture, while the third is based on edge content. Our results show that the directionality attribute effectively detects salt bodies in all the seismic images used in testing. The other two attributes correct the false positives detected by the directionality. The overall results show that the proposed method can fairly detect salt regions when compared to manual interpretation.

Automatic fault surface detection by using 3D Hough transform

Detection of faults plays an important role in the characterization of reservoir regions. In this paper, we propose an automatic fault surface detection method using 3D Hough transform to improve the interpretation efficiency. We first highlight the likely fault points in seismic data by thresholding the corresponding discontinuity volumes. Then, we apply 3D Hough transform to detect the likely fault planes in seismic volumes. After filtering out the noisy planes, we apply the weighted plane fitting method to extract the smooth fault surfaces from the remaining fault planes. Experimental results show that the proposed method has the capability of detecting fault surfaces in real seismic data with high accuracy and fewer human interventions.

About the tutorial

We have come a long way since the first successful seismic survey that discovered oil field in Texas, USA in the year 1924. Seismic surveys can save oil companies hundreds of millions of dollars by giving precise information about the subsurface geological features. Marine Seismic surveys have been used for decades to assess the location and size of oil and gas deposits which are buried several kilometers deep beneath the ocean floor.Various types of techniques and equipment are used for seismic exploration in offshore. It depends upon the marine environment, geological objectives and financial consideration.

Tutorial Outline & Objective

The tutorial will cover the fundamentals of seismic wave generation and propagation, reflection of seismic waves, various techniques used in marine seismic data acquisition, design & operation of marine seismic source, design & functioning of seismic sensors, seismic data recording system, positioning & navigation and Geophysical & Operational challenges in offshore seismic surveys. At the end of the tutorial the participants should be able to understand different marine seismic survey techniques, their merits and demerits and their application in oil and gas exploration.

Who should attend ?

The tutorial is designed for non-geophysicists who wish to gain an overview of different kinds of equipment & techniques used in marine seismic survey for hydrocarbon exploration.

• Introduction to geophysics
• Seismic waves
• Propagation and interface effects
• Seismic signal and noise
• Seismic wavelets
• Seismic data acquisition
  • Equipment
  • 2D field procedures
  • 3D seismic exploration
  • Time-lapse (4D) seismic exploration