Constantine Tsingas

Diffraction imaging as an interpretation tool

In naturally fractured reservoirs, detailed mapping and understanding of the subsurface fracture network is necessary to optimize field development. There are a variety of seismically driven technologies for mapping and detecting fracture zones. For example, by investigating seismic anisotropy one can hope to obtain preferential fracture orientation. Moreover, by generating and extracting volume and/or horizon-based attributes, potential fracture corridors can be identified and mapped. In this work we present an imaging technology that focuses diffraction energy produced by sharp discontinuities and at the same time suppresses specular reflection arrivals. The diffraction-enhanced seismic sections assist and contribute significantly in the interpretation and identification of small-scale faults and fractures, and they are used in addition to other derived post-stack attributes such as coherency and curvature cubes. We describe the diffraction imaging methodology and illustrate its application using synthetic and real data examples. We also show the ability of the technique to map fracture swarms by focusing the associated diffracted energy in the pre-stack time domain.

Depth processing; an example

The objective of velocity analysis procedures in depth processing is to construct an interval velocity model as a function of depth and a spatial coordinate. This model, consisting of the major velocity layers, is sometimes called a “macro velocity model.” The structure of the model also has geologic meaning; thus, velocity analysis is a highly interpretive process and requires knowledge of the area’s geology.

Fast Beam Migration using Plane Wave Destructor (PWD) Beam Forming

In some embodiments, input seismic data is decomposed into Gaussian beams using plane wave destructor (PWD) filters. The beams are used in a fast beam migration method to generate a seismic image of a subsurface volume of interest. PWD filters are applied to groups of neighboring traces to generate a field of dips/curvatures that fit the input trace data. Beam wavelets are then formed according to the dip/curvature field. Multiple dips (PWD slopes) may be determined at each location in time/space in order to handle intersecting reflection events. Exemplary methods allow an improvement in processing speed by more than an order of magnitude as compared to standard industry techniques such as Kirchhoff migration.

Fracture Detection by Diffraction Imaging

The main objective of imaging diffracted arrivals is to produce high resolution seismic sections in time or depth, which in turn will enhance the interpretation of fault edges, pinchouts, reef edges, fracture zones and other geologic discontinuities. In naturally fractured reservoirs a detailed understanding and mapping of the subsurface fracture network is often necessary to optimize field development plans. There is a variety of seismic driven technologies that attempt to map and detect fracture zones. For example, by analyzing seismic anisotropy one can obtain preferential fracture orientation, generating volume and/or horizon based extracted attributes potential fracture corridors can be identified and mapped.In the following we illustrate the methodology for imaging discontinuities, which enables us to obtain high resolution fracture maps. We then present, using synthetic and real data examples the ability of the methodology to map fracture corridors by focusing the associated scattering energy in the prestack domain and conclude by highlighting the benefits of the application on land seismic data (i.e., sparse acquisition and low signal to noise ratio). Complementing one another, the diffraction image sections should be interpreted in conjunction with the conventional reflection time migrated results.

Diffraction Imaging as an Interpretation Tool

The main objective of imaging diffracted arrivals is to produce high resolution seismic sections in time or depth, which in turn will enhance the interpretation of fault edges, pinchouts, reef edges, fracture zones and other geological discontinuities. The accurate identification of these geological discontinuities plays an important role in the final interpretation of these features and their associated contribution in the formation of potential hydrocarbon traps. The seismic responses of these structural features can be observed in the diffracted part of the recorded wavefield. In the following we present, using real data examples the ability of the methodology to map fracture corridors and subtle geological discontinuities by focusing the associated scattering energy in the prestack domain. Finally, we conclude by highlighting the benefits of the application on land seismic data (i.e., sparse acquisition and low signal to noise ratio). The obtained diffraction image sections are interpreted in conjunction with the conventional reflection time migrated results and coherence type attributes.

Directional-oriented wavefield imaging: a new wave-based subsurface illumination imaging condition for reverse time migration

ABSTRACT The key objective of an imaging algorithm is to produce accurate and high‐resolution images of the subsurface geology. However, significant wavefield distortions occur due to wave propagation through complex structures and irregular acquisition geometries causing uneven wavefield illumination at the target. Therefore, conventional imaging conditions are unable to correctly compensate for variable illumination effects. We propose a generalised wave‐based imaging condition, which incorporates a weighting function based on energy illumination at each subsurface reflection and azimuth angles. Our proposed imaging kernel, named as the directional‐oriented wavefield imaging, compensates for illumination effects produced by possible surface obstructions during acquisition, sparse geometries employed in the field, and complex velocity models. An integral part of the directional‐oriented wavefield imaging condition is a methodology for applying down‐going/up‐going wavefield decomposition to both source and receiver extrapolated wavefields. This type of wavefield decomposition eliminates low‐frequency artefacts and scattering noise caused by the two‐way wave equation and can facilitate the robust estimation for energy fluxes of wavefields required for the seismic illumination analysis. Then, based on the estimation of the respective wavefield propagation vectors and associated directions, we evaluate the illumination energy for each subsurface location as a function of image depth point and subsurface azimuth and reflection angles. Thus, the final directional‐oriented wavefield imaging kernel is a cross‐correlation of the decomposed source and receiver wavefields weighted by the illuminated energy estimated at each depth location. The application of the directional‐oriented wavefield imaging condition can be employed during the generation of both depth‐stacked images and azimuth–reflection angle‐domain common image gathers. Numerical examples using synthetic and real data demonstrate that the new imaging condition can properly image complex wave paths and produce high‐fidelity depth sections.

Broadband Acquisition, Deblending and Imaging Employing Dispersed Source Arrays

During the last few years the importance of recording, processing and interpreting a wider range of frequencies has been highlighted with numerous field acquisition examples and case studies. A great effort has been dedicated in the recording of low as well as high frequencies for obtaining high resolution images. The ability to reduce the seismic wavelet’s side lobes by recording lower frequencies and at the same time the increase of bandwidth has been proven as the main advantage of recording broadband data. The land seismic data used in this paper was acquired in Saudi Arabia by using an acquisition configuration based on a variation of the dispersed source arrays concept (Berkhout, 2012). During this seismic experiment we were sweeping three different frequency bands, namely, 1.5 to 8 Hz, 6.5 to 54 Hz and 50 to 87 Hz and with various sweep lengths, (Kim and Tsingas, 2014). In order to increase productivity the data were continuously recorded in a blended mode. In this study we outline a novel seismic acquisition survey which aimed for the optimum and efficient recording of broadband data without sacrificing data quality and we demonstrate the methodology employed for optimum broadband processing in terms of deblending, Full Waveform Inversion (FWI) and Reverse Time Migration (RTM) technologies.

A Synthetic Simultaneous Source Wide-azimuth Acquisitions Study over a Complex Marine Environment

Marine blended source acquisition is becoming increasingly important in the seismic industry due to the possibility of reducing costs through higher productivity and improving seismic data quality through denser source sampling. One major drawback of marine blended acquisition is the crosstalk noise generated by the nearly simultaneous firing of the source arrays. It is essential to understand the characteristics of this type of noise interference and identify proper acquisition techniques and processing workflows to reduce its effects on image quality. We start by 3D finite difference modelling of a complex subsurface. We then combine the synthetic shots to simulate a four boat, wide azimuth (WAZ) marine seismic survey comprised of two streamer vessels with sources, and two additional source vessels located between the streamer spreads and off the tails of the streamers. All four sources fire nearly simultaneously with a randomized time lag of up to 500 milliseconds between sources. Overall, the gain from near-simultaneous source firing versus a conventional four-vessel WAZ marine design is an increase of approximately 2.67 times in terms of both source density and fold. This type of blended acquisition survey can also be acquired in about the same amount of acquisition time as a conventional four vessel WAZ survey. In general, most of the processing techniques for the simultaneous source blended data rely on the fact that crosstalk noise exhibits coherency in the shot domain, but appears random when viewed in a different data domain such as common channel, offset and midpoint domains. A number of processing techniques are applied in order to optimally deblend the data. These techniques are tested in several different domains and also in a cascaded manner. The results and effectiveness of each technique is evaluated and compared against the original non-blended synthetic data. Direct comparisons between the processed blended data and the single source non-blended data reveal comparable seismic images in both the prestack and post-stack domains.

Farcture Mapping by Diffraction Imaging

The main objective of imaging diffracted arrivals is to produce high resolution seismic sections in time or depth, which in turn will enhance the interpretation of fault edges, pinchouts, reef edges, fracture zones and other geologic discontinuities. In naturally fractured reservoirs a detailed understanding and mapping of the subsurface fracture network is often necessary to optimize field development plans. There is a variety of seismic driven technologies that attempt to map and detect fracture zones. For example, by analyzing seismic anisotropy one can obtain preferential fracture orientation, generating volume and/or horizon based extracted attributes potential fracture corridors can be identified and mapped. For the past two decades numerous authors (Landa et al., 1987, Kanasewich and Phadke, 1988, Khaidukov et al., 2004, Fomel et al., 2007, Moser and Howard, 2008 and Reshef and Landa, 2008) have conducted research on diffraction imaging and its associated super-resolution, post-stack velocity analysis in the dip-angle domain and separating and focusing only diffracted energy. All of the above methodologies aim first to differentiate reflections from diffractions and second to obtain higher resolution seismic images by imaging, primarily, diffracted arrivals.

Seismic Simultaneous Sources in Land: Challenges and Opportunities

essing of this optimally designed seismic blended dataset without applying any deblending algorithm produces satisfactory results. To improve the prestack analysis such as first break picking, noise removal and velocity analysis, deblending methodologies and workflows were also applied. In this paper, we present processing results related to land simultaneous sources acquisition. Novel deblending schemes will be shown along with their effectiveness in a production environment. Statics, surface consistency, noise attenuation and velocity estimation are seen as the main challenges for the processing of land blended data. Current processing schemes rely mostly on deblending so that conventional workflows can be subsequently employed for data analysis. Full blended data processing in land is still an open issue. Current practice dictates that we have to have well in advance nearsurface and velocity macromodels in order to proceed. Migration will do the rest. The real question therefore is: a) Do we develop tools to fully process blended data? or b) Do we develop effective deblending algorithms & proceed in a conventional manner? We all know the answer…it can be found in the middle!!! Of course everything starts with acquisition…do we play the game safe and acquire optimally distance-separated data or go wild and acquire data in a random fashion? Processing now becomes the key. In short, seismic acquisition and processing must be considered simultaneously!!