Ioan Sturzu

Diffraction imaging of the Eagle Ford shale

Diffraction imaging is a novel technology that uses diffractions to image very small subsurface elements. Diffraction imaging may: (1) improve prospect characterization and pre-drill assessment of the local geology; (2) improve production and recovery efficiency; (3) reduce field development cost; and (4) decrease environmental impact. Field development may be accomplished with fewer wells to optimally produce the reservoir using high-resolution images of small-scale fractures in shale or carbonate intervals. Standard approaches to obtain high-resolution information, such as coherency analysis and structure-oriented filters, derive attributes from stacked, migrated images. Diffraction imaging, in comparison, acts on the pre-stack data, and has the potential to focus super-resolution structural information. Diffraction images can be used as a complement to the structural images produced by conventional reflection imaging techniques, by emphasizing small-scale structural elements that are difficult to interpret on a conventional depth image. An efficient way to obtain diffraction images is to first separate the migration events according to the value of the specularity angle, in a similar way to offset gathers, and subsequent post-stack processing. The high-resolution potential is demonstrated by the diffraction images from the Kenedy 3D survey over the Eagle Ford shale, which show much more detail than conventional depth migration or coherence.

Diffraction imaging in fractured carbonates and unconventional shales

Diffraction imaging is recognized as a new approach to image small-scale fractures in shale and carbonate reservoirs. By identifying the areas with increased natural fracture density, reservoir engineers can design an optimal well placement program that targets the sweet spots (areas with increased production), and minimizes the total number of wells used for a prospective area. High-resolution imaging of the small-scale fractures in shale reservoirs such as Eagle Ford, Bakken, Utica, and Woodbine in the US, and Horn River, Montney, and Utica in Canada improves the prospect characterization and predrill assessment of the geologic conditions, improves the production and recovery efficiency, reduces field development cost, and decreases the environmental impact of developing the field by using fewer wells to optimally produce the reservoir. We evaluated several field data examples using a method of obtaining images of diffractors using specularity filtering that could be performed in depth and time migration. Provided that a good migration velocity was available, we used the deviation of ray scattering from Snell’s law to attenuate reflection energy in the migrated image. The resulting diffraction images reveal much of the structural detail that was previously obscured by reflection energy.

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.

Interpretation value of diffractions and sub-specular reflections – applications on the Zhao Dong field

We provide an overview of integrated pre-stack depth migration and diffraction imaging for the Zhao Dong field, Bohai Bay, China. This field is highly compartmentalized by complex faulting and further characterized by channel systems, fractures and volcanic features. The objective of the diffraction imaging is to better define these small-scale features. Tools to facilitate interpretation include displays with pre-stack depth migration and diffraction images overlain in different colour scales, as well as a weighted blending of them into a single volume. An important concept is that of the sub-specular reflection, which is obtained alongside the pure diffraction image by applying ultra-weak specularity tapers. Tuning properties of elementary diffractor images together with sub-specular reflectors provide a decisive uplift of diffraction imaging for the interpreter.