Towards a Unified Imaging Procedure for 2-D Land Multichannel Seismic Data

Authors: Jaiswal, Priyank, Zelt, C.A., Rice University, and Dasgupta, R., Oil India Limited

Venue: 70th EAGE Conference and Exhibition, Rome, Italy, June 11-14, 2008 (http://www.eage.org/events/index.php?eventid=57&Opendivs=s2 [external site).

Abstract: This project demonstrates that imaging of 2-D multichannel seismic data can be effectively accomplished by a combination of travel-time inversion and pre-stack depth migration (PSDM); this combined method is referred to as unified imaging. Unified imaging begins with inversion of direct arrivals for estimating a velocity model that is used in static corrections and stacking velocity analysis. The interval velocity model (from stacking velocities) is used for PSDM. The stacked data and the PSDM image are interpreted for common horizons and the corresponding wide-aperture reflections are identified in the shot gathers. Using the interval velocity model the stack interpretations are inverted as zero-offset reflections for constraining the corresponding interfaces in depth; the interval velocity model is maintained stationary. A coefficient of congruence, j, is defined which measures the discrepancy between the horizons from the PSDM image and their counterparts from the zero-offset inversion. A value of unity for j implies that the interpreted and inverted horizons are consistent to within the interpretational uncertainties and the unified imaging is said to have converged at this point. For j greater than unity, the interval velocity model and the horizon depths are updated by jointly inverting the direct arrivals with the zero-offset and the wide-aperture reflections. The updated interval velocity model is used again for both PSDM and zero-offset inversion. Interpretations of the new PSDM image are the updated horizons depths. The unified imaging is applied to seismic data from the Naga Thrust and Fold Belt, India. Wide-aperture and zero-offset data from three geologically significant horizons are used. Three runs of joint inversion and PSDM are required in a cyclic manner for j to converge to unity. A joint interpretation of the final velocity model and the final depth image reveal the presence of a triangle zone that appears to be promising for exploration.

Related NETL Project
This presentation is related to the NETL project DE-FC26-06NT42960, “Detection and Production of Methane Hydrate.” The objective of this effort is to better understand regional differences in gas hydrate systems from the perspective of an energy resource, geo-hazard, and long-term climate influence. Specifically, the effort will: (1) collect data and conceptual models that targets causes of gas hydrate variance, (2) construct numerical models that explain and predict regional-scale gas hydrate differences in 2- and 3-dimensions with minimal "free parameters", (3) simulate hydrocarbon production from various gas hydrate systems to establish promising resource characteristics, (4) perturb different gas hydrate systems to assess potential impacts of hot fluids on seafloor stability and well stability, and (5) develop geophysical approaches that enable remote quantification of gas hydrate heterogeneities so that they can be characterized with minimal costly drilling.

NETL Project Contacts
NETL – Rick Baker (richard.baker@netl.doe.gov or 304-285-4714)
Rice University – George Hirasaki (gjh@rice.edu or 713-348-5416)