Seismic imaging methods applied to Devonian carbonate reef enviroments of Western Canada

Burton, Andrew Joseph (1998) Seismic imaging methods applied to Devonian carbonate reef enviroments of Western Canada. Masters thesis, Memorial University of Newfoundland.

[English] PDF (Migrated (PDF/A Conversion) from original format: (application/pdf)) - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. Download (19MB) [English] PDF - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. (Original Version)

Abstract

A surface seismic profiling (SSP) reflection survey from south-central Alberta in Western Canada is reprocessed with the intent of differentiating between on-reef reservoir and off-reef non-reservoir rocks of the Devonian Nisku Formation. The associated seismic resolution is fundamentally low due to large seismic wavelength, thin reservoir formation, and large target depth. The reservoir response is also weak relative to strong impedance contrasts associated with the overlying clastic-carbonate-evaporitic stratigraphy. Hence, the reservoir identification component of seismic interpretation is based largely on subtle changes in the data character and event timing. For such an evaporation play, where geology is conformable to the method, conventional common midpoint (CMP) processing objectives include obtaining the maximum frequency bandwidth and true relative amplitude (TRA) in a surface consistent manner. However, since the primary indicators can be distorted by near-coincident multiple reflections generated by mechanisms that may vary laterally in timing and magnitude, it is necessary to distinguish between primary and multiple arrivals based on a combination of indicators including differential moveout, predictability, comparison with well log synthetics, and evaluation of vertical seismic profiles (VSP). The nature of the multiple determines whether conventional SSP methods can be adapted to multiple suppression, but existing techniques have been less than successful in the identification and/or suppression of significant multiples without compromising Nisku target response. The basis of this thesis research is to review CMP methods as applied to a particular Nisku SSP response, and to determine whether a practical solution to the multiple problem can be reached by integrating log and VSP wellbore data with SSP data. Because constraints on multiple energy are realisable when VSP data are incorporated, and since the available well control coincides closely with the SSP data, VSP analysis and multiple reflectivity inversion are considered as design criteria for an adaptive approach to multiple identification and suppression. -- The methodology employed in this analysis of Nisku reflectivity involves application of basic rime-sequence analysis tools and standard seismic processing tools as related to seismic wave propagation within a layered earth. It will be shown that multiple energy can be identified in SSP data using hyperbolic semblance velocity analysis, range-limited stacks, and trace autocorrelations. Further, it will be shown that VSP data can be used to identify the same multiple energy and also to identify the mechanism responsible for the multiple reflection. For this particular Nisku study, the conventional methods of multiple suppression by prediction and moveout discrimination are evaluated along with an adaptation of a least squares inversion method. All methods face limited success due to the nature of the multiple contamination, but the overall analysis complements Nisku interpretation and thereby improves likelihood of drilling success.

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