Carbonate-Reservoir Characterization: Wide-Azimuth-Seismic Processing
Authors: Denney Dennis 
Published: February 2015

This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper SPE 162324, ’Wide-Azimuth-Seismic Processing for UAE-Carbonate-Reservoir Characterization,’ by Yoann Guilloux, Issam Tarrass, and Jean-Luc Boelle, Total; Evgeny Landa and Vadim Buzlukov, Opera; Abderrahim Lafram and Michel Radigon, CGGVeritas; and Mohamed Mahgoub, ADNOC, prepared for the 2012 Abu Dhabi International Petroleum Exhibition & Conference, Abu Dhabi, 11-14 November. The paper has not been peer reviewed.

This seismic study was performed on a seismic acquisition over a carbonate field in the UAE. One challenge was to reprocess these data ensuring that the azimuthal information was preserved properly all along the sequence. An additional challenge was related to the very shallow water environment that added complexity such as dispersive ground roll and water-layer-related guided waves, multiples that can be generated at the sea surface, seafloor, or internally near surface heterogeneities. Implementing multiazimuth diffraction imaging over this carbonate reservoir proved encouraging. Many detected features displayed geologically meaningful characteristics, some of which were not visible on conventional structural attributes.

Introduction

Hydrocarbon production from carbonate reservoirs can be improved greatly with a precise description of the internal heterogeneities such as fracture networks or vugs. Although well measurements and cores provide very precise information at specific locations, seismic interpretation is one of the main tools to help provide information between wells. The complete paper details an exhaustive seismic study performed on a subset of a wide-azimuth ocean-bottom-cable seismic acquisition over a carbonate field in the UAE.

Wide-Azimuth Processing

There were two main drivers of this processing.

To promote the use of the wide-azimuth tool, when available, to preserve the azimuthal information that is part of the useful signal (reflected-P-wave information). This preservation is required for techniques that use the seismic-azimuthal response for describing internal properties of reservoirs (e.g., fractures).

To avoid the use of random-noise-attenuation techniques to filter noise. Model-based noise attenuation is preferred, to avoid possible oversmoothing of the seismic data that could destroy potentially usable information for describing reservoir heterogeneity.

Some important processing steps were not reported in this work because no novel technique was used; in particular, the compensation of near-surface effects (i.e., time shift and amplitude) is not mentioned although it is recognized as a fundamental issue. Processing efforts in this domain were based on a conventional approach.

Acquisition and Data Quality. This processing test was conducted on a subset of the ocean-bottom-cable acquisition over a UAE carbonate field. Water depth ranged from 4 to 23 m. There were three receiver cables laid in a snake pattern, and a shoot-six-while-rolling-three operation mode was used. Nominal receiver-line separation was 225 m, and receiver spacing was 25 m. Sources of 1,760  in.3 at 5 m and 1,180 in. 3 at 3 m were used in a single-source mode with an 18.75-m shot-point interval. The source sail-line separation was 400 m (interleaving resulted in final shot-line spacing of 200 m). The source sail direction was orthogonal to the receiver-line direction.