Schlumberger

Technical Paper: Delineation of Karsts, a New Approach using Seismic Attributes – Case Study from Kuwait

Society: SEG
Paper Number: 927
Presentation Date: 2013
 

Abstract

The karsted limestone of the Cretaceous Shuaiba formation in Kuwait represents a major challenge seismic imaging as well as drilling. The heterogeneity of the eroded limestone results in strong lateral velocity variations that distort the deeper seismic image and affect porosity estimates for the Minagish Oolite reservoirs. These reservoirs make up 80% of the hydrocarbon production from the Minagish field. The conventional approach using prestack time migration (PSTM) and prestack depth migration (PSDM) results in a strong reflection at the top of the Shuaiba, but without details of internal structure within this 100 m thick layer. The detailed structure of the karst features at the surface and inside the Shuaiba limestone was picked and inserted manually. The resulting velocity model was used to reprocess the seismic cube. The result of this method showed that the effect of the Shuaiba heterogeneities could not be removed. This paper outlines the challenges, and a new approach using a combination of seismic attributes to extract the Shuaiba limestone and the karst features. The resulting model of the Shuaiba porous layer appears to be geologically more meaningful. In parallel, a revised PSDM workflow was tested, and points towards an integrated workflow for future enhancements.

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