Multiattribute Analysis of a Fractured-Vuggy Carbonate in the Tarim Basin

Abstract

The fractured-vuggy carbonate reservoirs characteristic of the Tarim Basin have become an important hydrocarbon objective over the past few years. The major carbonate platform, which was deposited during the Early Cambrian-Middle Ordovician, lie at a depth of more than 5000 m. When sea level dropped, the platform shelf was exposed giving rise to the formation of caves and sinkholes, both of which when filled with the appropriate material, form excellent hydrocarbon reservoirs. Karstification appears to be controlled by strike-slip faults, providing a conduit for deeper thermal fluids to further modify the reservoir, resulting in fractured, vuggy reservoir sweet spots. When zones of fractured, vuggy carbonates are significantly large, they appear as chaotic, high amplitude anomalies. Smaller zone often appears as a suite of aligned bright spots, often described as “a string of pearls” by seismic interpreters.

Interpretation of fractured, vuggy carbonates is critical to understand the storage and mobility of hydrocarbon fluids. While seismic attributes allow the identification of major faults, joints, and edges of karst collapse features, they are less effective in mapping the chaotic boundaries of the fractured, vuggy carbonates in the Tarim Basin. To address this issue, we have designed a workflow to highlight the chaotic seismic expression of the fractured, vuggy carbonate sweet spots. To construct an image of the structural framework, we apply a low-pass filter to an original seismic amplitude volume, which suppresses the high frequency signature internal to karst collapse, fault damage zone, and vuggy, fractured carbonate facies. Application of curvature and coherence to this low-pass filtered seismic amplitude volume provides images of the larger strike-slip faults, joints, and karst collapse feature edges. These discontinuity images are then further enhanced and skeletonized along structural dip, resulting in high lateral resolution discontinuity images. We compute texture attributes based on the Grey Level Co-occurrence Matrix (GLCM) that are sensitive to the interior of karst collapse, fault damage zones, and fractured, vuggy carbonates. These texture attributes are then used as input to modern probabilistic facies analysis software. The resulting clusters are then corendered with the skeletonized structural discontinuity images, linking the two together, and providing 3D images of the predicted facies geobodies within the proper structural context.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018