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Identification and Characterization of Paleo-Karsts within Deep-Buried Carbonates in Central Tarim Basin, Previous HitChinaNext Hit: Constraints Previous HitfromNext Hit Integrated Previous Hit3-DNext Hit Previous HitSeismicNext Hit Records

Yu, Jingbo; Li, Zhong

Carbonate reservoirs related to early karstification are well-developed in Ordovician System in the central Tarim basin, Northwest Previous HitChinaNext Hit. Stratigraphic framework and potential paleo-karsts of these carbonates, however, were not clearly revealed in past studies due to deep-burying, few drilling Previous HitdataNext Hit, and low resolution Previous HitseismicNext Hit profiles of weak amplitude, low signal-to-noise ratio and poor continuous reflections.

In this research, firstly, structure-oriented filtering which smooth Previous HitseismicNext Hit Previous HitdataNext Hit parallel to reflections was employed to highly improve the Previous Hit3-DNext Hit Previous HitseismicNext Hit Previous HitdataNext Hit quality. Then, stratigraphic framework of the deep buried carbonates was established through Previous HitseismicNext Hit interpretation. Secondly, the distribution of paleo-karsts within this stratigraphic framework was determined Previous HitfromNext Hit integrated Previous Hit3-DNext Hit Previous HitseismicNext Hit records. Two methods were presented to identify the distinct reflection characteristics of paleo-karsts. For large preserved karst caves characterized by bead-like Previous HitseismicNext Hit anomaly, a typical waveform was extracted Previous HitfromNext Hit the records and used to calculate similarities between the waveform and the other trace records through a running window. Then an index PCI (Preserved Cave Index) was introduced for recording the maximum similarity value of the trace. If PCI is greater than a certain threshold value (70%), it can be identified as a preserved karst cave. For collapsed caves or a group of small karst caves characterized by clutter reflection, the index PCI is invalid. So another index CCI (Collapsed Cave Index) was introduced for quantifying the variability of the reflection orientations. CCI is the sum of vector products of each unit vector parallel to reflections with the unit vector of average reflection orientation within a window. The large value of CCI denotes collapsed caves or a group of small karst caves. According to drilling Previous HitdataNext Hit, more than 90% of the wells confirmed the calculated distribution of the paleo-karsts.

Based on this study, deep-buried carbonates in central Tarim basin were divided into three segments Previous HitfromNext Hit northwest to southeast. The northwest segment is characterized by relatively weak Previous HitstructuralNext Hit deformation and undeveloped paleo-karsts. The middle segment with proper Previous HitstructuralNext Hit highs indicates a suitable setting for developing supergene karsts preserved during later deep-burial stage. Stronger Previous HitstructuralTop deformation with more karst caves collapsed occurred in the southeast segment, which resulted in few good reservoirs preserved.

 

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013