A new tectono sedimentary framework of the Jurassic succession in the Merjan oil field, Central Iraq

摘要

In the Merjan oil feld (Central Iraq), the previous 2D seismic interpretation of subsurface geometry had been revealed moundfacies which was interpreted as large carbonate buildup within carbonate Najmah formation of Jurassic age. The explorationwell (Me-1) had been drilled depending on these results, but carbonate buildup did not exist. The current research providesnew sight to interpretation of this feature in the Jurassic succession. High accurate 3D seismic refection data have beenused. Two scenarios have been presented to interpretation. Scenario (A) includes tectono stratigraphic study which fndsout that mound shape is due to fault system and tectonic activity during the sedimentation which led to the formation of agraben structure and after sedimentation led to tectonic inversion. These events cause the camoufage stratigraphic feature.Scenario (B) relies on conversion of seismic section from time into depth domain using appropriate velocity model. Theresultant seismic depth section helps to present another seismic analysis of feature. The proposed structural model accordingto the depth section interpretation is anticlinal fault-bend fold. Quantitative geometric relationships between fault and foldshapes were established. Both scenarios explain the causes of the formation of the mound seismic facies which was previously interpreted as carbonate buildup. In conclusion, the stratigraphy interpretation based on 2D data might be very riskyand 3D seismic is a must for exploration of stratigraphy traps.