Analysis of Effective Reservoir Structures Fractures on Borehole Unstability in Dezful Embayment, Zagros Fold Belt


1 Department of Geology, University of Birjand

2 Department of Geology, Tarbiat Modarres University


        In this Study, the effect of fractures on the anticlines of the Zagros folded as one of the most important factors of wellbore unstability at the reservoir wells of Asmari Formation located in the Zagros folded in Dezful Embayment has been studied. In this regard, fracture pattern were studied in three anticlines included Kuh-e. Asmari without faulting evidence (Type I), Kuh-e. Sulak affected by the thrust in Forelimb (Type II) and Kuh-e and Kamarab in the vicinity of the Izeh transverse fault (Type III). The information of fractures in the three anticline field & Satellite Images including Geometry, Frequency, Spacing, Intensity, Density and Length were studied during Field Studies and using Satellite Images. Moreover Comparison of parameters showed that the fracture concentration in several  parts of the anticlines is different. The result showed that the maximum Density and Intensity of fractures found in Hinge area in type I, Faulted forelimb in type II and SE-Nose in type III anticlines. Therefore, maximum Lost Circulation and wellbore instability expected in Hinge, Forelimb and SE-Nose respectively from First to third anticlines. Therefore, due to direct relation between fractures concentration and drilling fluid loss, and wellbore unstability is increased in the aforementioned zone.


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