Drilling mud loss is considered as one of common problems encountered during excavation. The aim of this study is to evaluate of mud loss of the Sarvak Formation (Cenomanian age) in Azadegan oil field which is known as the most important rich hydrocarbon reservoir in the Zagros region by providing the model in the environment of GS+ software. This formation consists of a thick sequence of limestone and clay limestone layers, which is divided into 7 zones based on petrophysical characteristics. For this purpose, available data such as drilling mud weight, pump pressure, mud loss, and related depths of 9 drilled wells were investigated. The results showed that despite of the operating factors including the weight of drilling mud and the pressure of the pumps were kept constant, the presence of fractures in the reservoir rocks causes to occur mud loss significantly in zone 3 while it is observed the lowest level of mud loss in zone7. Based on the results of mud lost data patterns, faults, sedimentary environments morphology (such as sedimentary channels) seem to play major roles in creating fractures or areas susceptible to mud loss. The difference in observed patterns of mud loss is more likely to confirm the relocation of channel status over the time in different parts of the reservoir. In general, the highest rate of mud loss was detected in the northern and southern edges while the lowest rate was happened in the middle part of the field. It is suggested to prevent mud loss hazards in this field, underbalanced drilling method should be used.
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