Lost circulation in fractured formations is one of the drilling's biggest expenses in terms of non-productive time (NPT), unit mud cost and safety issues. The severity and persistence of losses are to a large extent determined by the type of formation into which the fluid is being lost. It is imperative to identify whether the losses are to natural or induced fractures as losses into naturally fractured rocks require different treatments than those into drilling induced fractures. One way of identifying the type of the fracture is by image logs which are very local and limited to conductive muds, so still in their infancy and have yet to gain wide acceptance. An alternative way is possible by looking into flow behavior of mud losses (flow in/out) and associated downhole pressure response (PWD data).

This work presents an analytical formulation describing mud losses in drilling induced fractures based on which the volume and rate of losses in an induced fracture are quantified in terms of fluid properties, fracture parameters and operational conditions. Comparison between the predicted mud losses into induced and natural fractures indicates that much higher pressure sensitivity is anticipated during mud losses into induced fractures. Hence, the pressure sensitivity analysis can be used as a means to distinguish between the losses into natural and induced fractures. Once the fracture type is identified, the fracture parameters (hydraulic width or compliance) can be estimated by analyzing mud loss data. As the outcome of this study, guidelines are provided for the best practices to be used for prevention and control of lost circulation.

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