Fracture Width Logging While Drilling and Drilling Mud/Loss-Circulation-Material Selection Guidelines in Naturally Fractured Reservoirs

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Summary: In this article we discuss drilling mud losses in naturally fractured reservoirs with fracture permeability larger than 50 odd md and much larger than the matrix permeability. Type curves are provided that describe mud loss volume vs. time and allow the determination of the hydraulic width of natural fractures through the usual type curve matching technique of log/log plots. Real time logging while drilling of natural fracture width permits the proper selection of loss-circulation material (LCM) with respect to particle size distribution. Efficient (rapid) mud loss control is made possible, increasing the chances of minimizing fracture damage by the drilling mud, the cuttings and the LCMs themselves. The total mud losses experienced when drilling a long horizontal section are shown to agree with reservoir properties (derived by well testing) in particularly well-documented examples of the central North Sea. The equations provided can therefore be utilized as well by reservoir engineers to properly evaluate the contribution of natural fractures to the permeability and skin of any well, whether these fractures are clear or are invaded by drilling mud.

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