Fracture width logging while drilling and drilling mud/loss-circulation-material selection guidelines in naturally fractured reservoirs

In this article we discuss drilling mud losses in naturally fractured reser voirs with fracture permeability larger than 50 odd md and much larger than the matrix permeability. Type curves are provided that described mud loss volume vs. time and allow the determination of the hydraulic width of natural fractures through the u sual type curve matching technique of log/ log plots. Real time logging while drilling of natural fracture width permits the prop er selection of loss-circulation material (LCM) with respect to particle si ze distribution. Efficient (rapid) mud loss control is made possible, incre asing the chances of minimizing fracture damage by the drilling mud, the cu ttings and the LCMs themselves. The total mud losses experienced when drilling a long horizon; tal section are shown to agree with reservoir properties (derived by well testing) in p articularly well-documented examples of the central North Sea. The equations provided can therefore be utilized as well by reservoir engin eers to properly evaluate the contribution of natural fractures to the perm eability and skin of any well, whether these fractures are dear or are inva ded by drilling mud.