Investigation of Fracture Ballooning and Breathing in Naturally Fractured Reservoirs: Effect of Fracture Deformation Law

Abstract

Abstract Borehole ballooning-breathing is the term used to describe reversible mud losses and gains during drilling operations. In naturally fractured reservoirs borehole ballooning-breathing caused by opening/closing of natural fractures is the major mechanism of this phenomenon. An accurate model of the fracture-induced ballooning-breathing phenomenon could provide an aid in mud optimization and improve the well control procedures while drilling in naturally fractured reservoirs. Using this model, the hydraulic aperture of conductive fractures can also be obtained by continuous monitoring of mud losses and gains. Different models have been developed recently discussing this phenomenon. Each of these models considered some special conditions and investigated the effect of different parameters. This paper first discusses the previous models of fracture ballooning in detail. Then a new model is developed for radial flow of mud with Yield-Power-Law (Herschel-Bulkley) rheology in a single isolated deformable horizontal circular fracture. In this model exponential deformation law is used for fracture deformation, which is more realistic than the simplified linear deformation law. Also, this model is developed for both fracture ballooning and breathing phenomena. From the developed model it is concluded that cumulative loss in the case of exponential deformations less than that of linear deformation during fracture ballooning. This difference is due to pressure distribution in both cases. The pressure builds up faster for exponential deformation due to higher transmibility of the fracture. Different conditions are discussed in detail which could help in better understanding of the factors controlling borehole ballooning-breathing during drilling operation. Shortcomings of the developed modeling approach are outlined.