A New Approach in Modeling of Fracture Ballooning in Naturally Fractured Reservoirs

Abstract

Fracture ballooning usually occurs in naturally fractured reservoirs and is often mistakenly regarded as an influx of formation fluid, which may lead to misdiagnosed results in costly operations. In order to treat this phenomenon and to distinguish it from conventional losses or kicks, several mechanisms and models have been developed. Among these mechanisms under which borehole ballooning in naturally fractured reservoirs take place, opening/closing of natural fractures plays a dominant role. In this study a mathematical model is developed for mud invasion through an arbitrarily inclined, deformable, rectangular fracture with a limited extension. A governing equation is derived based on equations of change and lubrication approximation theory (Reynolds's Equation). The equation is then solved numerically using finite difference method.Considering an exponential pressure-aperture deformation law and a yield-power-law fluid rheology has made this model more general and much closer to the reality than the previous ones. Describing fluid rheology with yield-power-law model makes the governing equation a versatile model because it includes various types of drilling mud rheology, i.e., Newtonian fluids, Bingham-plastic fluids, power-law, and yield-power-law rheological models. Sensitivity analysis on some parameters related to the physical properties of the fracture shows how fracture extension, aspect ratio and length, and location of wellbore can influence fracture ballooning. The proposed model can also be useful for minimizing the amount of mud loss by understanding the effect of fracture mechanical parameters on the ballooning, and for predicting rate of mud loss at different formation pressures.

A new model for predicting fluid loss in fracture-porosity reservoir

“…At the beginning of the leakage, pressure in the fracture is equal to the formation pressure. At the same depth, pressures are equal at anywhere [30]:…”

Hydrodynamic modeling of mud loss controlled by the coupling of discrete fracture and matrix

“…In addition, the field data on the rheological parameter of drilling mud can be directly employed. Thus, the YPL is subsequently selected as the model to describe the fluid rheology (Majidi et al, 2008a(Majidi et al, , 2008b(Majidi et al, , 2008cPordel Shahri et al, 2011;Pordel Shahri and Mehrabi, 2012;Mehrabi et al, 2012;Livescu, 2012):…”

“…In the previous numerical model (Majidi et al, 2008a(Majidi et al, , 2008b(Majidi et al, , 2008cPordel Shahri et al, 2012), the mass balance equation for an incompressible fluid in the absence of a leak-off through the fracture wall is given by…”

“…They presented an analytical formula to describe the mud loss in drilling-induced fractures based on the notion that the volume and rate of loss in an induced fracture are quantified in terms of fluid properties, fracture parameters and operational conditions . Some authors have also examined the influence of fracture fractal dimension (Ozdemirtas et al, 2009) and various deformation laws (Pordel Shahri and Mehrabi, 2012) on mud loss.…”

New Leakage Model for Naturally Fractured Formations Considering the Effects of Dual-System Hydro-Mechanical Coupling

“…Lietard et al and Majidi et al developed models for the radial flow of non-Newtonian fluid into a single natural fracture, neglecting the effect of drilling fluid leak-off and fracture deformability [10][11][12]. Other researchers have proposed an elastic equation to incorporate the impact of the fracture deformability, which relates the fracture width variation to the local pressure through the fracture normal stiffness [13][14][15][16][17][18][19]. To analyze fluid leak-off, Bychina conducted threshold processing for this leak-off process; that is, when the well-bottom differential pressure is greater than a fixed value, the fluid seeps into the formation at a certain leak-off velocity [20].…”