“Effect of Fracture Orientation on Induction Logs: A Modeling Study,” SPE Annual Technical Conference and Exhibition, Florence, Italy, SPE 133802, Sept. 19-22, 2010.
A common difficulty associated with fracture modeling is the need for a very fine mesh to simulate the detailed geometry of the fracture. Such a fine discretization in the 3D numerical model leads to a lengthy computation time; with tilting fractures complicating the problem further. In our work, we apply a novel technique that has recently been used in modeling non-conducting membranes in biological studies. This technique makes it practical to model even very thin fracture apertures.
The response of induction tools to fractures has been of interest to the oil industry for decades. Fractures are important indicators of formation characteristics. Several recent papers (Xue, et al., 2008 and Tang, et al., 2006) address vertical fractures intersecting a borehole wall in which the induction tool response was numerically simulated with 3D Finite Difference or Finite Element methods. However, in the cited publications, only vertical fractures were studied. In nature, fractures are not necessarily vertical and the wellbore can have an arbitrary inclination with respect to the fracture. The effect of fracture orientation therefore needs to be understood since it pertains to the nature of the fracture and the characteristics of the formation of interest. The innovative 3D Finite Difference simulation developed in this work reduces the size of the solution domain significantly and overcomes the challenge of geometry modeling in dipping, finite-length fractures. These breakthroughs allow us to look into the dipping effect of thin fractures accurately and efficiently. We look at the effect of a fracture with respect to dipping angle, fracture resistivity, aperture and length. As a result, we discuss the complications in the interpretation of induction logs influenced by fractures intersecting the borehole, both vertically and non-vertically.