ROHRBAUGH, M. BRUCE, JR.¹, MATTHEW MAULDON², and WILLIAM M. DUNNE^1
1Dept. Geological Sciences, University of Tennessee, Knoxville, TN
²Dept. Civil and Environmental Engineering, Univ. Tennessee, Knoxville, TN

Abstract: Estimating Fracture Intensity Using Circular Scanlines

Straight scanlines and area maps are currently used to characterize fracture intensity. The straight scanline method is quick but is subject to sampling biases. The area method, which yields a fracture trace map, reduces these biases, but is time consuming. We propose that a third, under-utilized method, the circular scanline, combines advantages from both straight scanline and area methods by simultaneously minimizing work time and eliminating sampling biases. A key speed advantage of circular scanlines is that the only required information for intensity estimates is the number of fractures that intersect the circle.

The accuracy of this method was tested using a newly developed Monte Carlo simulation program for creating and sampling synthetic fracture patterns (e.g. log-normal spacing, fixed orientation, etc.). Intensity estimates from circular scanlines, within fracture trace maps, were compared to direct intensity measurements using the area method. Based upon these results, circular scanlines yield statistically unbiased intensity estimates.

As a further test, intensity values from the circular scanlines and area methods will be compared for trace maps of natural fracture patterns. Natural pattern geometries that will be tested include an orthogonal pattern with one throughgoing master set, a pattern with two orthogonal, vein-filled, cross-cutting master sets, and a pattern that contains four joint sets that are each independently oriented with respect to the others.

AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas