Most frac theories and design models assume the hydraulic fracture is created in tension, planar and symmetric with respect to the wellbore. In reality, because of the heterogeneity of most reservoirs, the hydraulic fracture extends in a mixed mode (both tensile and shear) with numerous branches. Well configuration and treatment design also contribute to this complex fracture growth. This random, irregular fracture geometry has come to be called "off-balance growth." An off-balance fracture does not occupy a single plane, its growing tip moving randomly around the fracture and not necessarily at the farthest point from the wellbore. These features also control the movement and deposition of the proppant inside the fracture, giving it an irregular and random pattern. In off-balance fracturing, the proppant nearest the wellbore may be the segment first pumped into it.
This presentation will reveal how off-balance fractures usually have narrower widths, shorter lengths and often less height than computed by simple fracturing models. The causes of off-balance growth and its consequences on fracture geometry, proppant position, proppant flowback, zonal production, and fracture longevity will be examined. Methods for determining the presence and extent of off-balance growth and options for reducing same will also be included.