Understanding hydraulic fracture growth: tricky but not hopeless

SPE 56724 Understanding Hydraulic Fracture Growth: Tricky but Not Hopeless
C.A. Wright, L. Weijers, E.J. Davis and M. Mayerhofer; Pinnacle Technologies, Inc.

Copyright 1999, Society of Petroleum Engineers, Inc. This paper was prepared for presentation at the 1999 Annual Technical Conference and Exhibition in Houston, Texas, U.S.A., Oct. 3-6, 1999. This paper was selected for presentation byan SPE Program Committee following review of information contained in an abstract submitted by the author(s). Contents of the paper, as presented, have not been reviewed by the Society of Petroleum Engineers and are subject to correction by the author(s). The material, as presented, does not necessarily reflect any position of the Society of Petroleum Engineers, its officers, or members. Paperspresented at SPE meetings are subject to publication review by Editorial Committees of the Society of Petroleum Engineers. Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by whom the paper was presented. Write Librarian, SPE, P.O. Box 833836, Richardson, TX 75083-3836,U.S.A., fax 01-972-952-9435.

fracture height growth. Observations of fracture width, length, and asymmetry will also be presented and discussed.

Introduction This paper attempts to step back a bit from the flurry of new diagnostic observations of hydraulic fracture growth that have appeared over the last few years.1-21 We present examples of observed fracture growth and discuss the implicationsof what was observed. These are not unique examples, or even the best examples. These are simply examples that allow us to make some general observations about fracture growth that we believe apply to far more than the examples presented. The examples presented are not detailed case studies. They do not contain answers for how to best fracture stimulate wells in the respective areas. They are usedonly to illustrate how fracture growth is more complicated than we – particularly us modelers – like to think it is. However, this does not mean that modeling or attempting to understand and predict fracture growth is hopeless. It simply means that we need to re-think our assumptions, and maybe our confidence levels, about how we expect fractures to grow. Many of the realizations of the last fewyears, greater fracture height confinement for example, are not random events. Instead, they are possibly just physical phenomenon, like tip blunting across material interfaces, playing a much more significant role than we had previously assumed. If we can begin to understand where and why these “other” factors play a major role in fracturing, we can begin to incorporate them into our thinking,design processes, and even fracture models. The goal of this paper is to raise awareness of the fact that we cannot just take an “uncalibrated”, theoretical fracture model result as a definitive answer. Of course, this does not mean that fractures always behave very differently from what fracture growth models tell us and that models are always wrong. To the contrary – we have observed that modelsoften do provide results that are quite consistent with direct observations. But perhaps more often we observe significant shortcomings in fracture model predictions. This paper aims to provide a “flavor” of the differences between direct observations and fracture growth model predictions. The discussion in this paper will be limited to

Abstract Hydraulic fracturing has proven to be a fruitfulwell stimulation technique in an ever-increasing range of environments. Application has spread from the original target of enhancing production rates from low permeability reservoirs to fracturing of poorly consolidated high perm reservoirs, fracturing of horizontal and deviated wellbores, fracturing of unconventional (often naturally fractured) reservoirs, fracturing for waste disposal, etc....