Fracture Geometry Optimization: Designs Utilizing New Polymer-Free Fracturing Fluid and Log-Derived Stress Profile / Rock Properties
Authors: Rimmer Brett , MacFarlane Curtis , Mitchell Chuck , Wolfs Henry , Samuel Mathew 
Published: December 2007

Newport Petroleum Co. embarked on an exploration and development drilling program in a channel sand. This clastic channel was situated within a much larger, fully developed field located in Central Alberta. The new wells were drilled for a target interval that that is known to have low reservoir permeability, and would have to be fracture stimulated to produce economically. The offset wells were all drilled and duly stimulated using a design based on historical knowledge. Following treatment, they produced at a rate that wascost effective; however, the rate was not as high as expected. In addition, post job pressure analysis of the treatments showed that the actual recorded job pressures could not be matched with the initial simulator predictions. The net pressure indicated uncontrolled fracture height growth.

The fracture designs on the offset wells were made utilizing rock properties and a stress profile based on conventional open hole logs. These indicated a sandstone pay zone bounded below by a calcite cemented sand then shale and dirty sand / shale above. There were no signs of a weak zone that would have accounted for the height growth that was indicated from the actual job data.

In order to have a better understanding of how the fracture was actually growing; it became apparent that an improved knowledge of the stress profile and rock properties from wireline logs (conventional open hole logs plus the dipole shear sonic imager) would be required. Using this information an optimized fracture design could be made on future wells. Coupled with the log derived stress profile, the new polymer-free, visco-elastic surfactant (VES) based fracturing fluid was also used to maximize conductivity and minimize height. This fluid has a much lower viscosity than conventional polymer fluids. Due to its polymer-free nature, VES fluids provide a great improvement in retained fracture conductivity. When using crosslinked polymer fluids, very high viscosity is required for proppant transport and in most cases; this high viscosity can result in uncontrollable fracture height growth. Proppant transport capability of a VES fluid is not viscosity related, but due to the network structure created by the worm-like micelles. When this fracturing fluid (with low viscosity) is utilized, the generation of the unnecessary height growth is reduced.

The paper includes the case histories and overall processes that were used to optimize fracture designs with Dipole shear sonic imager derived stress profile / rock properties,Investigation for preventing fracture height growth, andUse of a visco-elastic surfactant based fracturing fluid. The result of this work was a 3–4 fold production increase for all of the subsequent wells. This success led to an expanded drilling program of approximately 25 wells.

The result of this work was a 3-4 fold production increase for all of the subsequent wells. This success led to an expanded drilling program of approximately 25 wells.