Estimating Fracture Reorientation Due to Fluid Injection/Production

Authors: Zongyu Zhai and Mukul M. Sharma, University of Texas at Austin.

Venue: Society of Petroleum Engineers’ Production and Operations Symposium, Oklahoma City, OK, April 1–3, 2007 (http://www.spe.org/ [external site]).

Abstract: The injection or production of large volumes of fluid into or from a reservoir can result in significant changes to the effective in-situ stress distributions. Field evidence of this has been provided in the past by mapping refracturing treatments in tight gas sands and microseismic monitoring of injection wells in waterflooded reservoirs. A poro-elastic model is presented to show how the extent of fracture reorientation can be estimated under different conditions of fluid injection and production. The extent of fracture reorientation is a function of the in-situ stresses, the mechanical properties of the rock, and the pore pressure gradients. In reservoirs where the pore pressure gradients are complicated due to multiple injection and production wells, fracture reorientation is sensitive to the net pore-pressure gradients. Fractures tend to reorient themselves towards the injection wells and away from production wells, if the pressure gradients are comparable to the in-situ stress contrast. While far-field principal stress orientations are impacted only by in-situ stresses and pore-pressure gradients, near-wellbore in-situ stress orientation is also impacted by the hoop stress and the wellbore pressure. These can have a significant effect on near-wellbore fracture reorientation. The results of our model are compared with field observations obtained from microseismic monitoring of water injection wells. The implications of the results to refracturing operations and candidate well selection are discussed.

Related NETL Project: The goal of the related NETL project entitled “Design and Implementation of Energized Fracture Treatment in Tight Gas Sands” (DE-FC26-06NT42955) is to develop methods and tools that can enable operators to design, optimize, and implement energized fracture treatments in as systematic way. The simulator that will result from this work would significantly expand the use and cost-effectiveness of energized fracs and improve their design and implementation in tight gas sands.

NETL Project Contacts:
NETL – Virginia Weyland (virginia.weyland@netl.doe.gov or 918-699-2041)
UT-Austin – Dr. Mukul Sharma (msharma@mail.utexas.edu or 512-471-3257)