SPE Journal
Volume 15, Number 3, September 2010, pp. 770-782

SPE-119522-PA

Quantifying Transient Effects in Altered-Stress Refracturing of Vertical Wells

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DOI  More information 10.2118/119522-PA http://dx.doi.org/10.2118/119522-PA

Citation

  • Roussel, N.P. and Sharma, M.M. 2010. Quantifying Transient Effects in Altered-Stress Refracturing of Vertical Wells. SPE J. 15 (3): 770-782. SPE-119522-PA. doi: 10.2118/119522-PA.

Discipline Categories

  • 5.3.1 Well Candidate Recognition
  • 5.3.3 Hydraulic Fracturing and Gravel Packing

Keywords

  • refracturing, stress reorientation, candidate-well selection, time-window, unconventional gas

Summary

The production or injection of fluids in reservoirs results in a redistribution of stresses. In this paper, the extent of stress reorientation has been calculated for fractured production and injection wells and the results have been analyzed for their effect on refracturing operations. Rules of thumb and charts have been provided to help with candidate-well selection for refracturing on the basis of the study.

For previously fractured wells, it is possible to create a secondary fracture that is perpendicular to the first. The secondary orthogonal fracture can be created only within a certain time window that, in turn, depends on the reservoir properties. Conditions leading to orthogonal secondary fractures in different kinds of reservoirs (oil, gas, and tight gas reservoirs) have been analyzed to establish some rules of thumb. The effects of the layers bounding the pay zone and of permeability heterogeneity and anisotropy on stress reorientation are also discussed.

Our results allow us to quantify the phenomenon of orthogonal secondary fracturing around fractured production wells by calculating the extent of the stress-reversal region as a function of time. The results of our model are shown to agree qualitatively with field observations obtained from microseismic measurements. The model presented in the study helps to clarify the concept of refracturing and provides a quantitative estimate of the time window for refracturing as a function of dimensionless parameters. The final result demonstrates the potential of the model to increase the reservoir sweep in unconventional reservoirs for which the optimum time window for refracturing is on the order of months to years. The conclusions of this study are useful for the design of refracturing operations and for candidate-well selection.

© 2010. Society of Petroleum Engineers

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History

  • Original manuscript received: 12 November 2008
  • Meeting paper published: 20 January 2009
  • Revised manuscript received: 26 October 2009
  • Manuscript approved: 11 November 2009
  • Published online: 27 April 2010
  • Version of record: 22 September 2010