Flow prediction: understanding short-range coal permeability

May 2015April 2017
Coal permeability is spatially highly variable between adjacent wells

Improved spatial models of short-range permeability variation

This project sought to understand and better characterise the short-range variation in permeability between wells.

The amount of coal seam gas that can be produced from a coal bed is dependent on the thickness of the coal, gas content, permeability and the depth of the coal seam. Determining permeability of coal seams is an important part of estimating gas production from a well in reservoir models. Currently permeability is estimated from well test analysis. However, permeability estimates based on well test analyses have become more challenging as coal permeability is spatially highly variable between adjacent wells. Variability in permeability is also present at different scales and is determined by coal seam distribution and continuity, composition, diagenesis, geomechanical characteristics and reservoir stress evolution. Over a short range (at the near well to inter-well scale) an even higher variability in permeability exists due to the connectivity of fracture networks between adjacent wells, and this makes predicting associated porosity and permeability difficult. It is for instance not unusual to find a variation in production of 50-70% between neighbouring wells within short distances (few kilometres) of each other. One of the key challenges is modelling short-range continuity of different categories of absolute permeability.

This project sought to understand and better characterise the short-range variation in permeability between wells. The project aims were to:

  • Examine measurements of different (proxy) properties at the short range scale to provide information on continuity, variability and randomness of coal permeability.
  • Develop single well and interference test models based on the new characterisation of short range permeability.
  • Use different approaches in modelling (correlation schemes, geostatistical inference, etc.) to improve current modelling practice
  • Calibrate and validate test models using field data.   

PROJECT OUTPUTS

  • Research poster: Improved Spatial Models of Short Range Permeability Variations, UQ-CCSG Research Review (2015)
  • A set of guidelines in the determination of optimal reservoir scale properties for coal seam gas reservoirs of varying permeability heterogeneities. These guidelines and workflows will be calibrated and verified with well pressure test data and interference test data.
  • Guidelines on the selection of appropriate estimation algorithms over inter-well scales and recommendations on appropriate modelling strategies.
  • Guidelines on the selection of upscaling algorithms and their suitability to use models constructed at the inter-well scale.
  • Identification of new algorithms and software tools and, if applicable, a scope variation to develop these tools
  • Project status: Complete
  • Project title: Improved spatial models of short-range permeability variation
  • Project leader: Professor Suzanne Hurter
  • Research team: Professor Steve Tyson
  • Research group: The University of Queensland Centre for Coal Seam Gas & The University of Queensland School of Earth Sciences
  • Timeframe: May 2015 - April 2017
  • Project funders: APLNG, Arrow Energy, Santos, QGC, University of Queensland

 

Image "coal" by Todd Smith-Salter is licensed under CC BY-NC-SA 2.0