Obtaining formation characteristics, especially permeability, in a conventional or non-conventional environment is sometimes highly challenging: formation-testing tools run during openhole logging are often unsuccessful, conventional well tests are not always appropriate for tight formations, as no gas flow usually is observed before hydraulic fracturing.

Brouard Consulting and LMS (Ecole Polytechnique, France) have developed with TOTAL a new well-testing methodology adapted from techniques used in the salt industry and successfully applied to conventional and non-conventional reservoirs. The new technique called WTLog uses only wellhead pressure sensors and surface flowmeters without any downhole tools. The WTLog delivers an injectivity log and a permeability log along an openhole, or a perforated casing, allowing a better identification of zones with the best potential and optimizing the production strategy.

Standard well tests often imply:

  • Data from long gas-production tests
  • Wellbore storage effect to be considered
  • Modeling using constant flow boundary conditions
  • Steady-state flow regime
  • Use of Laplace transformation

WTLog implies:

  • Short liquid injection tests, a few hours only
  • No wellbore storage effect as the wellbore is very stiff
  • Constant pressure boundary conditions in the wellbore
  • Transient flow regime to be considered (low permeability)
  • Laplace transformation is not suitable for low permeabilities

New modeling/Analyzing tools, based on Bessel/Fourier series, have been developed since 2007 for the WTLog Simulation & Data analysis

WTLog key features

  • Modeling of injectivity: monophasic model with or w/o skin
  • Boundary conditions: constant pressure or no flux
  • Modeling of deviated wells (3D path)
  • Semi-analytic implementation based on Bessel functions allows relatively fast computations
  • Calculation of pressure losses while circulating
  • Back-calculation of permeability and average skin from closing WTLog (openhole)
  • Back-calculation of clusters/stages injectivity (cased hole)
  • Very user-friendly software, numerous pre and postprocessing capabilities