UNCERTAINTY IN WELL TEST AND CORE PERMEABILITY
ANALYSIS
Reservoir
permeability is one of the important parameters derived from well test
analysis. Small-scale permeability measurements in wells are
usually made using core plugs, or more recently, probe permeameter measurements. Upscaling
of these measurements for comparisons with permeability derived well tests (DST
&/or Pressure Build-Up) can be completed by statistical averaging methods.
Well Test permeability is often compared with one of
the core plug averages: arithmetic, geometric and harmonic. A question that
often arises is which average does the well test-derived permeability represent
and over what region is this average valid? A second
important question is how should the data sets be reconciled when there are
discrepancies?
In practice,
the permeability derived from well tests is often assumed to
be equivalent to the arithmetic (in a layered reservoir) or geometric
(in a randomly distributed permeability field) average of the plug measures.
These averages are known to be members of a more
general power-average solution. This pragmatic approach (which may include an
assumption on the near-well geology) is often flawed
due to a number of reasons, which will be expanded in this study. The
assessment of in-situ, reservoir permeability requires an understanding of both
core (plug and probe) and well test measurements in terms of their volume
scale of investigation, measurement mechanism, interpretation
and integration.
This study
will compare core and well test measurements in B.R. Field (carbonate
reservoir) which is in South East of Turkey. An evaluation of well test data
and associated core plug data sets from a single field will be resulting from
the interpretation of small (core) and reservoir (well test) scale permeability
data. The techniques to be used are traditional uspscaling combined with the use of the Lorenz Plot to
identify the dominant flowing interval. Carbonates are very heterogeneous and
this exercise will be instructive in understanding the heterogeneity for the
guidance of reservoir models in such a system.
Related Publications