Huade Yang's dissertation
by
Huade Yang, Ph.D.
University of Texas at Austin, 1999
Supervisor: Mark A. Miller
The objective of reservoir description or evaluation is to provide detailed and accurate estimates of reservoir
petrophysical properties such as permeability, porosity and residual saturation. The lack of measured data over
the reservoir domain makes this objective difficult to achieve. Geostatistical and other interpolation methods
are therefore frequently employed to provide detailed distributions of petrophysical properties. However,
geostatistics or other interpolation methods as mathematical tools provide little physical meaning to the
estimates. In this research, relationships between petrophysical and petrographic properties are developed
based on physical models and theory. Regression analysis is also employed to incorporate some parameters that
are difficult to model.
A conceptualized tetrahedron model combined with a Monte Carlo procedure is used to
investigate and analyze the relationship between porosity and texture properties of grain size distribution.
Quantitative relationships between porosity and the coefficient of variation and the Trask sorting coefficient
have been developed based on the conceptualized tetrahedron model. A general quantitative relationship between
porosity and petrographic properties is established by combining theoretical and statistical analyses.
Relationships between permeability and formation factor and texture properties of pore size
distribution have been developed based on network theory. A simplified cementation model and regression analyses
are employed to investigate effects of other petrographic properties on permeability and formation factor. This
work demonstrates that permeability can be predicted from texture properties of pore size distribution. It is
also found that the texture properties of grain size distribution of unconsolidated sand are representative of
its pore size distribution and can be used to help predict permeability. A general relationship between
formation factor and petrographic properties has also been constructed by combining theoretical and statistical
analyses.
Simple regression analysis of the relationship between irreducible water saturation and
petrographic properties was also performed. It is found that irreducible water saturation is best correlated
with silt content, mean and sorting coefficient of grain size distribution, matrix and feldspar contents and
micro porosity in the rock.
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