A mineral solver is an algorithm that tries to find the proportions
of already assumed minerals present in the rock. Several mathematical methods
have been tried historically, from linear system of equations, to artificially
trained neural networks, and even empirical heuristic approaches. Linear system
solvers require a set of good quality log curves, and not too many minerals to
solve, otherwise the problem would be mathematically undetermined. Mineral solvers
offer only a coarse guide to understand the rock composition. Nothing replaces
the experience of qualified geologists and petrophysicists.
The GeolOil Petrophysical Functions module has mineral solvers for carbonate systems with
limestones, dolomites, anhydrites, and halite salts (NaCl).
GeolOil also solves clean eolian systems with sandstones and dolomites.
The figure below shows the GeolOil mineral solvers panel to compute the proportion of dolomites
No mineral solver is perfect. Curves may be noisy, unreliable, and even if the log
curves are perfect, many other not considered minerals might be present.
In the well log plot shown below from a Montana carbonate reservoir, GeolOil achieved
very good results computing the mineral proportions of limestone, dolomite, anhydrite,
and salt.

Changes in sedimentary environments
A mineral solver not only helps to estimate the mineral composition of the reservoir's rock.
In some cases —like the figure to the left— it may detect changes in the sedimentary
environment.
A pay zone is found at the upper interval. It is a fairly clean dolomitic limestone with
a maximum porosity of around 10%.
The bottom zone is essentially a tight, shaly limestone sealing rock.
The change is abrupt, and happened within 12 feet of transition or less.
The log had enough resolution and quality to capture the sharp change.
Without a mineral solver, it would be very difficult to infer such
change of environment.

The rightmost thin bar from the figure below, with colors grey (anhydrite), light green (limestone, and salt),
and dark green (shaly dolomite), is the interpretation manually
made by an experienced geologist already familiarized with the depositional
environment. The Minerals track on the right, shows the result of the mineral
proportions solved by GeolOil from the PEFZ photoelectric factor,
and RHOZ bulk density curves. The pink are filling represents the proportion
of dolomite, indigoblue represents the proportion of limestone, orange the
proportion of anhydrite, green the proportion of salt, and blank white represents
the zones for which GeolOil could not find a stable or reliable solution.
Notice that there are blends limestones and dolomites, and the overall match is
good.
The figure below shows a well log plot result of a mineral solver for limestone, dolomite, anhydrite, and salt
GeolOil provides also a QuartzDolomite solver for eolian environments. It is particularly useful to
estimate the matrix density for partial blends of quartz and dolomites:
The figure below shows the mineral solver panel for a sandstonedolomite eolian environment to compute matrix density
The figure below shows a mineral solved log plot for a sandstonedolomite eolian environment
GeolOil Petrophysical Functions module also ships with a clays solver for clastic environments, aimed to solve approximate proportions
of quartz, silt, illite, smectite, kaolinite, and chlorite. It offers mostly
semiquantitative analyses of the clay minerals present. Even "hard lab" techniques
like XRD X Ray Diffraction are also semiquantitative.
The figure below shows the mineral solver panel for clays.
✔ NOTE: The GLOG file workflow for this log is available for download with the set of optional interpretation
examples.
The figure below shows a mineral solved log plot for a clay minerals in a clastic environment
Another mineral solver shipped with the GeolOil Petrophysical Functions module
is a clayscarbonate mineral solver, aimed to solve approximate proportions
of clays, silt, quartz, calcite, and dolomite. It is usually more accurate than the former clays solver,
(clays mineral composition is always very difficult to separate, but GeolOil does a useful qualitative work on this)
so the proportions found can be more similar than those found via XRD diffraction.
The figure below shows the mineral solver panel for clayscarbonates.
✔ NOTE: The GLOG file workflow for this log is available for download with the set of optional interpretation
examples.
The figure below shows a mineral solved log plot for clays and carbonates. Notice the reasonable match with XRD lab points

Related article:

How to learn petrophysics by practicing with log log interpretation examples.
Highly recommended: This learnset contains fully interpreted examples with clastic and carbonate mineral solvers.


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