Modified Approach for Probabilistic Petrophysical Software Used
for Evaluation of Shale Reservoirs
Paul Pavlakos*, Weatherford Petroleum Consulting, Calgary AB
paul.pavlakos@ca.weatherford.com
Ashok Bhatnagar, Weatherford Petroleum Consulting, Houston TX
Khaled H. Hashmy, Weatherford Geoscience Development, Houston TX
Abstract
Most stochastic or probabilistic petrophysical analysis softwares are designed to correct for effects of
shale contained in the reservoir rocks. However, when shale reservoirs are to be evaluated with these
programs difficulties are encountered since now it is required to correct the non-shale fraction in the
shale “reservoir” for the effect of clays in the shale. The end points for clays in the shale reservoir have
to be inferred indirectly since adjacent “clay” beds are almost never met with in the course of field
development.
This presentation describes how the original GRI approach may be used to infer the clay end points for
the Gamma Ray, Compressional and Shear Acoustic travel times, Volumetric Cross-section, U, as also
for the Potassium, Thorium and Uranium measurements. This is accomplished by extrapolation from
the end-points of the predominant non-shale mineral and that of the zero porosity shale to obtain the
clay point based on an a priori knowledge of the ratio of the non-clay fraction in the shale “reservoir”.
Once the appropriate clay end points are obtained, they may be used in the probabilistic/stochastic
petrophysical analysis software to obtain realistic answers in producing shale reservoirs. Information to
the system may be readily supplemented by furnishing constraints based on local geologic information
and from the log-core relationships often available for Pyrite, Apatite, TOC, porosity, etc.
A major advantage of using this technique is that the TOC is determined simultaneously with other
minerals without the need to resort to separate empirical procedures based on differences in the log
responses of organic-lean and organic-rich shales. These approaches are quite subjective and, often
an organic-lean shale may not be present in the same stratigraphic unit as the organic-rich shale that is
to be evaluated – leading to the necessity for sheer guess work.
Results presented here testify to the fact that standard probabilistic petrophysical analysis platforms
perform very well for unconventional reservoirs where proper clay parameters are input. The available
constraints lend themselves to improvement of results by providing a means for incorporating
geological information to supplement the well log data. Comparisons with deterministic approaches
and with core data are presented to establish the veracity of the computed data.
http://www.geoconvention.com/uploads/2013abstracts/305_GC2013_Modified_Approach_for_Probabilistic_Petrophysical_Software.pdf
Отправлено: 22.07.13 07:04. Заголовок: Hashmy дозрел применять оптимизационную инверсию для оценки TOC
