Print this pageAbstract: Potential Reservoir Identification in the Rio Blanco Formation (Argentina), Using New Techniques of Log Analysis
Mancilla, Oscar; Daniel Crivaro; Claudio Haring - YPF
Cuyana Basin, located in Mendoza Province, Argentina, has a rift origin related to a simple shear model filled by Triassic continental sediments (Fig.1). The Rio Blanco Fm. was analyzed in order to be able to identify and classify its reservoirs. The sequence stratigraphy analysis criteria was used to divide the column along with a complete set of well logs, cores and cuttings. As such, distribution and relationship of contemporaneous sedimentary bodies could be established.
A method of objectively 
determining
the best levels
of the reservoir was implemented using new well log analysis techniques
that allowed to develop a predictive tool to identify potential reservoirs
and their distribution, in order to search for subtle traps.The first step
consisted in dividing the stratigraphic column according to the electric
response, lithologic composition and vertical bed design. In addition to
the conventional use of the cross-plots, the use of the Briggs Cube Technique
allowed to match several physical parameters and see their variations,
continuity or cyclicity in depth, in the analyzed interval, most of them
in coincidence with the previously known.The Briggs Cube is the representation
of three well log-related physical parameters, by mean of the color cube.
Color variations with depth represent measured changes in rock composition,
fluid type, petrophysical characteristics, etc. Adequate choice of measured
properties results in a powerful tool for petroleum geology analysis.
The Rio Blanco Fm. is built up by 4 sequences,
being the lower two fluviodeltaic and the upper two fluvial in origin.
This array can be clearly recognized on the Briggs Cube and the Collin-Doveton
log. It was determined to separate each unit with objective criteria and
treat each interval individually, taking into account lithologic types
and fluid salinity (Rw) to determine Vsh, Total and Effective Porosity
and Sw and to analyze well logs from each sequence. Pikett's plots were
used to determine Formation Factor and a.m. parameters. Therefore it was
possible to compare Porosities, Vsh, etc. between different sequences.
The results were checked later with the outcome
of the production tests. This procedure allowed the calibration of the
results, the standardization and the definition of two important Critical
Parameters in the reservoir's behavior: the Minimum Effective Porosity
(MEP) and the Maximum Clay Volume (MCV). Based on cross-plots analysis
and tests results Potential Reservoirs were defined as units with more
than 9% of MEP and less than 40% of MCV (Fig. 2). After this classification,
maps for the potential reservoirs from each sequence were drawn (Medium
Effective Porosity, Isopach, Number of Beds, Sand-Clay Percentage) which
allowed analysis of the evolution of different properties through time.
The results obtained from this study can contribute to several analyses.
For the reservoir characterization, sequence stratigraphic division was
of fundamental importance. In addition, individual treatment of each sequence
simplified the well logs analysis, as critical parameters
do not show significative
changes within them. The relationship between well and seismic information
allows the extension of observations from the holes to undrilled areas.
AAPG Search and Discovery Article #90933©1998 ABGP/AAPG International Conference and Exhibition, Rio de Janeiro, Brazil