Print this pageAbstract: Defining Producing Zones with Open Hole Logging
Graterol, Jose and Ovidio Suarez - PDVSA
The information from production logging
is very valuable in reservoir management, but the results sometimes are
disappointing because a significant number of perforated intervals does
not contribute to the 
well
production. The characteristics of the producing
zones have to be defined to correct this situation. Open Hole Logging analysis
correlated with production logging results is the best way to identify
permeable zones in absence of a continuous permeability survey.
This type of correlation was applied in an area,
located in Lake Maracaibo, Western Venezuela, where several wells did not
produce at all, although the sedimentological descriptions pointed to the
presence of hydrocarbon facies in the perforated zones. The results of
the correlation indicate productive zones as being characterized by a minimum
relation of 1.6 between the corrected Deep (LLD) and Shallow (LLS) curves
of the Dual Lateral log. The application of the method showed consistent
results in the fifteen wells completed in the reservoir, and also indicated
that the LLD/LLS relation in the perforated zones is directly correlatable
with the initial well production (Fig. 1).
The success of the above described experience
led to the proposal of defining producing zones based on correlations between
production logs and open hole logging for another area, also in Lake Maracaibo,
where four different Eocene-age sands are producing commingled. The production
logs from four wells indicated that 66% of the perforated zones in the
three lower sands, C-3, C-4 and C-5, did not contribute appreciably to
the well production. The petrophysical analysis of the routine logs in
these four wells showed the productive zones of the three lower sands should
have total porosity values derived from the Formation Density log without
any correction, of at least 17%, which equates to an approximate value
of 100 mD of air permeability from core analysis. The consistency of this
petrophysical characterization is confirmed by seven additional production
logs and several production tests. The results of nine production logs
in the C-2 sand showed the productive zones of this upper interval characterized
by resistivity values from the Induction log greater than 40 ohms-m and
Formation Density log readings less than 2.45 gr./cc. Additionally, the
initial well production for the C-3 sand has been estimated using the product
of True resistivity and thickness (Fig. 2).
The consistency of the producing zones definition
has demonstrated that the reason for zones not contributing to well production
is poorer rock quality rather than well zone damage as indicated by preliminary
interpretations.
The application of these results has optimized
well completions, redesigned well
stimulations, redefined reserve calculations
and modified the exploitation strategy for the area.
AAPG Search and Discovery Article #90933©1998 ABGP/AAPG International Conference and Exhibition, Rio de Janeiro, Brazil