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Figure Captions
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Petrophysical  Properties of the Reservoirs
Both Comodoro Rivadavia and Mina El Carmen
formations consist of feldspathic shaly sandstones with volcanic tuff
and conglomerates. A summary of the reservoir characteristics is
presented in Figure 2. Additional
information can be found in Stinco et al. (2001).
Magnetic Resonance Imaging Logging (MRILPrime
®) service measures several key factors that influence the ability of a
well to produce commercial quantities of oil or gas.
One of the fundamental measurements of the
MRIL-Prime tool is total fluid-filled porosity. MRIL in general is a
fluids-only measurement as the rock matrix is invisible to the tool;
therefore, it is unaffected by matrix effects that can influence
conventional logs. In fact, the total porosity measurement is the sum of
clay-bound water, irreducible water saturation and free fluid volumes —
all of which are measured separately by the tool. These measurements are
utilized to predict hydrocarbon production reliably. They are critical
in identifying low-contrast and low-resistivity pay, where high
immovable water volumes or fresh formation water may cause overlooking
productive zones when evaluated solely with conventional logs.
In addition, the MRIL tool derives a
permeability measurement and is able independently to determine fluid
type, pick fluid contacts, and detect changes in oil viscosity.
MRIL Porosity and
Permeability
Coates et al. (1999) provide
a thorough explanation of the theory and the procedures for determining
MRI-based porosity and permeability.
It should be noted that, in general, the
MRIL permeability should be used initially to compare good-quality from
poor-quality reservoirs in a relative fashion. When calibrated to MRI
core analysis, MRIL permeability can be used in its absolute form. See
Marschall et al. (1999) for discussion.
MRIL Analysis
and Interpretation Models
In order to achieve the objectives of the
study, different models of analysis and interpretation were used. They
are:
Refer to Coates, et al., (1999) for
explanations of these individual methods.
The main problem to solve when dealing with
these reservoirs is that the responses of conventional logs do not
always indicate fluid types. These shortcomings have been documented by
post-logging well testing.
A job plan for acquiring MRIL data in El
Tordillo field wells was made in this study, based on specific
parameters from the well design and anticipated formation and
hydrocarbon characteristics (Fam, 2003). The plan was designed to
acquire MRIL data that would provide the best opportunity of meeting
objectives.
Figures 3 and
4 illustrate the powerful capabilities of
MRI logging. A good match is seen between the MRIL prediction of light
oil (or high GOR oil) and a test that produced light oil or with some
gas (Figure 3).
Figure 4 shows
a different situation. Here the MRIL prognosis called for oil with some
water for the two zones shown on the figure. The test results confirmed
the prognosis.
As a consequence of these good matches
between forecasts and the test results, a high level of confidence was
achieved for forecasting fluid types using MRIL logging in different
intervals for the Comodoro Rivadavia and Mina El Carmen formations.
Coates, G., Xiao, L., and Prammer,
M., 1999, NMR logging principles and applications: Halliburton Energy
Services. 234 p.
Fam, M., 2003, MRIL-Prime analysis
and evaluation report: Internal Report, Halliburton Energy Services.27
p.
Fitzgerald, M., Mitchum, R.,
Uliana, M., and Biddle, K., 1990, Evolution of the San Jorge Basin,
Argentina: AAPG Bulletin, v. 74, p. 879-920 p.
Marschall, D., Gardner, J., Mardon,
D., and Coates, O., 1995, Methods for correlating NMR relaxometry and
mercury injection data: 1995 SCA Conference, paper number 9511.
Muruaga, E., Antunez, E., Nogaret,
C., Stancel, S., 2001, Integrated reservoir study in El Tordillo Field:
2001 SPE Latin American and Caribbean Petroleum Engineering Conference,
Buenos Aires, March 25-28. Paper SPE 69688.
Stinco, L., Elphick, R., and
Moore, R., 2001, Electrofacies and production prediction index
determination in El Tordillo Field, San Jorge Basin, Argentina: Paper UU.
SPWLA, 42nd Annual Symposium. Houston, Texas, 14 p.
Taboada, R., Condat, P., Corsini,
V., Mir, E., Conti, J., Fortunato, G., and Villivar, O., 2001, El
Tordillo reservoir static characterization study: El Tordillo Field,
Argentina: 2001 SPE Latin American and Caribbean Petroleum Engineering
Conference, Buenos Aires, March 25-28. Paper SPE 69660.
Track # 1 displays the GR
curve in green, SP in red, and Caliper shaded yellow from bit size. Also
presented are 10 raw MRIL porosity curves on scale 30 – 0 %. The shading
between these porosity curves present the corresponding T2 times
associated with that porosity curve. The T2 relaxation time ranges from
4 - 1024 msec.;variation of porosity value at different T2 relaxation
time depends on fluid type and pore size.
Track # 2 is the depth
track displaying the depth in meters and a bad hole flag in black
shading.
Track # 3 shows the deep
resistivity curve in dashed black, medium resistivity curve in dotted
blue, and the shallow curve in solid magenta. Permeability curve is
presented in solid red. All curves are presented on logarithmic scale
from 0.2 – 2000.
Track # 4 displays the raw
T2 spectra from the data acquired with long wait “Tw” and
short inter-echo spacing ‘Te”. The color indicates porosity such
that the brighter the color the higher the porosity. The lateral
logarithmic scale presents the T2 relaxation time on scale 0.3 –
3000.
Track # 5 displays the
differential T2 spectra (the difference between the T2
spectra of the long Tw and the short Tw). Again the color
indicates porosity such that the brighter the color the higher the
porosity. The lateral logarithmic scale presents the T2
relaxation time on scale 0.3 – 3000. In general the differential T2
spectra signal in this track presents either light hydrocarbon or
water in large pore size.
Track # 6 displays the
final MRIL porosity, on scale 30 – 0 %, after applying the Hydrogen
Index and the T1 corrections. This final MRIL porosity is
obtained after processing the data using the Time Domain Analysis “TDA”
technique. The dashed light green shading indicates clay bound water ‘CBW”;
the red shading indicates condensate or gas; the solid darker green
shading indicates light oil; the blue shading indicates free water; and
the gray shading represents bulk volume irreducible water “BVI”. This
interpretation is within the MRIL-Prime tool’s depth of investigation,
which is about 2.5 – 3 inches in the formation.
Track # 7 displays MRIAN
analysis, which is based on the “Dual Water Model” using the deep
resistivity curve and the MRIL porosity from TDA. The green shading
presents the clay bound water “CBW” porosity; the black shading shows
the hydrocarbon volume (based on a known Rw); the blue curve
presents free water; and the gray shading presents bulk volume
irreducible water “BVI”. This interpretation indicated presence of
hydrocarbon within the deep resistivity depth of investigation, which is
about 90 inches into the formation.
Track # 8 displays the
Enhanced Diffusion Method “EDM” interpretation directed towards
intermediate oil viscosities ranging from 2 – 50 cP. The dashed light
green shading indicates clay bound water ‘CBW”; the solid darker green
shading indicates intermediate oil; the blue shading indicates free
water; and the gray shading presents bulk volume irreducible water “BVI”.
This interpretation is within the MRIL-Prime tool’s depth of
investigation, which is about 2.5 – 3 inches in the formation. Also
displayed on this track is the oil viscosity as the dotted red curve on
scale 0 – 20 cP.
Track # 9 displays the raw
T2 spectra from the data acquired with long wait “Tw” and
short inter-echo spacing ‘Te”. The yellow color indicates
porosity such that the higher the amplitude of the yellow shading the
higher the porosity. The lateral logarithmic scale presents the T2
relaxation time on scale 0.3 – 3000.
Track # 10
displays the raw T2 spectra from the data acquired
with long wait “Tw” and long inter-echo spacing ‘Te”. The
blue color indicates porosity such that the higher the amplitude of the
blue shading the higher the porosity. The lateral logarithmic scale
presents the T2 relaxation time on scale 0.3 – 3000. The dark
blue vertical line presents the T2DW (T2 diffusion of
water), which is expected to be the maximum T2 value of the water
signal. In other words, a signal found to the right side of the T2DW
indicates that signal would be an indication of oil.
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