uAbstract
uFigure
captions
uDatabase
uSeismic
interpretation
uFramework
uStructure
uStratigraphy
uPetrophysics
uConclusions
uReferences
uAbstract
uFigure
captions
uDatabase
uSeismic
interpretation
uFramework
uStructure
uStratigraphy
uPetrophysics
uConclusions
uReferences
uAbstract
uFigure
captions
uDatabase
uSeismic
interpretation
uFramework
uStructure
uStratigraphy
uPetrophysics
uConclusions
uReferences
uAbstract
uFigure
captions
uDatabase
uSeismic
interpretation
uFramework
uStructure
uStratigraphy
uPetrophysics
uConclusions
uReferences
uAbstract
uFigure
captions
uDatabase
uSeismic
interpretation
uFramework
uStructure
uStratigraphy
uPetrophysics
uConclusions
uReferences
uAbstract
uFigure
captions
uDatabase
uSeismic
interpretation
uFramework
uStructure
uStratigraphy
uPetrophysics
uConclusions
uReferences
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Figure Captions
![](thumbs/01.jpg) |
Figure 1. Location map of the study
area. Bare Field is located in the Hamaca area in the Orinoco
Heavy Oil Belt, in the southern part of Anzoategui state
(Eastern Venezuela). |
![](thumbs/02.jpg) |
Figure 2. Seismic section showing detail
of horizons and faults, based on 3D seismic interpretation. Four
seismic horizons were mapped: FS20 (flooding surface 20), FS62
(flooding surface 62), FS68 (flooding surface 68) and Basement.
|
![](thumbs/03.jpg) |
Figure 3. Using the four seismic
horizons and geologic markers, application CPS3©
generated the other horizons that complete the 3D Geological
Model. In the upper left is the structural model with the four
seismic horizons and interpreted faults; in the upper right are
all the markers defined in all the wells studied. The lower
image shows all the generated horizons. |
![](thumbs/04.jpg) |
Figure 4.
Evolution of the static model. Separation into blocks, with
isolation of the sands of economic interest, using the
PROPERTY 3D© application. The blocks were defined by the
interpreted faults in the area. |
![](thumbs/05.jpg) |
Figure 5. Stratigraphy of the Eastern
Venezuelan Basin and the Bare Field. An imaginary well in the
Orinoco Heavy Oil Belt in the Bare Field is used to show details
of the local stratigraphy. This study assumes the absence of the
Oligocene Merecure and the Cretaceous Tigre formations and the
presence of the Cretaceous Canoa Formation. |
![](thumbs/06.jpg) |
Figure 6. Stratigraphic cross -section
illustrating the methodology used in stratigraphic correlation,
with definition of flooding surfaces (markers), genetic units,
and sands of economic interest. |
![](thumbs/07.jpg) |
Figure 7. Petrophysical evaluation obtained by applying the
cut-off to the mathematical combination of lithologies generated
by the application ELAN PLUS©. The final visualization
allows the analysis of mineralogy, lithology, and petrophysical
properties. |
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The database for this study consists of a 3D
seismic survey within the Bare-Arecuna fields covering over 188 km2
and approximately 240 log curves from
about 48 wells (Figure 1). These logs
included Gamma-ray, SP, resistivity, density, neutron, and sonic.
Another type of data included water and hydrocarbon saturations (Sw,
So), intrinsic permeability (K), effective porosity and shale volumes (Vsh).
All of these data were loaded in the GeoFrame©
3.8 computerized platform from GeoQuest©.
The wellbase information, such as location, geographic coordinates, shot
point maps , cultural, petrophysical, and production information, was
loaded in the Finder©
database manager. Sixteen
cross - sections , covering the whole area of study, were constructed and
analyzed, using the Stratlog©
and Wellpix©
software. The correlation of nine
genetic units with their corresponding flooding surfaces and facies
definitions was used to generate a set of maps in the CPS-3©
software in order to visualize and
model the structural setting of the different layers.
The interpretation of the seismic data,
integrated with the well information, was used to prepare structural
maps of the three main flooding surfaces and of the basement identified
in the correlation of 48 wells located in the study area. Seismic
velocities were analyzed in detail in order to have an acceptable
conversion of time to depth of the interpreted seismic horizons (Figure
2).
Structural correlation of three key flooding
surfaces (FS-20, FS-62, and FS-68), as well as acoustic basement,
allowed compartment demarcation throughout the seismic data volume and
contributed to establishing reservoir limits through the integration of
geophysical, geological, petrophysical, and production data. Structural
analysis revealed several episodes of faulting, identifying the NNW-SSE
and NNE-SSW faults as being the most important for hydrocarbon
entrapment (Meléndez, 1998).
Once the seismic correlation was completed,
the variance seismic cube was generated in the GeoCube©
application.
Structural Maps
Faults were identified using 3D seismic data.
Using the Charisma©
software, time maps corresponding to four
seismic reflectors and previously tied to geological tops, were
converted to depth maps , and structural maps were prepared for the nine
genetic units. Subsequently, the CPS-3©
software was used to visualize and
generate the final structural maps with the best geological subsurface
configuration. The Original Oil in Place (OOIP) for these areas was
estimated to be 233 MMSTB; recoverable oil was estimated to be 32 MMSTB
(Figures 3 and 4).
The interval of study covered the most
prospective reservoirs located within the Tertiary Lower Oficina
Formation, with an average thickness of approximately 1500 ft of fluvial
sediments (Figure 5). Modern concepts were
used to make stratigraphic correlations based on the definition of
stratigraphic sequences (Galloway,
1989). Regional shales were identified
that were deposited in the fluvio-deltaic environment of the prospective
Oficina formation in the Bare area (Figure 6).
The concept of facies was applied to define
the sedimentological model for each genetic unit deposited between two
flooding surfaces. Previously, the Gamma ray well logs were analyzed to
identify the blocky, coarsening upward, fining upward, and serrate
sequences. Six facies were defined in a fluvial system: A (braided
channels sands), B (meandering channels sands), C (crevasse splay
sands), D (sandy sequences), E (clays), and F (coals) (Flores and Arias,
1996).
In order to evaluate petrophysically the
interval of interest, data were gathered from tapes (SP, density,
neutron, Gamma ray, sonic, and resistivity logs) and from the Finder©
database. The data was then edited and
depth-matched. Data from cores, such as mineralogical analysis, X-ray
diffraction, and lithological core description from well MFA044 ( Casas,
1999), were used to create the petrophysical model, which consists of
sandstone, illite, kaolinite, and fluids (oil and water).
The petrophysical parameters were estimated
from the core analysis and Pickett plots: Saturation Index (n)=2,
Saturation exponent (m)=2, Coefficient of tortuosity (a)=0.81, and the
Water resistivity (Rw)=0.34.
In order to calculate the total net pay, the
following cutoffs were used: Shale Volume (Vsh) < or=30%, Effective
Porosity (fe)
> or=20%, and the Water Saturation (Sw) < or=50% for which relative
permeability curves were used (Bureau of Economic Geology, (1997) (Figure
7).
Based on the integration of stratigraphic,
structural , and petrophysical analyses, the 3D geological model in the
area of the Project MFB165 was defined, and subsequently, the static
model of the existing reservoirs in the study interval. The whole
database was preserved in a "rescue" file; then up-scaling to the
dynamic model will allow for establishing the best strategy of future
exploitation.
Through the construction of the stratigraphic
model and, specifically, the correlations made in 16 sections , 15
flooding surfaces (FS), with an additional marker (R4), establish the
limits of nine genetic units; from bottom to top, they are designated as
90, 70, 69, 68, 65, 63, 62, 60, and 50; there are three sands of
economic interest: U1- 2, S1-2, and R4. Stratigraphic analysis
corroborates the pinchout of the Cretaceous to the southeast.
The structural model was assembled, through
integration of four seismic horizons and 23 fault planes interpreted
along three seismic surveys in the Arecuna- Bare area. This process
subsequently allowed generation of structural maps for 15 flooding
surfaces.
The structure observed with 3D visualization
corresponds to a homoclinal bowed slightly to the north, with dip of the
sedimentary sequence in the basal sands of the Oficina Formation, not
greater than 1°, contrasting with the inclination of the basement, which
is greater than 2°.
The structural model corresponds to an
extensive system of two very defined episodes: the first with faults of
northwest-southeast direction, displaced slightly by other faults with
northeast-southwest trend. The two families of normal faults have dips
around 80°, throws not greater than 90 feet, and cutting the Basement to
the top of the Oficina Formation.
The petrophysical evaluation for the
sedimentary sequence studied is as follows: average values of porosity
around 29%, permeability of 1498 millidarcies, water saturation of 36%,
oil saturation of 64%, and 13% clay content. Likewise, the values in the
sands of commercial interest vary as follows: porosity—28-32%,
permeability--1354-4040 millidarcies, oil saturation--66-74%, and clay
content--12-14%. Through the calculations, 54 petrophysical maps
(porosity, permeability, water saturation, net thickness, net pay) were
obtained for nine genetic units, along with reservoir maps for three
sands of interest.
The OOIP was estimated to be 233 MMMSTB and
recoverable reserves to be 32 MMSTB.
Bureau of Economic Geology, 1997, Targeted horizontal
wells for maximizing recovery of heavy oil resources: Arecuna Field,
Venezuela: The University of Texas at Austin Internal Report for
Corpoven S.A., Puerto La Cruz.
Casas, J., 1999, Core data for the Ameriven Project:
PDVSA-Faja Internal Report for Ameriven S.A., Caracas.
Flores, D., and Arias. W., 1996, Caracterización del
Yacimiento MFB-53, Trampa B-15, Faja Petrolífera del Orinoco: Ingepet
’96 Internacional, Petroperú. Lima, Perú.
Galloway, W., 1989, Genetic stratigraphic sequences in
basin analysis I: Architecture and genesis of flooding-surface bounded
depositional units: AAPG Bulletin v. 73, p. 125-142.
Meléndez, L.,
1998, Interpretación Sísmica 3D, Área Arecuna-96: PDVSAEPM Internal
Report for the U.E.I-XP San Tomé. Puerto La Cruz.
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