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CHAPTER
7
Chapter 7: 3-D
 Seismic Examples from Central Lake Maracaibo, Maraven's
Block I Field, Venezuela Martin H. Link*Ý,
Christopher K. Taylor*ý,
Nicolás G. Muñoz J.**,
Emilio Bueno*, and Pedro J. Muñoz*
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| Link, M. H.,
C. K. Taylor, N. G. Muñoz J., E. Bueno, and P. J. Muñoz,
3-D seismic examples from Central Lake Maracaibo, Maraven's Block I Field,
Venezuela, in P. Weimer and T. L. Davis, eds., AAPG Studies in Geology
No. 42 and SEG Geophysical Developments Series No. 5, AAPG/SEG, Tulsa,
p. 69-82. |
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Paleocene Guasare Formation.
In between, eight seismic sequences occur within the Eocene horst section.
The adjacent stratigraphic sections east and west of the horst block are
thicker than the East Flank section. The C sands in Block I form a retrogradational
clastic sequence deposited as transgressive (70-80%), highstand (10-15%),
and lowstand wedge and incised valley fill (10-15%) systems tracts with
prominent marine-flooding surfaces separating these systems tracts. The
main reservoirs are thick-bedded transgressive sandstone deposits.
INTRODUCTION
The use of 3-D seismic data
to interpret old producing fields has become very important in field development.
When integrated with well, core, and production data, 3-D seismic data
provide the best tool to determine the stratigraphic and structural framework
for an area. Maraven, S.A., one of Venezuela's three national oil companies,
has been using 3-D seismic data to locate new wells by accurately defining
faults and stratigraphic terminations/pinchouts and by developing new geologic
models to better develop their existing fields. In addition, the mapping
of seismic horizons and amplitudes combined with time and horizon slices
have been used to determine reservoir trends in fields.
The Maracaibo Basin is an
intermontaine basin today, lying between the Perija and Merida Andes in
the northwest corner of Venezuela. Maraven's Block I is 10 ¥ 22 km
and is in the north-central part of Lake Maracaibo along the Icotea fault
(Figure 1). This field has more than 550 wells, which have produced more
than 1800 MMBO during the past 40 years, mainly from structural traps.
The Block I area is the southern continuation of the Lagunillas field and
the northern part of the Lama field (Delgado, 1992). The purposes of these
examples are to show the use of 3-D seismic data to (1) define the structure
and stratigraphy of this Block by integrating older log, core, and production
data, (2) to develop a seismic and sequence stratigraphic model for the
Lower Eocene Misoa C sands in the East Flank, and (3) highlight two successful
wells that were drilled using 3-D seismic technology. The 3-D seismic data
allow, for the first time, the complex fault relationships of the Icotea
and Eastern Boundary faults to be resolved and major sequence boundaries
and systems tracts to be recognized. The 3-D seismic data were utilized
to illustrate some of the various methodologies used to better visualize
the reservoir at both a regional and a prospect scale.
METHODOLOGY
The structure and stratigraphy
of Maraven's Block I were re-interpreted using 3-D seismic data integrated
with well logs, cores, older 2-D seismic lines, and synthetic seismograms.
Both Landmark and Charisma software with Sun |
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ABSTRACT
The structural and stratigraphic
framework of Maraven's Block I was re-interpreted using 3-D seismic and
existing data as part of an evaluation of the remaining oil potential.
More than 1800 MMBO have been produced from Block I in the past 40 years,
mainly from structural traps. In order to maintain production levels, it
has become increasingly important to define the seismic stratigraphic framework
for the area and to accurately locate faults and stratigraphic pinchouts.
The dominant structures are
the Icotea fault, its conjugate fault system, and the Eastern Boundary
fault. The most prominent fault is the NE-striking Icotea fault, which
subdivides the area into two main structural blocks, a graben in the West
Flank and a horst in the East Flank. The Icotea fault is a highly complex
fault zone with a long history of deformation. It is a nearly continuous
fault zone with both vertical and lateral offsets and is locally inverted.
Along the eastern flank of the Icotea, prominent reverse-fault bounded
upthrown blocks, called the Attic, have developed. Along the western flank,
contraction has re-activated listric faults into reverse and thrust faults.
Major northwest-striking normal faults delineate a large paleoarch that
occurs in the south-center of the East Flank. This phase of faulting produced
small horst and graben blocks bounded by normal faults that dip to the
northeast and southwest. The Eastern Boundary fault is subparallel to the
Icotea fault and is an east-dipping normal fault that has been locally
inverted and occurs in a synclinal area of the block. Two play concepts,
utilizing (1) horizontal wells in Attic and (2) vertical wells along the
Eastern Boundary fault, were successfully tested during this study.
The stratigraphic section
includes, from oldest to youngest, pre-Triassic basement rocks; the Jurassic
graben-fill Quinta Formation; the Cretaceous Rio Negro, Cogollo Group,
La Luna, Colon, and Mito Juan formations; the Paleocene Guasare Formation;
the Eocene Misoa Formation; the Miocene La Rosa, Lagunillas, and La Puerta
formations; and the Quaternary El Milagro Formation. Only the lower part
of the Eocene Misoa Formation (C sands) is preserved in Block I, and most
of the Eocene B sands and all of the Pauji were either eroded or not deposited
in this area. The main reservoirs occur in the Eocene Misoa Formation and
the basal Miocene Santa Barbara member of the Lagunillas Formation. Sedimentation
occurred throughout the Eocene and was strongly influenced by tectonism.
The Eocene section in the horst block is up to 760 m thick and is bracketed
by two major unconformities. The upper angular unconformity places the
basal Miocene Santa Barbara member (16-25 Ma) over the Eocene Misoa C sands
(45-54 Ma). The lower disconformity (54 Ma) occurs at the top of the
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