Photogeology and GIS in oil exploration in ecuador
Applications of the GDIM within the amazonic region
In order to demonstrate the use of the proposed
methodology, we describe here its application within a
pilot area in the Equatorian Amazon region. The pilot
area is the oil exploration block 28 of the Tripetrol
Exploration Company, which is located west of the
Andes, at the beginning of the Amazon Basin and
between the main rivers Pastaza, Puyo and Napo (see map
1). The exploration block and its direct surroundings
cover an area of about 8,000 km2.
Within the area there are sedimentary rocks present of
marine and continental origin, expressed mainly as
Cretacic, Tertiary and Quaternary terrains. The resulting
lithologies generate favorable environments for the
formation of petroleum generating rocks.
The Tectonic environment of block 28 is a compressive
"back arc, in which the Jurassic/Cretaceous terrains form
tight folds at one side and Abitagua intrusive at the other
side. The Tertiary terrains on the other hand, form very
wide foldings and softer thrusts towards the west plain.
The geological formations are oriented in a North-Northwest
direction, towards the Pastaza faults, where it
turns east in a North Northeast direction.
The intrusive body of Abitagua is highly fractured
because of its rock nature and limits with the West basin
with faults contact.
The remote sensing products which were used are the
following:
1) Landsat TM images, of several years, joined
together in a mosaic.
2) SAR Radar imagines
3) Aerial photographs scale 1:60.000.
These products were obtained by the company
INFOESPACE.
For the interpretation of the Landsat TM satellite images
a 2,7,4 band combination was used, this combination
permits to study the geological structures but furthermore,
is of use in a second phase when access roads to the
exploration have to be planned, to often very in hostile
areas.
Geological lineaments
In spite of the thick and continuous vegetation layer of the
humid tropical forests, the cartographic alignments by
photo geology are various and well recognized.
An old system of Geological Lineaments, with a North-Northwest
direction is located at one side of of the study
area, and at the other side the great alluvial plain known
as the Pastaza Depression is found. A young or
reactivated system of an old system of Geological
Lineaments with a North-Northwest direction can be
recognized witin the remote sensing due to the
transperancy of the younger sedimental Meza formation
and is located in the surroundings of the two comunities
“El Puyo” y “10 de August”. This system limits the
Mirador anticlinal and controls the course of the great
Pastaza River. The young Geological Lineaments with the
North-Northeast direction are associated to Pastaza River
and cuts the proceding of the older or reactivated
Geological Lineaments. The youngest Geological
Lineaments with a North-South direction cut the recent
alluvial deposits.
Faults
The Geological Lineaments that prove some kind of
displacement have been considered as line faults. While
on the other hand, Geological Lineaments, varying
between North-Northwest and North-Northeast are
interpreted as thurst faults. The most remarkable thrust
faults are the following:
- The faults associated to the intrusive rocks,
- The Fatima Fault that is bordered at East by the
anticlinal Mirador, and crosses the beginning of the
Bobonaza river, and,
- The Cosano Villano Bobonasa fault that borders in
the East the Oglan-Autapi anticlinal.
Geological Lineaments with an East-West direction
coincide with the normal faults expected at the bottom
and at the beginning of the Mirador folding system. This
way the Geological Lineaments that can be identified in
the terrain through remote sensing images are limited to
the North and the South by the anticlinal Mirador. The
Geological Lineament that forms the main course of the
Pastaza River is interpreted as a right or dextral fault that
displaces former structures and is generrally known as the
Pastaza River fault.
Foldings
Within the study area there are tectonic forzes with
Eastwest and Southwest characteristics of the back arc
that result in different folding, faults and fractures systems
with clear defined directions.
Therefore any structural element can be predicted by
guiding us by the Geological Lineaments. Based on this
analysis, it can be concluded that the combination of an
anticlinal structure and a fault, forms a double structure
which is favorable for the presence of high structures, or
with other words the possibility of oil reservoirs. When
Geological Lineaments are identified that correspond to
faults, it is also probable that high structures are found.
The axis of the foldings in the remote sensing images are
evidenced of the morphologic oval characteristics of the
formation. Meanwhile, the curved form of the drainage
patterns and the riverbed, can be of great help to find the
axis of the foldings, because these suggest obstacles of a
structural nature. The main directions of the foldings axis
South of the Pastaza River fault are North-Northwest –
South-Southeast. North of the same fault the directions
are North-South and NorthNortheast – South-Southwest.
The most pronounced anticlinal within the study area is
the Mirador anticlinal.
Construction and use of GDIM
With the use of the different remote sensing images as
were indicated before, the PDIM was applied, generating
density isoline every 5 units of intersection density. Based
on the intersection density units, and considering a map
scale of 1:100,000 a classification was made in which
maximum values are considered to be superior to the 40,
high values start at 30 and go up to 40, medium values are
in a range between 15 and 30, and finally, low values are
the minor to 15.
Taken into account this classification it was found that the
PDIMethodology gives high values at the Westside of
block 28 following a North-South direction, which
corresponds with the instrusive rocks belt and the
instrusive fault zone. From a prospection point of few this
indicates that it is possible to find fractured deposits at the
high structure near the Pastaza River and Illocullin River.
Areas with high values of intersection density are found in
the Arajuno River, which starts in the center of block 28
and heads towards its Northeast and Southeast corners.
Clear trends that can be distinguished with the PDIM in
this study area, are the North-Northeast and North-West
directions of the geological lineaments, the first one
coincides with the failure transcurrent dextral system type
strike-slip while the second one coincides with the
transcurrent sinestral antithetical systems that aligns
following the Pastaza River.
