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Chapter 1 Petroleum Geology of Venezuela

General geology The history of oil exploration in Venezuela Petroleum basins

PETROLEUM GEOLOGY OF VENEZUELA

Figure 1.0

100,000 m

200,000 m

300,000 m

400,000 m

500,000 m

600,000 m

700,000 m

900,000

La Vela offshore

– 1,300,000 m

Gulf of Venezuela

La Vela Coro

Tiguale

W.Mara Mara

La Paz

er

Tocu y o

YARACUY

Valencia

Riv

CARABOBO

Barquisimeto

Lama

ZULIA o

Ca

tat u

m

Lake Maracaibo

er R iv

b

Yucal - Placer

San Juan de los Morros San Carlos

Trujillo

Motatán

El Rosario

r

MIRANDA

ARAGUA

Lago Ceuta Lamar centro Tomoraro

Río de Oro

Tu

Los Teques

Mene Grande

Alturitas

Caracas

Maracay

LARA

Bachaquero

Urdaneta

D.F.

San Felipe

Cabimas Tía Juana Lagunillas

Boscán

– 1,100,000 m

FALCON

Las Palmas Hombre Pintado Media Maracaibo La Mene de Maurda Concepción Ambrosio Sibucara

e

Gu a

1.43

y

sa re

Ri

– 1,200,000 m

er

Caribbean Sea

Cumarebo

El Mamón

Ri v

v

Fig

– 1,000,000 m

800,000 m

Jobal Roblecito Valle

COJEDES 48

1.

PORTUGUESA

ig

Dakoa Guavinita Ruiz Belén Palacio

fig

Barinas

48

40

Mérida

1.45

1.

Tarra

Bella Vista Fig

36

1.

Las Cruces

Copa Macoya Saban Ipire

Las Mercedes

F

Guanare

fig

Los Manueles

Tucupido

Punzón

TRUJILLO

1. ig

F

Ri

Apure River G uá

rico R ive r

1.48

r ve

Fig

p

e

v

A

ur

er

TACHIRA

Sinco

MACHETE aR i

BARINAS

GUARICO

Silvestre

at

Silván

MERIDA

– 900,000 m

San Fernando de Apure

San Cristóbal La Alquitrana

APURE

– 800,000 m La Victoria Guafita

Arauca R i ver

Ri auca ver Ar

BOLIVAR

Legend Oil field

State Boundaries

Gas field

Cross Section

Condensate field

State Capitol

Oil + Condensate field

River

– 700,000 m

0 0

20

40 20

Meta River

60 80 100 120 km 40 60 80 miles

COLOMBIA

– 600,000 m 100,000 m

200,000 m

Location map of oil fields in Venezuela.

1

1

300,000 m

400,000 m

500,000 m

600,000 m

700,000 m

800,000 m

900,000

00 m

700,000 m

800,000 m

1,000,000 m

1,100,000 m

1,200,000 m

1,300,000 m

1,400,000 m

1,300,000 m –

Tobago

Caribbean Sea

Dragón Patao

Margarita Island Mejillones La Asunción

Río Caribe

N. ESPARTA

1,200,000 m –

Coche Cubagua

SUCRE Cumaná

Caracas

r

e

y

Barcelona

ig

F

Dakoa Guavinita Las Mercedes Ruiz Belén Palacio

Copa Macoya Saban Ipire Bella Vista

Un ar e

Riv e

r

Fig PAO

1.50

HAMACA

Ori n

River co v

1.50

BELT

ZUATA

Ciudad Bolívar

t

v

Fig

Aro iv R

er

San Fernando de Apure

Caroni

ua

1.48

Z

rico R ive r

Fig

o

ORINOCO

MACHETE

er

G uá

Pilón

Morichal

aR i

Apure River

1,000,000 m –

Bitor Area Cerro Negro

1.45

GUARICO

DELTA

Bombal Uracoa Tucupita

Jobo

Barso

ig

F

re iv Tig R e

Greater Temblador area Temblador

Fig

48

1.

ive r

r

Punzón 8

4 1.

Tajali

R

Maturin El Furrial Carito a ip a Santa BárbaraG u n

es

Tucupido

al

La Ceiba Tacat Greater Oficina area

Greater Anaco area

Loran

rn

Jobal Roblecito Valle

Jusepín Pirital

ANZOATEGUI

1,100,000 m –

de

Yucal - Placer

Quiriquire Orocual

Manresa

Quiamare

San Juan de los Morros

Posa

MONAGAS Pe

MIRANDA

ARAGUA

er

5

Riv Tu

Los Teques

Gulf of Paria

iv

1.5

Maracay

Trinidad

Jua San R

n

Fig

D.F.

BO

Ri

er

900,000 m –

AMACURO

Reclamation Zone

BOLIVAR

Greater Anaco area

Greater Oficina area

Santa Rosa La Florida

C

u

El Roble

Casca

a

Carisito

Maulpa

aR

Onado

r

ver

i

00 m

900,000 m

BOLIVAR

Aguasay

San Joaquín

Casma

Cantaura

San Roque Santa Ana El Toco

Acema Mata

Acema - Casma

Mapiri Kaki

Naroo Boca

Guere

Oscurote

Nipa

Oritupano Guara

Leona

Chimire Budare

Elotes

Oficina

Dación

Lobo

Adas

Trico

Oveja 700,000 m

800,000 m

Melones

900,000 m

1

2

PETROLEUM GEOLOGY OF VENEZUELA

Figure 1.1 68˚ 64˚ 60˚ Guajira Aruba Peninsula Paraguaná Bonaire Grenada Caribbean Sea Peninsula Gulf Coro of Venezuela La Tortuga Tobago Porlamar nge Paria Maracaibo uis Ra ange Araya La Costa Range Cumaná C. de La Costa L R Trinidad a Caracas Cariaco Carúpano Sanaragu Barcelona Valencia B Los Teques Interior Range Lake Barquisimeto Interior Range ipa Maturín Maracaibo es uan d Trujillo (Central Branch) (Eastern Branch) R. G igre T An Tucupita Rio Guanare n a el zu ne Mérida Barinas e Ciudad Bolívar V o ric ua o G sa Ri e gu rtu Po

o Ri

Apu

co

rino

San Rio O Fernando

re

7˚

100- 250 m 0-100 m

Rio Meta

Puerto Ayacucho

Mountain Belts

a an ay if u s G as M

Foothill Regions Plains and Coastal Plains

Colombia 100

0 50

200 km

Brazil

150

The Venezuelan physiographic provinces are: 1) The mountain belts: Venezuelan Andes and the Caribbean Mountain System (Perijá, San Luis; Baragua and La Costa Range); 2) the foothills; 3) the coastal plains; 4) the plains between the Orinoco River and the mountain belts; 5) and the Guayana Province or Massif (after NB-18-ll map; MMH,

3

3˚

Brazil

72˚

1976).

Reclamation Zone

250 to > 5000 m

Rio Arauca

Sea Level 3˚

1

11˚

Guyana

Rio

S. Cristóbal 7˚

N

ic nt n tla a A ce O

Co

lom

11˚

bia Pe rijá Ra ng e

72˚

68˚

64˚

the chapter, and also a time chart with the main geological ages indicated and a geopolitical map with all Venezuelan cities and places cited in the text (Fig. 1.0). Also, we include a section called the “History of Oil Exploration in Venezuela” for those who may be interested in the history and growth of Venezuela’s most important industry. At the end of the chapter, a list of references consulted for the compilation of figures and text is provided. We also include references to other papers and books that should be useful to those who wish to study the geology of Venezuelan petroleum basins in more detail.

60˚

Introduction The purpose of this chapter on the Petroleum Geology and Basins of Venezuela is to give the reader a general overview of the geology of the country. Our knowledge has been greatly enhanced by the oil industry and mining activities that have been ongoing for almost a century. Without entering into a detailed analysis of the numerous and unsolved problems with the geology, we have integrated the information presented in many papers and books written on Venezuelan geology. We have tried to attribute the original contributions of all authors, and have also presented summations based upon our own experience. We have avoided specialized and detailed points of view concerning stratigraphy, sedimentology and geotectonic evolution, instead choosing to simplify the geology because of our diverse readership and limited writing space. For non-specialized readers, we include a Glossary at the end of

Physiographic provinces There are five main physiographic provinces in Venezuela (Fig. 1.1): 1. Mountain ranges a.Venezuelan Andes system b. Caribbean mountain system (Perijá Range, San Luis and Baragua Ranges, La Costa Mountain Range) 2. Foothill regions 3. Coastal plains 4. Mainland plains 5. Guayana Province. Rocks of a wide age range (Precambrian through Neogene) are found in the mountain ranges of La Costa and the Andes. Their formation history is closely associated with the evolution of the northern margin of the South American plate from the Eocene to the present. The foothill regions (9430 km2) are covered by Neogene molassic sediments whose main physiographic features are terraces formed during glaciation/deglaciation processes.

GENERAL GEOLOGY

PRECAMBRIAN

Figure 1.2

Cenozoic Orogenic Belt

0

Caribbean Sea Caribbean Frontal Thrust

300 km

us Santa hm Marta Upper Ist a Paleozoic m a n Orogenic Pa Belt

Caracas Valencia Lower Paleozoic Orogenic Belt

Mérida

4˚

San Cristóbal Apure Fault

Venezuela

Weste rn Ran ge East ern R ange

Pacific Ocean

8˚

Bogotá

62˚

Paleozoic and Cenozoic Basins as a Precambrian Basement

Trinidad

o pin n Es rabe G Ciudad Bolívar

ult Fa ira tam Al Cuchivero

Imataca Province

Province

Guayana Shield

Pastora Province Roraima Province

Reclamation Zone

78˚

N

Cuchivero Province

Brazil

Colombia

Cenozoic Orogenic Belt

Imataca Province

Late Paleozoic Orogenic Belt

Pastora Province

Early Paleozoic Orogenic Belt

Cuchivero Province

Paleozoic and Cenozoic Basins of the Precambrian Basement

Roraima Province

Eastern Basin of the Precambrian Basement, Imataca Province Possible Extension

Boundaries of the Cordilleran Systems Overthrusting

Northern South America´s distribution of allochthonous terranes in which Precambrian rocks are present. These terranes were sequentially sutured to the South American continent during the Ordovician-Silurian and later during Late Mesozoic through Recent.

The coastal plains (117,220 km2) are concentrated in four broad regions: 1) north of Falcón State (Fig.1.0), 2) Barcelona coastline (Anzoátegui State), 3) Orinoco River delta (Delta Amacuro State), and 4) north of Sucre State. The mainland plains (260,000 km2), with an extensive drainage network, encompass the land between the northern mountain ranges and the Guayana Province; they are the result of the sedimentary filling of the Eastern and Barinas-Apure Basins. In the south is the Guayana Province (also called “Guayana Massif,” “Guayana Shield,” or “Guayana Cratón” in the geological literature) with 425,000 km2 of Precambrian-age terranes, with some Pleistocene plains built by the Orinoco River and some of its tributaries.

Precambrian terranes The Venezuelan Precambrian terranes outcrop in the main mountain ranges of the country and in the Guayana Province. Because of the tectonic history of the northern South American plate, both allochthonous and autochthonous Precambrian rocks are found. Figure 1.2 shows the distribution of these terranes; those located north of the Orinoco River were overridden by Paleozoicage crustal fragments that were accreted, or added, to the South American plate. The autochthonous terranes are located in the Guayana Province, and also form part of the basement of the Paleozoic to Cenozoic sedimentary basins south of the Apure Fault. There are four provinces of Precambrian rocks in the Guayana Province: Imataca, Pastora, Cuchivero and Roraima (Fig. 1.2). It has not been possible to discriminate different provinces (with respect to age) in the basement of the oil basins to the north of Guayana Province; this is because there are few wells that have reached the basement in these basins and the available descriptive information is scarce. The accretion of allochthonous terranes on the South America plate began during the Early Paleozoic (Caledonian Orogeny: 570 to 385 Ma); part of these rocks outcrop near Mérida and San Cristóbal in western Venezuela. Later, during the Hercinian Orogeny (385 to 245 Ma), occurred the suturation, or welding of the allochthonous blocks. These included Precambrian rocks, among which only the granitic rocks of the Sierra Nevada in the Santa Marta Massif (Colombia) have been dated (Fig. 1.2). The last collision began during the Cretaceous; this allochthon includes rocks of Precambrian age near the city of Caracas (Federal District) and south of Valencia (Carabobo State).

1

4

PETROLEUM GEOLOGY OF VENEZUELA

Distribution

Figure 1.3

78˚

0

100

62˚

300 km

200

Cenozoic Orogenic Belt

Panamá Isthmus

Caribbean Frontal Thrust

Santa Upper Marta

Caracas

Paleozoic Orogenic Belt

El Baúl Early Paleozoic Orogenic Belt

78˚

nge rn R a

Weste rn Ra nge

Caparo ult re Fa Apu

Bogotá

East e

Pacific Ocean

8˚

4˚

N

Caribbean Sea

no pi en lt Es rab Fau G a

ir

Venezuela Reclamation Zone

Lower Paleozoic Basin

Colombia

8˚

m

ta

Al

Guayana Shield 4˚ 62˚

Cenozoic Orogenic Belt

Lower Paleozoic Basin

Upper Paleozoic Orogenic Belt

Guayana Shield

Lower Paleozoic Orogenic Belt

Boundaries of the Cordilleran Systems

Brazil

Overthrusting

Northern South America´s distribution of allochthonous terranes in which Paleozoic rocks are present. These terranes were sequentially sutured during the Ordovician and Silurian, then during the Carboniferous and finally during Late Mesozoic through Recent.

1

5

Paleozoic terranes The rocks of Paleozoic age in Venezuela are found in several regions, geologically grouped as allochthonous or autochthonous terranes of South America. The autochthonous terranes are found in the subsurface of the Barinas-Apure and Eastern Basins (Fig. 1.21), south of the Apure Fault (Fig. 1.3). These rocks are typical “red beds” from Gondwana (South America and Africa before its rupture) and Laurentia (North America and Greenland before its rupture); they are preserved only in the deep structural depressions of these Venezuelan basins. The allochthonous terranes are distinguished by the age in which they were tectonically accreted to the north of the South American plate; there are those accreted during the Early Paleozoic, others during the Late Paleozoic and the latest during the Mesozoic.

Figure 1.3 shows the distribution of allochthonous terranes that were welded to the Lower Paleozoic autochthons during Ordovician–Silurian time. Those rocks accreted during the Lower Paleozoic are now considered part of the basement from the point of view of later Caribbean tectonic history. They include that part of the orogenic belt north of the Apure Fault, the actual Andes and Maracaibo Basin. In the Andes, rocks of the Lower Paleozoic allochthonous terranes include granitic and shelf/slope sedimentary rocks (Ordovician–Silurian). Ordovician metasedimentary rocks are found in the subsurface basement of the Maracaibo Basin and in the Andes. Devonian-age allochthonous terranes, welded to South America during the Late Paleozoic, outcrop in the Perijá Mountains. Part of the accretionary history of the Upper Paleozoic onto the Lower Paleozoic includes granitic rocks, formed as a result of subduction below the northern border of South America. These include rocks of the El Baúl region (Permian age) and those found in the subsurface of Eastern, Barinas-Apure and Maracaibo Basins (Carboniferous age). The accreted belt included sedimentary sequences of Carboniferous and Permian ages; these rocks now outcrop in the Perijá and Andes Mountains. The last of these allochthonous terranes is the Caribbean Mountain System that extends from Guajira Peninsula (Western North Venezuela) to Paria Peninsula (Eastern North Venezuela), including the subsurface basement of the Gulf of Venezuela and the La Costa Mountain Range. In this terrane Paleozoic rocks of Devonian to Permian ages are found.

GENERAL GEOLOGY

PA L E O Z O I C A N D M E S O Z O I C

Figure 1.4

Age

Perijá and Guajira

Andes

Guárico and Cojedes

La Costa Range

Ipire

Pueblo Nuevo Las Brisas (Zenda) Macuro

?

?

Seco Cojoro/COCINAS La Quinta Conglomerates El Totumo Macoita

Jurassic

La Quinta

La Gé Tinacoa Volcanics

Guacamayas ?

Triassic

Correlation chart of the most

Mesozoic terranes

important Triassic-Jurassic units in Venezuela.

Triassic-Jurassic

The Triassic is not present in Venezuela or, at least, no evidence of its presence has been found and documented. The oldest part of the Jurassic system (208 to 181 Ma) is represented by Volcánicas de la Ge (Perijá) and Volcánicas de Guacamayas (El Baúl), which predated the red bed sedimentation of the La Quinta Formation and the whole expansion process related to the Gulf of Mexico or Proto-Caribe opening. They are the lateral equivalents of the Volcánicas de El Totumo (Perijá) (Fig. 1.4),

Figure 1.5 Guajira

73˚

63˚

Paraguaná

12˚

1

2

3

Pe

rij

á

3

N

Caribbean Sea

12˚

Coro

Maracaibo

El Pilar Fault Ur Caracas ica 4 Fa ul Espino t Graben

In Venezuela, the Pangean continent (the supercontinent comprising America, Europe and Africa) rifting produced several main structural features that later influenced the evolution of the Venezuelan sedimentary basins. Inside continental Venezuela, the Proto-Caribe opening induced the development of northeast-oriented extension valleys or grabens (Fig. 1.5). Among these valleys are the Apure-Mantecal, Espino, Andes-Perijá and Maracaibo grabens. It has been postulated that the Jurassic rocks in the deepest parts of the Interior Mountain Range of Eastern Venezuela were involved in this deformation, as deduced by the trend of the main grabens, such as Apure-Mantecal and Espino. However, this theory has not yet been proven. All these grabens were filled during the Jurassic by red bed (continental) sediments, diverse volcanics, and occasional shallow-marine clastics and limestones. Their preserved sequences outcrop in many places: the Guajira and Paraguaná Peninsulas (Cojoro and Cocinas Groups; Pueblo Nuevo Formation), and the widespread La Quinta Formation of Western Venezuela. They also occur in the subsurface of Eastern Venezuela Basin (Ipire Formation).

Trinidad

Maturín

Andes 3 8˚

8˚

Santander Massif 73˚

Colombia

Apure-Mantecal Graben

0

100

200

300 km

63˚

Distribution of Jurassic rocks: 1) in Perijá Range; 2) as part of the economic basement of Maracaibo Basin; 3) in the Andes; 4) in Barinas-Apure and Eastern Venezuela Basins (Apure-Mantecal and Espino Graben). It is believed that they are involved in deep thrusting within Eastern Venezuela´s Interior Range (after Bartok, 1993; Passalacqua et. al., 1995; and Lugo and Mann, 1995).

1

6

PETROLEUM GEOLOGY OF VENEZUELA

Cretaceous

Figure 1.6

Early Cretaceous. The major sedimentary facies distribution and stratigraphy of Early Cretaceous rocks (146 to 95 Ma) are shown in Figs. 1.6 and 1.7. In Western Venezuela, the sedimentation was initially controlled by the Jurassic grabenfault systems. This is evidenced by the variable thicknesses of Rio Negro Formation clastics, which range from more than 2 km near the south of Machiques Trough, to only a few meters thick in some places of the North-Andean flank. Later the subsidence stabilised and there was an extensive transgression of an open sea over the Western Venezuelan shelf causing the carbonate sedimentation of the Cogollo Group. The lateral clastic equivalent of these carbonates in the Cratón or Guayana Province margins is the Aguardiente Formation. In Central Venezuela, there are some remains of an older

N

(?) S Chimana U C El Cantil R E Barranquín

COGOLLO

TEMBLADOR

Through U Th riban rou te gh

Río Negro

Machiques

Peñas Altas Aguardiente

Canoa

Guayana Shield

200 km

0

Exposed Igneous and Metamorphic Basement (Guayana Shield).

Shelf Environment Carbonates

Continental-Fluvial Environment Sandy Clastics

Hemipelagic/Pelagic Limestones and Shales

Coastal and Transitional Environment Sandy-Shale Clastics

Sediment Supply Direction

Distribution of dominant sedimentary facies during the Neocomian-Albian (Early Cretaceous) north of the Guayana Shield. Representative stratigraphical units of this facies association are indicated.

Figure 1.7

Perijá and Lake Maracaibo

Age

Andes and Barinas-Apure

Northern Guárico

Eastern Interior Range

La Grita (Capacho)

Albian

Aptian

Querecual(*) (Cutacual, "Valle Grande")

Maraca

C Aguardiente O G Lisure O Guáimaros Piché Apón L Tibú Apón L Machiques O Río Negro Tibú

Chimana

?

S

"Punceres"

(Exotic Blocks)

"Guácharo"

El Cantil

?

U

"El Mapurite" García Taguarumo

C

"Basal Clastics" Picuda

?

Barremian

Barranquín

Río Negro

Neocomian

Morro Blanco

? Macaira Limestone ?

Venados "Río Solo" ?

?

Carbonate Reservoir

Sand / Seal Pairs

Sand / Sandstone Reservoir

Seal

1

7

E

Source Rock

(*)

The Querecual Formation extends to the Late Cretaceous

Correlation chart of the most important Early Cretaceous units of Venezuela. Informal units are within quotation marks. See Yoris, 1985, 1988, 1992, on Sucre Group.

R

GENERAL GEOLOGY

MESOZOIC

(also Early Cretaceous) carbonate shelf, which is discontinuous along the deformation (mountain) front to the north of Guárico State (Macaira Limestone). Figure 1.8

?

N

Maracaibo Socuy

Caracas

La Luna

Mucaria Navay

Infante

Gu ay ac án

Capacho

Barcelona Maturín GUAYUTA TEMBLADOR

Escandalosa

Guayana Shield 0

200 km

Igneous-Metamorphic Basement (Guayana Craton)

Shelf Carbonates

Continental-Fluvial Sandy Clastics

Bathyal (Pelagic) and Shelf Shaly Limestone, Chert and Siliceous Mudstone

Coastal and Transitional Sandy and Shaly Clastics

Bathyal and Abyssal Hemipelagic/ Pelagic Shales and Limestones

Dominant sedimentary facies distribution during the Cenomanian-Campanian (Late Cretaceous) at the northern edge of the Guayana Shield North. Typical units of these sets of facies are indicated.

In Eastern Venezuela, the sedimentary history resembles that of a passive “Atlantic” type margin. These rocks belong to the Sucre Group, which at the base are sandy clastics and some shelf limestones of the Barranquín Formation (whose thickness is more uniform than its Western Venezuela equivalent). Later, extensive and well defined carbonate-clastic shelf sedimentation was developed (El Cantil and Chimana Formations). The main difference with the Early Cretaceous of Western Venezuela is that in the Interior Range of Eastern Venezuela, the lower contact with older sequences is unknown and the thicknesses of the Early Cretaceous units are greater. For example, the Barranquín Formation is more than 1 km thick everywhere, with massive, carbonate shelf sedimentation in its middle part (Morro Blanco Member of Barremian age–114 to 118 Ma) in the northernmost outcrops.

The thickness of both El Cantil and Chimana Formations is several times the thickness of their lateral equivalent in Western Venezuela, the Cogollo Group. Late Cretaceous. The distribution of paleoenvironments and stratigraphic units during the Late Cretaceous is shown in Figs. 1.8 and 1.9. Figure 1.10 condenses the correlation chart for these units for all of Venezuela. A diachronic and extensive marine invasion began at the end of the Albian, moving from east to west and invading the south of Venezuela, which had been emerged and undergoing erosion since Late Jurassic and possibly Paleozoic times. This marine invasion coincides with the worldwide transgressive pulse of the Late Cretaceous, recorded in America and Europe through the sedimentation of organic-rich limestones, shales and cherts; these rocks are recognized in Venezuela as the QuerecualSan Antonio (Guayuta Group), Mucaria, Navay and La Luna Formations. The maximum transgression and lack of oxygen is believed to have occurred between the Turonian and the Campanian (72 to 91 Ma). The La Luna, Navay and Querecual Formations are the source rocks for the oil basins of Venezuela, and were deposited during the late Albian to the Turonian (95 to 88 Ma). The La Luna Formation ranges between 50 and 300 m thick in Western Venezuela, while the Navay Formation is close to 600 m thick in the South-Andean Flank and thickens to the northeast. In Western Venezuela, the lateral facies variations of these source rocks consist of pelagic and phosphatic limestones, dark shales and shelly limestones that grade to sandy clastics and glauconitic facies in the southeastern flank of the Andes in Tachira State. In North-Central Venezuela, these facies occur in the Mucaria Formation and Guayuta Group .

1

8

PETROLEUM GEOLOGY OF VENEZUELA

Figure 1.9 on e ati c m van r d fo A ? De nt o Fr

Marine Sediments (Undifferentiated)

N

?

Mito Juan ?

Colón

San Juan

?

Cujisal ? Positive areas that include Paleozoic and Mesozoic rocks

Río de Oro

?

Burgüita

Guayana Shield

?

Igneous-Metamorphic Basement Sandy Clastics

Clay-Silt Clasts

Sedimentary Supply Direction

Positive Areas

Shallow Marine Carbonates

Postulated Depocenter Axis Thrust Front

Sedimentary facies distribution during the Maastrichtian (Late Cretaceous) at the northern edge of the Guayana Shield. Typical units of these sets of facies are indicated. Notice that the axis of the Western Venezuela depocenter is subparallel to the deformation front, as a consequence of the plate collision between Nazca and South American plates.

The Guayuta Group is thickest in NorthEastern Venezuela, being more than 1 km thick in its type area (Anzoátegui State). In the Eastern Basin, this unit changes laterally to the south, losing its source rock character by giving way to sedimentation from shallower environments, from shelf to coastline and even continental, which are defined in the subsurface as the Canoa and Tigre Formations (Temblador Group). The Late Cretaceous in Venezuela ends in the Maastrichtian, with units that are regressive relative to the deeper environments of the source rock. In Perijá and the Maracaibo Basin, the La Luna Formation grades vertically to glauconitic limestones (Socuy Member), and dark shales with thin sandstones defined as the Colon and Mito Juan Formations. In the North-Andean Flank, the glauconiticphosphatic Tres Esquinas Member is present, which is the possible diachronic equivalent of the Socuy Member, underlying the dark shales of the Colón Formation. In the South-Andean Flank, the upper contact with the source rock is gradational to erosive with the basal sandstones of Burgüita Formation.

Figure 1.10 Perijá and Lake Maracaibo

Age

Mito Juan Maastrichtian

Colón

North-Andean Flank Mito Juan

South-Andean Flank

Colón

Burgüita

Tres Esquinas Socuy

Santonian

La Luna

Navay

Campanian

Quevedo

La Morita Coniacian

La Luna Guayacán / Caliza "O"

Southern Flank Eastern Basin Infante

G U A (Mucaria, San Antonio Y "Río Chávez" , Querecual, "Querecual of the North " ) U T A

(Regional hiatus at the base?) ?

Capacho

Sand / Seal Pairs

Reservoir (Sandy)

Seal

A

? "Exotic Blocks " ?

Canoa

Querecual

T A

continue through the Paleocene; Canoa and Querecual Formations start by the end of Late Albian.

9

Y U

Source Rock

Correlation chart of the most important Late Cretaceous units of Venezuela. Guárico and Vidoño Formations

1

G

TEMBLADOR GROUP

?

Reservoir (Carbonate)

Vidoño San Juan

San Antonio U

Escandalosa

Seboruco

Eastern Interior Range

Tigre

Guayacán

Turonian

Cenomanian

North of Guárico Guárico

GENERAL GEOLOGY

CENOZOIC

Figure 1.11

N

V

Lesser Antilles Arc

Caribbean Plate

V

Early Paleocene *

La Victoria

Middle Paleocene * Early Eocene*

Trujillo Maracaibo P Guasare/Marcelina agü e

en

am

M Cl arin Trujillo as e tic Paují s

ne

Li

s ic st

úl

Shallow Clastics

t

Western Range of Colombia Collision

Peñas Blancas a Cl

South American Block

Orocué/Mirador B

Humocaro

Ba

Farallón Plate

Andean Block

deep Fore Gobernador

w

V

Misoa

Barcelona

Roblecito

llo

-B SM

V

Morán

EL

Shallow Clastics

C

Matatere

a Sh

Central American Arc

on

b ar

y

MaracaiboSta. Marta Block

V

es

at

Guárico

Guayana Shield (*) Deformation Front Position

0

50 km

Orocue/Mirador = Barco-Los Cuervos-Mirador-Carbonera Fms. Event (Paleocene-Eocene) Guárico = Garrapata-Guárico Fms. Event (Paleocene)

Gobernador = Gobernador-Masparrito Fms. Event (Eocene)

Trujillo = Trujillo Fm. Event (Paleocene-Eocene)

Humocaro

= Humocaro-Quebrada Arriba Fms. Event (Eocene)

Misoa = Misoa-Caús-Paují Fms. Event (Eocene)

La Victoria

= La Victoria-Santa Rita-Jarillal Fms. Event (Eocene)

= Direction of sediment supply

= Thrust front

ESE migration of the Caribbean deformation front and associated episutural sedimentation during Paleocene-Eocene times. The Andean-South American boundary was located at the present position of the Santa Marta-Bucaramanga (SM-B) and Bocono (B) fault systems.

= Exposed areas

In North-Central Venezuela, the lateral equivalents of the Mucaria Formation grade vertically to the hemipelagic and turbidite sequences of the lower Guarico Formation. To the east, the bathyal sandstones of the San Juan Formation overlie the black cherts and sandstones of the San Antonio Formation. Then, in turn, the San Juan Formation grades vertically to the dark shales of the Vidoño Formation (late Maastrichtian–60 to 65 Ma). Cenozoic terrains Paleogene

Paleocene-Eocene of Western Venezuela. During late Cretaceous (Fig. 1.9) to early Paleocene, Western Venezuela was affected by the collision between the Nazca Plate (Pacific Ocean) and Western Colombia. There is evidence that the sedimentation of the Orocué Group (and probably Guasare and Marcelina Formations) was controlled by the deformation fronts of this collision (Fig. 1.11).

These fronts generated successively younger depocenters to the east of the actual Perijá Mountain range. Figure 1.11 summarizes the sedimentation and gradual evolution of the deformation front as the Caribbean plate passed north of the South American plate during the Paleocene-Eocene. For simplicity, several formations are summarized by one name only (e.g., “Misoa” refers to the sedimentation of lateral equivalents and/or closely related units, such as the Misoa, Caús and Paují Formations). Each “event” carries the most distinctive formation or group name. To the northeast of the South American plate, the oblique collision of the Lesser Antilles arc generated a series of sheets, or nappes, trending towards the south and southeast. These control the turbidite sedimentation of formations such as Trujillo and Morán.

1 10

PETROLEUM GEOLOGY OF VENEZUELA

Figure 1.12

Volcanic Arc

N

Caribbean Plate

Late Eocene

200 Km

Oca Fault System

Frontal Thrust

Maximum Subsidence Area

? South American Plate Advance of Allochthonous Terranes

? Shallow Clastic Sediments

Foredeep Sediments

Positive Areas

Pull-Apart Basin

Thrust Front

Generation of pull-apart basins at the boundary between the Caribbean and South American plates; the maximum subsidence areas were located north of Falcón State at this time (Late Eocene) (after Macellari, 1995).

Figure 1.13

Lesser Antilles

eV olc an ic c

V

Ar

Ac

tiv

V Caribbean Plate Extinct Volcanic Arc X XPampatar-Punta Carnero

Oceanic

?

Sedi me

Caribbean Deformation Limit Peñas Blancas ? Foredeep

ntat

io n

(U n

d iff

Vid o

ño-

?

Car

Barcelona

?

?

n ti

ate

d)

ata

s

e

Tinajitas

Caratas

?

50 Km

0

ere

Sl op

Roblecito

N

Atlantic Ocean

Maturín

Clastic Shelf

Positive Area

? ?

South American Plate

Paleocene-Eocene

Shallow Sandy Clastics

Lime-Clay Clastics Predominate over the Sandy Clastics (Slope Environment)

Turbidites

Positive Areas

Limestones

Direction of Sediment Supply Thrust Front

Regional geologic framework for the sedimentation at the northern flank of the Eastern Basin during the Paleocene-Eocene.

1 11

On the other hand, during the Paleocene, to the north and west of Maracaibo Basin, the Guasare Formation was deposited in shallower environments further away from the deformation fronts, and afterwards the Marcelina Formation in coastal-marsh environments. During the Eocene, a complex sedimentary setting existed in the Maracaibo Basin. Distinct deltaic/estuarine, coastal/fluvial and marine systems developed, depending on their geographic position with respect to the different deformation fronts, such as in Perijá or later on in Lara to the east. Formations such as Barco-Los Cuervos and Mirador-Carbonera (deposited between the Paleocene and Middle Eocene–65-40 Ma) represent two similar sedimentary pulses of fluvial-deltaic origin in the western part of Maracaibo Basin. In the central part of the basin, the Guasare, Trujillo, Misoa, Caús and Paují Formations were more marine lateral equivalents of the Barco-Los Cuervos and Mirador-Carbonera, with a relative, gradual deepening of environments to the northeast. In the Barbacoas region, east of Trujillo State, the average depth of the Eocene sea was shallow enough to deposit the transitional and coastal-marine sediments of Gobernador-Masparrito and HumocaroQuebrada Arriba Formations. Meanwhile, in Falcón State just north of the south-verging deformation fronts, the La Victoria-Santa Rita and Jarillal Formations were deposited. This sedimentation was associated with extensional basin subsidence related to along-strike faulting (i.e., a “pull- apart” basin) (Fig. 1.12). Paleocene - Eocene of North - Central Venezuela. Part of the accretion due to the Lesser Antilles is probably represented by the sediments of the Guárico Formation, plus the limestone and other older units in the olistostromes. During the Paleogene and Neogene, this fold and thrust belt migrated to the south and east of the nothern margin of

GENERAL GEOLOGY

CENOZOIC

Figure 1.14

Western Venezuela: Perijá, Lake Maracaibo, North-Andean Flank

Age

Carbonera E o c e n e

Paují

Western Venezuela: Trujillo, Lara and South-Andean Flank and Barinas-Apure

Carbonera Mene Grande Paují

?

Guasare Barco ?

Colón/Mito Juan Colon/mito Juan

Maastricht

Los Cuervos

Barco

O R O C U E

T r u j i l l o

H u m o c a r o

M o r a n

V a l l e

?

Roblecito

La Pascua/ Los Jabillos ?

Peñas Blancas

Tinajitas ?

H o n d o

Guárico

Colón

Sand/Seal Pairs

Eroded/Unconformable

Formation extends into the Campanian; the Carbonera, Paují, La Pascua, Roblecito and Los Jabillos Formations extend into the Oligocene. The Guárico Formation may reach down to the top of the Maastrichtian wherever the

Vidoño

San Juan

Eroded Interval

Venezuela. The Colón

Caratas

? (?) Garrapata

Reservoir (Sandy)

Paleocene-Eocene of

?

?

Seal

Correlation chart for the

absent.

Eastern Venezuela

Jarillal

Reservoir (Carbonate)

Garrapata Formation is

North-Central Venezuela

Santa Rita

Marcelina O R O C U E

La Victoria

(Misoa/Qda. Arriba/Gobernador)

Los Cuervos P a l e o c e n e

?

Masparrito

(Misoa/Mirador)

Cerro Misión ?

Pagüey

Caús (Mirador/La Sierra)

Falcón

the South American plate. Those rocks originally sedimented in the trough just in front of the belt (the foredeep) were later uplifted, eroded and re-sedimented into the trough. While the Caribbean plate moved to the east between the South American and North American plates, the influence of the fold and thrust belts also moved, but to the south, producing the new foredeep of the Roblecito Formation, with a probable age between the Late Eocene and Oligocene (?) (39-23 Ma). South of the new foredeep, the lithosphere bent due to the new load, causing the influx of the clastics that produced the La Pascua Formation. Paleocene-Eocene of Eastern Venezuela. During the Paleocene and Early Eocene, the sedimentation was not influenced by the Caribbean deformation fronts. The Vidoño (hemipelagic marls, siltstones and clays) and Caratas (sandstones) Formations accumulated on a passive continental margin slope.

It is possible that the influence of the oblique collision of the Caribbean plate on Eastern Venezuela began in the Middle Eocene—the first evidence may be in the sandy-glauconitic and foraminiferal-rich carbonates deposited on the foredeep margins located north of Venezuela (Peñas Blancas and Punta Carnero Formations and Tinajitas Member of Caratas Formation). On Margarita Island, the sandy and carbonaterich turbidites of the Pampatar (sandy rich) and Punta Carnero (carbonate rich) Formations represent a separate sedimentation from the Guárico and Roblecito, both in time and space, and are probably related to accretion near Barbados. Figure 1.13 summarizes conceptually the relationship between stratigraphic units and deformation fronts. Figure 1.14 summarizes the Paleocene-Eocene stratigraphic nomenclature, emphasizing the potential character of each unit as a seal or reservoir.

1 12

PETROLEUM GEOLOGY OF VENEZUELA

Figure 1.15

Positive Area

N

? San Luis / Patiecitos

?

da a Sala a/Agu Pecay

Guacharaca

Castillo

Casupal

El Paraíso

Churuguara

Positive Area

? Positive Area

Carbonera

ito Roblec

El Baúl Arc

?

La Pascua

? ?

Co

León

lo

?

Guafita

?

?

m

bi

a

0

Guayana

Shield rea eA v i t i s Igneous-Metamorphic Po

50 km

Basement

Shallow Sandy Clastics

Limestones

Depocenter Axis

Sandy and Pelitic Clastics of Shallow and Deep Environmen(Turbidites)

Positive Areas

Extensional Basin

Direction of Sediment Supply

Pelitic Clastics of Shallow Marine Environment

Thrust Front

Sedimentary regional framework in Western Venezuela (Maracaibo, Falcón, BarinasApure Basins and Guárico Sub-Basin) during the Oligocene. The main depocenters are located in Táchira (León Formation), Falcón (Pecaya and Agua Salada Formations) and Guárico (Roblecito Formation). Figure 1.16

Caribbean Plate Main Depocenter

N

Oligocene-Miocene La Vela Cove

La Pascua-Roblecito (Central-North)

Urumaco Trough Oca Fault System

Basin"Foreland" Incipient

Capiricual-Carapita (Eastern)

Frontal Thrust Advance

South American Plate Shallow Clastic Sediments

Positive Areas Plate Movement Vectors

200 km

Extensional Trough Thrust Front

Maximum development of the Falcón State pull-apart and generation of extensive positive areas in Maracaibo Basin and northern Falcón. Toward the south and east, the foreland basin evolved, developing "troughs" like those of the La Pascua-Roblecito Formations (Late Eocene-Oligocene) and Carapita-Capiricual (Early-Middle Miocene) (after Macellari, 1995).

1 13

Oligocene of Western and North-Central Venezuela. Since the Oligocene, the sedimentary accumulation in Maracaibo Basin was preserved mainly on its flanks. To the west are the sandy clastics of the Carbonera and Ceibote Formations (El Fausto Group), to the south and east are the fine clastics of the León Formation (Fig. 1.15), and to the center is the Icotea Formation (assigned by several authors to the Oligocene). The Icotea is only found in structurally controlled depressions, and its characteristic lithology consists of siltstones and claystones, with minor proportions of sandstones. The Falcón Basin reached its maximum development and deepening during the Oligocene. The sedimentation in the Falcón region resulted from a different tectonic setting than that of the Maracaibo Basin, Barinas-Apure and Eastern Basins. Figure 1.16 shows the extensional basins associated with major strike-slip faulting, especially in the north of Falcón State. These gradually evolved to the east, while the Caribbean plate moved in the same direction. In the north of central Venezuela, the trough containing the Roblecito Formation migrated to the east and southeast, favoring the advance of La Pascua sandstones to the south. These were followed and overlaid by clastics from the foredeep. Oligocene of Eastern Venezuela. During the latest Eocene and Oligocene, the sedimentation in the Interior Mountain Range is represented by the Los Jabillos (diverse sandy clastics), Areo (fine marine and glauconitic clastics) and part of the Naricual (shallow marine and coastal-fluvial pelitic and sandy clastics) Formations.

Figure 1.18

GENERAL GEOLOGY

CENOZOIC

sediment source for the Naricual Formation and its equivalents (e.g., Quebradón Formation) is shown—on the north side is a fold-and-thrust belt source, and on the south side is a Cratón Interior source. Something similar occurs with the La Pascua and Roblecito Formation equivalents, called the Merecure Formation in the subsurface of the southern flank of the Maturín Basin. Following the diachronism principle, it is assigned a younger age (Miocene), similar to the surface Merecure Group. Figure 1.18 summarizes the Oligocene stratigraphic nomenclature, characterizing the units as potential seals or reservoirs.

Figure 1.17

v

Extinct Island Arc

X A

X

X

v

N

ve Isl an dA rc

Caribbean Plate

Limit of the Caribbean Deformation

cti

?

Roblecito

?

Areo(?)

Areo(?)

Barcelona Clastic Shelf/Transitional Environment/Deltas ?

La Pascua

?

Slope

Naricual/Quebradón

Los Jabillos

Merecure/"Naricual"

Chaguaramas ?

Oligocene

South American Plate

Merecure

0

50 km

Shallow Sandy Clastics

Positive Areas

Silt-clay Clastics Predominate over the Sand Fraction (Slope Environment)

Direction of Sediment Supply Thrust Front

Regional geologic framework for the sedimentation at the north flank of the Eastern Basin of Venezuela during the Oligocene. There is a strong difference between the Naricual in the subsurface and as defined in its type region: the "Merecure Formation" name has been used for subsurface equivalents of the Merecure Group formations (Los Jabillos, Areo and Naricual Formations) that crop out in the Interior Range.

Figure 1.17 summarizes conceptually the relationship between the stratigraphic units and deformation fronts. The double

Neogene and Quaternary

In Venezuela, the Neogene is characterized by important mountainbuilding episodes, which are a direct consequence of the Caribbean and South American plate interactions. Figures 1.15 and 1.16 show in a general way the beginning of the Andean uplift, and the structures generated by the eastern movement of the Caribbean plate between the North American and South American plates during the Late Oligocene to Early Miocene.

Figure 1.18

O l i g o c e n e

Western Venezuela, Trujillo, Lara, South-Andean Flank and Barinas-Apure

Western Venezuela Perijá Lake Maracaibo, North-Andean Flank Palmar Ceibote

Palmar/Parángula PALMAR/PARANGULA ?

G u

León

Western Venezuela Falcón Basin

North-Central Eastern Venezuela Venezuela Naricual

Naricual (Churuguara/Castillo/Pecaya/ San Luis/Agua Salada)

? Quebradón

a

Areo

f Icotea

Carbonera

Age

i Carbonera ?

Paují/Mene Grande

Late Eoc.

Guardulio El Paraíso

M E R E C U R E

Roblecito

t

?

a Arauca

Pagüey(?)

Eroded/Unconformable Contact

Sand/Seal Pairs

Sandy Reservoir

Seal

La Pascua ?

Los Jabillos

Caratas/ Roblecito ?

Eroded Interval

Correlation chart of the most important Late Eocene through Oligocene units of Venezuela. Paují, Mene Grande and Pagüey Formations extend into Middle Eocene; El Fausto Group and Churuguara, Castillo, Pecaya, San Luis, Agua Salada and Quebradón Formations extend into the Miocene.

1 14

PETROLEUM GEOLOGY OF VENEZUELA

During this time, extensional (Falcón Basin) and foreland basins were created. In Western Venezuela, the Barinas-Apure foreland basin was influenced by the formation of the Colombian and Venezuelan Andes. The Eastern Venezuela basins resulted from the oblique collision between the Caribbean plate and the northwestern margin of the South American plate. In the Pliocene (Figs. 1.19 and 1.20), the uplifting of Northern Venezuela produced the present-day distribution of petroleum basins (Fig. 1.21) and generated the La Costa and Venezuelan Andes mountain ranges (dividing the Maracaibo and Barinas-Apure

Basins). Figure 1.22 summarizes the Neogene and Pleistocene stratigraphic units, showing their potentiality as source rocks, seals or reservoirs. In Western Venezuela, the Andean uplift produced significant thicknesses of molasse sediments (Guayabo Group, and La Villa, La Puerta and El Milagro Formations—Fig. 1.22). In places, both the North-Andean and SouthAndean flanks have molasse sediments that reach more than 5 km thick (15,000 ft). In the Perijá Mountain range, the El Fausto Group is the molasse-equivalent unit, and is related to the mountains of the deformation front on the west side of Maracaibo Basin.

El Pilar Fault

Coro

Capadare

PPee rriijjá

Ra ng e

Oca Fault Lake Maracaibo

GUAYABO

Mérida Mérida

Co

A

lo

bi

bi m

lo

m

P

El Ba úl

uccaa YYu Rííoo

Quebradón Quiamare Quiamare

Ar c

Carapita Carapita La La Pica Pica

Capiricual Capiricual Quiamare Quiamare

Oficina-Freites Merecure Chaguaramas

Merecure

??

Guayana Shield

R a -augl ul nagrá á P ar

Guayana Shield

a

a

Quiriquire Quiriquire Las Piedras Las Piedras

La Costa Range

La Rosa Lagunillas La La Puerta Puerta Lagunillas

Co

Isl an d

Agua Salada

Urumaco Urumaco Caujarao Caujarao Socorro Socorro

ss de n n A

Ar cc

Caribbean Plate

? ?

N

BBaa rrb Pr a d ism os

Figure 1.19

00

100 50 50

200 200km km

Igneous-Metamorphic Basement Basement

150 150

Continental Environment Conglomerates Continental Environment Conglomerates and SandyClastics Clastics and Sandy Deltaic-Fluvial Environment, Sand and Pelitic Clastics

Deltaic-Fluvial Environment, Sand and pelitic Clastics Open-Marine and Foredeep Environment,

Fluvial and Coastal Environment Sandy Clastics Fluvial and Coastal Environment Sandy Clastics Shallow Environment Carbonates Shallow Environment Carbonates

Positive Zones

Pelitic Clastics Open-Marine and Foredeep Environment, Pelitic Clastics

Sediments Supply

Positive Zones Thrust Front

Regional geologic framework for the sedimentation in all Venezuela (Maracaibo, Falcón, Barinas-Apure and Eastern basins) during the Miocene-Pliocene. The largest accumulations of continental sediments occur on the flanks of the Andes and La Costa Range. The most important reservoirs of Venezuela were deposited during this epoch: La Rosa, Lagunillas, Isnotú (Guayabo Group), Carapita, Oficina, Chaguaramas and Merecure Formations.

1 15

GENERAL GEOLOGY

CENOZOIC

Figure 1.20

Pliocene/Recent Caribbean Plate

North

of Ven

ezuela

Curaza

N

Deep

o Prom

inence

Oca Fault San Sebastián Maximum Fault Subsidence Areas

o jill e Truang R

Maracaibo Basin

Falcón Basin

Boconó Fault

South-American Plate

s

de

An

200 km

Positive Areas Shallow Clastic Sediments

Thrust Front

Plate Movement Vectors

Northern Venezuela regional

The La Rosa and Lagunillas Formations predate the distal environments of the Perijá and Andes molasses. The La Rosa Formation, with its basal sandstones (Santa Bárbara Member), is of major petroleum importance. Its characteristic “middle shale” interval has lateral sandy variations that are important reservoirs in the eastern coast of Lake. Maracaibo. Its thickness varies from 70 to 1100 m (230 to 3600 ft) because the unit was deposited over an irregular erosional surface

filling of the foreland basins and uplifting due to the deformation of extensive areas associated with the Bocono, San Sebastián and Oca fault systems. Extensional basins persist north of Falcón State (after Macellari, 1995.)

Figure 1.21 68˚

Peri já R ang e

Falcón Maracaibo Basin

Caribbean Sea

60˚

Maracaibo Basin Trujillo s de An n ela Barinas zu ne Ve Barinas-Apure S. Cristóbal Basin

Cumaná La Costa Range Barcelona Maturín Eastern Maturín Basin Sub-basin

Guárico Sub-basin

.L

a 100

0 50

200 km 150

72˚

11˚

Porlamar Caracas La Costa Range

B E.

bi

m lo

Co 7˚

N

68˚

o Belt Orinoc San Fernando

r

co

no Ori

e Riv

64˚

Trinidad

At O lan ce tic an

Ciudad Bolívar

a an ay if Gu ass M 60˚

Reclamation Zone

Coro 11˚

64˚

Margarita Basin

7˚

Guyana

72˚

and is fault-controlled. The La Rosa Formation is believed to be Early to Middle Miocene age (20 to 15 Ma). The Lagunillas Formation overlays the La Rosa and consists of transitional shallow, coastal, and continental sediments that reach more than 1000 m (3280 ft) thick in the center of Maracaibo Basin. It is a very important reservoir in the eastern coast fields, where it has been divided into five members, all of which have oil potential. It is equivalent in age (Middle to Late Miocene—15 to 6 Ma) to the La Puerta Formation and part of Guayabo and El Fausto Groups. In the Barinas-Apure Basin, the Parangula and Río Yuca Formations (continental sediments) are the distal equivalents of the Guayabo Group. In the Falcón region, open sea environments can be found, ranging from deep-marine turbidites (e.g., Pecaya Formation) to shallow clastics (e.g., Cerro Pelado Formation) and carbonates (e.g., San Luis Formation). The final filling of the Falcón Basin during the Pliocene was with the conglomeratic-marine clastics of La Vela Formation and the continental Coro Conglomerate (Pliocene-Pleistocene). In North-Central Venezuela, the main environments of deposition are fluvial and continental, resulting in the upper Quebradon and Quiamare Formations. They increase in thickness considerably to the east and south.

Venezuelan petroliferous basins on the basis of its Sedimentary Provinces (after Pérez de Mejía et. al., 1980). E. B. L. = El Baúl Lineament, Eastern and BarinasApure basins limit.

1 16

PETROLEUM GEOLOGY OF VENEZUELA

Figure 1.22

Age

Perijá and Lake Maracaibo

Andes

El Milagro

Terrazas

Pleistocene

Barinas-Apure

Maturín

(N) Sub-Basin (S) Mesa

Betijoque La Villa, Los Ranchos, Lagunillas Isnotú

Middle Miocene EL FAUSTO/ La Rosa

Río Yuca

?

G U A Y A B O

Las Piedras

Las Piedras/ Quiriquire

AGUA SALADA Castillo/Agua Clara Pedregoso/San Luis ?

Freites

Chaguaramas

Sand/Seal Pairs

Reservoir (Sandy)

Seal

Uchirito/ Capiricual

Oficina Carapita Merecure

Guacharaca

Reservoir (Carbonate)

Quiamare

La Pica

Socorro Cerro Pelado

Parángula

Palmar

Interior Range

?

LA PUERTA/Codore/ La Vela/Urumaco/ Caujarao

Carapita

LA PUERTA (*)

Early Miocene

Guárico Sub-Basin

San Gregorio/Coro

Pliocene

Late Miocene

Falcón

Guanapa

Source Rock Figure 1.23

Correlation chart of the most important units in the Venezuelan Neogene. (N) and (S) indicate northern and southern flanks of the Maturín Sub-Basin. The El Fausto Group, and the Palmar, Guaharaca, Chaguaramas and Merecure Formations extend into Late Oligocene.

1 17

To the south of the Guárico Mountain front, in the Guárico and Maturín Sub-Basins (including the eastern Interior Mountain Range), transitional deltaic to shallowmarine environments are represented by the Merecure and Oficina Formations (Guárico and western Anzoátegui States). They are both of great importance as petroleum reservoirs. These units change gradationally to the east to deeper-water environments represented by the Capiricual and Carapita Formations. The Carapita Formation is a distinctive turbidite unit and is also of great petroleum importance. To the south, in the Oficina fields and the Orinoco Belt, are found the diachronical younger equivalents of the Neogene cycle. The basal unit, usually discordant over the Temblador Group, is the sandy Merecure Formation, and overlying it is the deltaic Oficina Formation. The Miocene equivalents of these units in the Guárico SubBasin–Orinoco Belt have been named the Chaguaramas Formation.

(*)

Group

To the northeast, the Maturín Sub-Basin is filled with shallower facies, such as the Uchirito and Quiamare Formations in its northern flank. The Quiamare Formation represents a great variety of environments: lagoon, fluvial channels and alluvial fans, reaching several kilometers in thickness in Eastern Anzoátegui. On the southern flank, the Freites Formation shales overlie the Oficina Formation. These shales are eventually overlain by the deltaic La Pica Formation and the molassic Morichito, Las Piedras and Quiriquire Formations (Pliocene age). The sedimentary cycle ends with the Mesa Formation of Pleistocene age.

THE HISTORY OF OIL EXPLORATION IN VENEZUELA

The beginning Before the 1800s, only brief references were made to Venezuelan hydrocarbons in the literature. The first mention of hydrocarbons was made by Fernandez de Oviedo in 1535, where he wrote of oil seepages off the western shore of Cubagua Island. In 1540, he referred to the presence of bitumen on the Gulf of Venezuela shores (Martínez, 1976). Nothing more is found in the literature until the early 1800s.

Crew - month

500

Nationalization

O.P.E.P. Foundation

End of concessions

Massive concessions

World War II

600

Great Depression

700

World War I

Figure 1.23

400

Surface geology

300

Seismic (2-D + 3-D) Gravimetry (+magnetometry from 1936)

200

100

0 1910

1920

1930

1940

1950

1960

1970

1980

1990

2000

Year

Exploratory activity in Venezuela. Surface methods. (Source: Martínez, 1976 and 1994; M.E.M., 1985 to 1995; J. Méndez Z., 1976 and R. Varela, 1987, in Méndez Z., 1989; M.M.H.,1962 to 1984).

1800 to 1900 In 1814, Alexander von Humboldt reported asphalt deposits along Venezuela’s northern shoreline (Martínez, 1976). Geologist Herman Karsten (1851) published a description of oil seepage sites located between Betijoque and Escuque, towns in Trujillo State, southeast of Lake Maracaibo (Urbani, 1991). Oil seeps along La Alquitrana Creek in Táchira State lured local investors into applying for an exploitation concession under the name of “Cien Minas de Asfalto.” It was granted to them in 1878 (Martínez, 1976). Compañía Minera Petrolia del Táchira exploited this concession by “open mining”

until 1883, when the first well which produced oil, Eureka-1, was completed. Eureka-1 had a production of 1.5 bbl (194 liters) per day (Méndez, 1978). Previously Salvador-1, the first well drilled in Venezuela, had been abandoned as dry by this company after reaching a final depth of 53 m. These wells were drilled with a percussion rig, the first oil drilling rig in the country. 1901 to 1920 Well locations were chosen by surface geology and direct hydrocarbon observation during the first decades of this century. Bababui-1, a 188-m (617-ft) deep well, discovered the Guanaco oil field in 1913. Mene Grande, near Lake Maracaibo’s eastern shoreline, was the first giant find in Venezuela (Fig. 1.25). The discovery well was Zumaque-1, a 135-m (443-ft) well, drilled after a recommendation by geologist Ralph Arnold. Arnold and a team of about 50 colleagues systematically explored more than 50 million hectares assigned to General Asphalt (later Caribbean Petroleum) all over Venezuela. Of these, 512,000 hectares were selected for exploitation. Totumo, discovered in 1913, was the first producer from the basement, and La Rosa Field, found by the well Santa Bárbara-1 drilled in 1917, was the first of a giant later recognized as the Bolívar Coastal Field (BCF). BCF covers an extensive land and offshore region on the eastern coast of Lake Maracaibo. The maximum depth reached by an exploratory well by 1917 was 1,400 m (4,600 ft). 1921 to 1940 From 1920 onward, surface exploration activity increased (Fig. 1.23). Efforts were concentrated on Zulia and Falcón States in western Venezuela, and northern Anzoátegui and Monagas States in Eastern Venezuela.

1 18

PETROLEUM GEOLOGY OF VENEZUELA

Pioneering gravimetric surveys started in 1924 and contributed to the identification of regional highs, mainly of igneousmetamorphic basement close to the surface. As a result of the surface exploration effort and subsequent exploratory drilling during the 1920s, several important discoveries occurred: La Paz in 1923, and La Concepción in 1925, in Zulia State; Quiriquire in 1928, in Monagas State (a giant oilfield in a Pliocene alluvial fan), and Pedernales (Delta Amacuro) in 1933, in an anticline produced by mud diapirism. Other relevant discoveries during this period were the Bachaquero area (now within BCF, Zulia) in 1930, and Cumarebo Field (Falcón State) in 1931. Figure 1.24

End of concessions

7

World War II

Great Depression

World War I

200

Massive concessions

6

5 Nationalization Evaluation of the Orinoco Belt

4

3 100 2

Maximum depths reached km

Number of exploratory wells per year

300

1

0 1910

1920

1930

1940

1950

1960

1970

1980

1990

2000

Year

Exploration drilling in Venezuela. (Source: Martínez, 1976 and 1994; M.E.M., 1985 to 1995; Méndez Z., 1976 and Varela, 1987, Méndez Z., 1989; M.M.H.,1962 to 1984).

The year 1933 heralded the beginning of the use of seismic as a surface tool for exploration (Fig. 1.23), and results were quickly seen. Large discoveries occurred in Eastern Venezuela: in 1936, Temblador, the first field discovered in southern Monagas; in 1937, the first field of the Greater Oficina Area was discovered in Anzoátegui State; and Jusepín Field was found in northern Monagas in 1938.

1 19

Surface geology continued to render benefits in Monagas: Santa Ana, the first field of the Greater Anaco Area, was found in 1936; and El Roble and San Joaquín were found in 1939. Subsurface geology methods, using regional knowledge, data from core and ditch samples obtained during drilling, and electrical well logging as of 1929, gave very significant results. Some of the discoveries include Orocual Field (Monagas) in 1933, and the Eocene Misoa Formation oil sands of the LL-370 Area (Lagunillas, BCF, Lake Maracaibo) discovered in 1938. The maximum exploratory drilling depth reached by 1940 was 3,400 m (11,150 ft) (Fig. 1.24). 1941 to 1950 The exploratory activity during this decade was affected by World War II and the post-war world, with large oil needs prompting an increase in exploratory drilling (Fig. 1.24). Surface exploration, however, diminished, since most of the field personnel went to war. It was not until the end of WWII that surface activities showed a strong upward rebound, reaching levels never before seen in Venezuela (Fig. 1.23). With an increase in exploratory drilling after the war, reserves and production doubled during the decade (Fig. 1.26), and 63 fields were found. This compares to the 41 fields found from 1880 to 1940. The three most relevant discoveries were the Las Mercedes Field (Guárico State) in 1941, commercial oil in the Cretaceous of La Paz Field (Zulia State) in 1944, and the giant accumulation of extraheavy crude in Boscán (also in Zulia State), in 1946.

THE HISTORY OF OIL EXPLORATION IN VENEZUELA

Figure 1.25

Mene Grande C.C. Bolívar Los Barrosos–2 La Paz La Concepción Quiriquire Bachaquero Pedernales La Canoa–1 Oficina Jusepín Las Mercedes La Paz and Mara (K) Boscán La Paz and Mara (Basement) Urdaneta Lama, Centro Orocual, Lamar, Jobo–Morichal Onado Sur del Lago Cerro Negro Patao Río Caribe Loran, cocuina Guafita Incorporation of El Furrial

200

1.500

1.000

100

Millions of barrels

Millions of cubic meters per year

300

.500 Note: From 1914 to 1954 a total of 3.0 billion cubic meters were incorporated into the reserves through revisions, new discoveries and extensions. 0 1910

1920

1930

1940

1950

1960

1970

1980

1990

0 2000

Year

Reserves from exploratory drilling in Venezuela. (Increments and revisions not included). (Sources: Martínez, A.R., 1976, 1987 and 1994; M.E.M., 1985 to 1995; M.M.H., 1962 to 1984).

Exploratory drilling added more fields to the Greater Areas of Oficina, Anaco and Las Mercedes. The new Hydrocarbons Law of 1943 provided for the duration of all existing concessions to be extended 40 more years, a positive move for the oil industry, although the state’s share in exploitation benefits was increased by way of taxes. In addition, abundant new concessions were granted during 1944 and 1945, which also had a significant positive effect on exploration. From 1945 on, exploratory evaluation intensified and all technology on hand was applied. Gravimetry and seismic surveys were carried out in areas offshore of Lake Maracaibo, and aerial magnetics and other advanced techniques under development were tested in Venezuela. These technologies contributed to a significant increase in the regional knowledge of the Venezuelan sedimentary basins. Exploration drilling rigs reached depths of approximately 5,200 m (17,000 ft), as can be seen in Fig. 1.24.

1951 to 1960 The oil from the Middle East, less expensive and of good quality, affected the intensity of Venezuelan exploration, and surface activity was reduced by more than half (Fig. 1.23). However, drilling activity maintained a high level during the decade. New concessions granted in 1956 and 1957 kept the interest in Venezuelan oil high throughout the rest of this decade. Discoveries continued in the Greater Oficina Area and, to a lesser extent, in Guárico. During 1957 and 1958, the Lake Maracaibo region yielded large Tertiary finds in its central and central-eastern areas, including Ceuta, Centro, Lama, Lamar and Lago Fields. The first Venezuelan continental platform find was Posa-112A, an offshore field in the Gulf of Paria. The maximum exploratory drilling depth reached during this period was 5,348 m (17,541 ft). 1961 to 1976 The “no more concessions” policy adopted by the Venezuelan State greatly affected the operating strategies of the concession holders during this prenationalization period. A drastic reduction in surface exploration activities is shown in Fig. 1.23. By 1968, exploratory drilling reached the lowest level of activity since 1940. Exploratory wells were restricted to already identified areas, with their objectives being new reservoirs above, below or near known oil reservoirs. This type of exploration yielded discoveries such as the deep Cretaceous in Central Lake and Urdaneta Fields. Frontier drilling and surface exploration activities by the concessionaires ceased completely.

1 20

PETROLEUM GEOLOGY OF VENEZUELA

The Corporación Venezolana del Petróleo (CVP), the Venezuelan State oil company, was founded in 1960 and started operations the following year. This company became the leader in exploration on land and offshore Venezuela. It acquired 80,000 km of seismic and drilled nearly 200 exploratory wells during this period (Velarde, 1991). CVP started exploration of the La Vela area, offshore Falcón State, in 1972, and the evaluation of southern Lake Maracaibo in 1971 by means of service contracts. After a bidding process, service contracts were signed the same year.

70 10 60

Massive concessions End of concessions O.P.E.P. Foundation

50 40

5

30

BSTB

Cumulative production and reserves at year end (Bm3)

Figure 1.26

20 10

Reserves 0 1910

Production 1920

1930

1940

1950

1960

1970

1980

1990

0

2000

Year

Production and reserves in Venezuela. (Sources: Martínez, A.R., 1994; M.E.M., 1985 to 1995; M.M.H., 1962 to 1984).

1 21

A significant discovery during the period, besides findings in the abovementioned La Vela and southern Lake areas, was Onado Field (1971) in Monagas State. The exploratory drilling record was 5,813 m (19,067 ft) in 1976.

CVP and the Ministerio de Minas e Hidrocarburos started evaluating the Orinoco Belt by seismic surveys and drilling. By then, about 60 wells had been drilled by the concessionaires in the so-called Tar Belt, and most of them had been abandoned without testing. The La Canoa 1, a 1,176-m (3857-ft) deep exploratory well, tested 6 m3 (40 bbl) per day of 7˚API gravity before being abandoned (Martínez, 1987). This well, located in southern Anzoátegui, is considered to be the discovery well of the Faja del Orinoco. 1976 (nationalization) to the present By 1978, state-owned Petróleos de Venezuela, S.A., a holding in charge of the nationalized oil industry, assigned the Orinoco Belt to its existing operating affiliates: Corpoven, Lagoven, Maraven and Meneven. They each proceeded to evaluate their assigned portion. The campaign was finished five years later (Fig. 1.24) after 669 wells were drilled, and 15,000 km of Vibroseis seismic lines and 54,000 km2 of aerial magnetics were acquired (Martínez, 1987). Since the nationalization, surface exploration is based almost exclusively on geophysics, remote sensing and geochemistry. It steadily increased until the 1980s (Fig. 1.23), when it reached its maximum level for the last 15 years. This activity was directed toward frontier and traditional areas. 3-D seismic has been used since the 1980s as an additional tool for both exploration and reservoir description.

THE HISTORY OF OIL EXPLORATION IN VENEZUELA

Figure 1.27

Number of discoveries Total number of exploratory wells

0.50

0.48

0.46

0.44

0.42

0.40

0.38 1950

1960

1970

Year

1980

1990

2000

Cumulative exploratory success since 1950, showing an almost 47% success rate with no downward trend (from M.E.M., 1985 to 1995; M.M.H., 1962 to 1984).

Exploratory objectives have become deeper and more remote, as the most significant recent finds show (Fig. 1.25). These include Patao and other giant gas fields offshore north of Paria Peninsula (1979 to 1982); Río Caribe condensate accumulation also in the same region (1981); Morro heavy oil in the Gulf of Paria (1980), and Loran and Cocuina, gas accumulations east of Delta Amacuro (1983) (Fig. 1.0). Northern Monagas and Anzoátegui, both in Eastern Venezuela, contain the largest discoveries since 1986 along the El Furrial Trend: Tertiary and Cretaceous reservoirs that are more than 4,000 m deep. Western Venezuela’s Guafita and Victoria findings near the Colombian border are also quite significant. An exploratory drilling depth record of 6,640 m (21,780 ft) was set in 1993.

What now? The future points to more discoveries in the above frontier areas, as well as exploration and re-exploration in traditional areas near existing facilities. New, high-risk objectives will become the standard of dayto-day exploration activities; exploration for bypassed hydrocarbons already has high priority. Modern drilling technology will allow deeper and more precise subsurface evaluation. Improved knowledge of Venezuelan basins, supported by new geological and geochemical criteria, and new seismic acquisition and processing technologies, will open new frontiers and substantiate re-exploration. Modern petrophysical well logging technologies, some of which are described in other chapters of this book, already permit measuring and interpreting a large variety of rock and fluid properties. Their proper use will further enable us to accurately assess the subsurface. Venezuela still has a wealth of hydrocarbons to be discovered. Figure 1.27 displays graphically the exploratory success during the last 45 years, showing an almost 47% success rate with no downward trend, and Fig. 1.26 shows nearly 1 billion barrels of oil added during the period. This is the result of integrating all technologies, from exploration through enhanced oil recovery. Venezuelan oil provinces have not yet disclosed all their secrets; only by using modern exploration technologies will they be revealed.

1 22

Fossiliferous massive limestones, nodular, marly and often calcareous shales.

Río Negro