GEOLOGICAL ATLAS VERACRUZ BASIN

Transcription

1 GEOLOGICAL ATLAS VERACRUZ BASIN Centro Nacional de Información de Hidrocarburos Av. Patriotismo 580, Piso 4 Col. Nonoalco, Del. Benito Juárez, C.P , CDMX contactocnih@cnh.gob.mx

2 VERACRUZ BASIN Contents VERACRUZ BASIN... 2 INTRODUCTION... 4 REGIONAL GEOLOGICAL CONTEXT... 6 LOCATION MAP D AND 3D SEISMIC DATA... 7 WELL STATISTICS... 8 TECTONIC EVOLUTION... 9 REGIONAL CONTEXT VERACRUZ BASIN VOLCANISM MAGNETOMETRIC STUDIES GRAVIMETRIC STUDIES STRUCTURAL FRAMEWORK STRUCTURAL DOMAINS STRUCTURAL-STRATIGRAPHIC SECTIONS STRUCTURAL CONFIGURATION INTRODUCTION STRUCTURAL CONFIGURATION UPPER MIOCENE STRUCTURAL CONFIGURATION MIDDLE MIOCENE STRUCTURAL CONFIGURATION LOWER MIOCENE STRUCTURAL CONFIGURATION UPPER EOCENE STRUCTURAL CONFIGURATION UPPER CRETACEOUS STRATIGRAPHIC FRAMEWORK SEDIMENTARY COLUMN LOWER CRETACEOUS - FACIES PALEOCENE - FACIES EOCENE - FACIES OLIGOCENE - FACIES LOWER MIOCENE - FACIES MIDDLE MIOCENE FACIES

3 UPPER MIOCENE - FACIES PLIOCENE FACIES STRUCTURAL FRAMEWORK TECTONIC-SEDIMENTARY EVOLUTION CHART PETROLEUM SYSTEM SOURCE ROCK SEAL ROCK AND TRAP SOURCE ROCK UPPER JURASSIC TITHONIAN SOURCE ROCK UPPER CRETACEOUS - TURONIAN GENERATION TURONIAN TURONIAN PETROLEUM SYSTEM EVENTS PLAYS RESOURCES PLAYS - RESOURCES PLIOCENE RESERVOIR ROCK MIDDLE MIOCENE RESERVOIR ROCK LOWER MIOCENE RESERVOIR ROCK MIDDLE EOCENE RESERVOIR ROCK ALBIAN - CENOMANIAN _ PLAY UPPER CRETACEOUS SAN FELIPE AND GUZMANTLA _ PLAYS GLOSSARY TABLE - FIGURES TABLES REFERENCES

4 INTRODUCTION The Article 39 of the Ley Federal de los Órganos Reguladores Coordinados en Materia Energética, defines that the National Hydrocarbons Commission (CNH) performs its duties in ensuring that projects will be carried out according to the following points: Accelerate the development of knowledge of petroleum potential in the country Increase the recovery factor and obtain the maximum volume of crude oil and natural gas in the long-term, considering viable economic conditions, for wells, fields and abandoned conditions for reservoirs in process of exploitation and abandonment respectively. The replacement of hydrocarbons reserves, as a guarantee of energy security of the Nation, and parting of prospective resources, based on available technology and according to economic viability projects. The use of most appropriate technology for exploration and extraction of hydrocarbons, in function of productive and economic results. Ensure that all administrative processes in charge, in accordance to exploration and extraction hydrocarbon activities, will be performed with adherence to the principles of transparency, honesty, accuracy, legality, objectivity, impartiality, effectiveness, and efficiency. Promote the development of exploration and extraction of hydrocarbon activities for the benefit of the county. Ensure an adequate use of associated natural gas in exploration and extraction of hydrocarbon activities. 4

5 In the framework of next bidding rounds for hydrocarbon exploration areas, and in compliance with the aforementioned functions, the National Hydrocarbons Commission (CNH) elaborated this document, which contains a petroleum geological synthesis of the Veracruz Basin. Hydrocarbon exploration in the Veracruz Basin began in 1992 with the drilling of the Cocuite-1 wildcat well, unproductive well located near Tlacotalpan, Veracruz. Nonetheless, most seismic surveys and drilling result from PEMEX initiatives to develop this petroleum province from 1948 onward. In 1953, the Angostura-2 well was defined as oil producer well from limestones of the Upper Cretaceous age. Subsequently, the Mirador-1 well encountered tertiary sandstones as gas producers. From 1955 to 1980 most of the oil and associated gas fields of the basin were discovered in Cretaceous limestones of the Buried Tectonic Front, including the Cópite, Mata Pionche and Mecayucan Fields, as well as some gas fields in tertiary siliciclastic rocks such as the Cocuite Field. From 1999 to 2004, among other, the Playuela, Lizamba, Vistoso, Apertura, Arquimia and Papán Fields were discovered. Three source rocks have been identified in the Veracruz Basin: Upper Jurassic, Lower-Middle Cretaceous and Miocene levels. Existing data indicate that excellent quality rock occur in the Upper Jurassic and Lower-Middle Cretaceous, containing Kerogen Type II that has been referred to as thermogenic oil and gas. Secondary source rocks are encountered in the Lower Tertiary, which are characterized by the presence of biogenic gas in many reservoirs. All previous units are the source of nearly all of the oils, condensates and thermogenic gas in the Veracruz Basin and surrounding areas. Main reservoir rocks correspond to limestone of the Orizaba Formation, Carbonate rocks of the San Felipe and Méndez formation, as well as sandstones of the Miocene- Pliocene turbidite system. This document addresses the following topics for the Veracruz Basin: - Regional context. - Structural framework, which describes the processes of deformation of the sedimentary sequences. - Stratigraphic framework, from the Jurassic to the Pliocene, which includes a brief description of main sedimentological aspects and distribution of facies of sequences of high interest regarding hydrocarbon potential. - Petroleum systems, which defines main elements and processes of hydrocarbon generation, migration and accumulation. 5

6 REGIONAL GEOLOGICAL CONTEXT LOCATION MAP The Veracruz Basin is located to the east of Mexico, along the state of Veracruz and the tectonically active southwest margin of the Gulf of Mexico Basin (shallow waters). The Veracruz Basin covers an extension of approximately 34,825 km 2. Geologically limited by: the Trans-Mexican Volcanic belt to the north; the Zongolica fold-and-thrust belt to the west, as part of the continuity of the Sierra Madre Oriental fold-and-thrust belt; the Southeastern Basin to the southeast and It extends into deep waters in the Gulf of Mexico. This geologic province contemplates the Mesozoic elements of the Cordoba Platform, the buried Laramide-age tectonic front to the west, and the offshore Anegada High and Coastal Los Tuxtlas Volcanic Massif to the east. Conglomeratic and sandy-clay sedimentary rock sequences that constitute Cenozoic sediments of the Veracruz Basin were deposited under a foreland basin regime. Hydrocarbon exploration in the Veracruz Basin has been intermittent since Unfortunately, the first wildcat well, Cocuite-1, was classified as non-productive. Exploration activities have been focused on the onshore area of the basin, where more than 900 wells have been drilled. All these activities have contributed to the discovery, evaluation and production of oil and gas fields in Cenozoic rocks and Cretaceous limestones of the Buried Tectonic Front. The location of the Veracruz Basin is displayed in figure 1. Figure 1. Location Map - Veracruz Basin 6

7 2D AND 3D SEISMIC DATA Data coverage for 2D seismic lines (figure 2 - blue lines) and 3D seismic surveys (figure 3 - red polygons) is shown in the following maps. While 2D seismic studies partially cover onshore extension of the Veracruz Basin, it is possible to observe that no studies have been carried out in the offshore portion. Figure 2. 2D Seismic Studies - Veracruz Basin Furthermore, 3D seismic surveys (figure 3) cover almost the entire onshore extension of the basin, and some part of the offshore extension, complementing existing seismic studies in the area. Figure 3. 3D Seismic Surveys - Veracruz Basin 7

8 WELL STATISTICS Table 1 contains general information for the Veracruz Basin. Therefore, total number of fields, well statistics and well classification (including number, type and status of wells) are stated. In addition, existing wells are discretized as onshore, offshore or lacustrine. Table 1. Well Statistics - Veracruz Basin BASIN FIELDS WELLS WELL TYPE LOCATION VERTICAL DEVIATED HORIZONTAL MULTILATERAL N/A ONSHORE OFFSHORE LACUSTRINE VERACRUZ CLASSIFICATION HYDROCARBON TYPE SAMPLE EXPLORATORY DEVELOPMENT OIL GAS OIL & GAS CONDENSATE UNRATED N/A CHANNEL CORE PLUG THIN SECTION WELL STATUS PENDING - SUSPENDED PRODUCERS INJECTORS ABANDONED NEW PLUG AND ABANDONED WORKOVER/ WELL SERVICE DRY HOLE OTHERS UNKNOWN Location and distribution of existing wells in the Veracruz Basin are represented in figure 4. This is for informative purposes and represents the information available by CNIH at well level. It could be considered as a first look at the development of the province. Figure 4. Drilled Wells - Veracruz Basin 8

9 TECTONIC EVOLUTION The tectonic evolution of the petroleum province began its history since the Jurassic, with the opening of the Gulf of Mexico (figure 5). It is characterized by a rift stage from the Triassic to the Middle Jurassic, and a drift stage from the Middle Jurassic to the Early Cretaceous. The southeast movement of the Yucatan Block is associated by the effect of transform and strike-slip faults. Figure 5. Triassic - Middle Jurassic Tectonic Evolution During the Early Cretaceous (figure 6), the area remained in a passive margin regime, developing the Córdoba Platform which consists of Cretaceous carbonates. From the Late Cretaceous to the Eocene, the laramide deformation that is responsible of the Sierra Madre Oriental fold-andthrust belt, generated a foreland basin whose sediments represents the Tertiary Basin of Veracruz. The subsidence of this basin continued until the Middle Miocene. Figure 6. Early Cretaceous - Tectonic Evolution 9

10 Rift Stage and Passive Margin The syn-rift stage is represented by continental red beds of the Middle Jurassic, discordantly deposited on the Permian-Triassic crystalline basement, composed of granites and granodiorites. First marine sediments were deposited during the Kimmeridgian, leading to the development of carbonate platforms represented by sandy, oolitic and dolomitic limestones, as part of a transgressive system on the continental red beds of the Middle Jurassic. A marine transgression event allowed the deposition of bituminous and sandy limestones during all the Tithonian. A maximum flooding surface along the Upper Jurassic marked the end of this transgression event, and the beginning of the deposition in the Lower Cretaceous of limestones interleaved with evaporites rocks. Figure 7 corresponds to a cross section, where all previous events can be identified. Figure 7. Cross Section - Veracruz Basin 10

11 The laramide event deformed the western part of the province from the Middle Eocene and caused the formation of unstable slopes to the west of the basin, producing intermittent sedimentation of clastic sediments coming from slope. This allowed to form a foreland basin along the eastern edge of the fold belt. During the Eocene-Oligocene, a ridge alignment was developed, generating higher subsidence of the basin, attributed to tectonic loading, until the Early Miocene (figure 8). Figure 8. Middle Eocene Tectonic Event During the Miocene (figure 9), the basin was characterized by sedimentation on a slope system. Gravy-driven flows deposits prevailed in the area due to the gradual inversion of the basin in the Early Miocene-Middle Miocene, which is associated to the subduction of the Cocos Plate. For the Late Miocene, previous events ceased, allowing the filling of the basin by siliciclastic sequences, changing to carbonate siliciclastic rocks to the Early Miocene, and finally to siliciclastic rocks with volcanic influence from the Middle Miocene to the Pliocene. Figure 9. Miocene_Pliocene - Tectonic Event 11

12 REGIONAL CONTEXT VERACRUZ BASIN Figure 10 corresponds to a regional seismic section of the Veracruz Basin. It goes from the basement which is represented by red beds and calcareous shallow sediments, followed by the Jurassic deposition constituted by Tithonian source rocks, then the Cretaceous deposition that was influenced by extensive platforms referred to slope and basin environments, concluding with the Tertiary deposits that are linked to the Laramide Orogeny event, which began at the end of the Cretaceous increasing the influx of sediments. Figure 10. Seismic Section _ Interpretation - Veracruz Basin 12

13 VOLCANISM The Tuxtlas Volcanic Field is located on the coast of the Gulf of Mexico in the southern part of the state of Veracruz and to the south of main oil fields in the basin. This volcanic complex is part of the geology and physiography of the Veracruz Basin (figure 11), where existing igneous rocks are in contact with the sedimentary sequences of the Cenozoic. Drag and truncation of Neogene strata in the vicinity suggests that the age of emplacement of this volcanic massif occurred at least at the Early Miocene. Sediment transport was governed by the presence of this volcanic barrier. Thus, it difficulted the transport of sediments from the west to deep waters of the Gulf of Mexico. These sediments surrounded the Volcanic Massif, contributing volcanic material to the area and expanding sediment sources to the Gulf of Mexico. MAGNETOMETRIC STUDIES Figure 11. Seismic Section The Tuxtlas Volcanic Massif Figure 12 corresponds to a reduced to the pole map, where anomalous bodies of magnetic character are identified, same that have defined the regional structures of the Veracruz Basin. There are lineaments with NW-SE orientation. In addition, a positive structure is found to the SW of the basin, which probably served as a buttress for the formation of the tectonic front. Two circular anomalies are defined as main features in the los Tuxtlas, which are located next to another anomaly that gave origin to the Anegada High (apparently located on the same zone of weakness). 13

14 GRAVIMETRIC STUDIES Map in figure 13 represents the structural geological features contained in the crust, where the boundaries of the Veracruz Basin, the Buried Tectonic Front and the Zongolica fold and thrust belt can be delineated. The igneous and metamorphic bodies of the Los Tuxtlas Volcanic Complex, the Anegada High, Plan de las Hayas, the Neovolcanic Axis and the Sierra de Juárez mylonitic complex are also observed. This map shows the dimensions of the basin, in which three depocentres are identified in its deepest part (form the base). In its southwestern flank it is found the tectonic front of the Mesozoic rocks. The basin is delimited to the east and north by the structures of the los Tuxtlas, Anegada and the Plan de las Hayas, which have NW-SE orientation. Figure 12. Reduced to the pole Map Magnetometric Map 14

15 Figure 13. Bouguer Anomaly Map - Gravimetric Map STRUCTURAL DOMAINS STRUCTURAL FRAMEWORK The Veracruz Basin is subdivide in eight structural domains or regions that have common associations of structural style and timing of deformation (figure 14). 15

16 Figure 14. Structural Domains Veracruz Basin 1. Buried Tectonic Front (Mesozoic): It corresponds to the deformation front generated by the Laramide Orogeny in Mesozoic carbonate rocks of the Córdoba Platform. The Buried Tectonic Front is characterized by folds and thrust with vergence towards the East, which form a structural alignment where oil and gas reservoirs, hydrocarbons with high content of sulfur, have been discovered. 2. West Margin Homocline (Cenozoic): Miocene and Pliocene strata lap onto a simple, east dipping, homocline structural trend that contains the Buried Tectonic Front (onlapping). It was recognized that pre-miocene strata along the leading, eastward edge of the buried thrust of the tectonics front were folded in response to thrusting in the basement, forming structural traps, where gas reservoirs have been identified. 16

17 3. Loma Bonita Anticline: The Loma Bonita Anticline, with NW-SE orientation, is a strikingly linear fold that extends north-northwest for nearly 125 Km. It is associated to reverse and transform faults that contributed to the sectioning of the Anticline. Its origin and behavior is attributed to the reactivation of a high-angle basement structure during the Upper Miocene. Inversion of the feature resulted in uplift and created important geometries and migration pathways for the accumulation of hydrocarbons. 4. Tlacotalpan Syncline: It is the deepest part of the basin and represents a long-lived, crustal-scale fold that deepened during active sedimentation. Strata expand toward the center of the syncline and thin along the uplifted, inverted, bounding margins. 5. Anegada High: The Anegada High is a northwest oriented trend that extends into the offshore from the Los Tuxtlas Volcanic Complex and terminates offshore near the city of Veracruz. The Anegada High is interpreted as a peripheral bulge driven by foreland subsidence from loading by the tectonic front. 6. Antón Lizardo Trend: The Antón Lizardo trend lies along the east margin of the basin and consists of mainly steep, normal faults that merge into a subvertical zone of modest, irregular apparent dip offset along the crest of the Anegada High. Many of the major faults extend from the sea floor to Mesozoic strata. Active deformation in this sector is characteristic since the Middle Miocene and is associated with volcanism that precedes and extends below the current volcanic centers. 7. Coatzacoalcos Reentrant: The Coatzacoalcos reentrant is a fold-and-thrust belt that makes up the south third of the basin. Stratigraphic data indicate that tectonic activity began in the later part of the Early Miocene. Many folds are active today. The unusual reentrant geometry is thought to result from a buttress effect induced by the volcanic centers (the submarine Aengada volcanic center and the Los Tuxtlas volcanic center) along the Antón Lizardo trend. 8. The Tuxtlas Volcanic Complex: This complex is mainly composed of alkaline, calcoalkaline and andesitic-basaltic rocks. According to recent studies, this volcanic field began its location at the end of the Early Miocene, process during which the sedimentary column of this area was deformed. 17

18 The structural domains of the Veracruz Basin, previously described and show in figure 14, are represented in section A (figure 15). Figure 15. Seismic Section Western Homocline, Loma Bonita Anticline, Tlacotalpan Syncline and Antón Lizardo Trend Structural Domains 18

19 The structural domains of the Veracruz Basin, previously described and show in figure 14, are represented in section B (figure 16). Figure 16. Seismic Section Western Homocline, Loma Bonita Anticline, Tlacotalpan Syncline and Coatzacoalcos Reentrant 19

20 STRUCTURAL-STRATIGRAPHIC SECTIONS As part of a compressive system, the Buried Tectonic Front is formed by limestone blocks that lies on tertiary terrigenous sediments, forming anticline structures whose main axis have NW-SE orientation, which are limited by reverse faults. The Veracruz Tertiary Basin is a foreland basin composed of alternations of conglomerates, sandstones and shales of tertiary age, located at 1,200 meters of depth. Figure 17. Structural-Stratigraphic Sections _ Veracruz Basin and Buried Tectonic Front 20

21 STRUCTURAL CONFIGURATION INTRODUCTION The Veracruz Province is characterized by two main geologic entities: The Córdoba Platform and the Veracruz Tertiary Basin. The first corresponds to a geologic and physiographic element that extends to the west of the basin and that emerges constituting the orography of the Sierra Madre Oriental fold-and-thrust belt. Its eastern portion extends to the subsoil, under the tertiary sequences of the Veracruz Basin, constituting the so-called Buried Tectonic Front. This front has great petroleum importance due to the fact of being structured in Mesozoic rocks of the Guzmantla and San Felipe Formations (reservoir rocks). The Veracruz Basin developed to the east of the Cordoba Platform spanning from the coastal plain to the continental shelf. This basin is characterized by stratigraphic series of sandy-clay sediments reaching up to more than 10,000 meters thick. The structural configuration for the Upper Miocene, Middle Miocene, Lower Miocene, Upper Eocene and Upper Cretaceous are represented from figure 18 to figure 22, respectively. STRUCTURAL CONFIGURATION UPPER MIOCENE Figure 18. Structural Configuration - Upper Miocene 21

22 STRUCTURAL CONFIGURATION MIDDLE MIOCENE Figure 19. Structural Configuration - Middle Miocene STRUCTURAL CONFIGURATION LOWER MIOCENE Figure 20. Structural Configuration - Lower Miocene 22

23 STRUCTURAL CONFIGURATION UPPER EOCENE GEOLOGICAL ATLAS VERACRUZ BASIN Figure 21. Structural Configuration - Upper Eocene STRUCTURAL CONFIGURATION UPPER CRETACEOUS Figure 22. Structural Configuration - Upper Cretaceous 23

24 SEDIMENTARY COLUMN GEOLOGICAL ATLAS VERACRUZ BASIN STRATIGRAPHIC FRAMEWORK Figure 23. Veracruz Basin _ Sedimentary Column Atoyac Formation (Paleocene): Bioclastic limestones with thickness values up to 1,200 meters. Méndez Formation (Upper Cretaceous): Turbidity current characterized by the presence of conglomerates, marls and shales. San Felipe Formation (Upper Cretaceous): Debris flows deposited in the slope, formed by conglomerates and breccias whose clasts are of calcareous composition, which change at the top to mudstone and wackestone-packstone (planktonic foraminifera) with variable contribution of clay, with thickness values between 200 and 500 meters. 24

25 Guzmantla Formation (Conacian-Santonian): Ooidal grainstone-packstone deposited on calcareous sand banks at the bottom. The upper section is composed by wackestone and packstone (calcisphaerula) whose matrix is composed of coccolithophoridae and planktonic foraminifera. Maltrata Formation (Turonian): Mudstone and argillaceous laminated wackestone, with planktonic foraminifera deposited under anoxic conditions. Its thickness values varies between 50 and 150 meters. This lithostratigraphic unit represents a surface of maximum flood. Orizaba Formation (Albian-Cenomanian): Platform limestones of the mudstone, wackestone, packstone and grainstone type (Miliolida) intercalated with dolostones and anhydrites, whose thickness values varies between 300 and 400 meters. Xonamanca Formation (Lower Cretaceous): Sandy limestone with volcanic influence, peelitic limestones and dolomitic limestones, intercalated with evaporites. Thicknesses values varies between 300 and 400 meters. Tepexilotla Formation (Tithonian): Dark-gray to black bituminous limestone and sandy-clay limestones with average thickness values of 200 meters. San Pedro and San Andrés Formations (Kimmeridgian): Marine sediments that correspond to sandy-clay limestones (with tendency to be oolitic in some parts) and argillaceous dolomitic limestone with thickness values around 100 and 400 meters. 25

26 LOWER CRETACEOUS - FACIES The lower Cretaceous level is constituted of sandy limestones with volcanic influence, peelitic limestones, as well as dolomitic limestones, interbedded with evaporites in the area of the Córdoba Platform. Pelagic limestones are encountered towards the East and West (Lower Tamaulipas Formation), influenced in some areas by dacitic to andesitic volcanic rocks. The Albian-Cenomanian is formed by platform limestones of the mudstone, wackestone and packstone type, interbedded with dolostones and anhydrites rocks, with thickness values that varies between 1,000 and 2,000 meters. The Maltrata Formation is constituted by Mudstone and argillaceous laminated wackestone, with planktonic foraminifera deposited under anoxic conditions. Its thickness values varies between 50 and 150 meters. This lithostratigraphic unit represents a surface of maximum flood. In the Coniacian-Santonian (Guzmantla Formation) platform facies are present in the southwest of the region that gradually change to slope and basin conditions towards the East. Its thickness reach values of 1,500 meters. Figure 24 corresponds to a Lower Cretaceous facies map. Figure 24. Lower Cretaceous - Facies Map 26

27 PALEOCENE - FACIES The Laramide Orogeny generated an important relief in the Veracruz Basin in which numerous folds and reverse faults can be found. These constitute the Buried Tectonic Front, corresponding to the lower limit of the clastic Cenozoic sequence of Veracruz, event that allow the accumulation of terrigenous sediments (considerable thickness) coming from the Paleocene. That tectonic condition favored an increase in the volume of clastic sediments that were deposited on the Veracruz Basin. Transgressive and regressive systems were associated to this event, due to the change in the sea level, as a result of the contribution of sediments. The Paleocene is characterized by a flysch sequence, where fine-grained sandstones and calcareous shales predominate. In addition, conglomerates of igneous and metamorphic composition of the Velasco and Chicontepec Formations prevailed in the area. These formations show thickness values up to 1,000 meters. Distribution of facies for the Paleocene in the Veracruz Basin are represented in figure 25. Figure 25. Paleocene Facies 27

28 EOCENE - FACIES The Upper Eocene (Tantoyucan Formation) is constituted by conglomeratic limestones, sandstones and marls that change to shales, interbedded with fine to medium-grained sandstones cemented with clayey-calcareous material (Chapopote Formation), with thickness values that varies from 500 to 700 meters (these sediments represent paleobatimetrias batiales ). The Middle Eocene is represented in its lower portion by debris flows that are interspersed with sandstones and turbidite conglomerates deposited in basin-floor fans. The top of the Middle Eocene consists of sandy shales, alternated with small thin horizons of calcareous sandstones with traces of bentonite. It is considered an average thickness value greater than 500 meters. Distribution of facies for the Upper Eocene in the Veracruz Basin are represented in figure 26. Figure 26. Eocene Facies 28

29 OLIGOCENE - FACIES The Oligocene is composed of plastic shale, partially sandy, alternating with few fine to mediumgrained sandstones. These rocks are of lower batial paleobatimetry, having thickness values of a few meters until the 1,300 meters. Upper Oligocene sediments are located towards the center and east of the basin where gray shales were deposited, interspersed with poorly-cemented sandstones that contain coral limestone fragments (La Laja Formation); towards the top, medium-grained sandstones predominate, interbedded with some tuffs. The Southeast area of the Veracruz Basin is composed of a series of shales and tuffs, with varying amounts of sands and conglomerates. Distribution of facies for the Oligocene in the Veracruz Basin are represented in figure 27. Figure 27. Oligocene Facies 29

30 LOWER MIOCENE - FACIES The Miocene-Pliocene column of the Veracruz Basin has been divided into several sequenceboundary units. This subdivision is based on available 3D seismic and well data. The Lower Miocene level is characterized by the presence of carved canyons of the tectonic front, which were the conduit of debris flows, basin floor fans and channels. The northwest source of sediments for the Lower Miocene corresponds to sandstones coming from the Buried Tectonic Front. Furthermore, sediments coming from the south, are related to the Sierra de Juarez and La Mixequita area. Within the context of regional depositional environment, two producing fields have been located in the canyon dikes, which tend to increase their dimensions to the Gulf of Mexico. Distribution of facies for the Lower Miocene in the Veracruz Basin are represented in figure 28. Figure 28. Lower Miocene Facies 30

31 MIDDLE MIOCENE FACIES In the Middle Miocene, to the north of the basin, the emplacement of intrusive and volcanic rocks gave rise to a strong contribution of sediments of volcanic origin, with north and northwest direction. Structural conditions allowed the development of submarine fans to the north and along the eastern edge of the Sierra Madre Oriental fold-and-thrust belt. These were distributed along the Veracruz Basin. High-resolution paleontological studies suggest that in the Middle Miocene, turbidite deposits were generated in deep water conditions (lower slope / basin-floor). Distribution of facies for the Middle Miocene in the Veracruz Basin are represented in figure 29. Figure 29. Middle Miocene - Facies 31

32 UPPER MIOCENE - FACIES Facies of the Upper Miocene correspond to channel complexes, proximal and distal overflows associated with submarine fans. Due to the structural complexity of this basin, the morphology of these fans show a clear contrast, depending on the area where they are located. In the northern part of the basin, large submarine fans were developed with source of contribution in the northwest direction and distribution towards the south and southeast, forming large lobes in the main depocenter of the basin. In the south, the development of fans was conditioned by the intrabasin structural highs and by the presence of the Tuxtlas Volcanic Complex. The channeled facies reach lengths of up to 150 km, to finally form lobes. This sequence is one of the most important, since it encompasses seven of the main producing fields of the Veracruz Basin. Distribution of facies for the Upper Miocene in the Veracruz Basin are represented in figure 30. Figure 30. Upper Miocene Facies 32

33 PLIOCENE FACIES The Pliocene is constituted by channel complexes, with their respective associations, proximal and distal overflows. These complexes are interbedded with clays of important thickness values. As in previous periods, the presence of the structural high generated by the volcanism of the Los Tuxtlas influenced largely the sedimentation process of the region, channeling the flow of the currents and the deposits of high energy toward the north part of the basin. Distribution of facies for the Pliocene in the Veracruz Basin are represented in figure 31. Figure 31. Pliocene - Facies 33

34 STRUCTURAL FRAMEWORK Due to the morphology of the region, the Paleogene and Neogene systems, present on the front of the Sierra Madre Oriental within the Veracruz Basin, extend into the deep waters of the Gulf of Mexico (visible in figure 32). Figure 32. Veracruz - Cross Section. 34

35 TECTONIC-SEDIMENTARY EVOLUTION CHART Figure 33. Tectonic Evolution - Chart 35

36 PETROLEUM SYSTEM SOURCE ROCK Geochemical studies that have been taken in the Veracruz Basin allowed the identification of the following source rocks: Tithonian, Middle Cretaceous and Upper Miocene. Richness and quality of these rocks confirm them as oil/gas source rocks, while the upper Miocene shales are classified as biogenic gas source rocks. Figure 34 describes kerogen, plays and traps of the Veracruz Basin. Figure 34. Petroleum System Events Chart 36

37 SEAL ROCK AND TRAP Seal Rock: Seal rocks of the Veracruz Basin are constituted by intraformational siliciclastic shales from the Middle Eocene and Miocene. Trap: The Veracruz Basin has a wide array of structures that are related to transpressional and transtensional origins. Structural and stratigraphic traps are characteristics of the basin (figure 35), represented by lateral facie changes. The structural element is composed by faulted anticlines, generating staggered blocks limited by inverse faults. Hydrocarbon generation and migration in the Veracruz Basin have been located during the Oligocene-Miocene-Pliocene, while the formation of traps for the Burial Tectonic Front is located in the Eocene-Oligocene and Neogene for the tertiary series of the basin. Figure 35. Seal Rocks - Veracruz Basin 37

38 SOURCE ROCK UPPER JURASSIC TITHONIAN Figure 36. Van Krevelen Diagram _ Kerogen Types Table 2. Characteristics - Source Rock _ Upper Jurassic - Tithonian 38

39 Figure 37. TOC Values _ Upper Jurassic - Tithonian SOURCE ROCK UPPER CRETACEOUS - TURONIAN Figure 38. Van Krevelen Diagram _ Kerogen Types 39

40 Table 3. Characteristics - Source Rock _ Upper Cretaceous - Turonian GENERATION TURONIAN TURONIAN Figure 39. TOC Values _ Upper Cretaceous - Turonian From all petroleum systems identified in the Veracruz Basin, the Turonian-Turonian system is the only one that presents favorable conditions for the existence of both; conventional and unconventional systems (Maltrata Formation from the Cenomanian-Turonian), specially at the Buried Tectonic Front. Numerous oil and gas manifestations of existing wells in the area reinforce the importance of this prospective area (Maltrata Formation). High tectonic complexity stands out because it is related to the Buried Tectonic Front of the Sierra Madre Oriental. 40

41 Turonian-Turonian System Source Rock (Maltrata Formation): From dark argillaceous limestones of the Turonian (Maltrata Formation), half of its samples exceed 1% of total organic carbon and more than one third generated more than 5 mg of hydrocarbons per gram of rock, indicating its potential. Nevertheless, in almost all the Córdoba Platform, the Maltrata Formation is classified as immature, reason why it is little feasible to consider its importance regarding to its contribution in the generation of the hydrocarbons that are produced from the Cretaceous level. Kerogen predominant in this unit is type II, showing important mixtures of kerogen type IV. Towards the east, drilled wells have not proved its existence, but it is considered overmature. Reservoir Rock: Due to the fact that no fluids, associated to this source rock, were found in the plays of the area, the Turonian sequence was postulated as reservoir rocks in those fractured zones, related with Laramide deformation. TOC values for Turonian sequences are displayed in figure 40. Figure 40. TOC Values- Turonian 41

42 Seal Rock: Low porosity and permeability values of Turonian source rocks, allowed to define them as proper seal rocks within the same carbonate sequence. At the subregional level, the stratigraphic sequences of the Santonian (Guzmantla Formation) in its pelagic facies also conform the regional seal for this petroleum system. Trap: Conventional traps associated with this petroleum system are mainly of structural type, related to the structural domain of the Buried Tectonic Front, represented by ridges that have spread to the east from detachment of Jurassic and Cretaceous clay rocks, during the Eocene (Laramide Orogeny). Stratigraphic components are sometimes present (figura 41). This system has been proposed as a conventional play. However, when fractures are not associated with deformation events, the play tends to be cataloged as unconventional. 42

43 PETROLEUM SYSTEM EVENTS Three source rocks have been identified in the Veracruz Basin: Late Jurassic, Middle Cretaceous and Early Miocene. On the other hand, reservoir and seal rocks were defined for the Middle-Late Cretaceous, Eocene and Early Miocene, as well as the Middle-Pliocene Miocene, respectively (figure 42). In the central portion of the basin, the Mesozoic and Tertiary source rocks are currently located in the gas generation window, having reached its maximum level of thermal maturity. Figure 412. Petroleum System, - Veracruz Basin Events 43

44 PLAYS RESOURCES Table four describes plays, reservoir rocks, seal rocks, traps, hydrocarbon type and fields encountered in the Veracruz Basin. Table 4. Veracruz Basin - Resources Verarus Basin Play Reservoir Rock Seal Rock Trap Hydrocarbon Type Fields Orizaba Karstified and fractured shelf shales, primary and Argillaceous limestones Structural (anticlines associated with secondary porosity (Orizaba, Albian-Cenomanian) (Maltrata Formation) the Buried Tectonic Front) Light oil, condensate, sour gas (Jurassic and Cretaceous) Mata Pionche, Mecayucan Cretaceous Breccias Carbonaceous breccia, primary and secondary porosity (San Felipe-Méndez, Santonian- Maastrichtian) Argillaceous limestones, marls and calcareous shales (San Felipe and Méndez) Structural (anticlines associated with the Buried Tectonic Front) Heavy and light oil, condensate, wet gas, dry gas (Cretaceous) Angostura, Mata Pionche, Cópite, San Pablo, Rincón Pacheco Tertiary Conglomerates Conglomerates (Middle Eocene - Lower Miocene) Calcareous Shales (Eocene, Oligocene, Miocene) Combined (eroded/faulted anticline, truncation by erosion) Oil (Jurassic-Cretaceous) Perdiz-Mocarroca, Novillero, Mirador Turbidite Sandstone Sandstones - channels and submarine fans (Depósito-Encanto, Miocene-Pliocene) Intercalated Shales (Depósito-Encanto) Stratigraphic and combined (lateral facies change, tertiary anticlines) Dry gas (Jurassic, Cretaceous, Oligocene - Miocene) Lizamba, Vistoso, Papán, Cocuite, Playuela 44

45 PLAYS - RESOURCES Table 5. Veracruz Basin - Plays Figure 423. Seismic Section - Veracruz Basin Plays 45

46 PLIOCENE RESERVOIR ROCK Reservoir rocks are conformed by turbidite sandstones, deposited in submarine fans and proximal overflows. Their maximum thickness value is found in intrabasin structures, reaching gross thickness values up to 100 m. The sandstones that constitute these fans are immersed in clays, which are characterized for being considered as seal rocks. Thickness values for seal rocks in the basin varies from 30 m to 750 m. This element shows a great concentration throughout the northern part of the basin. Figure 43 shows thickness values at Pliocene level. Traps in the basin are mainly stratigraphic and combined. Figure 434. Thickness Value Pliocene Figure 44, which is a seismic section, demonstrates thickness values for the Pliocene.5 Figure 445. Cross Section - Pliocene 46

47 MIDDLE MIOCENE RESERVOIR ROCK GEOLOGICAL ATLAS VERACRUZ BASIN The Tuxtlas represent a barrier that obstructs the entrance of sediments towards the Gulf of Mexico. In the west of the basin, the sedimentation enters from several points along the Tectonic Front in the North and South flanks of the los Tuxtlas. The source rock corresponds to sandstones deposited in submarine fans that filled the depocenters. Sandstones with the highest thickness values are located along the west of the basin, reaching gross thicknesses of up to 170 meters (figure 46). Locally, the seal rock is made up of shales. Recognized traps in the area are combined and stratigraphic (figure 47). Gas production is associated with submarine fans, composed of medium-to-large-grained sandstones. Figure 456. Middle Miocene - Thickness Map Figure 467. Middle Miocene - Cross Section 47

48 LOWER MIOCENE RESERVOIR ROCK GEOLOGICAL ATLAS VERACRUZ BASIN Reservoir rocks of the Lower Miocene Play corresponds to conglomerates, conglomeratic sandstones and sandstones deposited in slope and basin systems. Its main source of contribution was the Buried Tectonic Front in the northwestern part of the basin. In the South, the contribution of sediments comes from the Sierra de Juárez and La Mixtequita. This play is characterized by the presence of fans. This level was defined as dry gas producer of thermogenic origin in the Novillero Field. The Figures 48 and 49 corresponds to a map, where thickness values for the Lower Miocene are represented. Figure 478. Lower Miocene - Thickness Map Figure 489. Lower Miocene - Cross Section 48

49 MIDDLE EOCENE RESERVOIR ROCK GEOLOGICAL ATLAS VERACRUZ BASIN Reservoir rocks were deposited in fan complexes. Its main source of contribution are the carbonate rocks of the Cretaceous. The Eocene sandstones in the basin tend to be thinner, until disappear in the West of the basin. The play extends eastward into the Gulf of Mexico. While in the northern part of the basin the submarine fans are distributed within the Gulf of Mexico. To the center and South of the basin, the fans were located between the Buried Tectonic Front and the highs of the Los Tuxtlas, where they were stacked vertically. Thickness values for the Middle Eocene level are represented in figure 50. Figure 51 corresponds to a seismic section, where values for this sequence are confirmed by some wells. Figure 50. Middle Eocene - Thickness Map Figure 491. Middle Miocene - Cross Section 49

50 ALBIAN - CENOMANIAN _ PLAY Anticline structures located in the Buried Tectonic Front, which extends for more than 200 Km with NW-SE orientation and width values of 10 Km, have been defined as trap type of these area. These traps are originated by folding and reverse faulting events. In addition, reverse faults and fractures have served as migration routes. It has been postulated that the rocks of the Tithonian, which were buried beneath the thrust, are the source rocks responsible of oil, gas and condensate production in this play. Figure 50. Facies Map - Albian-Cenomanian 50

51 UPPER CRETACEOUS SAN FELIPE AND GUZMANTLA _ PLAYS Seal rocks are constituted by argillaceous limestones, marls and shales. Existing traps are mainly classified as structural. However, the existence of combined structures was governed by stratigraphic components that marked the change of facies between the carbonate platform and the slope deposits. The Play extends over 200 km with NW to SE direction It produces wet gas, as well as, gas and condensate hydrocarbons. While gross thickness values reach 200 m, net thickness values vary from 20 to 60 m. Porosity is associated with slope and slope facies: debris flows formed by calcareous breccias, improved by fractures. Figure 51. Upper Cretaceous San Felipe and Guzmantla _ Depth Values 51

52 Figure 52. Stratigraphic Correlation - Guzmantla Formation Source Rocks and San Felipe Formation Seal Rocks 52

53 GLOSSARY Basement: The rock layer below which economic hydrocarbon reservoirs are not expected to be found, sometimes called economic basement. Basement is usually older, deformed igneous or metamorphic rocks, which seldom develops the porosity and permeability necessary to serve as a hydrocarbon reservoir, and below which sedimentary rocks are not common. Basin: A depression in the crust of the Earth, caused by plate tectonic activity and subsidence, in which sediments accumulate. Cap rock: A relatively impermeable rock, commonly shale, anhydrite or salt that forms a barrier or seal above and around reservoir rock so that fluids cannot migrate beyond the reservoir. Carbonate: A class of sedimentary rock whose chief mineral constituents (95% or more) are calcite and aragonite (both CaCo3) and dolomite [CaMg(CO3)2], a mineral that can replace calcite during the process of dolomitization. Clastic Sediments: Sediment consisting of broken fragments derived from preexisting rocks and transported elsewhere and redeposited before forming another rock. Depocenter: The area of thickest deposition in a basin. Dolostone: A rock composed chiefly (> 90%) of dolomite. The rock is sometimes called dolomite, but dolostone is preferable to avoid ambiguity between the mineral and rock names. Evaporite: A class of sedimentary minerals and sedimentary rocks that form by precipitation from evaporating aqueous fluid. Common evaporite minerals are halite, gypsum and anhydrite, which can form as seawater evaporates, and the rocks limestone and dolostone. Foreland Basin: A foreland basin system is defined as: an elongated region of potential sediment accommodation that form on continental crust between a contractional orogenic belt and the adjacent craton, mainly in response to geodynamic processes related to subduction and the resulting peripheral or retroarc fold-thrust belt. Formation: The fundamental unit of lithostratigraphy. A body of rock that is sufficiently distinctive and continuous that it can be mapped. In stratigraphy, a formation is a body of strata of predominantly one type or combination of types; multiple formations form groups, and subdivisions of formations are members. Kerogen: The naturally occurring, solid, insoluble organic matter that occurs in source rocks and can yield oil upon heating. Kerogen is the portion of naturally occurring organic matter that is nonextractable using organic solvents. Kerogens are described as Type I, consisting of mainly algal and amorphous kerogen and highly likely to generate oil; Type II, mixed terrestrial and marine source material that can generate waxy oil; and Type III, woody terrestrial source material that typically generates gas. 53

54 Petroleum system: Geologic components and processes necessary to generate and store hydrocarbons, including a mature source rock, migration pathway, reservoir rock, trap and seal. Play: An area in which hydrocarbon accumulations or prospects of a given type occur. These are controlled by the same set of geological circumstances. Reservoir: A subsurface body of rock having sufficient porosity and permeability to store and transmit fluids. Sedimentary rocks are the most common reservoir rocks because they have more porosity than most igneous and metamorphic rocks and form under temperature conditions at which hydrocarbons can be preserved. Rift: Region in which the Earth's crust is pulling apart and creating normal faults and downdropped areas or subsidence. Sabkha: An environment of coastal sedimentation characterized by arid or semiarid conditions above the level of high tide and by the absence of vegetation. Evaporites, eolian deposits and tidal-flood deposits are common in sabkhas. Sandstone: A clastic sedimentary rock whose grains are predominantly sand-sized. The term is commonly used to imply consolidated sand or a rock made of predominantly quartz sand, although sandstones often contain feldspar, rock fragments, mica and numerous additional mineral grains held together with silica or another type of cement. Source rock: A rock rich in organic matter which, if heated sufficiently, will generate oil or gas. Typical source rocks (shales or limestones) contain about 1% organic matter and at least 0.5% total organic carbon (TOC). Rocks of marine origin tend to be oil-prone, whereas terrestrial source rocks tend to be gas-prone. Under the right conditions, source rocks may also be reservoir rocks, as in the case of shale gas reservoirs. Syndepositional: Occurring at the same time as deposition Synsedimentary: That forms or grows within a sediment during sedimentation Total Organic Carbon [TOC]: The concentration of organic material in source rocks as represented by the weight percent of organic carbon. A value of approximately 0.5% total organic carbon by weight percent is considered the minimum for an effective source rock, although values of 2% are considered the minimum for shale gas reservoirs. Total organic carbon is measured from 1-g samples of pulverized rock that are combusted and converted to CO or CO2. Vitrinite reflectance: A measurement of the maturity of organic matter with respect to whether it has generated hydrocarbons or could be an effective source rock. 54

55 TABLE - FIGURES Figure 1. Location Map - Veracruz Basin 6 Figure 2. 2D Seismic Studies - Veracruz Basin 7 Figure 3. 3D Seismic Surveys - Veracruz Basin 7 Figure 4. Drilled Wells - Veracruz Basin 8 Figure 5. Triassic - Middle Jurassic Tectonic Evolution 9 Figure 6. Early Cretaceous - Tectonic Evolution 9 Figure 7. Cross Section - Veracruz Basin 10 Figure 8. Middle Eocene Tectonic Event 11 Figure 9. Miocene_Pliocene - Tectonic Event 11 Figure 10. Seismic Section _ Interpretation - Veracruz Basin 12 Figure 11. Seismic Section The Tuxtlas Volcanic Massif 13 Figure 12. Reduced to the pole Map Magnetometric Map 14 Figure 13. Bouguer Anomaly Map - Gravimetric Map 15 Figure 14. Structural Domains Veracruz Basin 16 Figure 15. Seismic Section Western Homocline, Loma Bonita Anticline, Tlacotalpan Syncline and Antón Lizardo Trend Structural Domains 18 Figure 16. Seismic Section Western Homocline, Loma Bonita Anticline, Tlacotalpan Syncline and Coatzacoalcos Reentrant 19 Figure 17. Structural-Stratigraphic Sections _ Veracruz Basin and Buried Tectonic Front 20 Figure 18. Structural Configuration - Upper Miocene 21 Figure 19. Structural Configuration - Middle Miocene 22 Figure 20. Structural Configuration - Lower Miocene 22 Figure 21. Structural Configuration - Upper Eocene 23 Figure 22. Structural Configuration - Upper Cretaceous 23 Figure 23. Veracruz Basin _ Sedimentary Column 24 Figure 24. Lower Cretaceous - Facies Map 26 Figure 25. Paleocene Facies 27 Figure 26. Eocene Facies 28 Figure 27. Oligocene Facies 29 Figure 28. Lower Miocene Facies 30 Figure 29. Middle Miocene - Facies 31 Figure 30. Upper Miocene - Facies 32 Figure 31. Pliocene - Facies 33 Figure 32. Veracruz - Cross Section 34 Figure 33. Tectonic Evolution - Chart 35 Figure 34. Petroleum System Events Chart 36 Figure 35. Seal Rocks - Veracruz Basin 37 Figure 36. Van Krevelen Diagram _ Kerogen Types 38 Figure 37. TOC Values _ Upper Jurassic - Tithonian 39 55

56 Figure 38. Van Krevelen Diagram _ Kerogen Types 39 Figure 39. TOC Values _ Upper Cretaceous - Turonian 40 Figure 40. TOC Values- Turonian 41 Figure 41. Petroleum System, - Veracruz Basin Events 43 Figure 42. Seismic Section - Veracruz Basin Plays 45 Figure 43. Thickness Value Pliocene 46 Figure 44. Cross Section - Pliocene 46 Figure 45. Middle Miocene - Thickness Map 47 Figure 46. Middle Miocene - Cross Section 47 Figure 47. Lower Miocene - Thickness Map 48 Figure 48. Lower Miocene - Cross Section 48 Figure 49. Middle Eocene - Thickness Map 49 Figure 50. Middle Miocene - Cross Section 49 Figure 51. Facies Map - Albian-Cenomanian 50 Figure 52. Upper Cretaceous San Felipe and Guzmantla _ Depth Values 51 Figure 53. Stratigraphic Correlation - Guzmantla Formation Source Rocks and San Felipe Formation Seal Rocks 52 TABLES Table 1. Well Statistics - Veracruz Basin 8 Table 2. Characteristics - Source Rock _ Upper Jurassic - Tithonian 38 Table 3. Characteristics - Source Rock _ Upper Cretaceous - Turonian 40 Table 4. Veracruz Basin - Resources 44 Table 5. Veracruz Basin - Plays 45 56

57 REFERENCES Activo de Exploración Tampico Misantla Golfo y Pemex Exploración Producción, 2014, Reunión de Trabajo CNH SENER PEMEX: Proyectos Integral Veracruz y Alosa, Veracruz 112 pp. González, E., and Medrano, M., 2014, Structural Slope Fans Resulting from Paleogene Compression in the Veracruz Basin, Mexico: AAPG Anual Convention and Exhibition, Houston, Texas., 17 pp. Instituto Mexicano del Petróleo y PEMEX Exploración y Producción, 2000, Atlas de las Cuencas Petroleras de México, Tomo II: Cuenca de Veracruz. México, D.F., Inédito. Jennette, D., Wawrzyniec, T., Fouad, K., Dunlap, D.B., Meneses-Rocha J., Holtz, Mark H., Sakurai, Shinichi., Talukdar, S., Grimaldo, F., Muñoz R., Lugo, J., Barrera D., Williams, C., Escamilla, A., Dutton, S. P., Ambrose, W.A., Dunlap, D.B., Bellian, J.A., and Guevara, E.H., 2002, Play-Element Characterization of the Miocene and Pliocene, Veracruz Basin, Southeastern Mexico, pp PEMEX Exploración y Producción, 2010, Provincia Petrolera Veracruz, Versión 1.0, 38 pp. Pindell J., 1994, Kinematic Evolution of the Gulf of Mexico and Caribbean: U.W.I. Publishers Association, Kingston, 50 pp. Schlumberger, 2010, Well Evaluation Conference: WEC, México., 175 pp. 57