A. T. Picarelli1, R.R. Savini1, V. Abreu2, S. Grosso1, J. Arguello1 and D. Salas1

(1) Perez Companc de Venezuela

(2) Exxon-Mobil URC

Sequence Stratigraphic Evolution of the Oficina Formation, Eastern Venezuela Basin: Depositional Systems and Sand

Body Geometry in a Non-Marine to Estuarine Environment

Develop a high-resolution seq-strat framework to support field revitalization.Develop a high-resolution seq-strat framework to support field revitalization.

Relate stacking patterns, sand body geometry and seismic expression to base level changes in a Relate stacking patterns, sand body geometry and seismic expression to base level changes in a foreland basin distal zone.foreland basin distal zone.

Objectives

LlanosBasin

BarinasBasin

MaturinBasin

GuyanaCraton

CaribbeanPlate

CocosPlate

NazcaPlate

GuyanaCraton

30 Km

Mata

Oritupano-Leona

Acema

MaturinSub-basin

Shallow marine

ShelfBreak

Geotectonics and Paleophysiography

Mod. from Parnauld et al. (1995)

Orinoco River

Mata/Acema

S N

Oficina/Merecure fms (Oligocene/Miocene)

Mesa and Las Piedras fms (Late Mioc./Pliocene)

100 km

4 km

0 km

4 km

8 km

12 km

16 km

La Pica fm (Late Miocene)

Freites/Carapita fms (Late Mioceno)

Collision FrontSerranía del Interior Oritupano/Leona

LlanosBasin

BarinasBasin

MaturinBasin

GuyanaCraton

GuyanaCraton

200 kmMaturinSub -basin

Shallow marine

ShelfBreak

Paleophisiographical Setting

Well logs (spacing from 40 to 160 acres, basic suite Well logs (spacing from 40 to 160 acres, basic suite SP, GR, Resistivity and Micrologs. More recently: SP, GR, Resistivity and Micrologs. More recently: Induction, density, neutronic, acoustic, magnetic Induction, density, neutronic, acoustic, magnetic resonance)resonance)

Pressure and production dataPressure and production data

2D/3D seismic data2D/3D seismic data

Core dataCore data

Data Base

Stacking pattern analysis from 2nd to 5th order: Seq. Stacking pattern analysis from 2nd to 5th order: Seq. Strat. Framework (well-log analysis) Strat. Framework (well-log analysis)

Relationship between stacking patterns, sand body Relationship between stacking patterns, sand body geometry (net sand maps and production data) and geometry (net sand maps and production data) and systems tracts systems tracts

Seismic Expression of key surfaces, systems tracts and Seismic Expression of key surfaces, systems tracts and sand-body geometry (mapping of key surfaces; horizon sand-body geometry (mapping of key surfaces; horizon slices every 2 ms and amplitude extraction).slices every 2 ms and amplitude extraction).

Model Integration with core analysis.Model Integration with core analysis.

Method

Foredeep Cycles and Paleobatimetry

Lithostratigraphy

MERECURE Fm

OFICINA Fm

FREITES Fm

LAS

PIEDRAS FmPliocene

Late Middle Miocene

Early toMiddle

Miocene

OligoMioc

Chronostratigraphy

HST

TST

LST

LST

U

O-P-RL-MI-J

F-G-H

A-B

D-E

SP Res

Flo

od P

lain

Co

ast

al P

lain

(U.T

ida

l)

Co

ast

al P

lain

(M.T

ida

l)

Co

ast

al P

lain

(L.T

ida

l)

Em

baym

ent/L

agoo

n

Coa

stal

Inne

r sh

elf

Out

er s

helf

Upp

er S

lope

Mid

dle

shel

f 2 nd OrderEvents

LST

Seismic Expression - 2nd Order Events

WSW ENE SSE NNE

Foredeep Cycles and High-Frequency Stacking Patterns

23,8 Ma

17,3 Ma

16,4 Ma

15,1 Ma (?)

14,8 Ma (?)

12,8 Ma (?)

Foredeep 1 LST (Merecure Formation and Foredeep 1 LST (Merecure Formation and Lowermost Oficina)Lowermost Oficina)

LST Deep Incised valley fills, fluvial-dominatedLST Deep Incised valley fills, fluvial-dominated

Foredeep 1 TST (Oficina Formation)Foredeep 1 TST (Oficina Formation) LST Shallow and multi-branched incised valley fills, LST Shallow and multi-branched incised valley fills,

tidal-dominatedtidal-dominated TST Littoral tidal- and wave-dominated sand ridges TST Littoral tidal- and wave-dominated sand ridges HST Deltaic sedimentation and littoral sand ridgesHST Deltaic sedimentation and littoral sand ridges

Systems Tracts and Sand-Body Geometry

Seismic Expression - Sequence Boundaries

LST - 24

LST - 26(SB - Burdigalian 4)

30 Km

Mata

Oritupano -Leona

Acema

5 Km

50

’

70

’

Net Sand Map: LST Sequence Oficina VIII (U1 Sand)

Channelized reservoirs.Channelized reservoirs. South to north oriented incised valley fills (fluvial dominated). 50 to 100’ thick. South to north oriented incised valley fills (fluvial dominated). 50 to 100’ thick. Trap: Updip Structural and lateral stratigraphicalTrap: Updip Structural and lateral stratigraphical Vertical communication due to widespread and deep erosive events.Vertical communication due to widespread and deep erosive events. Compensational stacking between 4th order LSTs.Compensational stacking between 4th order LSTs. 10

00’

LST fluvial-dominated Incised valley fills

30 Km

Mata

11471’11480’

11550’ 11541’ 11520’

SB

SB

11511’ 11500’

TS

11490’

Fluvial-dominated Incised Valley FillsExample from High-Frequency Sequence Merecure I

Multi-branched channelized reservoirs.Multi-branched channelized reservoirs. Mainly estuarine filling, 30-50’ thick. Mainly estuarine filling, 30-50’ thick. Trap: Updip Structural and lateral stratigraphical.Trap: Updip Structural and lateral stratigraphical. Strong lateral compartmentalization, only local vertical communication caused by erosion between 4th order LST.Strong lateral compartmentalization, only local vertical communication caused by erosion between 4th order LST. Compensational stacking between 5th order LSTs. Compensational stacking between 5th order LSTs.

1000

’

LST tidal-dominated shallow and multi-branched incised valley fills

5 Km

20’

60’40’

20’

20’

60’

40’

20’80’40

’

40’

40’40’

0

0

20’

60’80’

Net Sand Map: LST Sequence Oficina VI I (S3 sand)

30 Km

Mata

SB

MFS

SB

10589’ 10579’

10569’ 10559’

TS/PS

10549’ 10539’

30

‘

PS

PS

PS

PS

Cross stratified, medium to coarse grained tidal channel sandstone, fining upward (individual sets 2 - 3 ft), water escape related structures and mud drapes eroding offshore mud.

High-Frequency Sequence Architecture within 3rd Order LST:Sequence Boundary and LST

SB

MFS

SB

10589’ 10579’

10569’ 10559’

TS/PS

10549’ 10539’

30

‘

PS

PS

PS

PS

Siltstone to very fine sandstone layer strongly bioturbated (Planolites isp and Teichichnus isp), ripple cross lamination, siderite nodules overlaid by offshore mud.

High-Frequency Sequence Architecture within 3rd Order LST: Transgressive Surface

SB

MFS

SB

10589’ 10579’

10569’ 10559’

TS/PS

10549’ 10539’

30

‘

PS

PS

PS

PS

Offshore mud bioturbated by Thallassinoides isp, with pipes filled by coarse grained sands from the overlying unit.

High-Frequency Sequence Architecture within 3rd Order LST: HST Deposits/Sequence Boundary

SB

MFS

SB

10589’ 10579’

10569’ 10559’

TS/PS

10549’ 10539’

30

‘

PS

PS

PS

PS

Coarse grained sandstone, massive to horizontal/low angle lamination, bioturbated. Interpreted as a fluvial distributary channels, marine influenced, with sharp contact with offshore mud.

High-Frequency Sequence Architecture within 3rd Order LST: HST Deposits and Sequence Boundary Expression

TST and MFS - Seismic ExpressionTST - 6

TST - 8

TST - 10

TST - 18

MFS - Burdigalian 4

30 Km

Mata

Oritupano -Leona

Acema

Non-channelized reservoirs. Non-channelized reservoirs.

Isolated, encased in offshore mud, east-west/northwest-southeast oriented sandbodies.Isolated, encased in offshore mud, east-west/northwest-southeast oriented sandbodies.

Trap: Mainly Stratigraphical.Trap: Mainly Stratigraphical.

Vertical communication limited to fifth order erosional events. Vertical communication limited to fifth order erosional events.

1000

’

TST/(HST) Littoral Sand Ridges (tidal- and wave-dominated)

5 Km

20’0

0

0

0

10’ 0

20’

20’10’

0

0

0

0

Net sand Map: TST Sequence Oficina VI I (R2M Sand)

30 Km

Mata

PS

10599’

30 ‘

Medium to fine grained sandstone, massive strongly bioturbated, overlying offshore mud with Thallassinoides isp.

3rd order Sequence Boundary

High frequency SB and TS

TST/(HST) Deposits and Sequence Boundary Expression: Core data

HST - Seismic Expression

HST - 50

HST - 44

HST - 38

30 Km

Mata

Oritupano -Leona

Acema

HST - Deltaic Sedimentation

1

4

3

Distributary channels tidally influenced

Distributary channels

Tidal bars

Overbank

2

Hydraulic Communication

W E

SB

SB

S

E

12 4

3

N

SB

SBTS

1 2 3 4

5th Order Events

Stratigraphical and sedimentological Model - LST Deep Incised valley fills, fluvial-dominated

W E

S N

1

2

4

3

5

6

71 2 43 5 6

1

24

3

5 6

23

5

6

7

4

Distributary channels tidally influenced

Tidal channels

Tidal bars

Tidal bars (distal)

Transgressive surface

Sand ridges7 Offshore

SB

TS

SB

SB/TS

SB/TS

SB SB

Hydraulic Communication

5th Order Events

Stratigraphical and sedimentological Model - LST tidal-dominated Shallow incised valley fills

Fluvial channelsPaleosoils and Crevasse splay

Paleosoils, swamp and tidal flats

Tidal and Channel barsor fluvial channels tidal influenced

Pedogenic Profiles, swamps and tidal flats

Internal and External Platform Muds and Storm Related Sands

W/NW E/SE

Paleosoils, swamps and tidal flats

Tidal and Channel barsor fluvial channels tidal influenced

Hydraulic isolatedIncised valley fills

Pedogenic Profiles, swamps and tidal flats

High-resolution Sequence Architecture and Base level Change

W E

NS

1

2Transgressive sands (medium to fine grained sandstone, bioturbated)

Offshore shale with Thallassinoides isp(Glossifungites ichnofacies)

2Offshore shale

1 2 3

1 2

2

SB/TSSB

TS

SB/TS

Hydraulic Communication

5th Order Events

1 SB/TS

Stratigraphical and sedimentological Model TST/(HST) Littoral Sand Ridges (tidal- and wave-dominated)

3

Subsea Depth (m)0 -20 -40 -60 -80 -100

0

2

4

6

8

10

12

14

16

18

20

Ag

e (k

a)

IDobday (1981)

Dillon and Oldale (1978)

Stuiver and Daddario (1963)

Atlantic Shekf project study sites

0 500mVE-55x

I

IIIIIIIIII

1B

1A

2

3

0 500mVE-55x

Snedden and Dalrymple, 1999

Foreland Setting and Base Level Evolutionin the Mata, Acema and Oritupano Areas

T

Foreland Basin

(Forebulge)

Main Sediment Source

Zona A Zona B

T

T

S

S

Shallow marine Ramp-likeBasin

Foreland Basin - Distal Zone

Zona A

Zona B

Atmospheric Circulation

Pattern

MioceneGulf

Main source ofsediment supply(Guyanna Craton)

400 km

Guyanna Craton

Perija Ridge

Andean Cordillera

Caribbean Sea

MaracaiboLake

Ciudad Bolivar

Paleogeographical Model

The second order cycle developed during the Late Oligocene/Late Middle Miocene (foreland basin) show an overall thinning and fining upward stacking pattern in the studied area.

The lower frequency cycles (2nd and 3rd order) controlled the higher frequency (4th and 5th orders) sand body geometry.

Within the third order events major reservoir development happened during the Late LST and TST (estuarine valley fill and transgressive sand ridges).

The predominantly retrogradational stacking pattern could be explained by the relatively distal position of the studied area in relation to the thrust belt zone.

Conclusions

The shallow marine ramp geometry trigger the development of fifth order SB,

with erosion and valley cutting and LST/TST fillings.

The fifth order sequence boundaries allowed the communication between

different reservoirs. In this way the flow units are defined by the fourth order

sequences.

The production profiles of the sand ridges and IVF reservoirs show different

patterns, in close agreement with the sequence stratigraphy model.

Conclusions