Stratigraphy and Petroleum Plays of the late to middle ... · ickness is gre. 2). d into three lar leocene to Rec to Recent, par cent, fluvial fac ormations beco ing the long-te

International Journal of Scientific & Engineering Research, Volume 4, Issue 9, September‐2013 ISSN 2229‐5518 627

IJSER © 2013 http://www.ijser.org

Stratigraphy and Petroleum Plays of the late to middle Oligocene Sediments in the “XY” Field,

Onshore Niger Delta Basin, Nigeria Samuel Okechukwu Onyekuru

Abstract— Nigeria’s search for increased oil and gas reserves requires the discovery of additional petroleum plays using more accurate exploration techniques like sequence stratigraphy. Sequence stratigraphic technique was applied to sediments in the “XY” Field, onshore Niger Delta by integrating six well logs and biostratigraphic data to subdivide the field’s stratigraphic column into sequences, systems tracts and profitable plays. The analysis delineated seven complete (SEQs 1 to 7) and two incomplete 3rd order sequences. The key surfaces used for correlation across the sequences in Wells 002, 003, 005 and 001 were the 11.5Ma, 12.8Ma and 15.0Ma MFSs, while the link between these four wells and Wells 007 and 006 was the 15.9Ma MFS. The other constrained surfaces between Wells 007 and 006 were the 17.4Ma, 19.4Ma and 20.7Ma MFSs. These surfaces were delineated at varying depths in the wells, suggesting the existence of faults in the well field. The most laterally continuous sandstone unit, however, is the faulted prograding wedge complex (PGC) sands of SEQ 4 which represented the main petroleum plays in the field. Cyclic alternation of Transgressive Systems Tracts (TST), High-stand Systems Tracts (HST) and Lowstand Systems Tracts (LST) in the well field is suggestive of a union of the elements of a petroleum system which constitute favourable conditions for the generation, migration and structural and stratigraphic entrapment of hydrocarbons.

Index Terms— Petroleum, Plays, Sequence, Straigraphy, Faults, Compartmentalization, Hydrocarbon, Reserves.

—————————— ——————————

1 INTRODUCTION

xploration and exploitation activities in Nigeria had been concentrated in the Tertiary Niger Delta sequences of Eo-

cene to Pliocene age, until recently when exploration efforts are gradually being shifted to the offshore (Pliocene–Pleistocene) sections. These areas have accounted for the coun-try’s current oil reserves estimated at about 35 billion barrels and an average annual reserve addition of about 800 million barrels in the last ten years [1]. These reserves that were main-ly derived from the onshore, offshore and recently the deep offshore parts of the Niger Delta are presently intensely de-veloped. The Nigerian oil and gas industry is presently faced with the challenge of achieving the national crude oil reserves target of 40 billion barrels and production of increased volumes of Liq-uefied Natural Gas (LNG) in order to meet export and domes-tic needs. The domestic need is bolstered by the current gov-ernment policy thrust for additional gas turbines for power generation and industrial projects [2]. Therefore, the future reserve/production ratio for oil/gas in Nigeria will be a cause for serious concern based on the present available reserves data, if additional reserves are not discovered. The search for additional oil and gas reservoirs in the region will, therefore, require more accurate techniques of strati-

graphic analysis [3]. These techniques will assist in the discovery of hithertho hidden, deep and tight reservoirs which will give the required boost to the existing reserves. Sequence stratigraphy has become an indispensable tool in hydrocarbon exploration because of its ability to provide a chronostratigraphic framework for the analy-sis and correlation of lithic fills in basins that are deposited in re-sponse to sea level changes, tectonism and sediment supply. The search for additional reserves in the Niger Delta Baasin can be en-hanced by the use of this integrated approach for stratigraphic analy-sis and prediction [4], [5], [6], [7]. It will also give a better under-standing of the linkage between sedimentation patterns in different parts of the basin and location of reservoirs, their continuity and seal prone zones (traps) and perfectly predicts bypassed pay zones and step-out potentials in a basin [8]. Therefore, to realize optimal hydrocarbon exploration, recovery and production, the understanding of the depositional setting and location of play elements within the depositional setting is required for a real-istic or near realistic representation of the subsurface and paleoenvi-ronmental conditions within the basin. The aim of the present study in the onshore, Niger Delta is to subdi-vide the stratigraphic column of the “XY” well field into sequences and systems tracts based on the integration of well logs and high resolution biostratigraphic data for the delineation of reservoirs, their continuity and other elements of the petroleum system (source, traps, e.t.c) for the sustainable development of the resource in the region. 2 LOCATION OF STUDY The “XY” Field (a designation used for propriety purposes) is locat-ed at the fringe of the Greater Ughelli Depobelt in the Niger Delta Basin (Fig. 1). The Niger Delta is situated in the Gulf of Guinea on the west coast of central Africa (Fig. 1). It lies on Latitudes 40001N and 60031N and Longitudes 40301E and 80301E. During the Tertiary, the delta built out into the Atlantic Ocean at the mouth of the Niger-

E

———————————————— Samuel Okechukwu Onyekuru is currently a senior lectutrer in sedimentary

and petroleum geology in the federal University of Technology,Owerri, Nigeria, PH-+234- 8037175256. E-mail: [email protected]

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InternISSN 2

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n area of catchmominantly savannt, the delta hasepresent the movelopment [9]. eltas in the worof 500,000 km3

e basin depoceoverlies a relatawards [9].

OLOGY of the Niger D

n Nigeria and sary is the Beninthe West Africdefined by outc

and further east-g the adjacent Pvince is definern boundary of

transform-fault sediment thicknr in areas wheto the south ands in the basin h

hic units (Fig. 3the Akata Form

Formation, andation [13], [14],er farther into tositional enviroassive margin. the study area i

wedges as shalesad of progradinsits. A series owere formed a

ks down-droppchanged local drt paths into the

ngineering Resea

ment more thannna-covered los prograded souost active portioThese depobel

rld with an area3 [11] and a sedenter [12]. Thetively shallow

Delta Province issouthwestern Cn flank- an east-can Basement Mcrops of Cretac-south-east by tPrecambrian rod by the Came

f the Dahomey passive marginness contour ore sediment thd southwest (Figave been divide3): the basal Pa

mation, Eocene d Oligocene-Re, [15]. These fthe basin, recordonments of the

is complicated bs of the Akata F

ng deltaic Agbaof large-scale, bas underlying sped across thesdepositional slope basin. For any

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n a million squowlands. From uthwestward, foons of the deltalts form one of a of some 300,diment thicknese Greater Ughbasement with

s delineated by Cameroon (Fig. -northeast trendMassif. The noeous sedimentsthe Calabar flanocks. The offsheroon volcanic lbasin (the easte

n) to the west, or the 4000-mehickness is greg. 2). ed into three laraleocene to Recto Recent, par

ecent, fluvial facformations becoding the long-te

e Niger Delta o

by syndepositioFormation are m

ada and fluvial basinward-dipp

shales diapired e faults and filpes and compliy given depobel

sue 9, September

IJSER © 2013 tp://www.ijser.org

uare the rm-a at

f the 000 s of

helli in-

the 2).

ding rth-

s on nk-a hore line ern-and eter ater

rge-cent ralic cies ome erm onto

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the Nigedepositiostructuregrowth fly spaceparts of near the

r‐2013

er Delta provinon of the Benines, including sfault crests, baced flank faults [f the Agbada F

top of the Akat

nce, gravity ten Formation, wshale diapirs, ck-to-back featu[13], [16]. Thes

Formation and fta Formation.

ectonics was cowhich are expres

roll-over anticures and steeplyse faults mostlyflatten into det

636

ompleted beforssed in complelines, collapse

y dipping, closey offset differentachment plane

e x d

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IJSER

InternISSN 2

5 DaThe d‘XY” and reevents1) andacquirPort (DPRsectiothose

5.1 SeAthousectiowell lwell lNigerinformfrom t 5.2. DtionalThe wphysicgammclay-mresponThe lsand, mud wAPI (units


ata Sets and Mdata sets used fo Field, Greater esistivity logs (s) including pald the Niger Delred from Shell Harcourt, thro

R), Nigeria. Theons of the studie

depths.

equence Stratigugh sequence sons, its principlelogs [3]. Sequelog suites from r Delta Basin wmation (stratigrathe wireline log

Determination l Settings wireline logs wcal criteria ext

ma ray log recorminerals) commnses and conselog is thus usewhich contains

with high gamm(American Petr(in anhydrite) to

of Scientific & En

Methodology or this study inUghelli depobe

(Fig. 5), biostralynological andta ChronostratigProducing and

ough the Direce non-availabiled intervals, ho

graphic Applicstratigraphy waes can readily b

ence stratigraphthe “XY” Fieldas achieved by aphic markers) g suites using th

of Lithology,

were used to detracted from thrds radioactivitmonly have relequently taken ed to infer deps little mud, wilma ray signal. Goleum Instituteo over 200 API

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ncluded 6 well lelt, logged withatigraphic data d foraminiferal igraphic Chart [Development C

ctorate of Petrity of GR and

owever, affected

cation in “XY”s originally desbe applied to o

hic analysis of ed in the Greaterthe integration and lithologica

he approach of [

Stacking Patt

elineate lithofahe electric logty of formationslatively high gas good measu

positional energl have low gam

Gamma ray value) units and ran units in shales.

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log suites from h gamma ray (G(faunal zones

information (Ta19]. The data wCompany (SPDroleum Resour

d SP logs at sod interpretation

” Field signed for seism

outcrops, cores each of the six r Ughelli depobof biostratigrap

al data distilled [5].

terns and Depo

acies based on gs’ responses. Ts, hence shales

gamma radioactures of grain sgy. Coarse-grai

mma ray value, tues are measurednge from very .

sue 9, September


the GR) and able

were DC), rces ome ns at

mic and (6)

belt, phic out

osi-

the The (or

tive size. ned

than d in few

Table 1.of Well 0

Form C

D1000

D1000

D1100

D1100

D2000

D2000

D3000

D3000

D3000_

D4000

D4000

D5000

D5000

E1000

E1000

E2000

E2000

E2000_

E2000_

E3000

E3000

E3100

E3100

E4000

E4000

E4000_

r‐2013

. Representativ001 Greater U

Code

base

top

base

top

base

top

base

top

_HWC_contact

base

top

base

top

base

top

base

top

_DHO_contact

_HWC_contact

base

top

base

top

base

top

_HWC_contact

ve StratigraphiUghelli Depobel

Depth

63

63

64

64

66

6

69

66

t 66

69

69

73

70

74

74

76

7

7

t 7

76

76

77

77

80

79

t 79

ic Markers lt

(AH), Ft

390

350

487

403

656

542

960

677

689

998

972

340

004

465

402

610

518

532

574

690

647

792

782

026

933

952

636

IJSER

International Journal of Scientific & Engineering Research Volume 4, Issue 9, September‐2013 ISSN 2229-5518 636


Form Code Depth (AH), Ft

E5000 base 8095

E5000 top 8075

E6000 base 8253

E6000 top 8179

E8000 base 8515

E8000 top 8407

E9000 base 8617

E9000 top 8593

F1000 base 8760

F1000 top 8703

F1400 base 8917

F1400 top 8768

F2000 base 9178

F2000 top 9123

F2000_DLG_contact 9155

F2100 base 9229

F2100 top 9202

F2100_DHO_contact 9203

F2200 base 9260

F2200 top 9250

F2300 base 9350

F2300 top 9328

F3000 base 9688

F3000 top 9360

F3000_DHO_contact 9362

F3000_HWC_contact 9404

F3100 base 9782

F3100 top 9720

F4000 top 10172

ZZC 7464 The intervals of progradation, retrogradation and aggradation were delineated from the succession patterns of strata expressed in the logs, which depict various parasequences and/or parasequence sets. These patterns which display vertical occurrences of repeated cycles of coarsening upwards (CU) or fining upwards (FU) sequences were inferred from the gamma ray log signatures. The environment of deposition for the respective units was inferred from the gamma log expression of grain size [5] and depositional systems determination distilled from stacking patterns [3].

Progradation or Cleaning-up Trend (funnel shape) means a coarsening upward sequence (Fig. 6). It also means a gradual upward decrease in gamma ray response. In shallow marine settings, this trend reflects a change from shale-rich into sand-rich lithology and

an upward increase in depositional energy with shallowing-upward and coarsening. In deep marine settings, this trend reflects an in-crease in the sand content of turbidite bodies [20]. Retrogradation or Dirtying-up Trend (bell shape) means a fining upward sequence or a gradual upward increase in gamma response (Fig. 6). This trend may reflect upward fining (example, a lithologic change from sand to shale) or upward fining of sand beds in a thinly interbedded sand-shale unit. This trend usually implies a decrease in depositional energy. In non-marine settings, fining upward is pre-dominant within meandering or tidal channel deposits with an up-ward decrease in fluid velocity within a channel (coarser sediments are usually at the base of channels). In shallow-marine settings, this trend usually reflects an upward deepening and a decrease in deposi-tional energy (net landward shoreline movement). In deep-marine settings, this trend reflects waning of submarine fans resulting in the reduction of sand contents [20]. Aggradation or Boxcar Trend (cylindrical or blocky shape) means piling up of sediments on top of each other, hence the gamma ray shows neither increase nor decrease (Fig 6.). Sometimes the gamma ray response has low gamma and sharp boundaries and no internal change. This trend is predominant in fluvial channel sands, turbidites (typically with greater range of thickness) and aeolian sands. Evaporites also can have a cylindrical gamma trend.

5.3 Definition of Key Stratigraphic Sequences from Logs The definition of key stratigraphic surfaces from well logs, which includes for example, Sequence Boundary (SB) and Maximum Flooding Surface (MFS) and their relative ages was done by identi-fying candidates and events of the surfaces in the following ways: Candidate SBs on log-motifs were marked by the sharp-based bot-tom of the basin floor thicks and incised-valley fills and in updip areas by the sharp-top of the uppermost prograding transgressive parasequence, low gamma, high resistivity and the use of the provid-ed stratigraphic markers [21]. Candidate SB was also identified from facies discontinuities in the logs. From the logs, a change from for-ward stepping to back stepping parasequence stacking pattern was looked out for in the gamma ray log. The trend of shale resistivity shows increased resistivity towards SB and a decrease away from SB. From the biofacies data, candidate SB was inferred using the provided stratigraphic markers. Facies expression of the SB depends on the paleogeographic location of the section in the basin and the Systems Tract.

MFS and condensed sections were identified from log trend bounda-ries and/or log character and the provided biostratigraphic data. Gamma ray logs have high values at MFS and condensed sections. Shale resistivity values decrease towards MFS and increase away from MFS [21]. Faunal/floral density trends display increased densi-ty towards flooding surface and decreased density away from the flooding surface. 5.4 Delineation of Systems Tracts Delineation of systems tracts was done after the surfaces were identi-fied. Parasequence stacking patterns were used to identify the Lowstand Systems Tracts (LST), Transgressive Systems Tracts (TST) and Highstand Systems Tracts (HST), enveloped by the con-strained surfaces (MFS, TS and SB). The enveloping Sequence Boundary (SB) of a sequence, or its down dip correlative conformity, lies between the Highstand Systems Tract (HST) and the Lowstand Systems Tract (LST) according to the se-

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InternISSN 2

quencTrans(LST)FloodTST iupwarcan alThe Hstackitimes ment/shallobelowLST parasebound(Fig.

5.5 DDatinachiev9) in (Tablesp, andata wCorresequesoftw


ce stratigraphic gressive Surfac) and the Tran

ding Surface (Mis characterizedrd stacking pattlso be aggradatiHST is usually ing patterns of associated with

/particle size ofow or shoaling w by the MFS an

(PGC) is charequences. It canded below by a8).

ating of identifg of identified ved by correlatassociation wit

e 1), wherever nd Chiloguembwere used to asselation of sequeence sets of theares.

of Scientific & En

depositional mce (TS) lies betwsgressive Syste

MFS) caps the TSd generally by tern of a sequenional. delineated by pparasequences h blocky/serratef HST sedimenpaleobathymet

nd above by theracterized by pn also be blockyan SB and abov

fied Surfaces key stratigraph

tion to the thirdth chronostratigthey were reco

belina sp, etc.,sign geologic agences, systems e wells was do

ngineering Resea

model propoundeween the Lowstems Tract (TSTST (Fig. 8). an overall retronce (Fig. 6). Th

progradational/c(Fig. 6). The H

ed log motifs. Hnts remains relatric setting. Thee SB [3], (Fig. 7progradational/cy (BFF/PGC) (F

ve by a Tansgre

hic surfaces (whd order cycles cgraphically signrded. The mark identified fromge to the inferretracts, parasequone using Petr

rch Volume 4, Is

htt

ed by [3], (Fig.tand Systems TrT). The Maxim

ogradational/finhe stacking patt

coarsening upwHST is also somHowever, the se

atively coarser ie HST is boun7). coarsening upwFig. 6). The LSTssive Surface (T

here possible) wchart of [19], (Fnificant bio-eveker shales Bolivm biostratigraped surfaces. uence and/or parel and Strata b

sue 9, September


. 7). ract

mum

ning tern

ward me-edi-in a

nded

ward T is TS)

was Fig. ents vina phic

ara-bug

Fig. 7. Stems Tra

FIG. 9

r‐2013

Sequence Stratiacts and accomp

9. NIGER DELTA CHR

igraphic Modelpanying key Str

RONOSTRATIGRAPHIC

l for the Interpratigraphic Surf

C CHART [19]

636

pretation of Sysfaces [3].

s-

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6 RES

The wspatiacordinwells time o 6.1 SeThe refield fwhile ed in 006, r


ULTS wells in “XY” fal distributions ng to affinity anwere numbere

of drilling and c

equence Stratigepresentative sefor Wells 006 a the comprehentables 2, 3, 4, 5

respectively.

of Scientific & En

field were arranin the well fie

nd not with resped (001, 002, 0completion.

graphy equence stratigrand 007 are shonsive interpretat5, 6, and 7 for W

ngineering Resea

nged and interpeld which arranpect to well num003, 005, 006 a

raphic interpretown Figs. 10 antions for the sixWells 002, 003,

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preted accordingnged the wells mbers (Fig. 5). Tand 007) based

ations in the “Xnd 11, respectivx wells are prese

005, 001, 007

sue 9, September


g to ac-

The d on

XY” vely, ent-and

Table 2. T

Interval

(m)

2820-2755

2755-2700

2700-2460

2460-1960

1960-1915

1915-1640

1640-1510

1510-1460

1460-1218

Table 3. Th

Interval

(m)

2865-2800

2800-2400

2400-1990

1990-1960

1960-1900

1900-1550

1550-1260

1260-1160

1160-1107

6.2 Corr

The stra007 and ing Surf(002 andtions bet

The keyand 001 betweenother co17.4Ma,

r‐2013

The summary of the seq

Lithology Stacki

tern/L

Sand/shale Progra

– Block

Sand/Shale Retrog

(FU)

Shale/Sand Progra

Stacks of Sand/

Shale + Silt

iontercalations

Progra

Blocky

Sand/Shale Retrog

Shale/Sand i.e.

(Bar Deposits)

Genera

Progra

Sand/Silt/Shale Retrog

Sand (+ Shale

Laminae)

Aggrad


he summary of the sequ

Lithology Stacki

tern/L

SandSilt//Shale Retrog

(FU)

Sand/shale

intercalations

Progra

– Block

Sand/Shale

laminae

Blocky

Sand/Shale Retrog

Shale/Sand Progra


Shale + Sand) Progra

Sand/Shale Retrog

Shale/Silt Aggrad

section

relation of wel

atigraphic corre006) was carri

faces (MFSs). d 003; 005 andtween well pair

y surfaces used are the 11.5M

n these wells anorrelation surfa, 19.4Ma and 20

quence stratigraphic in

ing Pat-

Log Motif

Systems Trac

adational (CU)

ky log motif

HST

gradational TST

adational (CU) HST

adation (CU):

y SP log Motif

LST (PGC)

gradation (FU) TST (Short-

lived)

ally

adational (CU)

HST

gradation (FU) TST

dational HST

gradation (FU) TST

uence stratigraphic int

ing Pat-

Log Motif

Systems Trac

gradational TST

adational (CU)

ky log motif

HST

y- Serrated LST (PGC)

gradation (FU) TST (Short

interval)

adational (CU) HST

gradation (FU) TST

adational (CU) HST

gradation (FU) TST

dational (Toe

n of HST)

HST

ls in the “XY”

elation of the sied out using thThe wireline s

d 001 and 007ars.

for correlationMa, 12.8Ma andnd wells 007 anfaces between 0.7Ma MFSs (F

nterpretation of Well 00

ct Depth/type of

Chrono- Surface

Da

19

2755 -SB 15

2700 - MFS 15

2460 -SB 13

1960 -TS Su

ren

1915 -MFS 12

Uv

1640 -SB 12

1510 -MFS 11

1460 -SB 10

de

Peak not seen -

erpretation of Well 003

ct Depth/type of

Chrono- Surface

Da

19

2800 - MFS 15

oc

2400 -SB 13

1990 - TS SP

hig

1960 -MFS 12

th

1900 -SB 12

1550 -MFS 11

1260 -SB 10

1160 -MFS 11

Peak not seen (L

Field

six wells (002, he interpreted Msignatures of thand 006) also a

n between Welld 15.0Ma MFSsd 006 is the 15Wells 007 an

Fig. 12).

636

02 (2820-1218 m)

ate of Chrono- Surface (Ma; a

988)/Remarks

5.5 (Low SP and high Resistivity Va

5.0 (High SP & low Resistivity logs

3.1 (High resistivity & low Sp @

udden deflection of SP log to the

newed transgression

2.8 (High SP, low resistivity and to

Uvigerina sp at the depth of 1866m)

2.1 (Low SP & high resistivity)

1.5 (High SP and Low Resistivity va

0.6 (Low SP and high resistivity lo

epth

3 (2865-1107 m)

ate of Chrono- Surface (Ma; a

988)/Remarks

5.0 (retrogradational SP log m

ccurrence of Bolivina sp @ 2700m}

3.1 (Low SP Values)

P log showed a sudden deflection

gh SP) initiating another transgressi

2.8 (High SP and top ooccurrence o

e depth 1920m)

2.1 (High resistivity @ 1900m)

1.5 (High SP)

0.6 (Low SP & high resistivity)

1.5 (High SP and Low Resistivity va

Late rise of sea level)

003, 005, 001Maximum Floodhe genetic wellaided interpreta

ls 002, 003, 00s; while the lin.9Ma MFS. Th

nd 006 are th

fter Haq et al.,

lues)

values)

2460 m)

left (High SP) =

p ooccurrence of

lue)

og values at that

fter Haq et al.,

motif and rich

to the right (i.e.

on

f Uvigerinassp at

lue)

1, d-ls a-

5 k e e

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Table 4. The Summary of the sequence stratigraphic interpretation of Well 005 (2890-1113 m)

Interval

(m)

Lithology Stacking

Pattern/Log

Motif

Systems

Tract

Depth/type of

Chrono- Surface

Date of Chrono- Surface (Ma; after Haq et al.,

1988)/Remarks

2890-

2885

Silt/Shale Retrogradational

(FU)

TST 2890 - MFS 15.0 (very Low resistivity)

2885-

2770

Shale/Silt/Sand Progradational

(CU)

HST 2770 -SB 13.1 (Low GR & High resistivity)

2770-

2500

Shale/Silt/Sand Retrogradational

(FU)

TST 2500 - MFS 12.8 (very Low resistivity & high GR)

2500-

2300


(CU)

HST 2300 -SB 12.1 (High Resistivity)

2300-

1950

Sand/Shale Retrogradation

(FU)

TST 1950 -MFS 11.5 (Top occurrence of Nonion sp at 1824m)

1950-

1610

Shale/Sand Progradational

(Blocky Motif)

HST 1610 -SB 10.6 (High resistivity)

1610-

1400


(FU)

TST 1400 -MFS 10.4

1400-

1200


(Blocky Motif)

HST 1200 -SB 10.35 (High resistivity and low SP values esp.

b/w 1285-1200)

1200-

1113


(FU)

TST Peak not seen Abrupt shift of Resistivity log to the left and SP log

to the left is suggestive of transgression

Table 5.The summary of the sequence stratigraphic interpretation of Well 001 (3057-756 m)

Interval

(m)

Lithology Stacking

Pattern/Log

Motif

Systems

Tract

Depth/type of

Chrono- Surface


1988)/Remarks

3057-

2865

Sand/Shale Progradational

(CU)

HST 2865 -SB 16.7 (Low GR & High resistivity)

2865-

2750

Sand/Silt/Shale Retrogradational

(FU)

TST 2750 - MFS 15.9 (very Low resistivity & high GR)

2750-

2665


(CU)

HST 2665 -SB 15.5 (Low GR & High Resistivity)

2665-

2550

Sand/Silt/Shale Retrogradation

(FU)

TST 2550 -MFS 15.0 (Low Resistivty; NO SP and GR logs at this

depth; Rich occurrence of Bolivina sp at depth 2598

assisted interpretation)

2550-

2300


(CU)


2300-

2100

Silt/Shale Retrogradation

(FU)

TST 2100 -MFS 12.8 (Low Resistivity & high GR)

2100-

2040

Shale/thin sand

unit

Progradational

(CU)


2040-

1920


(FU)

TST 1920 -MFS 11.5 (Low Resistivity value; Top occurrence of

Nonion sp at 1854m)

1920-

1690

Sand Blocky

(Channels)


1690-

1370

Sand/Silt/Shale Retrogradation

(FU)

TST 2370 -MFS 10.4 (Low Resistivty)

1370-

1030


(CU)

HST 1030 -SB 10.35 (1035m is the base of sand body = incised

valley fill)

1035-756 Silt/Sand Blocky

(Channels)

LST

(PGC)

End of phase (TS) not seen at the top of the interval

Table 6. The summary of the sequence stratigraphic interpretation of Well 007 (3059-2100 m)

Interval (m) Lithology Stacking

Pattern/Log Motif

Systems

Tract

Depth/type of

Chrono- Surface


1988)/Remarks

3059-2950 Shale Retrogradational

(FU)

TST 2950 - MFS 22.0 (High GR, high SP & low Resistivity logs values)

2950-2830 Shale/Sand Progradational (CU) HST 2830 -SB 21.8 (Low GR and High resistivity)

2830-2730 Stacks of Sand/

Shale

Retrogradational

(FU)

TST 2730 -MFS 20.7 (High GR and SP with low Resistivity log values at

2730)

2730-2630 Shale/Sand i.e.

(Distr. Mouth

Bar Deposits)

Generally

Progradational (CU)

HST 2630 -SB 20.4 (Low GR, low SP & high resistivity)

2630-2575 Sand/Shale Retrogradation (FU) TST 2575 -MFS 19.4 (High SP and Low Resistivity values)

2575-2535 Shale + Sand Aggradational/

Progradational

HST 2535 -SB 17.7 (Low GR and high resistivity log values at that depth

2535-2460 Predominantly

Shale

Retrogradation (FU) TST 2460 -MFS 17.4 (High SP and Low Resistivity values)

2460-2410 Shale/Sand Progradational (CU) HST 2410 -SB 16.7 (Low GR and high resistivity log values at that depth


Shale

Retrogradation (FU) TST 2370 -MFS 15.9 (High SP and Low Resistivity values; Top occurrence

of Chiloguembelina-3 at 2311)

2370-2230 Shale/Silt/Sand Progradational (CU) HST 2230 -SB 15.5 (Low GR and high resistivity log values at that depth


Sand (Channel

Fill Deposits)

Progradational (CU) LST

(PGC)

Peak of the interval was not Observed

-

Table 7. The summary of the sequence stratigraphic interpretation of Well 006 (2895-2100 m)

Interval (m) Lithology Stacking Pat-

tern/Log Motif

Systems

Tract

Depth/type of

Chrono- Surface


1988)/Remarks

2895-2870 Sand Progradational (CU) HST 2870 -SB 21.8 (Low GR and High Resistivity). Onset of this

regressive phase was not observed at the TD.


Shale units

Retrogradational

(FU)

TST 2750 -MFS 20.7 (High GR and low Resistivity log values at 2750)

2750-2670 Shale/Sand Progradational (CU) HST 2670 -SB 20.4 (Low GR & high resistivity)

2670-2620 Sand/Silt/Shale Retrogradation (FU) TST 2620 -MFS 19.4 (High SP and Low Resistivity values)

2620-2570 Shale + Sand Progradational

/Blocky log motifs

HST 2570 -SB 17.7 (Low GR and high resistivity log values at that depth

2570-2480 Sand/Shale Retrogradation (FU) TST 2480 -MFS 17.4 (High GR and Low Resistivity values)

2480-2420 Shale/Sand Progradational (CU) HST 2420 -SB 16.7 (Low GR and high resistivity log values at that depth

2420-2375 Sand/ Shale Retrogradation (FU) TST 2375 -MFS 15.9 (High SP and Low Resistivity values; Top occurrence

of Chiloguembelina-3 at 2332 m)

2375-2215 Shale/Sand Progradational

(CU)/Bloky log

motifs

HST 2215 -SB 15.5 (Low GR and high resistivity log values at that depth)

2215-2100 Stacks of

blocky log

motifs (Sands

of Channel

Deposits)

Progradational (CU)/

Blocky

LST

(PGC)

Peak of this interval was not Observed at the top depth of the analysed interval of the

well

-

The result of the interpretations across the well field showed that Well 002 has three complete and one incomplete 3rd order sequence (SEQs 4 to 7), including a Low Stand Systems Tract (LST) of the prograding wedge or slope complex (PGC) in SEQ 4; Well 003 has two complete and two incomplete 3rd order sequences (SEQs 4 to 7), also with the LST (PGC) in SEQ 4; Well 005 has three complete 3rd order sequences (SEQs 5 to 7) and two incomplete sequences; Well 001 has five complete 3rd order sequences (SEQs 3 to 7) capped by a PGC unit in SEQ 7. Wells 007 and 006 both have four complete 3rd order sequences also capped by the PGC in SEQ 4 (Fig. 12). The LST in SEQ 4 delineated in four wells (002, 003, 007 and 006) was not observed in Wells 005 and 001. The unit may have been eroded before the deposition of the overlyng TST.

IJSER

InternISSN 2

Anothdelineextensdominbasedtions/

The kand 0differ

From Field one dtiary norma003 isdownthe de007 ashownrelativpared and thgree o

Tabletratig

Well No.

003 002 005 001

TabletratigWell No.

005 006 007


her PGC (LSTeated in the othsively logged dnantly sandy sy

d on the availab/sequences (less

key surfaces use01 (i.e. 11.5Maent depths in th

the foregoing is faulted and/o

direction. NormNiger Delta ofal faults is infes on the downththrown side ofepth of occurrenand 006 and than in table 9 alve to Well 007.

d to that betweehe down-droppof compartment

8. Showing obgraphic surfaces

Logged Depth (m)

2865-1107 2820-1218 2890-1113 3057-756

9. Showing obgraphic surfaces

Logged Depth (m)

D1Cs

2890-1113 2

2895-2100 23059-2100 2

of Scientific & En

T), delineated iher five wells (depth of 3057-7ystems tract (LSble data as sectis that 750 m) in

ed for correlatioa, 12.8Ma and 1he four wells (Ta

(Table 8), it cor have its accoal (growth) fauf Nigeria, hencerred for the sehrown side of Wf Well 001 (Tabnce of the 15.9 at for other surso highlighted . The throw is n Wells 005 aning of strata in talization in the

bserved variatios in “XY” FieldDepth of 11.5Ma Chrono-surface

(m) 1550 1510 1950 1920

bserved variatios across Well 00Depth of 15.9Ma Chrono-surface (m)

Depth17.4MChrosurfa

2750 2375 2480 2370 2460

ngineering Resea

in SEQ 7 in W(Fig. 12). Well 756 m. The conST) in SEQ 7 wions that represthe well field w

on between Well5.0Ma MFSs) wable 8).

can be establishompanying clinult regime is prece, displacemenequences in theWell 002 while ble 8). SimilarlMa chrono-sur

rfaces linking Wthe down-drop

relatively smallnd 006 (385m).

the well field “XY” well fiel

ons in depth ofd

Depth of 12.8Ma Chrono-surface

(m) 1960 1915 2500 2100

ons in depth of05, 006 and 007 h of

Ma no-

ace (m)

Depth o19.4Ma Chrono-surface (m

2620 2575

rch Volume 4, Is

htt

Well 001 was 001 has the m

ntinuity of the pwas not ascertaisent the upper swere not provid

ls 003, 002, 005were delineated

hed that the “Xnoforms dippingevalent in the Tnts resulting fr

e “XY” field. WWell 005 is on

ly, the variationrface in Wells 0Wells 007 and 0pping of Well 0l (about 5m) coThis discontinufingerprint the ld.

f the key chron

Depth of 15.0MChrono-surfac

(m)2800270028902550

f the key chronin “XY” Field

of

m)

Depth of 20.7MChrono-surface (m)

27502730

sue 9, September


not most pre-ned sec-

ded.

5 d at

XY” g in Ter-rom

Well the

n in 005, 006 006 om-uity de-

nos-

Ma e

nos-

Ma

7 DISC

7.1 DepThe studtotal of nsequencetributionone incoStand Syplex (PGplete 3rd

SEQ 4; W7) and torder seWells 00capped bThe otheformed dically lintems comes elemeprodelta The ovetion patField andepositiare laterathe LST Table 10. SEQ 4 in

Well

002

003

007

006

It has beLST in Sand erosasymme[23]. Tplacemefield.

Hence, “XY” Weustacy since threcorded

A tectonopment Greater

7.2 PetrThe “XYsyntheticof subsidsequenceresulting

r‐2013

CUSSION

positional Sequdied stratigraphnine genetic sees (SEQ 1-7) a

n in the field shomplete 3rd ordystems Tract (LGC) in SEQ 4; d order sequenceWell 005 has thtwo incompleteequences (SEQ07 and 006 bothby the PGC in Ser accompanyindistinct deltaic nked retrogradamprising of TSTents of the systea shales and progerall similarityttern of the send the observeional systems ally continuousin SEQ 4 slopeShowing the trenthe “XY”Field

Dep

2460

2400

2230

2215

een noted that thSEQ 4) in Wellsion, which coetrical subsidehese structureents (faults) th

local tectonicsWell Field. St

also played ahe delineated Md in the Chrono

no-eustatic coof stratigraphUghelli Depo

roleum Plays oY” Field is coc faults which adence. The weies may have trg main compart

uences in the “Xhic column in thequences made and two incomphowed that Weer sequences (SLST) of the pro

Well 003 has es (SEQs 4 to 7hree complete 3e sequences; Ws 3 to 7) capph have four comSEQ 4 (Fig. 12)ng systems traccomplexes con

ational, progradT, HST and LSTems include: shgrading slope c

y recorded in tequences and

ed gradational in non-faulted

s and traceable ies gently from wnd of LST in d pth (m)

0 – 1960

0 – 1990

0 – 2100

5 – 2100

he absence of tls 005 and 001orroborates thence in the Teres are probabhat have compa

s affected the ratigraphic ba

a role in the deMFSs matchedostratigraphic

ntrol is therefhic sequences belt, Niger De

of the “XY” Fieompartmentalizeare suggested tight of the ensutriggered faultintments are: Blo

XY” Field he “XY” field isup of seven coplete sequencesell 002 has threSEQs 4 to 7), iograding wedgetwo complete 7), also with th3rd order sequen

Well 001 has fiped by a PGC mplete 3rd order). cts in the sequnsisting of a nudational and agT. The major arhoreface deposicomplexes. he organizatiosystems tractmigration and

d blocks depictin the subsurfacwells 006 to 002

this depositiona is probably du

e existence ofrtiary and Quatbly responsiblartmentalized

sedimentationase level chanevelopment ofd with major Chart of [19].

fore, proposedof the Tertiar

elta.

eld ed into three mo have been fouing sand accumng in the well ock 1 comprisin

Direction o

in the “XY”

636

s comprised of mplete 3rd ordes. Sequence disee complete anincluding a Lowe or slope comand two income LST (PGC) innces (SEQs 5 tve complete 3r

unit in SEQ 7r sequences als

ences, howeverumber of genet

ggradational sysrchitectural faciits, channel fills

on and distributs in the “XYd gentle slopingt clinoforms thace. For example2 (Table 10).

al system (i.e thue to subsidencf episodic andternary periode for the disthe “XY” Wel

n pattern in thnges caused byf the sequencesea level rise

d for the develry strata in th

major blocks byrmed as a resulmulations in thfield [24]. Th

ng of Wells 00

of Gentle Slope

Field (?)

a er s-d w

m-m-

n o rd 7. o

r, t-s-i-s,

u-” g at e,

e e d s -ll

e y s s

l-e

y lt e e 2

IJSER



and 003; 2 housing Wells 001 and 005 and Block 3 with Wells 007 and 006. The throw between Blocks 1 and 2 is relatively small co-mapared to that between Blocks 2 and 3. This trend is consistent with the growth fault pattern in the Niger Delta. The compartmentaliza-tion of the “XY” field as a result of rifted fault blocks would no doubt reduce the areal extent and continuity of the reservoirs in the “XY” Field for exploration and development.

The most laterally continuous sandstone unit in the well field, how-ever, is the Prograding Wedge Complex (LST) sands of SEQ 4 ob-serevd in Blocks 1 and 3 (Fig. 12). Despite the obvious truncations observed in Wells 5 and 1 of Block 2, SEQ 4 was also observed to be laterally significant in Wells 7 and 6.

The sands of this Lowstand Systems Tracts (LST) of the earliest sequences (SEQ 4), within each of the two blocks, therefore hold great potentials for hydrocarbon accumulation and can be targeted as the major petroleum plays in the “XY” Field. Accumulation of hy-drocarbons can occur in the structural traps provided by the de-formed LST reservoirs of SEQ 4, if the other elements of a petrole-um system (source rock, timing, seal rock) are present. It has been widely reported that growth fault-related structural traps form the dominant traps in the petroliferous Niger Delta [24]. However, part of the reasons why sequence stratigraphy was ad-vanced in the study area was to discover subtle stratigraphic traps that result from rapid facies changes occurring between successive systems tracts. The cyclic pattern of the alternating Transgressive Systems Tract (TST) and the Highstand Systems Tract (HST) in the studied wells is indicative of a good environment for organic matter accumulation and generation. The pelagic shales of the TST could form good source rocks and cap rocks for the underlying and overly-ing HST and LST given the right conditions.

Reservoir quality sands within the HST could also serve as good reservoirs while faults, active in this area, could serve as traps and/or conduits for migration of hydrocarbons. The distal shale toes of the prograding wedge and transgressive shales would form seals for (potential) stratigraphic traps in the study area. In fact the alternation of HST and TST sands and shales respectively, provides a union of reservoir and seal rocks that are essential for hydrocar-bon accumulation and stratigraphic trapping.

If the sands within the prograding wedge complex are endowed with and sealed by the overlying transgressive shales, potential stratigraphic traps would be formed.

8 CONCLUSION The task of achieving Nigeria’s crude oil reserves target of about 40 billion barrels and production of increased volumes of Liquefied Natural Gas (LNG) in order to meet increasesd export and domestic demands necitated the search for oil and gas with a more accurate technique in the Greater Ughelli Depobelt, Niger Delta. Sequence stratigraphic technique was used to subdivide the strati-graphic column of the “XY” well field into sequences and systems tracts based on the integration of well logs and biostratigraphic data. The technique also delineated quality petroleum plays (reservoirs), their continuity and other elements of the petroleum system (source, traps, e.t.c) for the sustainable development of the resource in the Niger Delta Basin. The summary of the sequence stratigraphic interpretation of Wells

002 (2820-1218m), 003 (2865-1107 m), 005 (2890-1113 m), 001 (3057-756 m), 007 (3059-2800 m) and Well 006 (2895-2800 m) re-vealed a total of nine sequences comprising of seven complete and two incomplete 3rd order sequences.

The accompanying systems tracts in the sequences that formed dis-tinct deltaic complexes consisted of a number of genetically linked retrogradational, progradational and aggradational deltaic systems that recorded similar organization and spatial distribution that depict a number of clinoforms which would be traceable in the sub-surface.

The stratigraphic correlation of the six wells carried out using the interpreted Maximum Flooding Surfaces (MFSs) revealed the exist-ence of faults/discontinuities, which has compartmentalized the “XY” Field into three main blocks. The faults could form structural traps and conduits for migration of generated hydrocarbon if the other elements of a petroleum system (source rock, timing, seal rock) are present.

The absence LST of SEQ 4 in wells 005 and 001 is attributed to sub-sidence and erosion, which corroborated the existence of episodic and asymmetrical subsidence in the Tertiary and Quaternary periods. Local tectonics therefore, affected the sedimentation pattern in the “XY” Well Field, while stratigraphic base level changes caused by eustacy also played a role in the develop-ment of the sequences.

The sands of the Lowstand Systems Tracts (LST) in SEQ 4, within each of the mini-basins hold great potentials for hydrocarbon accu-mulation and can be targeted as the main petroleum plays in the “XY” Field. The cyclic alternation of Transgressive Systems Tracts (TST) and the Highstand Systems Tracts (HST) in the studied wells is indicative of good environments for organic matter accumulation and generation. The pelagic shales of the TST could form good source rocks and cap rocks for the underlying and overlying reservoirs of the HST and LST given the right conditions. ACKNOWLEDGEMENT I am particularly grateful to Dr. K.O. Ladipo and the man-agement of Shell Petroleum and Development Company (SPDC), Port Harcourt, the Directorate of Petroleum Resources (DPR), Nigeria and Dr. Mammah of the University of Nigeria, Nsukka, for graciously providing the data used for this re-search. REFERENCES [1] A. Avuru, “Structure and Operation of the Nigerian Petroleum

Industry” - Oil and Gas Financing in Nigeria: Issues, Challeng-es and Prospects, Avuru A. (Ed.). Chartered Institute of Bankers of Nigeia: Ibadan-Nigeria, 2006.

[2] K.K. Nwozor, M.L. Omudu, B.M. Ozumba, C.J. Egbuachor, A.G. Onwuemesi and O.L. Anike, “Quantitative Evidence of Secondary Mechanisms of Overpressure Generation: Insights from Parts of Onshore Niger Delta”. Nigeria Petroleum Tech-nology Development Journal: Vol. 3, No.1, pp., 2013.

[3] J.C. Van Wagoner, R.M. Mitchum, K.M. Campion and V.D. Rahamanian, “Siliciclastic Sequence Stratigraphy in Well logs, Cores and Outcrops: Concepts for High Resolution Correlation of time and facies.” AAPG Bull., Vol. 7, pp. 1-55, 1990.

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[4] R.M. Mitchum Jr., P.R. Vail, and S. Thompson, “Seismic Se-quence and Global Changes of the Sea Level, Part 2: the Depo-sitional Sequence as a basic unit fro Stratigraphic Analysis” :Payton, C.E., (Ed.), Seismic Stratigraphy- Application to Hy-drocarbon Exploration. Am. Assoc. Petrol. Geol. Mem., Vol. 26, pp.53-62, 1977.

[5] P.R. Vail and W.W. Wornadt, “Well Log Seismic Sequence Stra-tigraphy Course notes for SPDC Sequence Stratigraphy Course” Nov. 1992, Port Harcourt.

[6] D. Emery and K.J. Myers, “Sequence Stratigraphy”: Blackwell Science Oxford: 297pp, 1996.

[7] C.E. Bassey and A.O. Ojesina, “Sequence Stratigraic Interpreta-tion of E-bock in western offshore, Niger Delta, Nigeria”. Glob-al J. Appl. Sci.: Vol 5, p227-233, 1999.

[8] J. Neal, D. Risch and P. Vail, “Sequence Stratigraphy—A Global Theory for Local Success,” Oilfield Review, Vol. 2, No. 1, pp. 51-62, 1993.

[9] H. Doust and E. Omatsola, “Niger Delta”: J.D. Edwards, P.A. Santogrossi (Eds.), Divergent/Passive Margin Basins. American Association of Petroleum Geologists Memoir: Vol. 48, pp.201–238, 1990.

[10] H. Kulke, “Nigeria”: Kulke, H.,(ed.), Regional Petroleum Geol-ogy of the World. Part II: Africa, America, Australia and Ant-arctica: Berlin, Gebrüder Borntraeger, pp. 143-172, 1995.

[11] J. Hospers, “Gravity Field and Structure of the Niger Delta, Nigeria, West Africa”. Geological Society of American Bulletin: Vol. 76, pp. 407-422, 1965

[12] A. Kaplan, C.U. Lusser, and I.O. Norton, “Tectonic Map of the World, panel 10”: American Association of Petroleum Geolo-gists, Tulsa, scale 1:10,000,000. 1994.

[13] B.D. Evamy, J. Haremboure, P. Kamerling, W.A. Knaap, F.A. Molloy, and P.H. Rowlands, “Hydrocarbon habitat of Ter-tiary Niger delta.” American Association of Petroleum Ge-ologists Bulletin: Vol. 62, pp.1–39, 1978.

[14] K.C. Short and A.J. Stauble, “Outline of geology of Niger Del-ta” AAPG, Bulletin: Vol. 51, No. 5, pp.761-779, 1967.

[15] A.J. Whiteman, “Nigeria: Its Petroleum Geology, Resources and Potentil”. Graham and Trotman, London, 39pp, 1967

[16] H. Xiao and J. Suppe, “Origin of Rollover”: American Associa-tion of Petroleum Geologists Bulletin: Vol. 76, pp. 509-229, 1992.

[17] T.R. Klett, T.S. Ahlbrandt, J.W. oker Schm and J.L. Dolton, “Ranking of the world’s oil and gas provinces by known petro-leum volumes” U.S. Geological Survey Open-file Report, pp. 97–463, 1997.

[18] L.W. Tuttle, R.R Charpentier and M.E. Brownfield, “The Niger Delta Petroleum System: Niger Delta Province, Nigeria, Came-roon, and Equatorial Guinea, Africa” U.S. Geological Survey World Energy Project, Open-File Report: pp. 99-50-H, 1999.

[19] B.U. Haq, J. Hardenbol, and P.R. Vail, “Mesozoic and Ce-nozoic Chronostratigraphy and cycles of sea-level change”: Wilgus, C.K., Hastings, B.S., Kendall, C.G.St.C.. Posamen-tier, H.W., Ross, C.A., Van Wagoner, J.C. (Eds.), Sea-level Changes: An Integrated Approach. SEPM Special Publica-tion: Vol. 42, pp. 72–108, 1988.

[20] O. Catuneanu, “Sequence stratigraphy of clastic systems: con-cepts, merits, and pitfalls.” Geological Society of Africa Presi-dential Review No. 1. Journal of African Earth Sciences, Vol.

35, pp. 1–43, 2002. [21] S.O. Onyekuru, E.C. Ibelegbu, C.J. Iwuagwu, G.E. Akan and

C.Z. Akaolisa, “Sequence Stratigraphic Analysis of “XB Field”, Central Swamp Depobelt, Niger Delta Basin, Southern Nigeria”. International Journal of Geosciences: Vol. 3, No. 2, pp. 237-257, 2012.

[22] G.C. Obi, and C.O. Okogbue, “Sedimentary response to tec-tonism in the Campanian-Maastrichtian succession, Anam-bra Basin, Southeastern Nigerian.” Journal Africa Earth Sciences, Vol. 38, pp. 99–108, 2004.

[23] J.P. Bhattacharya and H.W. Posamentier, “Sequence Stratigra-phy and Allostratigraphic Applications in the Alberta Foreland Basin” Geological Atlas of the Western Canada Sedimentary Basin, Chapter 25, 2012.

[24] T.J.A. Reijers, Stratigraphy and sedimentology of the Niger Delta, Geologos, Vol. 17 (3): pp. 133–162, 2011,

IJSER

Documents

Stratigraphy and Petroleum Plays of the late to middle ... · ickness is gre. 2). d into three lar leocene to Rec to Recent, par cent, fluvial fac ormations beco ing the long-te