ORIGINAL PAPER

Seismic stratigraphy and attribute analysis of an offshore field,Niger Delta, Nigeria

Eniolayimika Jegede & Bankole Dayo Ako &

Peter Adetokunbo & Paul Edigbue & Sunday James Abe

Received: 6 July 2014 /Accepted: 30 September 2014# Saudi Society for Geosciences 2014

Abstract Three-dimensional seismic and composite well logdata from three wells were used to carry out log sequence/seismic stratigraphy and attribute analysis of an offshore fieldNiger Delta. The gamma ray and resistivity logs were used todelineate the reservoir sand bodies and carry out sequenceanalysis. From the log sequence analysis, two depositionalsequences were delineated in wells 1 and 2 from 1,820 to3,020 m and 1,860 to 3,000 m, respectively. The two deposi-tional sequences were mapped on the seismic section at timewindows 3.3 and 2.92 s for sequence 1, and for sequence 2 at2.92 and 2.0 s, respectively. Time slice maps of sweetnessattribute were generated to further investigate the hydrocarbonprospect of the field. The seismic facies analysis shows thatthe depositional setting in depositional sequence 1 is charac-terized by sheet- to lens-shaped variable amplitude and cha-otic reflection characters while depositional sequence 2 ischaracterized by (i) sheet-like shaped medium to high ampli-tude, subparallel, continuous reflections, (ii) wedge-shapedlow-to-medium amplitude, wavy, continuous reflections, and(iii) wedge-shaped high-amplitude, wavy, continuous reflec-tions. Results from the seismic stratigraphy show that thedepositional environment has prograded from the delta plat-form (delta front) in depositional sequence 2 down to thewave-dominated prodelta/slope (depositional sequence 1) inthe shallow marine of the deltaic environment. The reservoirquality sand bodies within this field occur within the deposi-tional sequence 2 and occur within all the systems tracts in thissequence.

Keywords Sequence stratigraphy . Attribute . Niger Delta .

Seismic

Introduction

For over 30 years, the oil and gas sector has been the mainstayof the economy of Nigeria. To this effect, oil and gas industrieshave been thriving so well in the nation, producing andexporting petroleum. In order to maintain the status quo, theoil and gas industries have intensified effort, exploring formore giant offshore oil fields.

To embark on any reasonable exploration exercise, knowl-edge of the sedimentary package of the environment is a keyfactor. To achieve this, accurate techniques of stratigraphic anal-ysis are needed. One of such techniques is sequence stratigraphy.In recent time, seismic stratigraphy together with attribute anal-ysis has been proved to be amajor tool in studying and analyzingthe geology and petroleum system of an area (Nauman et al.2010). The degree of reliability and precision of analyzing thegeology of a sedimentary package can be greatly enhanced byintegrating seismic data with well logs which, in some cases,have been used independently in hydrocarbon exploration andexploitation studies (Aizebeokhai and Olayinka 2011). Seismicattributes have been a common tool in seismic data analysis sincethe mid to late seventies. Seismic attributes may highlight geo-logical or geophysical effects, thus leading to a quicker analysisof the data (Randen and Sonneland 2005). In this study, 3Dseismic data were integrated with well logs to define the subsur-face stratigraphy of a field, offshore Niger Delta.

Study area and geology

This study was conducted in a field situated in the offshoreNiger Delta, Southern Nigeria (Fig. 1). The original name of

E. Jegede : B. D. Ako : S. J. AbeDepartment of Applied Geophysics, Federal University ofTechnology, Akure, Nigeria

P. Adetokunbo (*) : P. EdigbueEarth Sciences Department, King Fahd University of Petroleum andMinerals, Dhahran, Saudi Arabiae-mail: peterkunbo@gmail.com

Arab J GeosciDOI 10.1007/s12517-014-1665-7

the field was not released to maintain the confidentiality of thedata. This is in compliance with industry’s policy on informa-tion protection.

The Niger Delta is a large arcuate delta of wave-dominatedtype and is composed of clastic sequence which reaches amaximum thickness of about 12 km in the basin center(Aizebeokhai and Olayinka 2011). It is bounded in the westby the Benin flank and in the east by the Calabar flank, asubsurface expression of the Oban massif (Stoneley 1966).The deep offshore is situated over oceanic crust emplacedduring Cretaceous–Paleogene first related spreading of theSouth Atlantics. Offshore boundary of the province is definedby the Cameroon volcanic line to the east, the eastern bound-ary of the Dahomey basin to the west, and the 2-km sedimentthickness contour or the 4,000-m bathymetric contour in areaswhere sediment thickness is greater than 2 km to the south andsouthwest. The province covers 300,000 km2 and includes thegeologic extent of the Tertiary Niger Delta (Akata–Agbada)petroleum system (Michele et al. 1999).

The lithology of the Niger Delta shows an upward transi-tion from Akata Formation (marine pro-delta shales) throughAgbada Formation (paralic interval) to Benin Formation

(continental sequence). The three sedimentary environments(Fig. 2) extend across the whole delta and ranges in age fromUpper Cretaceous/Early Tertiary to recent. A separate member(the Afam claymember) of the Benin Formation is recognizedin the eastern part of the delta and is considered as an ancientvalley fill formed in Miocene sediments (Nyantakyi et al.2013)

Initial sedimentation in the offshore began within UpperCretaceous–Lower Oligocene hemipelagic mudstones of theAkata Formation. Late Oligocene through recent progradationof the Niger Delta into the slope rise environment allowed forturbidite deposition of the more coarse-grained siliciclastics ofthe Agbada Formation. The latter contains the lower andmiddle Miocene reservoir seal couplets responsible for themajor deep-water hydrocarbon accumulations discovered todate. The underlying Akata Formation is believed to containthe main source intervals. The oil accumulation of the NigerDelta basin is generally confined to various levels of theAgbada Formation. The age of the productive sand intervalvaries from Eocene to Pliocene becoming progressively youn-ger from north to south (Ejedawe 1981). This formation is themajor petroleum-bearing unit in the Niger Delta basin, as there

Fig. 1 Niger Delta map showingthe study area (modified afterGoogle Earth)

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is presence of source and reservoir or seal rock with bothsyngenetic and epigenetic (derived from Akata Formation)hydrocarbon.

Methodology

The materials used for this project are secondary data obtainedfrom the Shell Petroleum Development Company of NigeriaLtd. (SPDC). They include quality 3D seismic data set in SEGY format, composite well log data (resistivity log and gammaray log), and check shot. The 3D seismic reflection datacomprises 637 inlines and 595 crosslines both at 100-m inter-vals altogether and covers an area of 102 km2. Three verticalwells which include Yinkus-1, Yinkus-2, and Yinkus-3 weredrilled in the field. These wells were drilled covering from thenorthwestern to the northeastern part of the field leavingmajority of the southern part with no well control (Fig. 3).The check shot was used to obtain time–depth conversion

curves used for well-to-seismic tie to correlate hydrocarbonreservoirs, sequence boundaries, systems tracts, and facies.

Log sequence analysis

The general procedure of sequence stratigraphic analysis wasadopted from Vail and Wonardt (1991). The first approachinvolved delineation of the different lithologies and theparasequence stacking patterns using the gamma ray log signa-tures. In distinguishing between shale and sand, the gamma raylog used in this study has a shale reference line of 75 AmericanPetroleum Institute (API), chosen from the range of 0–150 APIvalues which respond to the natural radioactivity of theformation. Key surfaces (viz maximum flooding surfaces,transgressive surfaces, and sequence boundaries) wereidentified to subdivide the stratigraphic column intodepositional sequences and systems tracts. Using the resistivitylog, the reservoir sand bodies were delineated, and all these werecorrelated across the three wells using similarities in log motifs.

Fig. 2 Stratigraphic columnshowing the three formations ofthe Niger Delta (after Shannonand Naylor 1989 and Doust andOmatsola 1990)

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Seismic sequence analysis

On the seismic sections generated, faults were identified,picked, and named. Reflection termination mapping was car-ried out to deduce the sequence boundaries. Instantaneousphase attribute was used to enhance reflection terminationmapping on the seismic sections. Figure 4a is an exampleshowing reflection termination mapping on instantaneousphase display. The termination patterns were used in deducingthe environment of deposition. Various termination patternsinclude erosional truncations and lapouts—toplap, downlap,and onlap (Brown and Fisher 1979). These were marked witharrows on the seismic sections. The horizons of interest whichare basically the sequence boundaries were picked throughoutthe seismic section both on the inlines and the crosslines.

Well to seismic tie

The wells were tied directly to the seismic sections using thecheck shot data. This allowed correlation of the hydrocarbonreservoirs, sequence boundaries, systems tracts, and facies.Isopach maps were generated for the depositional sequencesfrom time maps using the time–depth curves.

Seismic facies analysis

Seismic facies analysis was carried out in this work to describethe environment of deposition and depositional system withinthe study area. Seismic waves penetrating into and reflectedwithin sedimentary rock bodies yield a seismic image of boththeir external shapes and internal texture (Schlaf et al. 2005).

Therefore, this analysis was carried out by recognizing boththe shapes and textures within the shapes.

Firstly, different external shapes of seismic bodies wereobserved on the seismic sections, and the boundary relation-ships between these bodies were identified after which theinternal textures (the internal reflection) within the variousseismic bodies were recognized. In other word, the seismicsections are subdivided into mappable three-dimensional unitsof reflections whose characteristics differ from those of theadjacent facies unit. Known different internal reflections in-clude the following: parallel, divergent, chaotic, etc. (Veeken2007); they are categorized based on reflection configuration,continuity, amplitude, and frequency. Internal reflections mayindicate the seismic response to stratal surfaces, lithofacies,fluid content, bedding thickness, etc.

Attribute analysis

Various 3D seismic attributes were engaged to enhance datainterpretation in this work. Apart from using variance edgeand instantaneous phase for fault and reflection terminationmapping, respectively, sweetness attribute maps were gener-ated to study the hydrocarbon prospect of the study areaqualitatively. The rationale behind this is to confirm if thewells are producing and to also discover other hydrocarbonprospect zones within the area.

Sweetness is an attribute that was developed and imple-mented into a seismic interpretation software in the late 1990sfor identifying sands and sandstones (henceforth collectivelyreferred to as “sands”) using three-dimensional (3D) seismicdata in clastic successions. It is derived by combining instan-taneous frequency and reflection strength. Mathematically,

Fig. 3 Base map of the studyarea showing seismic lines andwell locations

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LEGENDSB-Sequence Boundary LST-Lowstand Systems TractTS-Transgressive Surface TST-Transgressive Systems TractMFS-Maximum Flooding Surface HST-Highstand Systems Tract

LEGENDTS – Top of sandBs – Base of sand

a

b

Fig. 4 a Lithology, sequence boundaries, and systems tracts correlation panel. b Reservoir sand body correlation panel. c Parasequence stacking patterncorrelation panel

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sweetness is derived by dividing reflection strength (alsoknown as “instantaneous amplitude” or “amplitude enve-lope”) by the square root of instantaneous frequency (Hart2008). Since high reflection strength (amplitude) and lowfrequency indicate presence of hydrocarbon, combination ofthe two will have high sweetness (Hart 2008).

Sweetness attribute maps were generated across various timesof interest within the reservoir sequence. This attribute is pre-ferred because of its flexibility, following the fact that it can begenerated for a particular time of interest (Sucheta et al. 2008).Another advantage of sweetness attribute is that it is a sample-based volumetric attribute which operates on the seismic datavolume itself including zones that are lower, deeper, or adjacentto the primary zones of interest and therefore unaffected byinterpreter inability to pick continuous horizon due to noisy dataor lack of consistent impedance contrast at rock interfaces(Chopra andMarfurt 2007). It has the capability to identify subtlefeatures that are not represented by picks (Marfurt et al. 1998).

Results

Three wells, namely, Yinkus-1, Yinkus-2, and Yinkus-3 wereused for this work. Well log data, viz, gamma ray and

resistivity logs from these wells were interpreted using logshapes. Information on depositional sequences, systems tracts,lithologies, and reservoir sand bodies was provided from theinterpretation of these data; all these were correlated across thethree wells and are presented in Fig. 4a, c.

The three wells all penetrated an interval with a maximumdepth that ranges between 3,000 and 3,140 m. From thegamma ray log motif, two depositional sequences were rec-ognized. The lithology obtained is dominantly sand and shaleintercalations. Resistivity logs measure the resistance of rockunit to electric current. Porous and permeable sands within theinterval contain electric current-resistant fluid, while the shaleunits exhibit low resistivity. The key bounding surfaces iden-tified in the study area are the maximum flooding surfaces(MFSs) and sequence boundaries (SBs).

Yinkus-1

This well was logged from 1,820 to 3,020 m, a total thicknessof 1,200 m. From the well logs, two MFSs were mapped at2,400 and 1,940 m, also three SBs at 3,020; 2,380; and 1,820mwere recognized. Afterward, two depositional sequences wereidentified, viz, depositional sequence 1 from 3,020 to 2,380 mand depositional sequence 2 from 2,380 to 1,820 m. Thesummary of Yinkus well 1 log is represented in Table 1.

LEGENDMFS – Maximum Flooding SurfaceTS – Transgressive SurfaceSB – Sequence Boundary

c

Fig. 4 (continued)

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Yinkus-2

This well was logged from 1,860 to 3,000 m, a total thicknessof 1,140 m. Two MFSs at 2,740 and 2,020 m were alsorecognized, and three SBs at 3,000; 2,680; and 1,860 m weremapped. Two depositional sequences were also identified, viz,depositional sequence 1 from 3,000 to 2,680 m and deposi-tional sequence 2 from 2,680 to 1,860 m. The summary of thiswell log is represented in Table 2.

Yinkus-3

This well was logged from 1,770 to 3,140 m, a total thicknessof 1,370m. In these well logs, twoMFSs at 2,500 and 1,770mwere also mapped, but unlike the other two wells, only twoSBs at 3,140 and 2,480 m were mapped. Consequently, onlydepositional sequence 1 was identified here while depositionalsequence 2 was partly identified. In this well, depositionalsequence 1 is from 3,140 to 2,480 m. The summary of thiswell log is represented in Table 3.

Depositional sequence

Generally, a depositional sequence is defined as a stratigraphicunit composed of a relatively conformable succession of genet-ically related strata bounded at its top and base by unconfor-mities or their correlative conformities, known as SBs (Veeken2007). It consists of lowstand systems tract (LST), transgressive

systems tract (TST), and highstand systems tract (HST). Allthese can be recognized in well logs through the parasequencestacking patterns which are usually delineated by observing thegamma ray log motif. On the above premises, Yinkus-1,Yinkus-2, and Yinkus-3 were interpreted and a total of twodepositional sequences were recognized.

Depositional sequence 1 was identified in all the wells ofstudy, viz, Yinkus-1, Yinkus-2, and Yinkus-3. Sequence 1 isbounded at the base and top by SB1 and SB2, respectively. Itis made up of LST (prograding complex), TST, and HST, andthey are characterized by the progradational, retrogradational,and aggradational parasequence sets, respectively. The lithol-ogy in this sequence is dominantly shale intercalated with thinsand. The sand to shale ratio is about 30–70 %, respectively,with the lithology characterized with coarsening upward.

Depositional sequence 2 was identified in both Yinkus-1and Yinkus-2 but was partly identified in Yinkus-3. Just likesequence 1, it is bounded at the base and top by SB1 and SB2,respectively, except in Yinkus-3 where the upper boundary isMFS. It is made up of LST, TST, and HST, and the lithology iscoarsening upward. However, the lithology in this sequence isdominantly sand which makes up to about 70 %while shale isestimated to be about 30 %.

Seismic stratigraphic analysis

Seismic sequence stratigraphy was carried out by criticallyanalyzing the seismic sections of the 3D seismic data volume

Table 1 Depositional sequence information of Yinkus-1

Depth (m) Thickness (m) Sequence Parasequence stacking Systems tracts Bounding surface (upper) Bounding surface (lower)

1,820–1,940 120 2 Aggradation HST SB 1 MFS

1,940–1,980 40 Retrogradation TST MFS TS

1,980–2,380 400 Progradation LST TS SB 2

2,380–2,400 20 1 Aggradation HST SB2 MFS

2,400–2,520 120 Retrogradation TST MFS TS

2,520–3,020 500 Progradation LST TS SB 3

SB sequence boundary, LST lowstand systems tract, TS transgressive surface, TST transgressive systems tract, MFS maximum flooding surface, HSThighstand systems tract

Table 2 Depositional sequence information of Yinkus-2

Depth (m) Thickness (m) Sequence Parasequence stacking Systems tracts Bounding surface (upper) Bounding surface (lower)

1,860–2,020 160 2 Aggradation HST SB 3 MFS

2,020–2,040 20 Retrogradation TST MFS TS

2,040–2,680 640 Progradation LST TS SB 2

2,680–2,740 60 1 Aggradation HST SB2 MFS

2,740–2,860 120 Retrogradation TST MFS TS

2,860–3,000 140 Progradation LST TS SB 1

LST lowstand systems tract, SB sequence boundary, TS transgressive surface, TST transgressive systems tract, MFS maximum flooding surface, HSThighstand systems tract

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from an offshore field. This was carried out through reflectiontermination mapping for recognition and correlation of depo-sitional sequences and interpretation of depositionalenvironment.

Besides conventional seismic section, instantaneous phasedisplay of the seismic section was also used in the reflectiontermination mapping. Instantaneous phase is basically a mea-sure of reflector continuity. The reason for the introduction ofthis is the advantage that it has over conventional seismicsection. It is independent on the magnitude of peak ortrough amplitudes; the magnitude of instantaneous phaseis always same (0° for peak amplitude, +180° fortroughs). Therefore, instantaneous phase tends to bal-ance the weak and strong reflectors and make the inter-pretation of weak coherent reflectors easier and is veryeffective for detecting the fault discontinuity, wedge-out,fan, and internal deposition geometry of the sedimentarylayers and SBs (Sukmono et al. 2006). The instanta-neous phase display showing the reflection terminationmapping is presented in Fig. 5a.

Three sequence boundaries (SBs) which fall between timewindow 2,000ms (2 s) and 3,300ms (3.3 s) weremapped, andthese subdivide the seismic section into two packages ofconcordant reflections (depositional sequence) whichare genetically related strata (Fig. 5b, c). Depositionalsequence 1 which is the first recognizable depositionalsequence on the field falls between time windows 3.3and 2.92 s on the seismic section. It is bounded aboveand below by SBs (SB1 and SB2). These SBs wereidentified by characteristic downlap baselap (SB1) andtoplap (SB2) as upper boundary. Depositional sequence2 is directly underlain by depositional sequence 1. Itfalls between time windows 2.92 and 2.0 s on theseismic section. The baselap sequence boundary is iden-tified by characteristic downlap while the upper bound-ary (SB3) is concordant.

Figure 6a, b shows the thickness maps of sequences 1 and2, respectively. The maximum sediment thickness in sequence1 is 1,000 m; this is observed at the northwest, and it thinsgradually to the southeast to about 200 m. The thickness of thesediment within sequence 2 varies from 350 to 1,050 m. This

suggests good pay zone for hydrocarbon accumulation. Thesand body thinning toward southeast and thickening towardthe northeast explains the possible reason why the wells arelocated on structural high within the region.

Discussion

From the log analysis of sequence 1, the lithologies are delin-eated predominantly as shale with thin sand; the log motifshows a coarsening upward trend. From the seismicsections, this sequence is typified with toplap upperboundary and downlap baselap reflection terminationpatterns and variable amplitude chaotic reflection char-acters. From the factors above, considering the reflec-tion termination patterns, one can easily deduced thatsequence 1 is a prodelta/slope in the deltaic environ-ment. The variable amplitude reflection of seismic facies2 indicates that similar lithologies (shale/silty sand) aredominant in this area of the sequence. However, thechaotic appearance of the reflection configuration sug-gests that the dominant lithology could be overpressuredshales (Veeken 2007); this claim should be further ver-ified using sonic or density logs. Meanwhile, the exter-nal geometry of this facies—sheet to lens shape(Fig. 7)—indicates that the environment of depositionis prodelta (Brown and Fisher 1979). This further cor-roborates the environment of deposition deduced fromthe reflection termination pattern. The progradingclinoforms of seismic facies 1, which is interpreted asshingled, indicate a high-energy shallow marine envi-ronment. The termination pattern of the boundary be-tween sequences 1 and 2, which is a toplap, suggeststhat depositional sequence 1 was followed by a periodof nondeposition (bypass)

From the log analysis of sequence 2, the lithologies aredelineated predominantly as sand with thin shale; the logmotif shows a coarsening upward trend. The reflection termi-nation pattern in this sequence is typified with concordantupper boundary and downlap baselap. Facies analysis reveals

Table 3 Depositional sequence information of Yinkus-3

Depth (m) Thickness (m) Sequence Parasequence stacking Systems tracts Bounding surface (upper) Bounding surface (lower)

1,770–1,880 110 2 Retrogradation TST MFS TS

1,880–2,480 600 Progradation LST TS SB 2

2,480–2,500 20 1 Aggradation HST SB2 MFS

2,500–2,870 370 Retrogradation TST MFS TS

2,870–3,140 270 Progradation LST TS SB 1

LST lowstand systems tract, SB sequence boundary, TS transgressive surface, TST transgressive systems tract, MFS maximum flooding surface, HSThighstand system tract

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medium-to-high amplitude, moderate-to-high continuity sub-parallel reflection characters which indicates uniform sedi-mentation and uniform energy level condition. All these are

indications of a delta platform in the deltaic environment. Thehigh continuity of the subparallel reflections in this sequenceis more diagnostic of delta front in the delta platform than

Figure 5a: Instantaneous phase display showing reflection terminations (downlap, toplap and concordant terminations) of the sequence boundaries.

LegendSB: Sequence BoundaryS: Sequence

SB1

SB2

SB3

S2

S1

concordant

downlap

downlap

LegendF: FaultSB: Sequence BoundaryS: Sequence

SB 3

SB 2

SB 1

F1

F2 F3

F4

F5

S2

S1

concordant

toplap

downlap

downlap

a

b

Fig. 5 a Instantaneous phase display showing reflection terminations(downlap, toplap, and concordant terminations) of the sequence bound-aries. b Interpreted seismic section at crossline 1253 showing reflection

terminations of the sequence boundaries (downlap, toplap, andconcordant) and faults. c Seismic section at crossline 1253 with thestratigraphic surfaces and faults

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delta plain. The amplitude varies vertically and laterally.The portion with high amplitude indicates constant deltasandstone/prodelta shale lithological contrast while themoderate amplitude suggests presence of less contrast-ing lithology. Meanwhile, the external geometry of seis-mic facies 3 (sheet-like) indicates that the environmentof deposition is delta platform (Brown and Fisher 1979)which could be either delta plain or delta front. However, thewedge shape of seismic facies 4 and 5 indicates a suddenbreak in sedimentation pattern and gradual change in environ-ment (Veeken 2007).

Figure 8 shows time slice maps of sweetness attributes thatwere used to further investigate the hydrocarbon (both oil andgas sand) reservoir quality of this field. The interpretation forsweetness attribute was carried out adopting interpretationaccording to Hart (2008); high sweetness indicates high re-flection strength and low frequency; this points out the pres-ence of hydrocarbon. From the time slice maps, the wells areseen conformably seated on the portion with high sweetnesswhich confirms that the wells are producing. The green circlespoint out prospects within the area which are both structurallyand stratigraphically controlled.

Conclusions

Seismic stratigraphy and attribute analysis revealed the twodepositional sequences S1 and S2, the predominant lithology,and the hydrocarbon reservoir quality of the field. Logsequence/seismic stratigraphy reveals that the predominantlithology in sequence 1 is shale while that in sequence 2 issand. The depositional environment has prograded from the

delta platform (delta front) down to the wave-dominatedprodelta/slope in the high-energy shallowmarine of the deltaicenvironment. S1 and S2 are typified with toplap upperboundary/downlap baselap and concordant upper boundary/downlap baselap, respectively. The termination pattern of theboundary between sequences 1 and 2, which is a toplap,suggests that depositional sequence 1 was followed by aperiod of nondeposition (bypass). Seismic facies analy-sis also reveals that there is a vertical alternation ofcontrasting lithologies (sand/shale) in depositional se-quence 2. It can be concluded that the sand units arethe reservoirs while alternating shales are the seals. Theisopach maps generated from the SBs show that thewells are drilled on fault-assisted anticlinal structuresin the area. Seismic section reveals that there is agrowth fault beyond the wells further down which could serveas a seal for the entrapment of hydrocarbon and therebymaking the reservoir a good pay zone. This therefore givesthe rationale behind why the wells were drilled in that envi-ronment of the study area.

The reservoir quality sand bodies within this field, as seenon the seismic section at crossline 1253, fall within deposi-tional sequence 2 and occur within all the systems tracts(lowstand, transgressive, and highstand systems tracts) in thissequence. This depositional sequence falls within 2,000 and2,920 ms. The vertically alternating shales in sequence 2 arethe seals while the shale units in the depositional sequence 1may likely serve as a source rock since the source rocks in theNiger Delta are generally located in Akata Formation whichare predominantly shale as mentioned earlier in the geology ofthe study area. Sweetness attribute has given a clue in reveal-ing that the wells in this field are producing. However, it is

F1

F2F3

F4

F5

Sequence boundary

Transgressive surface

Maximum flooding surface

c

Fig. 5 (continued)

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Fig. 6 a Isopach map for sequence 1. b Isopach map for sequence 2

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obvious that the wells are targeted on the structural highswhereas the sweetness attribute has revealed that there arestratigraphic traps also in the field which can be targeted and

drilled for exploitation. The present study has revealed newhydrocarbon prospect zones for future exploitation in theoffshore field, Niger Delta.

3

5

4

21

Seismic Body Boundary

Fig. 7 Segmentation of a seismicsection into different externalshapes and internal texture

Sweetness Map of Reservoir at Z=2086.478 Sweetness Map of Reservoir at Z=2114.2969

Sweetness Map of Reservoir at Z=2150.7662Fig. 8 Sweetness time slice maps showing hydrocarbon prospects

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Acknowledgments The authors would like to thank the Department ofPetroleum Resources (DPR) and Shell Petroleum Development Compa-ny (SPDC) Lagos Nigeria for the provision of data and SchlumbergerNigeria for donating workstations and Petrel software used for this study.We also thank the King Fahd University of Petroleum & Minerals(KFUPM) for supporting this project.

References

Aizebeokhai AP, Olayinka I (2011) Structural and stratigaphic mappingof Emi Field, offshore Niger Delta. J Geol Min Res 3(2):25–38

Brown LF Jr, Fisher WL (1979) Principles of seismic stratigraphicinterpretation. AAPG Contin Educ Course Note Ser 16:1–125

Chopra S, Marfurt KJ (2007) Volumetric curvature attributes add value to3D seismic data interpretation. Lead Edge 26(7):856–867

Doust H, Omatsola E (1990) Divergent and passive basin of the NigerDelta. AAPG Mem 48:239–248

Ejedawe JE (1981) Patterns of incidence of oil reserves in Niger DeltaBasin. AAPG Bull 65:1574–1585

Hart BS (2008) Channel detection in 3D seismic data using sweetness.AAPG Bull 92(6):733–742

Marfurt KJ, Kirlin RL, Farmer SL, Bahorich MS (1998) 3-D seismicattributes using a semblance-based coherency algorithm.Geophysics 63(4):1150–1165

Michele LT Micael BE and Ronald CR (1999) Tertiary Niger Delta(Akata-Agbada) Petroleum System (No 701901) Niger Delta prov-ince Nigeria, Cameroon, Equatorial Guinea, Africa. Central RegionEnergy Resources Team U.S. Dept. of the interior U.S. Geologicalsurvey, p. 41-43

Nauman S, Farhan AK, Asam F, Amjad AK, Kashif H, Mohammad S(2010) Presenting seismic stratigraphy and attribute analysis aspioneer techniques for delineation of reservoir quality sand bodiesin the Indus Offshore Basin, Southwest Pakistan. Lead Edge 29(5):524–529

Nyantakyi EK, Li T, Hu W, Borkloe JK, Owusu PA, Nagre RD (2013)Determination of organic matter richness for Agbada Formation,Osioka South Area, Western Niger Delta, Nigeria. ARPN J SciTechnol 3(8):799

Randen T, Sonneland L (2005) Atlas of 3D seismic attributes.Mathematical methods and modelling in hydrocarbon explorationand production. Springer, Berlin Heidelberg, p 23–46

Schlaf J, Randen T, Sonneland L (2005) Introduction to seismic texture.In: In mathematical methods and modelling in hydrocarbon explo-ration and production. Springer, Berlin Heidelberg, p 3–22

Shannon PM, Naylor N (1989) Petroleum basin studies. Graham andTrotman Limited, London

Stoneley R (1966) The Niger Delta region in the light of the history ofcontinental drift. Geol Mag 103:385–397

Sucheta M, Anirbid S, Kavita B, Pushpal B (2008) Use of seismic attributein detecting hydrocarbon traps in deeper Olpad sands in Cambaybasin. Presented in Geo India (AAPG Initiative), Greater Noida

Sukmono S, Santoso D, Samodra A, Waluyo W, Tjiptoharsono S (2006)Integrating seismic attributes for reservoir characterization inMelandong Field, Indonesia. Lead Edge 25(5):532–538. doi:10.1190/1.2202653

Vail PR, Wonardt W Jr (1991) An integrated approach to exploration anddevelopment in the 90s: well log-seismic sequence stratigraphyanalysis. Gulf Goast Assoc of Geol soc Trans 41:630–650

Veeken PCH (2007) Seismic stratigraphy, basin analysis and reservoircharacterisation (handbook of geophysical exploration). Elsevier 37:7–109

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