SEQUENCE STRATIGRAPHIC IMPLICATION TO HYDROCARBONEXPLORATION IN BETA FIELD, NORTHERN DEPOBELT OF THE NIGER DELTA BASIN

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1 SEQUENCE STRATIGRAPHIC IMPLICATION TO HYDROCARBONEXPLORATION IN BETA FIELD, NORTHERN DEPOBELT OF THE NIGER DELTA BASIN Ukpong, A. J.1, 2 and Anyanwu, T. C.2 1 Department of Geology, Gombe State University, Gombe, Nigeria (Sabbatical), 2 Department of Geology, University of Calabar, Calabar, Nigeria Abstract : Seismic and checkshot data, geophysical data and biostratigraphic data extracted from ditch cutting samples, were used for the sequence stratigraphic analysis of Beta-24 well within the Beta field, Northern depobelt of the Niger Delta basin. The results revealed three Maximum Flooding Surfaces and three Sequence Boundaries. Systems tracts; Highstand Systems Tract, Transgressive Systems Tract and Lowstand Systems Tract were identified within the well. Foraminiferal bioevents: Last Downhole Occurrence (LDO) of Globigerina ampliapertura at 2928m, First Downhole Occurrence (FDO) of Bolivina ihuoensis at 2768m and the LDO of Bolivina imperatrix at 2648m delineated from the well were used to date the interpreted surfaces with the aid of the Niger Delta chronostratigraphic chart. The ages assigned to the Maximum Flooding Surfaces (MFS: 1, 2, 3) were 38.0Ma, 36.8Ma, 35.9Ma respectively and sequence boundaries (SB: 1, 2, 3) were 37.3Ma, 36.3Ma and 35.4Ma respectively. The depositional environment of the sediments penetrated by the well were inferred based on well log signatures and biostratigraphic information to have fluctuated from non-marine through coastal deltaic to marine. The Maximum Flooding Surfaces and Sequence Boundaries identified from the foraminiferal-well log sequence stratigraphy were tied to seismic using checkshot data. Seismic stratigraphic interpretation revealed two key bounding surfaces, two systems tracts and two major faults in the field. The faults (F2 and F3) were responsible for the structural truncations that limited the recognition of strata terminations in the vicinity of the well. An observation of the horizons within the systems tracts revealed that they may have potentials to serve as excellent reservoir rock and seals. Keywords: Sequence stratigraphy, Seismic stratigraphy, Biostratigraphy, Northern depobelt, Niger Delta. I. INTRODUCTION The concept of sequence stratigraphy has emerged as an important exploration tool for hydrocarbon in the Niger Delta basin fills. Sequence stratigraphy is the analysis of rock relationships within a chronostratigraphic framework of repetitive, related genetic strata bounded by unconformities or their correlative conformities (Posamentier et al., 1988; Van Wagoner, 1995; Onyekuru et al., 2012; Nton and Ogungbemi, 2011). Sequence stratigraphy is achieved through the integration of data sets such as petrophysical well logs, biostratigraphic and seismic data; it involves the delineation of stacking patterns and the key surfaces that bound successions as defined by their strata stacking patterns (Catuneanu et al., 2011). Sequence stratigraphic analysis is very important in hydrocarbon exploration as it gives companies competitive edge and reduces their risk of bidding on offshore fronts (Oyedele et al., 2012). This technique has been widely accepted in the oil and gas industry because it provides logical and powerful tool for the analysis of chronostratigraphic related sedimentary packages as well as serving as useful guide in predicting facies relationship (Van Wagoner et al., 1988). DOI: /IJRTER II9ND 405

2 The Niger delta is considered one of the highest hydrocarbon producing basins in the world, with the discoveries of giant oil fields in the deep-water areas making it a key target for exploration activities. The delta has prograded in southwest direction from the Eocene to the present, forming depobelts which represent the various active stages of its development (Doust and Omatsola, 1990). The five depobelts that constitute the delta are: Northern, Greater Ughelli, Central Swamp, Coastal Swamp and Offshore depobelt (Fig. 1). The Niger Delta is one of the largest regressive deltas in the world with an area of 75,000 km2 and estimated ,000m of clastic sediments thickness (Ojo et al., 2012; Oresajo et al., 2015). The study area is located in the Northern depobelt, considered the oldest productive hydrocarbon depobelt in the Cenozoic Niger Delta that lies between Latitudes 5 N and 6 N and Longitudes 5 E 6 E (Fig.1). The depobelt has high hydrocarbon potential because of the reported high discovery of oil and condensate (Esedo and Ozumba 2005; Avuru et al., 2011; Oladotun et al., 2016). Figure 1: Map of the Niger Delta depobelts showing the location of Beta field in the northern depobelt (modified from Ejedavwe et al. 2002). Previous studies have investigated the concept of sequence stratigraphy in relation to hydrocarbon exploration in different parts of the Niger Delta. Olusola and Olusola (2014) analyzed the clastic sedimentary succession in the Olay Field, Niger Delta using the sequence stratigraphic principles which involved integrating 3D seismic data, checkshot data for six wells and suites of well logs from 5 wells. Oresajo et al., (2015) subdivided the stratigraphic section within the Emi Field; eastern Niger Delta into genetically related packages bounded by significant chronostratigraphic surfaces based on wireline logs from six wells, 3D seismic data, checkshot and biostratigraphic data. Onyekuru et al., (2012) employed the sequence stratigraphic methods to reveal four 3rd order 406

3 depositional sequences bounded by three Sequence Boundaries, three 3rd order Maximum Flooding Surfaces dated 15.9, 17.4 and 19.4 Ma, respectively and Systems Tracts in the XB Field, Central Swamp Depobelt, Niger Delta Basin. Nton and Ogungbemi (2011) employed the concept of sequence stratigraphy in the K-Field, within the western Niger Delta by integrating wire line logs of four wells and high resolution biostratigraphic data. Adegoke (2012) integrated well logs and biostratigraphic data of three wells within the western offshore Niger Delta for the sequence stratigraphic analysis of sediments penetrated by the wells. The application of the concept of sequence stratigraphy is believed to improve the knowledge of stratigraphic framework, hydrocarbon distribution and facies geometry across several fields in the Cenozoic Niger Delta sedimentary basin as many studies have provided baseline for stratigraphic interpretation of these strata (Onyekuru et al., 2012; Oyedele et al., 2012; Olusola and Olusola 2014). This present study employs the concept of sequence stratigraphy in order to delineate sequence boundaries, maximum flooding surfaces and systems tracts for prediction of hydrocarbon reservoir, seal and source rock in Beta-24 well field, Niger Delta basin using integrated well logs data, 3D seimic volume, check shot data and biostratigraphic data. II. GEOLOGICAL SETTING AND STRATIGRAPHY The Niger Delta basin is located on the Gulf of Guinea in equatorial West Africa (Fig. 2). It is one of the largest regressive deltas in the world (Doust and Omatsola, 1990) considered a classical shale tectonic province (Wu and Bally, 2000). The delta is situated at the southern end of the Benue Trough exactly at the point where the three arms of a rift triple junction met. This triple junction was formed during the split of the African and South American plates which also resulted in the opening of the South Atlantic in the Early Jurassic Cretaceous (Corridor et al., 2005). The Niger Delta is bounded to the east by the Cameroon volcanic line, to the west by the Dahomey basin, and the 4000m (13,100-ft) bathymetric contour (Fig. 2). The delta is characterized by coarsening upward regressive sequences with thickness of 30,000 to 40,000 feet at its maximum and deposited in a series of offlap cycles truncated by sea level changes (Evamy et al., 1978). The Charcot fracture zone as well as other fracture zones expressed as trenches and ridges formed during the opening of the South Atlantic along the oceanic crust control the shapeand internal structure of the delta (Corridor et al., 2005). 407

4 Figure 2: Location Map of the Niger Delta region showing the main sedimentary basins and tectonic features (Corredor et al., 2005). The stratigraphy of the Niger Delta basin consists of Cretaceous to Holocene marine clastic strata that overlie oceanic and some continental crust fragments (Corridor et al., 2005). Though the Cretaceous section is yet to be penetrated beneath the Niger Delta basin, it has been inferred from the nearby Anambra basin (Reijers et al., 1997; Corridor et al., 2005).The Cenozoic stratigraphy of the Niger Delta is divided into three formations representing prograding depositional environments (Fig. 3); the Paleocene to Recent pro-delta facies of the Akata Formation at the base, overlain by the Eocene to Recent paralic facies of the Agbada Formation which is overlaid by the Oligocene torecent fluvial facies of the Benin Formation(Short and Stauble, 1967; Reijers et al., 1997; Corridor et al., 2005). 408

5 Figure 3: Stratigraphic column showing the three formations of the Niger Delta (After Tutlle et al., 1999). III. MATERIALS AND METHODS Materials provided for this study include seismic volume in SEG-Y format, geophysical well logs, base map, check shot data and ditch cutting samples (intervals m)from Beta field. The standard micropaleontological sample preparation method involving sample disaggregation and washing through a 63 micron mesh sieve, drying and picking of the foraminifera and accessory fauna were used (Armstrong and Brasier, 2005; Ukpong et al, 2017). The foraminiferal statistical data was imputed into Strata- Bugs (Biostratigraphy Data Management software) for data processing and integration with the well logs data. Seismic analysis was achieved on Petrel window (version 2014). The workflow plan involved: loading of seismic and well data, review of seismic and log data after loading, integration of biostratigraphic data and their calibration with seismic data, identification of sequence boundaries, maximum flooding surfaces and system tracts. Faults were picked on the seismic sections along the Dip sections. The time-depth relationship was determined using the check shot data provided for the study (Fig 4). 409

6 Checkshot plot 4500 y = x x R² = Depth (m) Time (ms) Figure 4: Check Shot Chart for the study well The following methods were adopted for the sequence stratigraphic interpretation: (a) Foraminiferal biozonation and paleobathemetric interpretation. The P16/17 and P16/17 P18/19 foraminiferal Zones of Blow (1979) which corresponds to the Late Eocene to Early Oligocene age was delineated. Paleobathymetric interpretation shows that the environment ranged from non-marine through shallow inner neritic, inner neritic, middle neritic and outer neritic (Fig. 5). (b) Geophysical well log interpretation (gamma-ray and resistivity logs) was confirmed from the lithologic information obtained from the analyses of ditch cuttings using a binocular microscope. The well log characteristics were used to delineate the different systems tracts (Fig. 5). Sequence boundaries were delineated at points of inflection from progradation to retrogradation of parasequences in shallowing upward sand sections, and at the fluctuation points of lowstand systems tract. Points of high gamma ray and lowest resistivity log response were used for the identification of maximum flooding surfaces (Vail and Wornardt, 1990;Onyekuru et al., 2012). (c) From the foraminiferal abundance/diversity curves and well log signatures, three Maximum Flooding Surfaces (MFS) were identified at 2,900m, 2,768m and 2,528m and dated 38.0Ma, 36.8Ma and 35.9Ma respectively and Sequence boundaries (SBs) at 2840m, 2728m and 2408m dated 37.3Ma, 36.3Ma and 35.4Ma respectively. Lowstand Systems Tract (LST), Transgressive Systems Tract (TST) and Highstand Systems Tract (HST) were also identified (Table 1). (d) The MFSs and SBs identified from the well log-foraminiferal sequence stratigraphy were integrated and displayed on seismic. The well intersected inline 1740 and crossline 6170 on the seismic volume (Fig. 6). Structural truncation by faulting and the subsequent attendant strata displacement around the area were the well intercepted the seismic, made it difficult for stratal terminations to be identified on the section that intersects the well and as such the surfaces were traced into sections where reflections are seen to lap out at their depositional limit. Seismic analyses delineated two key bounding surfaces: maximum flooding surfaces, sequence boundaries and two systems tracts: Highstand systems tract and lowstand systems tract. 410

7 Figure 5: Foraminiferal Distribution and Stratigraphy of Beta-24 Well within the Beta Field 411

8 Figure 6: Siesmic Base Map of Beta Field, Showing well intersected by Inline 1740 and Crossline

9 Figure 7: Niger Delta Cenozoic Chronostratigraphic Chart (Reijers 2011) IV. RESULTS AND DISCUSSION 4.1 LITHOSTRATIGRAPHY Lithostratigraphic analyses were based on detailed description of ditch cutting samples and gamma ray log signatures. The result shows an alternation of sand and shale in a progressive pattern. The sandstone sequences in the well studied were mostly light grey to smoky white, coarse to fine grained, moderately to well sorted and sub angular to subrounded while the shale units are dark grey, 413

10 subfissile to fissile, hard to moderately hard, calcareous and micromicaceous. The variation of sand and shale in different proportions as well as the foraminiferal information from the ditch cuttings was used to identify the Lower Agbada Formation as the major lithostratigraphic units in the well field (Fig 5). The Agbada Formation is comprised mostly of sands and minor shales in the upper section, and an alternation of sands and shales of equal proportions at lower levels (Reijers et al. 1997). Short and Stauble (1967) studied the Agbada Formation and described it as being characterized by the alternation of sandstone and sand units with shale layers. The Agbada Formation has been the major target for hydrocarbon exploration in the Niger Delta. 4.2 SEQUENCE STRATIGRAPHIC ANALYSES DATING OF KEY BOUNDING SURFACES The maximum flooding surface (MFS) and sequence boundaries (SB) are the key bounding surfaces identified in the well with their corresponding depths. The ages and bioevents were obtained based on the zonal correlations and cycles of Blow (1969, 1979) and by correlation with the Niger Delta Chronostratigraphic Chart (Fig. 7). The first Maximum Flooding Surface (MFS) identified in the well (Fig. 5) was dated 38.0 Ma using the LDO of Globigerina ampliapertura at 2928m corresponding to a regional marker Uvigerinella-8 and occurred within the P16/P17 foraminiferal zone of Blow (1979).The second MFS was dated 36.8 Ma. using the FDO of Bolivina ihuoensis at 2768m, and occurred within the P16/P17 foraminiferal zone of Blow (1979) while the third MFS was dated 35.9Ma based on the LDO of Bolivina imperatrix at 2648m corresponding to a regional marker (Orogho shale) of the Niger Delta Chronostratigraphic chart (Fig. 7). The surface occurred within P16/17-P18/19 foraminiferal zone of Blow (1979). Three sequence boundaries (SB) were equally identified and dated in Beta-24 well, the first was dated 37.3 Ma. at the depth of 2840m within the P16/17 foraminiferal zone of Blow (1979) while the second and the third SBs were dated 36.3Ma at the depth of 2728m and 35.4Ma at depth of 2408m respectively, both occurring within the P16/17-P18/19 foraminiferal zone of Blow (1979) (Fig. 5).The dating of these surfaces was done with the aid of the Niger Delta Chronostratigraphic Chart. Table 1 shows the age and depths of the key bounding surfaces and systems tracts as present in the studied well. SYSTEMS TRACTS Systems tracts are components of depositional sequences. They are divided into three groups according to relative sea level at the time of deposition: Lowstand at low relative sea level, Transgressive as shoreline moves landward (retrogradational) and Highstand at high relative sea level. The shape and content as well as the stratigraphic order of systems tract can be predicted. The Lowstand Systems Tract The Lowstand Systems Tract (LST) was defined at intervals of barren fauna in the upper sections while the lower section of the well is composed of few benthics and the planktonic foraminifera Globigerina sp. (Fig. 5).The section is characterized by massive blocky sands. The shale units in this intervals contained reworked materials of terrestrial origin. The lowstand deposits are derivatives of gravity movement due to sediments depositions by rivers as they traverse the shelf and upper slope proceeding towards the incised valleys and canyon along the continental slope (Armstrong and Braisier 2005). The Lowstand Systems Tract is characterized by interbedding of shale and sandstone that follow a coarsening upward pattern with initial progradational stacking pattern and a subsequent aggradational stacking pattern. There is shallowing upward trend of foraminiferal assemblages from regions with high foraminiferal abundance to complete barren regions (Fig. 5). 414

11 Transgressive Systems Tract Transgressive Systems Tract (TST) identified showed an upward increase in foraminiferal abundance and diversity, it represents the well sections with the highest foraminiferal abundance and diversity often culminating in the Maximum Flooding Surfaces. The TSTs identified exhibits retrogradational geometries. These deposits are composed of sand units characterized by fining and thinning upward trends which are overlain by the Maximum Flooding Surfaces and underlain by Sequence Boundaries and Transgressive Surfaces (TS).The TST contains rich preserved microfossils (Fig. 5). This has been reported to be due to the progressive supply of sediments in the process of transgression as turbidity current reduces leading to the high occurrences of clear water microfauna (Armstrong and Braisier 2005). Highstand Systems Tract Highstand Systems Tract (HST) are deposits that accumulates when sediment supply exceeds the rate of accommodation space at the onset of relative sea-level rise (Catuneanu et al. 2011). The HST deposits are capped by surfaces of erosion or non deposition and their correlative conformity (Posamentier and Allen 1999). The HSTs delineated were characterized by progradational sequences with an alternation of sands and shale, occurrences of sparse benthonic foraminifera and complete absence of the planktic assemblages (Fig. 5). The prograding HSTs consists of gravity flow deposits with high rate of microfossils reworking with shallowing upward trend of benthic fauna (Armstrong and Braisier 2005). Table 1: Sequence Stratigraphic Summary of Beta- 24 Well Depth Interval (m) Systems Tract LST HST TST HST TST HST TST LST Key Surfaces SB (35.4Ma) MFS (35.9Ma) SB (36.3Ma) MFS (36.8Ma) SB (37.3Ma) MFS ( 38.0 Ma) - 415

12 4.3 SEISMIC SEQUENCE STRATIGRAPHY An interpretation of the nature of strata terminations on the seismic profile assisted in the delineation of systems tracts and key bounding surfaces within the field. Structural truncation by faulting as well as the resultant stratal displacement hindered the mapping of Maximum Flooding Surfaces (MFSs) and Sequence Boundaries (SBs) on the inline section that intersects the well (Fig. 8). These surfaces were however mapped and traced into sections where reflections lapped out at their depositional limits as seen on the seismic profile. The mapping of these surfaces was on bases of reflection terminations. The Maximum Flooding Surface (MFS) was mapped as a downlap surface whereas the Sequence Boundary (SB) was mapped as both onlap and downlap surfaces. The Highstand Systems Tract (HST) reflectors are found downlaping on the MFS while the Lowstand Systems Tract (LST) reflections are seen as onlaping and downlaping surfaces on the Sequence Boundary (Fig. 9).Three types of reflection terminations, two systems tracts and key bounding surfaces respectively were identified. The Maximum Flooding Surface which defined the lower limit of the Highstand Systems Tract (HST) formed the basal surface. It is seen as a gently dipping downlap surface along which the more steeply dipping and prograding facies of the HST lapout at their lowest limit and having a width of more than 3,900m in its progradational direction. The Sequence Boundary (SB)forms the lower surface and marks the upper limit of the HST. The surface is more extensive, extending beyond the area covered by the seismic profile. The SB has a variable inclination, changing from gentle to steep geometries. This is contrary to the MFS whose inclination is more or less uniform. The SB at its most shallow part has a gentle disposition while the lowstand facies lapout on the surface in an onlap pattern. The Highstand Systems Tract (HST) identified is composed of two facies units, the upper unit characterized by intermediate frequency, moderate amplitude and moderate to low continuity progradational unit, and the lower discontinuous, low amplitude and high frequency clinoform unit which downlapped on the MFS. The presence of the topset unit within the prograding facies indicates that the reflection pattern is sigmoid and that the interpreted lapout could be an apparent downlap. The Lowstand Systems Tract (LST) identified overlies the Sequence Boundary, comprising of high facies continuity units. The reflections onlaping and downlaping on the Sequence Boundary are of variable amplitude; low frequency high continuity and parallel reflection pattern. The prograding facies with a wedge shaped external form has an approximate length of 3,900m and width of 1,150m. The internal reflection is high while the amplitude is high to medium. This facies also display topset reflections which is an indication that the shape is sigmoid and terminate downward on the seismically resolved and the delineated MFS in a lapout pattern. This facies unit occurred within a Highstand Systems Tract because it is bounded at the top by a Sequence Boundary and at the base by a Maximum Flooding Surface. 416

13 Figure 8: A structurally smoothed inline section of the seismic cube showing the position of the well within the seismic volume. F2 and F3 are interpreted faults, top of VOI and base of VOI represent the top and base of the interval of interest as mapped on the well data, while the SBs and MFSs are mapped formation top data from log signatures. 417

14 Figure 9: Reflection Pattern, Sequence Boundary and Maximum Flooding Surface Identified on Seismic Cross Sections in Beta Field 4.4 IMPLICATIONS TO HYDROCARBON EXPLORATION An observation of the shape and contents as well as stratigraphic distribution of the identified systems tracts in Beta-24 well shows they could have good reservoir potentials suitable for exploration. The Lowstand systems tracts (LSTs) identified contains thick sand units which are bounded by shales which could act as sealing rocks. The sands could act as good reservoirs while active growth faults seen in the vicinity of the well could serve as pathways for hydrocarbon upward migration. The shale unit in the overlying Transgressive Systems Tract and the underlying Highstand Systems Tract could form excellent seals assuming the right prevailing conditions. Olusola and Olusola (2014) identified hydrocarbon occurrences within Lowstand Systems Tracts and Transgressive Systems Tracts reservoirs where the major traps are structural and shales within the Transgressive Systems Tract. Sands of reservoir quality are also found within the Transgressive Systems Tracts, especially those occurring within the non-marine to shallow inner neritic environment (Mitchum et al, 1993). The transgressive sands constitute good potential reservoirs. These sands are capped by the overlying and underlying shales of the Highstand Systems Tracts and 418

15 Lowstand Systems Tract which provided good stratigraphic traps. The hemipelagic - pelagic shales found in the Transgressive Systems Tract, and the levees of the leveed channel of slope fans are possible excellent source rock in the well field. Also the Highstand Systems Tracts with identified thick sandy unit can serve as important reservoirs as they are also capped by pelagic shales within the systems tract. V. SUMMARY AND CONCLUSIONS Sequence stratigraphic analysis of Beta-24 well has enabled the subdivision of the stratigraphic succession of the well into packages of genetically related strata bounded by sequence boundaries (major erosion surface) and maximum flooding surfaces. Foraminiferal information extracted from ditch cuttings and the Niger Delta chronostratigraphic chart were used for dating the key surfaces identified. The ages assigned to the Maximum Flooding Surfaces (MFS: 1, 2, 3) were 38.0Ma, 36.8Ma and 35.9Ma respectively and sequence boundaries (SB: 1, 2, 3) were 37.3Ma, 36.3Ma and 35.4Ma respectively. The depositional environment of the sediments penetrated by the well fluctuated from non-marine through coastal deltaic to marine. The Maximum Flooding Surfaces and Sequence Boundaries identified from the foraminiferal-well log sequence stratigraphy were tied to seismic using checkshot data. Seismic stratigraphic interpretation revealed two key bounding surfaces (Maximum Flooding Surface and Sequence Boundary), two systems tracts (Lowstand Systems Tract and Highstand Systems Tract), and two major faults. The faults (F2 and F3) were responsible for the structural truncations that limited the recognition of strata terminations in the vicinity of the well. The horizons within the systems tracts revealed that they may have potentials to serve as excellent reservoir rock and seals. The transgressive sands constitute good potential reservoirs. The pelagic shales of the transgressive systems tract form seals which represent the (potential) stratigraphic traps in the well field. Hydrocarbon migration pathways within the field could be through structural truncations by faults and carrier beds. ACKNOWLEDGMENTS The authors are grateful to the management and staff of the Department of Petroleum Resource (DPR) and the Nigerian Agip Oil Company (NAOC), for providing the data set for this study. We are equally grateful to the Departments of Geology University of Calabar, Calabar Nigeria and Gombe State University, Gombe, Nigeria for providing conducive environments for the research. We appreciate South Sea Petroleum Consultants, Port-Harcourt, Nigeria for their useful inputs. REFERENCES I. II. III. IV. V. VI. VII. VIII. IX. X. Adegoke, A.K. (2012). Sequence Stratigraphy of Some Middle to Late Miocene Sediments, Coastal Swamp Depobelts, Western Offshore Niger Delta. International Journal of Science and Technology. (2) 1: Armstrong, H. and Brasier, M. (2005).Microfossils. (2nd ed). Blackwell Publishing Malden, USA Avuru, A.., Adeleke, V. and Gbadamosi, T. (2011): Unraveling the structural complexity of a marginal field The Asuokpu/Umutu study. Nigeria Association of Petroleum Exploration 23(1):1 4 Blow, W. H. (1969). Late Middle Eocene to Recent Planktonic Foraminiferal Biostratigraphy, Proc. First International Conf. Planktonic Microfossils Blow, W.H. (1979). The Cainozoic Globigerinida. Leiden, E.J. Brill, Catuneanu, O., Galloway, W.E., Kendall, C.G., Miall, A.D., Posamentier, H. W., Strasser,A. and Tucker, M.E. (2011). Sequence Stratigraphy: Methodology and Nomenclature. Newsletters on Stratigraphy. 44 (3): Corredor, F., Shaw, J. H. and Bilotti, F. (2005). Structural styles in the deep-water fold and thrust belts of the Niger Delta. AAPG Bulletin. (89) 6: Doust, H.and Omatsola, E. (1990). Niger Delta, in J.D. Edwards and P.A. and Santogrossi eds., Divergent/passive Margin Basins, AAPG Memoir 48: Tulsa, American Association of Petroleum Geologists Ejedavw,e J., Fatumbi,A., Ladipo, K and Stone, K. (2002): Pan Nigeria exploration well look back (Post-Drill Well Analysis). Shell Petroleum Development Company of Nigeria Exploration Report 2002 Esedo, R. and Ozumba, B. (2005).: New Opportunity identification in a mature basin: the Oguta North prospect in OML 20, Niger Delta. Nigeria Association of Petroleum Exploration 19(1):

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