DEPOSITIONAL  ENVIRONMENT  AND RESERVOIR ARCHITECTURE  OF “JI” FIELD NIGER DELTA

Abstract

This study is a contribution to the understanding  of the depositional environment and reservoir architecture of the “JI  Field”, Niger Delta Nigeria.  The main objective  was to integrate sequence stratigraphy and petrophysical  evaluation  in characterizing  the reservoirs  encountered in the wells.  Well logs from six wells (JI01, Il02,  Il03,  Il09, Jll0  and  1112-ST),  biostratigraphic  data  from  two  wells  (JI01  and  Il02)  and  3D seismic volume were analyzed to understand  the reservoirs  correlation pattern  with their environment of deposition (EOD), petrophysical properties  and fault patterns on the structural map of the field.

Result  from  facies  analysis  reveals  that  “JI field”  is composed  of foreshore  sand, upper  shoreface sand,  lower shoreface sand,  tidal channel and channel  sands which were  deposited  in  shallow  marine  setting.  Sequence  stratigraphic  analysis  result showed two depositional sequences (SQl  and SQ2). These depositional sequence are bounded   with   sequence   boundaries   (Vail’s   law)   dated   10.6Ma,    10.36Ma   and

7.4Ma.Maximum flooding  surfaces  (MSF)  datedl 1.6 Ma,  10.4Ma and 7.8Ma  were delineated. The delineated  system tracts are Lowstand, Highstand and Transgressive Systems  Tract  with  their  associated  progradation,  retrogradation   and  aggrading stacking patterns.  Well correlation  showed appreciable net sand reduction  along the dip direction.  Petrophysical analysisof F-sand reservoir shows an average net to gross thickness  of 0.55,  average porosity  value of 0.29v/v,  average permeability  value of

2506md  and average water saturation  of 0.14.  This reservoirconsist  mainly of tidal channel  sand  heteroliths  belonging  to  the  lowstand  system  tract.  Fault  mapping delineate faults composed of major  growth faults,  listric fault,  antithetic and synthetic faults.  Structural  features  such  as  collapsed  crestand  of back  to  back  structures constitute  the reservoir  architecture.  Majorfaults  trend in NE-SW  and dip SE,  SW. The structural map shows a two way fault dependent closure for JI field.

CHAPTER ONE

1.0      INTRODUCTION

The  Niger  Delta  is  a prolific   oil  provincewithin  the  West  African  subcontinent. Exploration  activities have been concentrated  in the onshore part of this basin but as the delta becomes better understood  exploration  activity are gradually being shifted to the  offshore   though  the  geology  tectonics   and  evolution  of the  Eocene-Pliocene sequence of the Niger Delta are fairly well known.

Reservoir   characterizationhas  been  a  major   concern  in  oil  and  gas  industries  to adequately  estimate  reserve;  reason  is  that  better  reservoir  characterization means higher success rates and fewer wells for reservoir exploitation. Thus there is a need to approach  these area of interest  with more robust  interpretation  techniques  that helps production  geologist  and reservoir  engineer understand  reservoir  heterogeneities  and reduce uncertainties.   .

This   studies   focus   on   delineating   the   depositional   environment    and   reservoir architecture   of JI  field  with  theintegration   of sequence  stratigraphic   analysis  and petrophysical  interpretation.Sequence stratigraphic  interpretation  which  in recent has developed   (Posamentier   and  Allen,   1999;   Posamentier,   2000;   Catuneanu,   2002;

12

Catuneanu   et   al.,   2005),   was   synergized   withpetrophysical   reservoir   geometric property interpretation  for reservoir characterization.

Environment  of deposition  (EOD) was inferred  from the integration of facies analysis with paleobathym etry.  Stacking patterns,  system tract and depositional  sequenceof the fieldwas  interpreted  and integrated withPetrophysical  parameters  such  asporosity(   ), water  saturation(Rw), permeability  (K) and net to gross (NTG).  These petrophysical parameters  are the key  reservoir  geometric  properties  used  in  characterizing  F-sand reservoir.   Fault   and  horizon   interpretation   further  helped   in  the  interpreting  the reservoir architecture.

1.1       OBJECTIVES OF THE STUDY

The objectives of this research work are to

I.      delineate  reservoir  facies  which  is integrated  with paleobathymetry  data  in inferring the environment of deposition (EOD)

II.     establish  reservoir  architecture  across  the field by  establishing  the  sequence stratigraphic and structural frame work

III.      determine key reservoir geometric properties acrossthe field

1.2      STUDY LOCATION:

The studied field is 17 km SE of Yenegoa and 90 km west of Portharcourt. The field is a seasonally flooded fresh-water swamp area located in the coastal swamp depobelt in OML  18  (Fig  I   and 2).  It has  a survey area  of 5x10km  and the seismic  volume rangesin-line   and  X-line   are  6649-7321   and  925-1349  respectively.The   seismic

13

volume  has  a  record  length  of 5750ms.  Fourteen  wells  have  been  drilled  most  of which  are water bearing.  Some are side tracks with  incomplete  logging details.  Only five of the wells which were used for this study have complete logs.  The depth range of the wells are from 9927ftss to 15000ftss.

14

—- —- —- —-

—- —-

—- —- – – – – – -·’·············””- ……

°30  km

QUATERNARY

meander belt, back swamps [Qa] alluvium

CRETACEOUS

Falsebedded sst. and U. coal measures [u Falsebedded sst, coal and shale

fresh water swamps             [@] sands, gravels and clays

mangrove swamps                [Qr] sands, clays and mangrove swamps abandoned beach ridges    sands and pebbles

Sombreiro deltaic plain         [Qsdl  sands, clay an mangrove swamps

coastal  plains  sands                [Qpl sands  and clays

TERTIARY

lower coal measures Nkporo shale group Cretaceous intrusion

Awgu-Ndeabah shale group Eze Aku shale group Odukpani formation

[Kc]  coat. sandstone and shale

[K@]  sale and muodstone

[i basic and intermediate intrusions

shale and limestone

[K@]   back shale and sitstone

[K] naggy shale and calcareous sst

lignite formation        [Ti] clays. sst, ignite and shales Bende Ameki group  [Tb]lays, clayey sands and shale Imo clay-shale group [Ti clays and shales with st

Asu river group                              • shale and limestone

PRE-CAMBRIAN TO UPPER CAMBRIAN

basement complex[P@g] older granite

Fig 1: Geologic map of the Niger Delta and surroundings After Reijers 2011

15

$

8        I  009

$

J.010

‘

J.001

©

42ST

$

JI 002

©

JI003

$01600          $0240          $03200                50400          50430          $05800                 50640          507200                $08,00              508800                 509600          51040

0    24  $00  10 10001250

Fig 2: Base Map of the study Area showing the locations of the wells in the field.

16

1.3      LITERATURE  REVIEW:

Stoneley (1966) and Burke et al (1970,  1972) analyzed and discussed the mega tectonic setting  of the  Niger  Delta.  The  syn-sedimentary tectonics  of the  Tertiary  Delta  was extensively described by Merki (1972) and Evamy et al. (1978), Ejedawe (1981 ), Knox & Omatsola (1987) and Stacher (1995).

Short and Stauble (1967) and Weber and Daukoro (1975) outlined the three major depositional cycles in the coastal sedimentary basin of Nigeria.  They first began with an Albian marine incursion and terminated during the Santonian time, the proto-Niger Delta started during the second cycle;  the growth of the Niger Delta continued from Eocene to Recent time.  At several  stages during the late Quaternary,  sedimentation was interrupted by uplift and erosion,  resulting in several  cycles of channels being formed(Evamy et al,

1978).

Burke et al (1972) correlated these late Quaternary canyons to the drowning of the river mouths,  which where incised  on the continental  shelf during the Wisconsin  fall in sea level which probably resulted in the formation of the Afam Canyon and the Qua Thoe clay fill, During the Miocene, in the south-east delta.

According to Short and Stauble (1967) and Doust and Omatsola (1990), the Niger Delta comprises of a regressive sequence of deltaic and marine elastics defined by three major lithofacies.From the base, it is predominantly marine shale of Akata Formation, followed by paralic sequence of Agbada Formation and topmost non-marine alluvial (continental) sands of the Benin Formation.

17

Oomken  (1974)  examined  the  sediments  in the  Terrestrial  and  Submarine  parts  of the modem    delta   and   grouped   them   into   three   major    lithofacies   using   lithological characteristics   and   other   sedimentary   features.   These   lithofacies   are   grouped   into sandstone, heteroliths and mudstone.

Weber (1971) reported the cyclic nature of sedimentation of the Tertiary paralic deposits. According  to him  a completed  cycle consists  of thin, fossiliferous  transgressive  Marine sands  followed  by  an  offlap  sequence  which  commence  with  marine  sediments  and another transgression may terminate the cycle.

Doust   and   Omatsola   (1990)   recognized   six  depobelts   in   Niger   Delta,   which   are distinguished   primarily   by   their   age.   They   are:   Northern   Delta(late   Eocene-Early Miocene), Greater Ughelli (Oligocene-Early Miocene), Central Swamp! (Early-Middle Miocene),   Central   Swampll   (Middle   Miocene),   Coastal   Swamp   I  and  II   (Middle Miocene) and Offshore  (Pliocene).

Adeogba et al (2005) interpreted a near surface, 3-D seismic data set from the Niger Delta continental  slope, offshore, Nigeria and revealed important stratigraphy and architecture. Architectural   features  and  sediment  deposits  interpreted   from  seismic  character  and seismic  stratigraphy in the absence  of borehole  data include mass-transport  complexes, distributary channels,  submarine  fans and hemipelagic drape complex.

Stacher  (1994 ),  produced  a  delta  wide  framework  of Cretaceous  Chronostratigraphic surfaces,  and  a  sequence  stratigraphic  chart  for the Niger  Delta,  using  digitally  stored biostratigraphic  data, obtained from over 850 wells.

18

Sequence stratigraphy thus facilitates the subdivision  of the Niger Delta into packages of sediments that are essentially bounded together by Chronostratigraphically  significant surfaces. Various works have been carried out, in relation to the sequence stratigraphy of different  parts  of Niger  Delta.  These  include Bowen  et al., (1994),  who  established  an integrated geologic framework of the Niger Delta slope, by applying established sequence stratigraphic  concepts,  on the newly acquired seismic dataset of the Niger Delta,  coupled with biostratigraphic  data,  from 26key wells.

Ozumba  (1999),  developed  a  sequence  stratigraphic  framework  of the  western  Niger Delta, using  foraminifera  and wireline  log data obtained  from  four wells  drilled  in the coastal  and  central  swamp  depobelts.  He  concluded  that  the  Late  Miocene  sequences were thicker than the Middle Miocene sequences.

Poston  et al. (1983) presented  the Geology and reservoir  characteristics  at Meren  field. They noted evidence of syn-depositional  displacement  on growth faults across the field. They also suggested  combined well-log interpretation and laboratory analyses of sidewall core  to  aid  in  the  determination  of the  spatial  variation  of porosity  and  permeability within particular reservoir interval.

Mode  and  Anyiam  (2007)  worked  on  Reservoir  Characterization   of paradise  Field. Theyconcluded  that the quality of the reservoirsis  moderate  to good and in  some  distal reservoirs they are excellent. The average porosity values are approximately the same, but have  variations  in  permeability  which  could be  as a result  of compaction  of the older reservoirs on the proximal part of the field.

19

John and Oluwaseyi (2013), in their petrophysical properties evaluation for reservoir characterization  of Niger Delta using a field they called SEYI oil field said that reservoir with porosity ranging from 0.22 to 0.31 indicates a suitable reservoir quality, permeability values from 881.58md to 14425.0lmd attributed to the well sorted nature of the sands and hydrocarbon   saturation   range   from  20.29%   to  91.97%   implying  high   hydrocarbon production.

₦5,000.00 – DOWNLOAD FULL PROJECT DOWNLOAD FULL PROJECT Added to cart

---

---

---

---

Related Project Topics :