Greater Ughelli Research Articles

Paleocene – Late Oligocene dinoflagellate cysts biostratigraphy, onshore Niger Delta

A new biostratigraphic biozonation for the Paleocene to Late Oligocene succession of the onshore Niger Delta has been developed based on the identification of significant stratigraphic dinoflagellate cyst events. This study is aimed at applying rarely used dinoflagellate cysts events in dating, correlating and inferring the paleoenvironment of penetrated sedimentary successions in the studied area. Palynological processing and analysis were carried out on two hundred and twenty ditch cutting samples recovered from two exploration wells (BN-1 and FJ-1) located in the Greater Ughelli and Northern Depobelts of the onshore Niger Delta respectively. Abundant and diverse dinoflagellate cysts recovered included marker Peridinales species Apectodinium sp., Palaeocystodinium australinum, and Gonyaulacales such as Areosphaeridium arcuatum, Cordosphaeridium gracile, Tuberculodinium vancampoae, Polysphaeridium zoharyi and Hystrichokolpoma rigaudiae. Three dinoflagellate cysts Palynological Zones - DPZ 100 (Early to Late Paleocene), DPZ 200 (Early to Late Eocene) and DPZ 300 (Late Eocene to Late Oligocene) are proposed herein. The biozones were subdivided into ten subzones based on the Top occurrence, Quantitative Tops and Quantitative base as well as ACME events of dinoflagellate cysts marker taxa which are used to date the rock sequence to be Paleocene to Late Oligocene. Abundant and diverse shallow outer neritic to inner neritic dinoflagellate cysts are identified from thick grey soft shales at the lower section of the studied wells. The upper section show significant reduction in dinocysts assemblage dominated by inner (coastal) neritic taxa. This dinocysts occurrence and distribution suggests inner (coastal) neritic paleoenvironment at the upper sections which deepened into shallow outer neritic conditions at the lower intervals of the studied wells. The thick brown to grey shales at the lower section and the medium to fine grained, moderately well sorted sandstone interbeds at the middle section of the studied wells are interpreted to be potential source and reservoir rocks respectively. These datasets are useful for correlating possible hydrocarbon source rocks and potential reservoir carrier beds in the Gulf of Guinea.

Quantifying a tide-dominated, wave-, and river-influenced delta in Miocene facies of the Niger Delta basin

ABSTRACT The modern Niger Delta has long been classified as a mixed tide-, wave-, and river-influenced delta. Still, no detailed studies have quantified the relative proportions of formative processes and facies. This work presents the first quantitative estimate of the relative influence of formative processes in Miocene deposits based on core data from the Greater Ughelli, Central Swamp, and Coastal Swamp depositional belts of the Niger Delta basin. Facies analysis of 288.2 m of core from four wells shows approximately 53% tidal facies, 33% fluvial facies, and 14% wave-formed facies, indicating deposition in a prograding tide-dominated, wave-, and river-influenced delta. Cores from the Greater Ughelli and Central Swamp depobelts exhibit coarsening-upwards, prograding deltaic facies successions overlain by fluvial mudstone. Tidal deposits in the Coastal Swamp depobelt show coarsening-upwards prograding deltaic facies successions with well-developed tidal bundles indicating seasonal deposition. The basal part of these facies successions also reveals repeated floods characterized by slump and load structures and dewatering features. Delta-plain and delta-front–prodeltaic facies associations are identified based on physical sedimentary and biological structures. The delta-plain facies association consists of weakly bioturbated mudstone, fissile mudstone, and coarse-pebbly stratified sandstone facies with sparse trace fossils. The delta-front–prodeltaic facies association contains muddy and sandy heteroliths, stratified, medium and coarse-grained, cross-bedded sandstone, and convoluted mudstone facies. The facies vary but characteristically contain trace-fossil assemblages of the recently proposed Rosselia and Phycosiphon Ichnofacies, indicating delta-front and prodeltaic settings, respectively. Variability in the facies is determined by the relative influence of hydrodynamic processes (tide, wave, and river), variations in physicochemical stress, and the episodic character of deposition. In addition, based on the relative influence of each hydrodynamic processes, the facies differ through the successions, sometimes subtly.

Evaluation of Facies Architecture and Depositional Environment of G-Field in the Greater Ughelli Depobelt of the Niger Delta Area, Nigeria

This study utilized well logs and core data to evaluate facies architecture and depositional environment of G-field in the Greater Ughelli Depobelt of the Niger Delta area in Nigeria. The study revealed five lithofacies unites, namely, Bioturbated Sandstone Facies (BSF), Coarse to Pebbly Sandstone Facies (CPSF), Mudsone Facies (MF), Very Fine Grained laminated Sandstone Facies (FGLSF), and Wavy- to Flaser-Bedded Facies (WFbF). The lithofacies were grouped into Two (2) Facies Assemblages that where established from the five mentioned lithofacies A-E. The Facies Assemblages are Open-marine Facies Association, Brackish-water Marginal-marine Facies Association and Tidal Flat Association. Gamma Ray (GR) logs within the cored interval defined an aggrading deposit. These assemblages were used to infer the various environments responsible for the deposition.

Chemical Classification of Sediments in JVX -Well, Greater Ughelli Depobelt Niger Delta Basin, Nigeria

This study evaluate the Chemical classification of sediments in JVX well, Greater Ughelli Depo belt Niger Delta Basin. Samples collected from different intervals were analyzed using geochemical proxies. Agbada Formation was suggested for the sampled intervals due to the presence of shaleand sand intercalations. lithofacies units gotten from sampled intervals are Sand, Shale and Shaly sand facies . The sands are milky in colour, translucent to opaque, medium to coarse grain, subangular to subrounded and are moderately sorted while the shales are Grey in colour,fissile with the presence of lignite streak and calcareous materials.The geochemical studies of the sediments revealed that SiO2 is the dominant oxide followed by Al2O3 and Fe2O3 which constitutes over 90% while others like CaO, K2O, TiO2, Na2O and MgO constitute 10%. The sediments were classified as Fe-shale, Fe-sand and Quartz arenite. Samples that plotted in the quartz arenites region suggests an intense degree of weathering and reworking. The SiO2/Al2O3 ratios for the sediments in the well are appreciably high indicating that the samples have been heavily weathered, evidenced from the enrichment of quartz and depletion of feldspars. Also, the relatively high concentrations of Fe2O3 and TiO2 is an indication of iron-titanium minerals such as haematite and anatase retiles.

Geochemical Maturity and Paleo-Weathering Indices of Sedimentary Succession in JV Field Greater Ughelli Depo-Belt Niger Delta Basin

This study evaluates the geochemical maturity and paleo weathering indices of X well JV-Field, Greater UghelliDepo belt Niger Delta Basin, using reflected light microscope and geochemical proxies. The data obtained identified three lithofacies units as Sand, Shale, and Shaly sand facies .The application of source area weathering using Chemical index of alteration (CIA) and Chemical index of weathering (CIW) values for the sampled intervals ranges from (48.6-94.9%) and (60.6-96.7%), and have median values of (83.2 and 90.3) % respectively which is an indication of high weathering at the source. The values are variable and it may be as a result of multiple provenances of the sediments which have variable proportions of source area weathering and related processes or may be due to low concentrations of the alkalis and alkaline earth elements. However, all the samples excluding one with depth (12430ft) show CIA and CIW values greater than 70% indicating high (intensive) weathering either at the source or during transportation before deposition .From the high alteration indices value recorded from the sampled intervals, it can be inferred that the sediments are geochemically and texturally mature.

Sequence Stratigraphic Interpretation of FX-1 and FX-2 wells, Onshore Western Niger Delta, Nigeria

The area of study is a portion of the Greater Ughelli Depobelt in Niger Delta Basin. The main aim of the paper is to interpret the sequence stratigraphy of FX-1 and FX-2 wells by employing data sets from biostratigraphic data and well logs. Standard laboratory techniques were used for data treatment while computer software such as Petrel and StrataBugs were used for data simulation, processing, integration and interpretation. Sedimentology, interpreted gamma ray and resistivity well logs integrated with biostratigraphic data were utilized to define the candidate maximum flooding surfaces and sequence boundaries. The wells have the following distributions of sequences: FX-1 well have five depositional sequences with eight candidate maximum flooding surfaces at depths 10011 ft., 9509 ft., 9437 ft., 6362 ft., 5752 ft., 5507 ft., 5161 ft. and 4816 ft. dated 34.0 Ma, 33.0 Ma, 31.3 Ma, 28.1 Ma, 26.2 Ma, 24.3 Ma, 23.2 Ma and 22.0 Ma and seven candidate sequence boundaries at 9616 ft., 6656 ft., 6116 ft., 5639 ft., 5424 ft., 4859 ft. and 4581 ft. dated 33.3 Ma, 29.3 Ma, 27.3 Ma, 24.9 Ma, 23.7 Ma, 22.2 Ma and 21.8 Ma, respectively. FX-2 well have four depositional sequences, five candidate MFSs were identified at 7764 ft., 7196 ft., 6721 ft., 5862 ft. and 5571 ft. dated 34.0 Ma, 33.0 Ma, 31.3 Ma, 28.1 Ma and 24.3 Ma and five candidate SBs at 6941 ft., 6029 ft., 5688 ft., 5653 ft. and 5542 ft. dated 32.4 Ma, 29.3 Ma, 27.3 Ma, 24.9 Ma and 23.7 Ma respectively. The correlation of the two wells and sequence stratigraphic interpretation is a supplementary understanding of the subsurface geology of the Onshore, western Niger Delta area of Nigeria.
 Keywords: Bio-stratigraphic data, Well logs, Sequence stratigraphy, Well correlation.

Heterogeneities and Intra Sand-Body Compartmentalization in Late Oligocene Delta-Front Deposit, Niger Delta, Nigeria

This paper presents the study of the heterogeneity in lithofacies, porosity, permeability, mineral grain density, pore-throats sizes and hydraulic rock types and the intra sand-body compartmentalization in cored delta-front deposit of Greater Ughelli depobelt of Niger Delta. Sedimentological study of core samples results in the identification of nine lithofacies and the interpretation of environments of deposition as mainly proximal and distal delta-front mouth bar. The sand unit indicates moderate to excellent reservoir quality with core porosity between 16.2 and 29.5% and permeability between 16.8 and 7,560 md. Dykstra-Parsons core permeability distribution coefficient of 0.97 indicates that the studied reservoir sand-body is vertically highly heterogeneous, with high potential for vertical intra sand-body compartmentalization. Graphical cluster analysis of Flow Zone Indicators (FZI) led to the identification of nine Hydraulic Flow Units (HFU) with distribution controlled by depositional facies. The prediction of permeability, porethroats (r35) and flow zone indicator values of the reservoir in an uncored-well using predictive mathematical models developed with multiple regression analysis enabled the inter-well correlation of hydraulic flow units and indicates lateral continuity of reservoir compartments. An intra sand-body compartmentalization evaluated with core permeability values, Winland r35 coefficients and flow zone indicators was corroborated with formation pressure data analysis. Results show that the studied delta front-mouth bar reservoir is vertically compartmentalized by intercalated shales. Fractures in over-pressured zones were found to reduce vertical reservoir fluid compartmentalization by intercalated shales. However, reduction in reservoir pressure due to hydrocarbon production can result in dynamic compartmentalization and consequently, reduction in hydrocarbon recovery.

Evaluation and Prospect Identification in the Olive Field, Niger Delta Basin, Nigeria

The study area lies in the Greater Ughelli Depobelt of Niger Delta. Recently, a major focus within the Niger Delta is the rejuvenation of older fields (also called brown fields) and the identification of new prospects from these old fields. This study is focused on the evaluation of the Olive Field and the identification of new prospects within the field. Data used were; 3D seismic cube, four composite well logs and check shot. 3 dimension seismic, well log and structural interpretation were done to evaluate the petroleum potentials of the reservoirs using the petrel 2010 and the interactive petrophysic v.36 softwares. Well data were used in the identification of reservoirs and determination of petrophysical parameters and hydrocarbon presence. Four horizons that corresponded to selected well tops were mapped after well to seismic tie. Time and depth structural maps were created from the mapped horizons. Four Hydrocarbon bearing reservoirs within the depth range of 6743 ft – 9045 ft, having volume of shale (Vsh) ranging from 15.32% - 29.06% were interpreted. The total porosity of the reservoirs ranges from 24.63% - 34.01%, while the effective porosity ranges from 17.26% - 31.71%, indicating the reservoirs have very good porosities. The ratio of the Net to Gross Thickness of the reservoirs ranges from 0.720 – 0.980 while the water saturation values ranges from 19.87% - 29.07%. From the water saturation deductions, the hydrocarbon saturation ranges from 70.93% - 78.86% of gas in the given reservoirs. Amplitude attribute extraction and analysis of the horizon maps was used in the identification of areas with hydrocarbon accumulations which are conformable with structures. The use of structural and attribute maps has aided the identification of prospects in the Olive Field. Therefore, it is recommended that wells be drilled to target the new prospects which will improve the hydrocarbon recovery in Olive Field.

Petrophysical Characterization and Flow Models for Agbada Reservoirs, Onshore Niger Delta, Nigeria

Three selected reservoirs (XB, XC and XE) from three wells (A, B and C) occurring within the Agbada producing sands in part of the Greater Ughelli Depobelt of the onshore Niger Delta have been studied. The study aims at evaluating the petrophysical characteristics of the sand-bodies and also identifies the various flow units present within each reservoir. Petrophysical parameters were used as input data to generate the Stratigraphic Modified Lorenzo Plots (SMLP). This model uses a graphical method to quantitatively determine flow units and to understand the flow and storage capacities of sedimentary rocks. Results of the analysis shows that average porosity and permeability range is between 7-28.8% and 1.20-529 mD, indicating poor to very good reservoir quality in different parts of the field. Generally, porosity and permeability decrease with increasing depth in the field reflecting burial diagenetic porosity loss in response to increasing thermal exposure with depth. Porosity and permeability change laterally across the field from west to east. Increase in porosity and permeability towards the eastern part of the field reflects lateral change in facies. Well C has the best porosity (28%) and permeability (529 mD), lowest water saturation (0.01), hence, highest hydrocarbon prospect. The stratigraphic Modified Lorenzo Plots (SMLP) revealed a total of seventy five (75) Flow Units (FU) in the three studied reservoirs. Each reservoir displays similar flow pattern relative to others suggesting that facies (rock properties) have a strong control on flow in each reservoir. Generally, poor quality units occur towards the bottom of each reservoir in a well and good quality units towards the top. The dominant flow units in the three reservoirs fall within the high storage and flow (normal flow unit) unit category, suggesting that the dominant depositional setting (shallow marine shoreface/beach/barrier) and facies type beside diagenetic effects play significant role in fluid dynamic behaviour of any rock body. Depositional environments and subsequent diagenesis are the primary factors controlling porosity distribution, pore connectivity and fluid flow in the three studied reservoirs.

Delineating the Proper Shooting Medium for Seismic Reflection Survey in the Greater Ughelli Depobelt, Niger Delta

The proper shooting medium for seismic reflection survey was delineated in a prospect within the Greater Ughelli Depobelt of the Niger Delta using a sample density of 37 Uphole surveys. This prospect is characterized by river tributaries with large and extensive column of sand bars lining the entire length of river banks, creeks, rain forests and flooded plains which pose difficult challenges in placing shots in the proper medium. Thickness and velocity of these unconsolidated weathered layer materials were computed. Graphical analysis using the UDISYS Software to plot the surface corrected first-break times, Ts (msec) against hydrophone offsets (m) showed a dominant 1-weathered layer model. The results reveal that the weathered layer velocity ranges between 209 and 593 m/s while the velocity within the consolidated layer ranges between 1131 and 1987 m/s. The weathered layer thickness ranges from 3.2 to 6.8 m with the prospect average of 4.7 m. These results suggest that, where possible, Pattern-shot types should be located at depths of about 7.0 m in the North-Eastern part, 5.5 m in the South-Eastern part and 3.5 m in the Western and East-Central parts. These depths are below the weathered layer where signals travel at velocities devoid of time delays during 3D/4D seismic surveys in this area. This has the advantage of cancellation of ground roll (surface noise) during acquisition thereby focussing all the seismic energy in the vertical direction and by-passing thus minimizing the spurious effects of the low velocity weathered layer during acquisition and initial processing of field data.