Ditch Cuttings Research Articles

Micropaleontological and sedimentological analyses of carbonates rocks in parts of Sokoto Basin, Nigeria: implications for paleoecological interpretation and exploration efforts

This study presents a detailed analysis of the Paleocene and Maastrichtian marine sediments in the Sokoto Basin, Nigeria, using boreholes GSN – BH – 2051 and GSN – BH – 4051, respectively. This study is aimed at integrating sedimentological, micropaleontological and petrographic data in paleoecologic interpretation of depositional environments of the Sokoto Basin. The methods adopted in this research involved the examination of ditch cuttings, carbonate thin sections, and microfossils analyses from the boreholes drilled in Sokoto Basin. The sedimentological data from the borehole showed that the studied stratigraphic unit comprises mainly fine to medium-grained limestone facies, sparitic intraclastic packstone and oolitic-elmicrite wackestone facies. The microfacies obtained from petrography data revealed micro-fossils abundance and diversity associated with the onset of shallow marine transgression which resulted in the deposition of the Dange and Kalambaina Formations, respectively. The assemblages of the larger foraminifera (Opercullnoides bermudezi) and the larger ostracod (Bairdia iIaroensis) in the borehole sections further suggested marginal marine depositional environment for the Kalambaina and Gamba Shale Formations. The paleoecological interpretation suggests varying salinities and dysaerobic conditions during deposition, with implications for understanding basin evolution. The study concludes by highlighting the importance of integrating multiple methods for a detailed understanding of paleoecological and depositional environment of Sokoto sedimentary basin.

PALYNOFACIES STUDIES OF THE LATE CRETACEOUS (TURONIAN-MAASTRICHTIAN) STRATA FROM JAURO JATAU, GONGOLA SUB-BASIN, NORTHERN BENUE TROUGH, NIGERIA

Geographically located within Gombe, Bauchi, and Yobe states, the Gongola Sub-basin has drawn attention from several academics looking to increase Nigeria's oil reserves relative to the inland frontier basins. This paper's goal is to determine the thermal maturity of strata from drill samples of the Fika shales in Nigeria's Northern Benue Trough, Gongola Sub-basin. To predict the well section's maturity and kerogen type, this study uses optical and organic facies studies. Twenty-seven samples of ditch cuttings were prepared using the universally accepted acid palynological procedure. The dispersed mounted slides revealed a variety of pollen, spores, and palynomacerals upon microscopic inspection. The well section under study exhibits a range of thermal maturation from mature to late mature, indicating the possibility of producing oil and gas. This corresponds to a range of thermal alteration values of 4 – 6 and equivalent vitrinite reflectance (%Ro) values of 0.6% – 1.35%. The total recovered Sedimentary Organic Matter (SOM) in this study was classified into Palynomorphs, Amorphous Organic Matter (AOM) and Phytoclasts and plotted on a ternary graph. The Percentage frequencies of AOM, Phytoclast and Palynomorphs were compared with the zones of the Tyson Ternary diagram. Most of the distribution frequencies lie within zones II, IX, VI and Iva suggesting Kerogen types III (gas-prone) and II (oil-prone).

Geochemical evaluation and hydrocarbon generation potential of the Upper Cretaceous–Pliocene succession, offshore Nile Delta, Egypt

The offshore Nile Delta is a prominent petroleum province; nevertheless, previous research focused mainly on evaluation of Miocene–Pliocene possible source rocks because of lack of data. The current study is the first to evaluate organic geochemical features of the Upper Cretaceous–Pliocene sequence in the western offshore Nile Delta, applying TOC, Rock-Eval pyrolysis and GC-MS procedures for 137 ditch cuttings collected from three wells. The main objectives are to infer organic richness, type of kerogen, maturation, and depositional paleoenvironment of organic matter for these possible source intervals.The analysed rock samples generally display fair to good organic enrichment. Most of these samples are enriched in Type-III and Type-II/III kerogen, suggesting a high influx of terrigenous organic matter. However, Abu Madi, Appollonia, and Khoman formations contain Type-II oil-prone kerogen, reflecting more marine organic matter, whereas Kafr El Sheikh and El Wastani cuttings display the lowest TOC contents and are more enriched in non-generating inert organic matter.Biomarker ratios indicate that Kafr El Sheikh, Abu Madi, Qawasim, and Qantara formations are rich in Type-II/III kerogen (mixed organic matter) preserved under suboxic nearshore or lacustrine depositional environments. In contrast, Sidi Salem, Tineh, Appollonia, and Khoman formations contain abundant Type-II marine-algal organic matter deposited under anoxic marine depositional settings. Vitrinite reflectance data and biomarker ratios indicate immature to peak mature rock samples. The stable carbon isotopic composition of condensate oil samples suggests nonmarine waxy oils. Ratios of n-alkanes and isoprenoids for a condensate sample from the study area reveal no similarity with the Upper Cretaceous–Pliocene rock extracts.

Sedimentology and Mineralogy of Sedimentary Sequences in Nanim Field in the Niger Delta basin, Nigeria.

A total of nineteen ditch cuttings from the sedimentary sequence of Nanim Field, were subjected to both sedimentological and mineralogical analysis with the aim of investigating the mineralogical composition of the studied section (1810 m - 2650m) in the study area. The shale samples were grinded, pulverized and sieved with less than 75μm and analyzed using X-ray diffraction techniques (XRD) for mineralogical composition. Results of the sedimentological analysis, suggests four lithofacies made up of sandstone, shaly sand, shale and sandy shale in he studied section. The studied section has been interpreted as a shallow marine environment  divided into two broad lithofacies sequences made up of beach sand (1810 m - 2290 m.) and upper shoreface (2300 m – 2650m) respectively. The beach sand sequences comprises thick sands, brownish, grey to black, fine to coarse grained, whereas the upper shoreface sequence is essentially a heterogeneous sequence of alternating sand medium to very fine grained sand and shale - grey. Results from the XRD analysis shows that the mineralogical composition of the basal part (upper shoreface) of the studied section is characterized by kaolinite a dominant in sediments of fluviatile environments and is known to concentrate in many near-shore sediments (shallow marine) with a decrease in abundance from the shoreline as other clay minerals increase basinward.

Foraminiferal Biostratigraphy of Well Ad, Western Niger Delta

Micropaleontological analysis of sixty (62) ditch cuttings rock samples collected from interval, 7800 feet to 12,002 feet of well AD, located offshore western Niger Delta was carried out for the investigation of their age and paleodepositional environment. Standard methods and techniques of foraminiferal sample processing and analysis were followed to disaggregate the microfauna from the rock matrix. The studied interval is predominantly made up of 80 to 100 % sandstone, minor shale and siltstone with variable textural properties. Foraminifera study revealed well preserved and diverse species dominated by the calcareous benthic forms. A total of seventy-four (74) foraminiferal species were recovered among which fifty (52) two are calcareous benthic, six (6) are agglutinating forms while sixteen (16) are planktonic foraminifera. On the basis of the faunal assemblage, abundance and diversity of the important foraminiferal events, four (4) foraminiferal zones (Valvulineria spp, Brizalina mandoroveensis, Hanzawaia concentrica and Lenticulina inornata) were recognised and correlated with F300 and F500 to assign an early to middle Miocene age for the sediments. Paleoenvironmental deductions were based primarily on the richness and diversity of foraminiferal species categories. The presence or absence of planktonic foraminifera aided in deciphering open ocean environments. The dominant biofacies associations recorded within the studied section of Well-AD is the Ammonia beccarii biofacies defined by the rare to common occurrences of Ammonia beccarii, Bolivina scalpratamiocenica, Florilus atlanticus and Epistominella vitrea. Brizalina mandoroveensis species, Lenticulina inornata, Hanzawaia strattoni, Eponides eshira, Cribroelphidium galvestonensis and Hanzawaia concentrica were also in association. The Ammonia beccarii biofacies is indicative of the Shallow/Inner Neritic Paleoenvironment, while the Inner Neritic/Middle Neritic Setting is characterized by top occurrence of Valvulineria spp, a rich continuous occurrence of Epistominella vitrea. The paleoenvironment of the studied section of Well-AD is dominantly inner to middle neritic with concomitant minor incursion of outer neritic setting.

Sequence stratigraphy and tectonic framework of the Gabo Field, Niger Delta, Nigeria

This research examines the sequence stratigraphic and structural framework of the Gabo Field Niger Delta, Nigeria. Materials used in this research include 3D seismic volume in Seg-Y, ditch cuttings and wells logs. The methods applied are standard methods in addition to using the Frazier and Galloway approach for genetic sequences. The tectonic framework was interpreted in terms of deformational, depositional and post-depositional structures. The deformational structures are faults F1 and F2 – which are closely spaced normal faults and F3 is a syn-depositional growth fault. The depositional structures are pinchouts and interbedded sand/shale sequences whereas the postdepositional structures are compaction and smearing or flexure of the shales. The well correlation shows the sequences are cyclic and the facies analysis of T4 – T9 sands are very fine to medium grained, light to dark brown, texturally mature and moderate to well sorted. The facies associations are fluvial distributary channel, tide dominated fluvial channels, abandoned channel or switching and flood plain deposits. While the depositional environments are upper delta plain, lower delta plain and delta front. Sequence stratigraphic analysis explained the observed increase in shale thickness in the intermediate sections and showed sediment deposition occurred in three (3) systems tracts- Lowstand Systems Tract (LST), the Transgressive Systems Tract (TST) and Highstand Systems Tract (HST). The sedimentological model showed the environments of deposition had a tidal influence and ranged from fluvial to estuarine. The findings of this research may be applied to similar deltaic basins around the world in planning of oilfield development. In addition it may correlate cyclic successions and predict facies distributions of similar depositional patterns.

Assessment of Fault Sealing in the Gabo Field, Niger Delta, Nigeria

This research assesses the sealing of the fault bounded stratigraphy of the Gabo Field, Niger Delta, Nigeria. Materials used comprises of 3D seismic volume in seg-y, ditch cuttings and well logs. The methods applied are standard fault plane evaluation techniques and they include seismic interpretation, well correlation, XRD analysis, and application of the Yielding et al., (1997) shale gouge ratio (SGR) algorithm for fault seal analysis. The tectonic framework was interpreted in terms of deformational, depositional and post-depositional structures. The order of magnitude of stress is SHmax > σv > Shmin. The juxtaposed strata relationships were analyzed by taking cross sections A-A1 and B-B1 and this showed the structural framework across the field. Cross section A-A1 showed that the depositional and post depositional structures are pinchouts (channel abandonment or switching) and shale smears respectively. The cross section B-B1, showed that the deformational structures are faults F1 and F2 – recognized as closely spaced normal faults and F3 is a syn-depoitional growth fault. The well correlation showed the vertical stratigraphy of the wells are comprised of cyclic succession of sands and shales and the shale thickness increased in intermediate sections. The X-ray diffraction (XRD) analysis of the shales showed that the predominant minerals are kaolinite, rutile, gypsum, albite, microcline and quartz. The rock property analysis showed that the net to gross ranges from 26.28 – 82.0% with an average of 73.7%. The volume of shale ranges from 18 – 73.72% with an average of 63.59%. The bulk density of the shales ranges from 2.379 – 2.692g/cc with an average of 2.46g/cc. The total porosity ranges from 0.159 – 0.317 with an average of 0.167 in the shales and 0.272 in the sand. The effective porosity range from 3.58 – 22.71 with an average of 6.028 in the shale and 20.13 in the reservoir. The drawdown mobility and temperature range is 2.2 – 4124.4mD/cP and 63.3 – 80.1oF respectively, while the average is 569mD/cP and 70.63oF respectively. The estimated pore pressure ranges from 0.4213 – 0.4762psi/ft with an average of 0.47psi/ft in the shales and 0.428 psi/ft in the sand. The fault seal analysis showed that the shale gouge ratio range from 0.2 – 0.7 and the stratigraphic juxtapositions are predominantly sand to sand, sand to shale and shale to shale. The results of this research reduces the fault seal uncertainty in the planning of oilfield development projects and enhanced pressure support for the recovery of bypassed hydrocarbons, most especially in compartmentalized reservoirs. In addition, the results of this research can be applied to similar deltaic successions around the world.

Paleoenvironment, sequence stratigraphy and source rock potentiality of the Cenomanian-Turonian boundary sediments of Southern Tethys

The Abu Qada Formation is a reference interval for the Cenomanian–Turonian boundary event in the northeastern margin of Africa. In this paper, geochemical, biostratigraphical, and carbon isotope ratio studies are presented using high-resolution well data yielded from the Gulf of Suez, Egypt to evaluate the paleoenvironmental condition, sequence stratigraphy and source rock potential of the Upper Cenomanian/Lower Turonian Abu Qada Formation. A total of 12 core samples and 4 ditch cuttings were collected from OCT-A8St1 well in the October Oil Field for geochemical, palynological and calcareous nannoplankton analyses. Cyclostratigraphic analysis was prepared to characterize the electrofacies change along the Cenomanian/Turonian boundary interval including the Oceanic Anoxic Event 2 (OAE2). The Predictive Error Filter Analysis (PEFA) patterns and Integrated Predictive Error Filter Analysis (INPEFA) curves found 3rd order cycle of the OAE2 within the global third-order cycle Ce5. A stable carbonate isotope analyses with total organic carbon (TOC) resulted in a remarkable positive excursion δ13Ccarb (3.67‰) associated with change in the TOC content. The quantitative analysis of calcareous nannofossils indicates the high productiveness of nannoplankton around the Cenomanian/Turonian boundary interval. The high abundance of the Discorhabdus genus proves the paleoenvironmental change during the OAE2 interval. The palynofacies interpretation indicates the lower part of Abu Qada Formation to be deposited in a slightly reducing conditions at the inner neritic setting, while the upper part of Abu Qada to lower part of Wata formations were deposited in deeper marine setting under anoxic conditions. These changes in the overall depositional conditions are documented by the remarkable change in palynofacies and organic carbon content (TOC). Dark gray shale and carbonate sediments are interpreted to be a good source rock potential by kerogen quantified palynofacies analysis indicating oil and gas prone producing materials (Kerogen types II and II/III). The best source rock quality is associated with the Abu Qada Formation's OAE2 record. These criteria allow us to identify the occurrence of OAE2 record in the Gulf of Suez petroleum province as a useful tool for high-resolution chronostratigraphic analysis.

Foraminiferal patterns and palaeoenvironmental inferences from DEL-1 well, offshore Niger Delta

The Miocene Epoch (23.3–5.3 Ma) represents a remarkable time in the Earth's geological history with significant palaeoclimatic and palaeoenvironmental relevance. In this study, microfossils recovered from the DEL-1 (4600–9460 ft) well in the western Detachment Fold Zone, offshore Niger Delta in the Gulf of Guinea were used to construe the age, palaeoenvironment, and palaeoecology of the penetrated successions. Standard foraminiferal analyses were carried out on one hundred and forty-eight (148) ditch cuttings retrieved from the studied interval following standard laboratory and identification procedures. Globigerinatella spp./Catapsydrax dissimilis Concurrent-range Zone (M3/N6), Fohsella birnageae Lowest Occurrence Subzone (M4b/N7), and Orbulina suturalis Lowest Occurrence Zone (M6/N9) of early to middle Miocene were identified. An overall progradational coastal and shelfal facies dominated by argillaceous and arenaceous sediment in the early and middle Miocene is construed, whereas interpreted palaeoenvironment of deposition indicates fluctuation between coastal deltaic, inner, middle, and outer neritic system with some fluvio-marine incursions between 4600 and 9460 ft intervals. The identified early Miocene succession is characterised by significantly high ecological parameters (diversity, evenness, richness), low salinity, and relatively high occurrence of foraminifera faunas compared to the middle Miocene. The relationships between the foraminiferal faunas and environmental factors suggest the local ecologic niche exhibits environmental heterogeneity that might have influenced even distribution of different microhabitat faunal preferences. Whereas the contributing influence of arenaceous sediment on the general dearth of microfossils in the upper section of the well cannot be neglected, the foraminiferal signatures reflect the ubiquitous middle Miocene carbonate crash event, and thus confirm its occurrence in the Gulf of Guinea.

Bio-electrosequence interpretation of late cretaceous sediments of the Southern Bornu Basin, Nigeria

Integrated analysis that involves physical sedimentological, standard palynological and electrofacies analyses on ditch cuttings and suite of wireline logs from Gaibu–1 Well, southern Bornu were examined to identify critical sequence elements and construct a bio-sequence stratigraphical framework. Four (4) palynozones consisting of Triorites africaensis, Cretacaeiporites scabratus - Odontochitina costata, Droseridites senonicus and Syncolporites/Milfordia spp Assemblage Zones construed to be Late Cretaceous – younger successions. Nine (9) depositional sequences each with candidate maximum flooding surfaces (375, 900, 1875, 2250, 2600, 3050, 3400, 3800, 4300 m) marked by marker shales with high abundance and diversity of palynomorphs. Thus, equate with the local lithostratigraphy and global large-scale depositional cycles with candidate sequence boundaries (50, 725, 1625, 2175, 2490, 2850, 3300, 3610, 3960, 4470 m) ranging about 96.28 to 70.07 Ma. The delineated transgressive surfaces along the built sequences mark the subjected onset of marine flooding characterised with interchange of progradational to retrogradational facies. Delineated sequence elements generally show up-hole from progradational to retrogradational and aggradational that represents Lowstand Systems Tracts (LSTs), Transgressive Systems Tracts (TSTs) and Highstand Systems Tracts (HSTs) respectively. The LSTs are seen in form of prograding complex and slope fans, suggestive of good reservoirs. The TSTs consist of channel sand units and shales that depict retrogradational marine units, which could serve as both seals and source rocks for the sand units. The HSTs are made up of interplay of aggradational to progradational sediment packages that could serve as a potential source rock. The palaeoenvironmental indices depict the successions are deposited within continental to open marine settings. 

Sedimentology and Calcareous Nannofossil Biostratigraphy of Alaka Well, Niger Delta, Nigeria

Calcareous nannofossil biostratigraphy of Alaka well was carried out to identify the biohorizons that exist, ultimately for biozonation, chronostratigraphy and geologic age calibration of the studied interval. The study involved sedimentology analysis, gamma ray description and preparation of two hundred and twelve (212) ditch cuttings, sampled at 9.144m intervals for the study of calcareous nannofossils on smear slides. Sedimentology and gamma ray analyse showed deposition within shallow marine paleoenvironments with alternating minor transgressions in a generally progradational delta setting, accounting for the low calcareous nannofossil occurrences. The calcareous nannofossil assemblages recovered from the slide preparations consist of fourteen (14) species, comprising nine (9) long ranged, non-stratigraphic significant forms and five (5) short ranged stratigraphic significant forms. The biohorizons identified included Base (B) occurrence of Catinaster coalitus at 3578m; Discoaster hamatus at 2874m; Top (T) occurrence of Discoaster hamatus at 2518m and Base absence (Ba) of Reticulofenestra pseudoumbilicus at 2280m. Other biohorizons included Top occurrence (T) of Discoaster bollii at 2435m and Discoaster deflandrei at 3578m respectively. The biohorizons defined boundaries between biozones and showed that the studied interval penetrated four biozones from CNM11 to CNM14 of Backman et al. (2012), NN7 to NN10 of Martini (1971) and CN5b to CN8a of Okada and Bukry (1980). The geologic age of the studied interval ranged between about 11.60 Ma within CNM11/NN7/CN5b zone to about 8.80 Ma within CNM14/NN10/CN8a zone, the standard chronostratigraphy lies within Tortonian stage. Two chronostratigraphic surfaces were mapped in the studied section and comprised one global maximum transgression at 3514m corresponding to 10.5 Ma maximum flooding event, and one localized maximum transgression at 2847m corresponding to 9.5 Ma maximum flooding surface, separated by sea-level lowstand mapped at 3331m and corresponding to 10.35 Ma.

Lithofacies Analysis and Qualitative Minerology of the Sediments of #3 Well in the Greater Ughelli Depobelt, Niger Delta Basin

The sediment of #3 Well of the Greater Ughelli Depobelt are represented by sand and shale intercalation. In this study, lithofacies analysis and X-ray diffraction technique were used to characterize the sediments from the well. The lithofacies analysis was based on the physical properties of the sediments encountered from the ditch cuttings. Five lithofacies types of mainly sandstone, clayey sandstone, shaly sandstone, sandy shale and shale and 53 lithofacies zones were identified from 15 ft to 11295 ft. The result of the X-ray diffraction analysis identified that the following clay minerals – kaolinite, illite/muscovite, sepiolite, chlorite, calcite, dolomite; with kaolinite in greater percentage. The non-clay minerals include quartz, pyrite, anatase, gypsum, plagioclase, microcline, jarosite, barite and fluorite; with quartz having the highest percentage. Therefore, due to the high percentage of kaolinite in #3 well, the pore filing kaolinite may have more effect on the reservoir quality than illite/muscovite, chlorite and sepiolite. By considering the physical properties, homogenous and heterogeneous nature of the #3 Well, it would be concluded that #3 Well has some prospect for petroleum and gas exploration.

Barnicarndy Graben, southern Canning Basin: stratigraphy defined by the Barnicarndy 1 stratigraphic well

Funded by Geoscience Australia’s Exploring for the Future initiative and operated by the Geological Survey of Western Australia, the Waukarlycarly 1 deep stratigraphic drillhole was designed to investigate the geology of the little-known Waukarlycarly Embayment and assess the petroleum, mineral, groundwater and CO2 storage potential of the area. Based on consultation with the Western Desert Lands Aboriginal Corporation on the cultural significance of the name, Waukarlycarly, it has been agreed to change the name of the well to Barnicarndy 1 and the tectonic subdivision to the Barnicarndy Graben. This and all future publications will now refer to the Barnicarndy 1 stratigraphic drillhole (previously Waukarlycarly 1) and the Barnicarndy Graben (previously Waukarlycarly Embayment). Drilling commenced on 1 September 2019 and reached a total depth (TD) of 2680.53m on 30 November 2019, recovering more than 2km of continuous core. The cored interval extended from 580m to TD in Neoproterozoic Yeneena Basin dolostone, which was unconformably overlain by a thick, lower Canning Basin Ordovician stratigraphy, including richly fossiliferous marine mudstones with common volcanic ash beds. A major unconformity is located at the top of the Ordovician section where it is overlain by sandstones and muddy diamictites of the Carboniferous–Permian Grant Group, followed by a Cenozoic succession near surface. Ditch cuttings were collected from surface to 580m at 3m intervals. The pre-Grant Group Paleozoic succession is unique within the Canning Basin, indicating that the Barnicarndy Graben’s depositional history is markedly different when compared with adjacent structural subdivisions, such as the Munro Arch and Kidson Sub-basin. Detrital zircon geochronology, biostratigraphy and borehole imaging interpretation assisted in the definition of two new geological units within the Ordovician stratigraphy of Barnicarndy 1: the Yapukarninjarra and Barnicarndy formations. Preliminary routine core analysis data indicates the potential for CO2 storage within the Barnicarndy Formation beneath a Grant Group seal. The well also provides new insights into the structural interpretation of the Barnicarndy Graben.

Lithological attributes of hd-001 well, shallow offshore, Niger delta basin, Nigeria

Lithological analysis was carried out on 96 ditch cuttings samples from HD-001 well located within the shallow offshore Niger delta basin, Nigeria. Three lithofacies sequences were delineated by the integration of wireline logs textural/lithologic attritudes and the distribution of index accessory minerals. They are transitional paralic, paralic and marine paralic sequences. The lithologic, textural and wireline log data indicate that the entire interval studied in the HD-001 well belongs to the Agbada Formation. The Formation is made up of alternating sand and shale units which suggests rapid shoreline progradation. The grain size increases from essentially fine to medium-grained at the basal part of the well to dominantly coarser grain at the upper part. The index accessories recognize shallow marine to coastal deltaic settings environment of deposition. Sand bodies which represent sub-environments within those settings are deposited in sequences. Each sequence begins with a transgressive phase followed by significant regressions.  Â

Assessment of quality and health risk of peri-urban groundwater supply from selected areas of Abeokuta, Ogun State, Southwestern Nigeria.

Groundwater is an important source of drinking water. However, pollution of groundwater resource could initiate serious health damage to the consumers. The present study aimed at assessing the quality and health risk of groundwater samples collected from the peri-urban areas of Abeokuta. Twelve (12) fresh ditch cuttings from wells sites and forty (40) well water samples were collected between August and September, 2018. Samples were analysed for important physical and chemical parameters using the standard procedure. Groundwater data were subjected to statistical manipulation of descriptive and inferential statistics. The health risk assessment was conducted for non-carcinogenic effect {hazard quotient (HQ), hazard index (HI)} and cancer risk (CR). Results showed the pH of groundwater ranged from 7.65 to 8.48. The electrical conductivity varied from 266.5 to 461.5 µS/cm, while the total dissolved solids ranged from 90.0 to 348.2mg/L. The concentrations of Pb (1.58-14.5µg/L), Mn (11.10-836µg/L), Al (64-2000µg/L) and Fe (30-5070µg/L) in groundwater were higher than the permissible limits of the World Health Organization in drinking water. The levels of metals/metalloids in the well cuttings were: Pb (8.9-27.6µg/kg), As (0.8-8.6µg/kg), Cr (14.0-98.0µg/kg) and Mn (138.0-1080µg/kg). The HQs of Cr (infants and children) and Ba (infants, children and adults) were greater than 1.0 indicating adverse health effects. The CRs of Cr, Co and Ni in water consumed by infants, children and adults were greater than the acceptable limit of 1.0 × 10-4 suggesting possible development of cancer. The health risk data of metals in groundwater indicated deleterious health effects on consumers.

Characteristics and generation modeling of some source rocks in the South Eastern offshore Mediterranean area, Egypt

The offshore North Sinai area contains attractive approaches to be investigated by means of hydrocarbon potential. The present work aims at evaluating three source rock units; the Upper Jurassic, the Lower Cretaceous, and the Upper Oligocene that have a varying lithology including limestones, marl, and shales. The evaluation is based on results of TOC, Rock-Eval pyrolysis, and vitrinite reflectance analyses for ditch cuttings from 5 wells. Besides, constructing 1D basin models for several wells took place in the present study to estimate the generation timing. The geochemical results show that the Upper Jurassic contains poor to good organic quantity with poor to good hydrocarbon generating potential of type II/III and type III kerogen. The Lower Cretaceous rocks are poor to very good in terms of organic richness and hydrocarbon generating potential as well and belong to type II/III and minor type III kerogen. Moreover, a poor to good richness was encountered for the Upper Oligocene, with poor to fair hydrocarbon generation potential of kerogen type III. 1D basin modeling results indicate that three main tectonic phases influenced the burial history comprising the Jurassic-Cretaceous rift, the Late Cretaceous-Oligocene uplift associated with the Syrian arc folding, and the Late Miocene rift. These movements affected the thermal maturity in the studied area. The Upper Oligocene source rock is immature to early mature in most of the studied wells, whereas the Lower Cretaceous and Upper Jurassic source rocks were entered the main stage of hydrocarbon generation earlier in the eastern wells than the western wells, related to a variant tectonic impact in the area. The top oil window was reached at depth ranges from 2300 m in Mango-3 well to 4000 m in Hout-1 well, while the base of the oil window is found only in Mango-1 well at 4300 m depth.

Modeling the Depositional Environment of the Sandstone Reservoir in the Middle Miocene Sidri Member, Badri Field, Gulf of Suez Basin, Egypt: Integration of Gamma-Ray Log Patterns and Petrographic Characteristics of Lithology

Understanding the depositional setting of siliciclastics reservoir is fundamental process to exploration and development of hydrocarbon reservoirs and to the multi-phase cycle of the oil and gas industry. Typically, core samples from existing or potential reservoirs can be used for interpretation of depositional environment. However, the lack of core samples in certain reservoirs represents a challenge for reservoir development plans and further exploration. To overcome the absence of core samples in the middle Miocene Sidri Member in the Badri field, Gulf of Suez, this study aimed to reconstruct its depositional settings by coupling well logging patterns and petrographic characterization of ditch cuttings. Consequently, 30 thin section samples representing the reservoir section of four wells were described in detail and standard petrographic characteristics were determined. Then, gamma-ray (GR) log patterns of the studied reservoir wells were used for interpretation of depositional environment. Petrographic analysis indicates that the sandstone reservoir is fine- to medium-grained arkose with dominant siliceous cement and composed mainly of quartz, feldspars, and lithic fragments. Pores reflecting primary and secondary porosity as well as inter-granular pores are dominant. The facies analysis indicates that the studied member has a heterogeneous nature and rapid facies change; its main lithofacies are blocky sandstones, intercalated sandstones and shales, and shales. Three electrofacies were interpreted in the studied section: (1) electrofacies-A (blocky sandstones), which is characterized by a cylindrical-shaped (right boxcar) GR trend; (2) electrofacies-B (intercalated sandstones and shales), which is characterized by an irregular log trend with serrated shape; and (3) electrofacies-C (shales), which is characterized by irregular GR trend and has no character. The interpreted results indicate a tidal channel depositional setting for electrofacies-A, mixed tidal flat depositional setting for electrofacies-B, and low relief offshore mudstone depositional setting for electrofacies-C. Finally, the results illustrate how the coupling of GR patterns with the analysis of petrographic characteristics can be used to understand the depositional setting of a hydrocarbon reservoir that lacks core samples. This work could be useful for assessment of reservoir distribution and quality, for reduction of uncertainty during field development, as well as for providing useful insight to similar hydrocarbon reservoirs elsewhere.

High-resolution Biostratigraphic Studies of Step-1 Well, Offshore, Western Niger Delta

Abstract A high-resolution biostratigraphic study of the STEP-1 well, offshore Western Niger Delta Basin, Nigeria, was carried out using foraminifera, calcareous nannofossils and palynomorphs. The study was aimed at identifying the biostratigraphic zones, age deductions as well as palaeoenvironmental and palaeoclimatic reconstructions. From the studied well section of 609 m (1,829–2,438 m), 50 ditch cuttings were used for foraminifera and calcareous nannofossils, while 25 samples were used for palynological studies at 12 m and 24 m intervals, respectively. Standard laboratory preparation techniques were employed for the three microfossil groups. Due to the occurrence of some forms such as Globigerina praebulloides, Haplophragmoides spp, Bolivina scalprata miocenica, Valvulina flexilis and Cyclammina cf. minima, two planktonic and one benthonic foraminifera zones were identified as follows: Lower N18, Upper N17 zone (early Pliocene, late Pliocene) and Cyclammina minima zone (late Miocene), respectively. Two biozones were recognized for the nannofossils and include NN12 (Ceratolithus cristatus zone) and NN11 (Discoaster berggrenii zone). These zones were assigned to early Pliocene and late Miocene, respectively. Other forms include Discoaster pentaradiatus, Sphenolithus abies and Ceratolithus armatus. Echitricolporites spinosus/P800zone has been assigned for the Palynomorph assemblages and was dated late Miocene due to the quantitative occurrence of Cyperaceaepollis spp. Four identified major condensed sections include intervals at 1,926, 1,987, 2,097 and 2,316 m, which have been dated 5.0, 5.8, 6.3 and 7.0 Ma, respectively. Based on the benthonic foraminiferal species and Palynological Marine Index, a shallow marine environment is deduced for the studied interval which was interpreted to be deposited under both wet and dry palaeoclimatic conditions. The findings, no doubt could serve as a template for a sequence stratigraphic model, generally beyond the resolution of seismic stratigraphy.

Palynomorphs and Age Characterization of Rock Succession in Well X-1, OML 108, Offshore Niger Delta Nigeria

Palynological studies in Nigeria are mainly confined to the Tertiary Niger Delta, where several studies have been carried out for the discovery of natural oil and gas in this particular basin during late 1950s. The accuracy and profitability of the exploration process can be enhanced by the micropaleontological monitoring through the palynological analysis of ditch cuttings for age determination. Fifty ditch cutting samples from intervals 8040 ft and 11010 ft of Well X-1, OML 108, Ukpokiti field, offshore Niger Delta Nigeria were analyzed for their palynofloral content, in a view to establish the biozonation framework for the purpose of age characterization of the rock succession. Palynological sample processing and analysis followed standard methods of treatments with different concentrations of Hydrochloric acid, Hydrofluoric acid and organic acid for digestion of carbonates, removal of silicates and washing or centrifuging for concentration of the palynomorphs respectively in order to liberate the palynomorphs from the extraneous organic matter in the rock matrix. The palynofloral analysis yielded a total number of forty-three (43) pollen, seven (7) spores and one dinoflagellate cyst, from which four subzones based on palynofloral assemblage of marker species, their stratigraphic tops and base including their abundance and diversity were recognized. The zones are from youngest to oldest: Stereisporites sp, Racemonocolpiteshians, Verrutricolporitesrotundiporus and Retibrevitricolporitesobodoensis/protundens zones corresponding with pollen sub zones:P850-830, P820, P780 and P770respectively, indicatingLate Miocene to Middle Miocene age.
 In conclusion, the palyno – zones of this study compare well with the pollen zones of [3], therefore shows that the rock succession was deposited during the Middle to Late Miocene epoch.

The biostratigraphic framework of CSDP-003 well, Central Swamp Depobelt, Niger Delta, Nigeria

The biostratigraphic framework of CSDP-003 well, Central Swamp Depobelt was investigated to establish the stratigraphic sequences penetrated in the well and the age of the sequences based on calcareous nannofossils recovered. The study was carried out with 138 ditch cuttings from the well and was prepared with the standard simple smear-slide technique of calcareous nannofossil sample preparatory method. The slides produced from the samples were viewed and 31 calcareous nannofossils were recovered which were used to characterize the well into 3 NN zones, following base (Last Downhole Occurrence/First Appearance Datum (LDO/FAD) of Sphenolithus heteromorphus, Top (First Downhole Occurrence/Last Appearance Datum (FDO/LAD) of Helicosphaera ampliaperta, and Top (First Downhole Occurrence/Last Appearance Datum (FDO/LAD) of Sphenolithus heteromorphus corresponding to NN3, NN4, and NN5 biozones respectively. Three Maximum Flooding Surfaces (MFS) and two Sequence Boundaries (SB) were delineated and their ages were determined using the diagnostic forms. MFS 17.40Ma was noted with high abundance and diversity of calcareous nannofossils and explosive events (ACME) of Sphenolithus heteromorphus, Helicosphaera ampliaperta, Sphenolithus moriformis, and Helicosphaera cartari at 2804m within NN4 zone, MFS 15.90Ma was identified based on abundance and diversity peak at 2429m corresponding to explosive events (ACME) of Sphenolithus heteromorphus, and Sphenolithus moriformis within NN4 zone while MFS 15.00Ma was delineated based on abundance and diversity peak with Helicosphaera cartari ACME at 1957m. The Sequence Boundary's SB 16.5 Ma (latest Burdigalian) and SB 15.5 Ma (Langhian) were delineated based on rare to non-occurrence of calcareous nannofossil at 2530m and 2228m respectively. ‬‬