Prof Adekoya John 's research grant

Lead Researcher

Title Prof
Firstname John
Surname Adekoya
Phone 08034091218

Research Grant Details

Research Topic Study of the Potential of the Nigerian Sector of the Chad basin integration of Appetite fission track analysis and basin modeling
Benefit to Oil and Gas High potential for hydrocarbon exploration and production in the Nigeria flange of the Chad Basin. Job creation and more geological studies.
Research Duration 2
University Federal University of Technology Akure
Abstract This is the final report of the research sponsored by PTDF with the principal aim of evaluating the petroleum potential of the Nigerian sector of the Chad Basin using integrated techniques. The research was greatly hindered by the 'Boko Haram' insurgence and failure of the National Frontiers Exploration Services (NFES) to cooperate with us. Researchers involved in this project have employed a combination of conventional methods and apatite fission track analysis to investigate the hydrocarbon potential of the Bornu .Basin Information and materials for the study were obtained from: (a) detailed literature review of the mega Chad basin and Bornu Basin; (b) samples of sedimentary outcrops in the basin and basement complex rocks surrounding the basin; (c) wireline log suites of 23 wells drilled in different parts of the basin; (d) ditch cutting samples of eight wells located in different parts of the basin; (e) 2D seismic sections covering different parts of the basin. Techniques employed for the project include: (a) inventory taking of the location and geological data of available wells in other sectors of the Mega Chad Basin where hydrocarbon has been produced; (b) fieldwork for detailed in situ geological studies of sedimentary outcrops and crystalline rocks including basement complex rocks and Tertiary basalt in and around the basin; (c) sampling of outcrops of the crystalline and sedimentary rocks for detailed laboratory studies; (d) sedimentological study of ditch cutting samples, wire line log interpretation of wells, clay mineral analysis using the XRD method for ditch cuttings of one of the wells (Ngor – 1) and laboratory analysis of selected borehole and outcrop samples in the Geological laboratories of the University of Glasgow, UK and The Federal University of Technology, Akure, Nigeria; (e) Foraminifera, nannofossil and palynological studies of the ditch cuttings leading to biostratigraphic analysis; (f) seismostratigraphic interpretation of available 2D seismic sections; (g) wireline log sequence stratigraphy study which involved identification of key sequence stratigraphic surfaces and recognition of systems tracts on wireline logs; (h) organic geochemical analysis of ditch cutting samples was carried out to determine the Rock-Eval parameters, vitrinite reflectance, source rock maturity and to evaluate the potential of the source rocks to generate hydrocarbon; (i) apatite fission track analysis of samples of selected crystalline rocks and ditch cuttings from selected wells located in different parts of the basin to determine basin thermal history, degree of cooling/exhumation and severity of erosion in the basin; and (j) integration of the results with a view to assessing the petroleum potential of the Bornu Basin and areas where future exploration efforts should be directed. The Chad Basin is an inland rift basin which is part of the West and Central African Rift System. The geodynamic evolution of the West and Central African Rift System (WCARS) can be linked to the development of the African plate throughout the Phanerozoic, which can be related to the polyphase break-up of the Gondwana supercontinent. The WCARS has been subdivided into two coeval Cretaceous genetically related but physically separated rift subsystems, which are the West African Rift Subsystem (WAS – Benue Trough, Yola/Garouna rift, Gongola/Bornu rift, Niger/Chad) and Central African Rift Subsystem (CAS – Doba, Doseo, Salamat). The geotectonic history of the WAS and CAS was divided into two pre-drift, two Cretaceous rift, one Paleogene rift and one post-rift phases. The Chad Basin with one tenth of its part located in Nigeria (Bornu Basin) is a large continental basin in the Central West Africa that covers a total area of about 2,335,000 km2 and straddles five countries, namely, Nigeria, Niger, Chad Republic, Cameroon and Central Africa Republic. So far the major lithostratigraphic units recognised in the basin are the Bima, Yolde/Gongila, Fika, Gombe, Kerri-Kerri and Chad Formations. The fieldwork carried out revealed three main suites of crystalline rocks in and around the Bornu Basin; which are (i) migmatite – gneiss complex, (ii) Older Granites (Pan African granites), and (iii) Tertiary Basalts. The log motifs of 23 wells studied are characterised by progradational, aggradational and retrogradational patterns. To a large extent, a very good correlation exists between the lithology derived from the ditch cuttings and the wireline log signatures of the wells. XRD patterns of clay mineral content from a well (Ngor – 1) indicate considerable variations in the clay mineral assemblages in terms of abundance and type with increasing depth. Kaolinite, illite, and I/S mixed layer are present throughout the well while chlorite appeared at deep depth (2885 m). Biostratigraphic analysis revealed the occurrence of different types of microfauna, which include planktonic and benthonic species, spores and pollens, ostracods, echinoid remains and fish tooth. The oldest sediments penetrated were Albian age (Kinasar – 1) based on the occurrence of Afropollis jardinus while the youngest were Tertiary. The sediments were deposited in varied environments from continental to shallow/marginal marine and open marine on the basis of the occurrence of the following fauna: Ammobaculites bauchensis, Ammobaculites spp., Haplophragmoides spp, Heterohelix globulosa, Heterohelix spp. Three areas of thick sedimentation which represented localised depressions or depocentres were identified in the basin by constructing formation thickness maps. The occurrence of the depressions was also confimed by seismic structural patterns. For ease of reference these depressions were labelled A (Chadian section) in the northeatern part, B (Maiduguri SE) in the southwestern part and C (Maiduguri SW) also in the southwestern area of the basin. A structural high D, is located between A and C depressions. The seismic stratigraphic studies revealed distinct Cretaceous and Tertiary seismic units. Eleven seismic packages were delineated within the Cretaceous sediments (CSS I to CSS XI) while three seismic packages were recognised within the Tertiary sediments (TSS I to TSS III). However two very significant unconformities in the tectono-stratigraphic history of the Bornu Basin were revealed by a study of the seismic lines; these unconformities were identified as intra-Cretaceous and Cretaceous – Tertiary boundary hiatus. Sequence stratigraphic studies of well logs revealed twelve well log sequences (DS I to XII) which were correlated in nine wells located in the three depressions (A, C and D). Significant surfaces identified on the well logs were the boundaries between formations and facies dislocations within the formations. Normal faults, few flower structures and significant folding of the Cretaceous sediments which occurred before the Cretaceous – Tertiary angular unconformity were recognised. As a result of our detailed studies seven lithostratigraphic units including two Groups were recognised; they are, Bima Formation, consisting of the Lower, Middle and Upper Bima units; Yolde Formation; Gongila Formation; proposed Fika Group made up of Kinasar Formation, Gaibu Formation, Ngor Formation and Mbeji Formation; Gombe Formation; Kerri-Kerri Formation; and Chad Group having three formations, wich consists Tuma Formation, Maiduguri Formation and Kutchali Formation. Organic geochemical analysis of the source rocks of the Bornu Basin showed that most probable source rocks are the Lower to Upper Cretaceous source rocks that occurred within the Bima Formation, Yolde and Gongila Formations and Fika Group. TOC values of samples from these formations vary from 0.17 to 3.80 wt %, indicating source rock quality of poor to excellent. Rock-Eval Tmax values vary from immature (<435 0C) to mature (>435 0C) and Hydrogen Index (HI) values revealed different types of kerogen - Type II, Type II/III, Type III and Type IV. Vitrinite reflectance (VR) values of the samples from six wells (Kutchalli – 1, Mbeji – 1, Faltu – 1, Herwa – 1, Kinasar – 1, and Ngor – 1) vary from 0.45 % to 2.85%. Although the VR values generally increase downhole in most wells, the distribution of the values in Faltu – 1 well exhibited three episodic segments with depth, suggesting apparent truncation and consequent uplift/cooling of the sediments. U – Pb age dating indicated that the majority of the sediments were derived from the surrounding Basement Complex rock areas predominantly from rocks of Pan African age with some being derived from Mesoproterozoic to Paleoproterozoic rocks (gneisses and migmatites). A significant observation of the results of the Apatite Fission Track (AFT) analysis is that pooled ages (94.26 + 2.05 to 1.96 + 2.39 Ma) obtained from Early to Middle Cretaceous samples (i.e. Bima, Yolde, and Gongila sediments) are younger than the stratigraphic ages of the sediments (125 to 93.5 Ma). In the case of Maastritchtian to Tertiary samples the AFT pooled ages (331 + 1.07 to 89.52 + 3.54 Ma) are much older than the depositional/stratigraphic ages (70.6 to 55.8 Ma). These observations indicate that the older sediments have been subjected to higher temperatures that reset the AFT thermochronometer while the Maastrichtian to Tertiary samples have not been heated to temperatures high enough to reset the AFT thermochronometer. Thermal models of the AFTA results using HeFTy software revealed periods of burial and cooling for the sediments. In the Early to Middle Cretaceous periods the sediments were heated to temperatures that varied from ca. 30 0C + 5 0C to ca. 110 0C + 5 0C, which occured for approximately 12 – 64 Ma during burial. The models also capture a major cooling event in the Early to Middle Cretaceous sediments. This cooling event began at a period estimated at > 90 + 10 Ma when the sediments cooled from their maximum paleotemperatures (900 - 1100 C) to the present day temperature (300 – 650 C). A sample from the Maastrichtian to Tertiary sediments revealed small rate of burial and longer period of cooling. The cooling event for the sample, which coincided with the Paleocene period, cooled the sample from ca. 500 C to the present day temperature of 330 C. The cooling events are equivalent to major exhumation/erosion events in the basin. Estimated eroded section varies from 870 m to 3.4 km in different parts of the basin and appears to be more severe in the present day Maiduguri section of the basin. These exhumation/erosion events recorded by the AFT agree with the existing geological knowledge of the basin, which had documented Santonian unconformity that represents period of basin inversion including uplift and erosion. It also records that the basin had also passed through a period of minor exhumation/erosion in the Tertiary period. Thermal annealing of the AFT thermochronometer in the Early to Middle Cretaceous periods suggests that this period was the key time for source rock maturation and hydrocarbon charging. It is unlikely that the Maastrichtian to Tertiary source rocks have been significantly heated because the AFT thermochronometer had not been annealed; hence they might have not attained the desirable maturation to generate hydrocarbon except where Tertiary burial was significantly pronounced. Integration of paleothermal data with known geology of the Bornu Basin dictates that future exploration in the basin should focus on identification of structures and stratigraphy that predate the Santonian basin inversion. This is based on the fact that any hydrocarbon generated from the Early to Middle Cretaceous source rocks would have been trapped and preserved and is not likely to have been destroyed by the Santonian basin uplift and erosion. Research efforts and investigations using AFTA and other techniques can be focused to identify areas where Tertiary burial could possibly override the effect of Upper Cretaceous cooling. In such areas hydrocarbon could have been generated in the upper stratigraphic section of the basin. There are still some untested very deep and shallow structures in the basin, to which exploration efforts can also be directed. Another graben (basinal horn in geometry) linked to the northern part of Bornu Basin (N'dgel Edgi) also calls for exploration. Geochemical data revealed that, although the Bornu Basin is predominantly a potential gas prone basin, there are organic facies intervals that are oil prone within the basin. In other to decipher the oil prone organic facies intervals more detailed geochemical analyses and deeper drilling for more samples should be carried out.

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