The Niamey sandstones belong to a group of Neoproterozoic (Infracambrian) deposits of the Nigerian Liptako, sporadically outcropping along the eastern edge of the West African Craton and following the Niger River valley. They rest in major unconformity on the Paleoproterozoic (Birimian) basement of the Niger Liptako. Previous work on these deposits has been fragmentary, particularly as regards their structure, and the investigations carried out aim to make up for these shortcomings. The aim of this study is to determine the deformations that have affected the Niamey sandstones. To achieve these objectives, an integrative approach based essentially on analyses and measurements of deformation structures in the field and their projections in the Win-Tenseur program, in order to calculate stress tensors (σ1, σ2, σ3), was implemented. Structural analysis has identified an extensive pre-Pan-African D1 phase, trending NNW-SSE to NNE-SSW, concomitant with the opening of the Neoproterozoic Ocean, and two Pan-African compressive episodes, NNW-SSE to NW-SE trending D2a and ENE-WSW trending D2b.

This study was carried out in the south-western part of Niger. The study area corresponds to the Niamey region, which straddles the south-eastern edge of the West African Craton and the south-western terminus of the Iullemmeden Basin. The general objective of this work is to determine the context in which the Ct3 deposits were emplaced in the Tondibia, «Rhodesia» and Kongou sectors. Specifically, the aim is to provide a petrographic description of the Ct3 deposits and to characterise the deformation that affected these deposits. The methodology used is based on the macroscopic and microscopic petrographic description of the samples taken and on structural measurements. Three sedimentological sections were taken from the three outcrops selected (Tondibia, Rhodesia and Kongou). The petrographic study of the Continental Terminal 3 (Ct3) deposits identified several facies whose sedimentological characteristics and number varied according to the sectors studied. The facies identified include: kaolinitic sandstones; ferruginous oolitic sandstones; sandstone clays; conglomeratic sandstones; clays intercalated with ferruginous oolitic sandstones; and iron oxide nodule conglomerates. Microscopic observations made it possible to identify several forms of oolitic concretions, namely: type α oolites (Oα), type γ oolites (Oγ), proto-oolites (PO), oolites of type γ (Oγ), oolites of type γ (Oγ), oolites of type γ (Oγ) and oolites of type γ (Oγ). proto-oliths (PO) and composite ooliths (OC). Tectonic analysis has revealed a NW-SE and NE-SW compressive phase of Oligo-Miocene age that affected the deposits of Terminal Continental 3 (Ct3).

Most of Niger's oil exploration and production activities take place in the Termit Basin. The Paleogene Sokor1 Formation, an important exploration target in the Termit Basin, is a typical sandstone hydrocarbon reservoir. The research presented in this paper used core, water samples and wireline logs, collected in the Dibeilla prospect to determine factors impacting the occurrence of low resistivity oil/gas reservoirs during their diagenetic processes to avoid exploration extra-cost and to recover the total reserves. Cores were analyzed based on thin sections, scanning electron microscopy, X-ray diffraction, and capillary pressure test. Wireline logs were analyzed using the Combined Log Pattern technique. The distributions of all potential influencing factors on porosity and permeability were quantified, making it possible to assess the influence of all potential controls on resistivity logs reading regarding to the fluid type. Diagenetic processes in the Sokor1 oil/gas reservoirs with low resistivity include cementation and dissolution, apart from mechanical compaction. Authigenic clay minerals, pyrite and siderite that account for resistivity controlling factors, occur as pore-filling and pore-lining cements, increase the reservoir conductivity. Sedimentary facies with fine lithological features resulted from relatively weak hydrodynamic deposition conditions induced by irreducible water and dual pore-structure system are the primary causes related to resistivity reduction in oil/gas saturated reservoirs. The low resistivity oil/gas reservoirs identified are the result of mix factors. Results demonstrate the robust application of combining diagenesis and Combined Log Pattern in predicting favorable reservoirs, useful in reducing exploration risk in undrilled areas and oilfields with similar geologic settings.

The present study concerns the south-centre of the Nigerien part of the Iullemmeden intracratonic Basin. A multidisciplinary approach involving sedimentological analysis of facies and determination of fossils has been implemented for the characterization and determination of the Maastrichtian to Paleogene paleoenvironments in the Garadaoua and Garadoumé areas. The stratigraphic series of the study area includes, from the bottom to top, the Formations of: Farin Doutchi, In Wagar, Garadaoua and Ader Doutchi (Ct1 or Ar). The Maastrichtian Formations of Farin Doutchi and In Wagar, as well as the Paleocene Formation of Garadaoua are fossiliferous. Indeed, the base of the Farin Doutchi Formation contains bivalves, foraminifera and sea urchins, while, In Wagar contains remains of vertebrates and casts of gastropods. In the Garadaoua Formation, presence of the benthic foraminifer Ranikothalia bermudezi species made it possible to assign to it an Upper Paleocene age. Moreover, the presence in the Garadaoua Formation of the sea urchin Linthia sudanensis species implies, during this periode, the pre-existence of an epicontinental sea in the Iullemmeden basin. Besides, in the Ader Doutchi Formation, the demonstration of α and γ oolites, as well as proto-oolites, testifies an agitated environment with at least two oolithization phases.