Riadh AHMADI

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Hydrocarbon exploration expert.University teacher: Geology Engineering.Structural geologist.Petroleum geologist, pore-pressure and non conventional reservoir specialist.
Address: Sfax, Tunisia

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Nicolas Coltice

École Normale Supérieure

Hemin Koyi

Uppsala University

Armando Marques-Guedes

UNL - New University of Lisbon

Paul E. Olsen

Columbia University

Gabriel Gutierrez-Alonso

University of Salamanca

Peter D Clift

University College London

Paulo Emanuel T F Fonseca

Universidade de Lisboa

Beata Gruszka

Adam Mickiewicz University in Poznań

Stephen W Merkel

Vrije Universiteit Amsterdam

Azealdeen Al-Jawadi

Mousil University

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Papers by Riadh AHMADI

Geomechanical Assessment Based on Borehole Image Logs and Drilling Data in the Oriental Platform of Tunisia: Evidence for a Strike-Slip Tectonic Regime

Hydrogeological investigation of karst aquifers using an integrated geomorphological, geochemical, GIS, and remote sensing techniques (Southern Mediterranean Basin—Tunisia)

Environment, Development and Sustainability, Feb 16, 2023

This study aims to present the hydrogeological and hydrochemical characteristics of Paradisos Kar... more This study aims to present the hydrogeological and hydrochemical characteristics of Paradisos Karst aquifer system (PAS), Northeast Greece. The average area of the PAS is estimated according to Thornthwaite and Mather (1957) (T-M) procedure at 74.2 km 2. The karst system, which is largely fault-controlled, discharges through three permanent karst springs: KS15, KS20 and KS21. The average discharge rate was calculated for two of them at 0.726 m 3 /s. The time series analysis shows that: (a) the memory effect for the PAS is extremely high; and (b) the karst system is a poorly developed with high storage capacity and absence of a quick flow component. The chemical type for the majority of the groundwater samples is of Ca-HCO 3 type. The chemical properties of the groundwaters are strongly influenced by alkaline earth metals and weak acids. The presence (sporadically) of high NH 4 + content and slightly increased nitrate, ammonium and phosphate values in springs KS20 and KS21 is attributed to the presence of anthropogenic sources, especially septic tanks and agriculture. All studied groundwaters are oversaturated in calcite and aragonite, which suggests a mechanism of diffuse flow. The morphology and geology of the PAS catchment area, and data from hydrographs and chemographs, show that the hydrologic system is dominantly of diffuse flow. The use of time series analysis combined with classic hydrogeological techniques (i.e., degree of karstification, T-M procedure, chemographs and

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Calculation and application of partition coefficients of light hydrocarbons in oil-based mud system

Petroleum Exploration and Development

Organic Geochemical Assessment and Shale Gas Potential of Lower Silurian Organic Rich Shale in the Ghadames Basin, North Africa

Oil Shale, 2019

The Silurian organic rich shale is the main source of hydrocarbons in the Ghadames Basin in North... more The Silurian organic rich shale is the main source of hydrocarbons in the Ghadames Basin in North Africa. The basin has been widely characterized as a source rock for Ordovician oil and gas; yet understanding this shale as a shale resource play remains problematic and challenging. In this study, geochemical and mineralogical analyses of drill cuttings derived from five wellbores were carried out to evaluate the unconventional potential of Silurian organic rich shale. The results of geochemical analysis show that the present day total organic carbon (TOC) of this shale is generally medium to good, varying between 1 and 5 wt%. The hydrogen index (HI = 55-201 mg HC/g TOC) and Tmax (435-454 °C) values indicate type II kerogen in a mature state and its ability to generate wet gas. The results of mineralogical analysis show that clay minerals dominate in all samples of Silurian shale (39-58%) followed by quartz (16-37%). Geochemical parameters such as Mo, V, As, Zr and TiO 2 indicate that these shales were deposited in anoxic conditions and were sourced from intermediate igneous rocks. In order to evaluate the potential of Silurian shale as oil and gas source, in this work, the chemostratigraphy technique was applied to identify the provenance of silica in shales, to characterize the shale brittleness and model a correlation between the mineralogy and organic matter content. In conclusion, the Silurian organic rich shale in the Ghadames Basin exhibits good characteristics for shale resource hydrocarbons production.

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Kinematic Evolution Model of Fault-Related Anticline based on the Study of the Striated Pebbles of the Related Growth-Strata: A Case Study of the Es Satah Anticline in Southern Tunisian Atlas, Tunisia

Geotectonics, 2019

Through several stations on the forelimb of the Es Satah anticline belonging to Gafsa basin part ... more Through several stations on the forelimb of the Es Satah anticline belonging to Gafsa basin part of the southern Tunisian Atlas, an analysis of the striations encountered on the pebbles surfaces in the conglomerates of the growth-strata shows a remarkable variation; vertically and laterally from one station to another. Taking into account of the simple shear deformation, field observations have revealed several indexes of the flexural flow. Both of the tectonic and micro-tectonic studies in the Gafsa basin have shown the trending shortening (σ1) ranging from 150° to 180° N. Therefore, the striation azimuths were determined according to three profiles, I, II and III. These profile stretch from the NE to the SW on the forelimb of Es Satah anticline which displays a variation ranging from 167° to 138° N, from 165° to 147° N and from 154° to 138° N, respectively. Since these variations are incoherent with the regional shortening (σ1) direction, it allows us to discard any evidence of a direct relationship between the regional trending shortening (σ1) and the striation azimuths of the pebbles surfaces of growth-strata and to speculate a possible direct correlation between those variations and the kinematic evolution of the Es Satah anticline. Accordingly, we have suggested a conceptual model which paved the way to follow step by step the anterior stages of the deformation and identify the different palaeo-periclinal limits of the Es Satah anticline.

Hydrogeological Investigation of a Karst Aquifer System

Environmental Processes, 2017

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Role des accidents hérités dans le transfert de matière: modèle de plissement dans l'Atlas méridional Tunisien

International audienc

Role of the pore pressure profile on the protection of wellbore integrity and the groundwater: Case studies of well integrity issues of CI-11, in southern Tunisia, and OKN-32 in Algeria

This study consists of an assessment of the ecological accident implicating the Continental Inter... more This study consists of an assessment of the ecological accident implicating the Continental Intercalaire-11 (CI-11) water well located in Jemna oasis, southern Tunisia. The CI-11 ecological accident manifested in 2014 with a local increase of the complex terminal (CT) shallow water table salinity and temperature. Then, this phenomenon started to spread over the region of Jemna, progressively implicating farther wells. The first investigation task consisted of logging the CI-11 well. The results revealed an impairment of the casing and cement of a huge part of the 9⅝ in. production casing. Historical production records show that the problems seem to have started in 1996 when a sudden production loss rate occurred. These deficiencies led to the CI mass-water flowing behind the casing from the CI to the CT aquifers. This ecological accident is technically called internal blowout, where water flows from the overpressurized CI groundwater to the shallower CT groundwater. Indeed, the upward CI hot-water flow dissolved salts from the encountered evaporite-rich formations of the Lower Senonian series, which complicated the ecological consequences of the accident. From the first signs of serious water degradation in 2014 through the end of 2018, several attempts have been made to regain control of annular upward water flow. However, the final CT groundwater parameters indicate that the problem is not properly fixed and communication between the two involved aquifers still persists. This accident is similar to the OKN-32 case that occurred in the Berkaoui oil field, southern Algeria, in 1986, and included the same CI and CT aquifers. Furthermore, many witnesses claim that other accidental communications are probably occurring in numerous deep-drilled wells in this region. Concludingly, Jemna CI-11, Berkaoui OKN-32, and probably many other similar accident cases could be developing regional ecological disasters by massive water resource losses. The actual situation is far from being under control and the water contamination risk remains very high. In both accidents, the cement bond failure and the choice of the casing point are the main causes of the internal blowout. Therefore, we recommend (1) a regional investigation and risk assessment plan that might offer better tools to predict and detect earlier wellbore isolation issues and (2) special attention to the cement bond settlement, evaluation, and preventative logging for existing wells to ensure effective sealing between the two vulnerable water table resources. Besides, in the CI-11 well accident, the recovery program was not efficient and there was no clear action plan. This increased the risk of action failure or time waste to regain control of the well. Consequently, we suggest preparing a clear and efficient action plan for such accidents to reduce the ecological consequences. This requires further technical detailed study of drilling operations and establishment of a suitable equipment/action plan to handle blowout and annular production accidents.

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Signatures géomorphologiques de la migration des charnières dans les plis de rampes ; exemples dans l'Atlas Tunisien

$Research paper thumbnail of Relationship between folding and fracture in fault-releted fold. Case of Jebel Sehib Tunisian Atlas : a single-step « fault-propagation fold »$

Relationship between folding and fracture in fault-releted fold. Case of Jebel Sehib Tunisian Atlas : a single-step « fault-propagation fold »

AhmadiI&al[1]

Geomorphology, fold growth and climate

Neogene tectonics and fault-related folds in the Gulf of Hammamet area, Tunisian offshore

Journal of African Earth Sciences, 2014

ABSTRACT The western part of the Gulf of Hammamet area lies in the Pelagian Platform, eastward of... more ABSTRACT The western part of the Gulf of Hammamet area lies in the Pelagian Platform, eastward of the Atlas front. This region shows large changes in structural style compared to the Pelagian Platform. During the Neogene, the Gulf of Hammamet recorded the convergence of the Eurasia and Africa plates. During the Pliocene to early Quaternary, the area recorded an NW-SE shortening related to the Atlas contraction followed by an NNE-SSW extension linked to the Pantelleria-Malta graben opening. Subsurface geology of the Gulf of Hammamet area allows us to propose a tectonic sketch, where the Neogene deformation is characterized by (1) Cenozoic age detachment level that located in the Mio-Pliocene and Quaternary series; (2) the growth of fault-related folds (mainly fault-propagation folds) and (3) a total shortening of about 6 km. The thin-skinned thrusting is late Miocene age and is synchronous to the Africa-Europe collision. During the upper Miocene (Tortonian), fault-propagation folds developed above inherited normal faults. The Pliocene age was tectonically calm period. Finally, post-Villafranchian contraction reactivated these structures. Despite the large number of hydrocarbon discoveries, the Gulf of Hammamet remains under-explored. This new interpretation of Neogene tectonic events and folding models could lead to a new play idea for the hydrocarbon prospectively in this proven oil province.

Source Rock Characterization and Petroleum Systems in North Ghadames Basin, Southern Tunisia

Resource Geology, 2011

This paper presents geochemical analysis of drilled cutting samples from the OMZ-2 oil well locat... more

Geochemical and isotopic study of the multilayer aquifer system in the Moulares-Redayef basin, southern Tunisia / Etude géochimique et isotopique du système aquifère multicouche du bassin de Moulares-Redayef, sud tunisien

Hydrological Sciences Journal, 2008

Major ion geochemistry, and water molecule isotopes (18 O, 2 H) and radiogenic carbon (14 C) of d... more Major ion geochemistry, and water molecule isotopes (18 O, 2 H) and radiogenic carbon (14 C) of dissolved inorganic carbon (DIC) were used to investigate the hydrodynamic functioning of the multilayer aquifer system in the Moulares-Redayef basin, southern Tunisia. The groundwater of different aquifer levels is characterized by sulphate to calcium sulphate water type. The major geochemical processes in the aquifer system are evaporite mineral dissolution and mixing. The isotopic study allows two groundwater types to be identified: an old palaeoclimatic groundwater, marked by low 14 C activity and relatively depleted stable isotope (18 O and 2 H) content characterizes the shallowest aquifers of the Plio-Quaternary and Miocene formations; however, a recent groundwater, distinguished by relatively high 14 C activity and slightly enriched 18 O and 2 H content, characterizes the deep Upper Cretaceous artesian aquifer. In addition to these two water groups, other groundwaters are identified, indicating a mixing effect. Key words southern Tunisia; Moulares-Redayef basin; semi-arid region; stable isotopes; radio-carbon isotope Etude géochimique et isotopique du système aquifère multicouche du bassin de Moulares-Redayef, sud tunisien Resume Une étude géochimique et isotopique, basée sur l'utilisation des éléments majeurs et des isotopes de la molécule d'eau (18 O, 2 H) et du CITD (Carbone Inorganique Total Dissous) (14 C), a été entreprise pour étudier le fonctionnement hydrodynamique du système aquifère multicouche du bassin de Moulares-Redayef, situé au sud de la Tunisie. Les eaux souterraines des différents niveaux aquifères sont caractérisées par un faciès sulfaté à sulfaté calcique. Les processus géochimiques majeurs du système aquifère sont la dissolution et le mélange des minéraux évaporitiques. L'étude isotopique permet d'identifier deux groupes d'eaux souterraines. D'une part, les eaux anciennes paléoclimatiques, à faibles activités 14 C et à teneurs isotopiques (en 18 O et 2 H) appauvries, caractérisent les aquifères superficiels des formations plio-quaternaire et miocène. D'autre part, les eaux récentes, à fortes activités 14 C et à teneurs relativement enrichies en 18 O et en 2 H, caractérisent l'aquifère profond à nappe artésienne du Crétacé supérieur. En plus de ces deux groupes, d'autres eaux souterraines sont identifiées, qui indiquent un phénomène de mélange. Mots clefs sud-ouest Tunisien; bassin de Moulares-Redayef; région semi-aride; isotopes stables; radio-isotopes du carbone Open for discussion until

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Groundwater evolution of the Continental Intercalaire aquifer of Southern Tunisia and a part of Southern Algeria: use of geochemical and isotopic indicators

Desalination and Water Treatment, 2014

ABSTRACT The expansion of irrigated agriculture and the overexploitation of groundwater aquifers ... more ABSTRACT The expansion of irrigated agriculture and the overexploitation of groundwater aquifers are leading to saltwater intrusion, severe deterioration of groundwater quality and soil subsidence at arid areas. The geochemical processes taking place along an 800km flow line in the non-carbonate Continental Intercalaire aquifer (CI) in North Africa are described using chemical (major and trace element) and isotopic indicators. The aquifer is hydraulically continuous from the Atlas Mountains in Algeria to the Chotts of Tunisia and the geochemical evidence corroborates this. The CI aquifer of North Africa is one of the largest confined aquifers in the world. The aquifer is hydraulically continuous from the Atlas Mountains in Algeria (recharge area) to the Chotts of Tunisia (discharge area) and the geochemical evidence corroborates this. The isotopic study (Delta18O, Delta2H) permits classifying groundwater into three groups. The first group is characterized by low 3H concentrations, low 14C activities and depleted stable isotope contents. It corresponds to an old end-member in relation with palaeoclimatic recharge which occurred during the Late Pleistocene and the Early Holocene humid periods. The second group is distinguished by high to moderate 3H concentrations, high 14C activities and enriched heavy isotope signatures. It corresponds to a modern end-member originating from a mixture of post-nuclear and present-day recharge in relation to return flow of irrigation. The third group is characterized by an average composition of stable and radiogenic isotope signatures. It provides evidence for the mixing between the upward moving palaeoclimatic end-member and the downward moving present-day end-member. Rainfall, originating from a mixture of Atlantic and mediterranean air masses.

Modeling of Mrihla anticline (Central Tunisian Atlas), combination fault propagation fold and halokenitic model

Arabian Journal of Geosciences, 2014

The modeling study on the Mrihla anticline was carried out using two techniques, i.e., excess are... more The modeling study on the Mrihla anticline was carried out using two techniques, i.e., excess area law and balanced cross section. The results show that this structure is likely affected by at least two compressive phases. The interpretation of surface (bedding dips, thickness, lithology, etc.) and subsurface (seismic lines) data along the cross section indicates that the Mrihla structure has a shortening of about 525 m that is evolved above a detachment layer formed by gypsum Triassic formation. The top of this layer is situated at a depth of about 3,890 m from the top of the Aptian dolomitic level, known in Central Tunisian Atlas as Serdj Formation. The kinematic of the investigated structure is a combination of two deformation models. The first is the halokenitic model, defined by the flowing of Triassic ductile material upward toward the surface through the deep Mrihla fault, which is parallel to Mrihla anticline. The second is the fault propagation fold model, characterized by thin-skin deformation mechanics in relation with the movement of the Mrihla fault.

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$Research paper thumbnail of Relationship between fractures patterns and fold kinematics; the case study of Jebel Sehib, a typical fault-propagation fold of southern Tunisia$

Relationship between fractures patterns and fold kinematics; the case study of Jebel Sehib, a typical fault-propagation fold of southern Tunisia

Journal of African Earth Sciences

Physical modelling of sub-salt gliding due to fluid overpressure in underlying sedimentary strata

Marine and Petroleum Geology, 2016

The Gulf of Mexico and the offshore Campos and Santos basins of Brazil provide good examples of s... more The Gulf of Mexico and the offshore Campos and Santos basins of Brazil provide good examples of sub-salt detachments, by shearing in the presence of overpressure. We have developed new physical models of such situations, including layers of ductile silicone putty, which simulated an evaporite, and fluid overpressure in porous brittle layers. We studied two configurations, in which the maximal overpressure was either beneath a single ductile layer of silicone (simulating salt), or between two such layers of silicone (simulating an evaporite sequence). The results of our analogue modelling showed that detachment faults appeared and persisted at the bases of the ductile layers, even though some ductile deformation occurred simultaneously within these layers. For models where maximal overpressure was between two ductile layers, detachment occurred mainly at the base of the upper silicone layer. On comparing our models with structures in the Gulf of Mexico or offshore Brazil, we find strong similarities, which lead us to suspect that detachment is indeed possible at the base of an evaporite sequence in nature. This conclusion has strong implications, not only for the understanding of petroleum systems, but also for better management of petroleum productionin sedimentary basins.

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The "hinge migration" question, a review. Folds kinematics in "fold and thrustbelts

Geomechanical Assessment Based on Borehole Image Logs and Drilling Data in the Oriental Platform of Tunisia: Evidence for a Strike-Slip Tectonic Regime

Hydrogeological investigation of karst aquifers using an integrated geomorphological, geochemical, GIS, and remote sensing techniques (Southern Mediterranean Basin—Tunisia)

Environment, Development and Sustainability, Feb 16, 2023

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Calculation and application of partition coefficients of light hydrocarbons in oil-based mud system

Petroleum Exploration and Development

Organic Geochemical Assessment and Shale Gas Potential of Lower Silurian Organic Rich Shale in the Ghadames Basin, North Africa

Oil Shale, 2019

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Geotectonics, 2019

Hydrogeological Investigation of a Karst Aquifer System

Environmental Processes, 2017

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Role des accidents hérités dans le transfert de matière: modèle de plissement dans l'Atlas méridional Tunisien

International audienc

Role of the pore pressure profile on the protection of wellbore integrity and the groundwater: Case studies of well integrity issues of CI-11, in southern Tunisia, and OKN-32 in Algeria

Download

Signatures géomorphologiques de la migration des charnières dans les plis de rampes ; exemples dans l'Atlas Tunisien

$Research paper thumbnail of Relationship between folding and fracture in fault-releted fold. Case of Jebel Sehib Tunisian Atlas : a single-step « fault-propagation fold »$

Relationship between folding and fracture in fault-releted fold. Case of Jebel Sehib Tunisian Atlas : a single-step « fault-propagation fold »

AhmadiI&al[1]

Geomorphology, fold growth and climate

Neogene tectonics and fault-related folds in the Gulf of Hammamet area, Tunisian offshore

Journal of African Earth Sciences, 2014

Source Rock Characterization and Petroleum Systems in North Ghadames Basin, Southern Tunisia

Resource Geology, 2011

This paper presents geochemical analysis of drilled cutting samples from the OMZ-2 oil well locat... more

Hydrological Sciences Journal, 2008

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Groundwater evolution of the Continental Intercalaire aquifer of Southern Tunisia and a part of Southern Algeria: use of geochemical and isotopic indicators

Desalination and Water Treatment, 2014

Modeling of Mrihla anticline (Central Tunisian Atlas), combination fault propagation fold and halokenitic model

Arabian Journal of Geosciences, 2014

Download

$Research paper thumbnail of Relationship between fractures patterns and fold kinematics; the case study of Jebel Sehib, a typical fault-propagation fold of southern Tunisia$

Relationship between fractures patterns and fold kinematics; the case study of Jebel Sehib, a typical fault-propagation fold of southern Tunisia

Journal of African Earth Sciences

Physical modelling of sub-salt gliding due to fluid overpressure in underlying sedimentary strata

Marine and Petroleum Geology, 2016

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The "hinge migration" question, a review. Folds kinematics in "fold and thrustbelts

Riadh AHMADI

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