Troudi, Habib (OMV Tunesien Production GmbH) | Chevalier, Francis (OMV Tunesien Production GmbH) | Alouani, Wael (OMV Tunesien Production GmbH) | Mzoughi, Wala (OMV Tunesien Production GmbH) | Abdelkader, Omri (OMV Tunesien Production GmbH)
In Tunisian Ghadames sag basin, a significant portion of natural gas resources are looked within low permeability Ordovician sandstones deposited immediately below the Early Silurian Tannezuft world-class source rock.
The objective of this study was to develop an integrated approach to better estimate the amount of gas stored in this emerging play via the analysis of four fundamental elements: 1) the thermal maturity of the Silurian ‘hot shales’ source rock, 2) the trapping mechanism and the architecture of Upper Ordovician paleo-valleys, 3) the impact of diagenesis-lithofacies association on petrophysical properties, and 4) the fracture distribution/density and their contribution in the production.
The Early Silurian hot shales constitute the essential ingredient for the development of a pervasive gas accumulation play. The gas generated at the deeper part of the basin has charged the underlying Ordovician low-permeability sandstones mainly through complex faults system inherited from the basement. During hydrocarbon maturation and charging, pore pressure increases at rates that exceed the normal gradients, leading to local over-pressure as seen in several wells drilled down to the Ordovician reservoirs. Lateral migration via regional faults is confirmed by numerous discoveries at the edges of the basin far away from the gas kitchen.
Besides the structural closures accumulations, more complex structural/stratigraphic or purely stratigraphic traps are deemed within the Late Ordovician, and documented for instance by the development of incised paleovalleys filled with multiple fluvio-glacial and marine clastic sediments (i.e Algeria, Libya). The discovery of hydrocarbon pay zones outside of structural closures and the result of the long term tests confirm this hypothesis.
Based on seismic data it is generally very hard to recognize the paleorelief marking the base of the Late Ordovician sequence. Key elements from core studies, regional correlations, isochore maps and sequence stratigraphy have been combined accordingly, leading to a conceptual model within the observed framework. It is then possible to identify the multiple incision surfaces associated with reservoirs of Jeffara and M'Krata Formations.
The reservoir quality is considered as a major risk in deep areas (>4 km). Although, the primary pores space have been occluded by quartz overgrowths and clay cementation or lost by lithostatic compaction. The substantial gas rates observed in several wells drilled in the junction of NE-SW and NS fault trends constitute an evidence of the contribution of open fracture into the flow.
This new insight into this play has been used by OMV to identify in Ghadames basin the area with possible "Tunnel Valley features", analogues to those drilled in Libya Murzuk basin (
ABSTRACT: The accumulation of phosphogypsum (PG) produced till 2015 makes its management a real challenge to the Tunisian authorities and puts the Chemical Tunisian Group (TCG) to face a challenge at large scale as the specified storage embankments knew considerable extensions in terms of heights and areas. Several studies were elaborated subsequently in 2007, 2012 and 2013 to focus on the stability of Sfax and Skhira Phosphogypsum embankments’ and showed two different chemical and mechanical behaviors according to the experienced deposition process. In 2012, it was revealed that the wet PG embankment of Sfax City with 56m height, 53Ha area and 32° slope can only be of 70m height maximum. This embankment can reach 100m in height if a reinforcement technique will be used. This deposition process is well recommended to ensure better interaction between the embankment and the existing ground surface. Using the dry deposited process, the area of the PG embankment of Skhira City covers 112 Ha and presents two elevation levels of 25m and 55m in 2013. However, the dry deposited process results in a damaged embankment profile, excessive settlements and lateral displacements. Therefore, a PG embankment of 100m height cannot be achieved. A reinforcement of the embankment by High Density Poly Ethylen geotextile layers of a rigidity modulus of 19MN/lm at increments of 4m from 55m from land allows reaching 130m of height. For technical reasons, a comparative study was raised between the wet and the dry process and lead to interesting conclusions in favor of the wet process from both industrial and geotechnical concerns. Thus, the TCG expects turning all its deposition processes to the wet one. This work aims at presenting a synthesis of the studies investigated to focus on the stability of Sfax and Skhira PG embankments as well as the actual challenges of PG storage.
ABSTRACT: Landslides are the major natural hazards among other hazards, leading to downward to outward movement of slope forming materials due to gravity and are particularly dangerous in the case of highways, railroads and dam reservoirs. Landslides characterizing infrastructures of mountains of the governorate of Jendouba, which are developed in massives formed by clay-sandstone levels alternated by fractured bedrock (Flysch Numidien), constitute complex systems of instabilities controlled by many factors. Remote sensing, GIS (geographic information system) and digital terrain modeling are the best application to have different thematic maps. An integration of geological, cartographic and spatial data enabled us to have a geographical and qualitative analysis of RN17 road’s landslides and a clear visualization of the spatial distribution of its predisposition factors along the Melah Watershed in the NW Tunisia. Thus, these combined techniques and methods allowed us the development of a GIS facilitating the mapping of factors controlling ground slides. A terrain motion vulnerability map is then generated, based on field missions, SRTM satellite data and basic mapping documents within a GIS environment. A spatial analysis and semantic queries shows that maximum landslide prone area is noticed beside the RN17 road. In fact, the inventoried disorders are located on clayey and clayey-sandstone sides along the slopes of the Melah basin, near the tributaries of the slopes and water sources, and especially at the level of previously fractured outcrops. In addition, stabilization studies, based on the results of the geotechnical calculations, recognize these factors (lithologic, hydrographic and morphotectonic factors) as the main precursors for these disorders. So, the solution of Wireless Sensor Network (WSN) system implemented all along the road RN17 and on very high-risk zones, may save more lives and may make smooth transportation system.
ABSTRACT: The quality of the aggregates used as building materials is noticeably linked to the quality of the source rocks. That is why researchers have invented many methods in order to control rock material quality. This paper aims to present a classification method of four limestone rocks from quarries in the northern part of Tunisia selected of different geological ages (Lower Jurassic, Upper Cretaceous, and Lower Eocene). This classification is based on ultrasonic measurements and physical and chemical characterization. These physical and chemical characteristics were determined from vacuum water porosity, helium porosity and XRay diffraction tests. This showed a noticeable difference in porosity between the studied rocks. Mineralogy analysis confirms that Calcite is the most predominant mineral. To complete this analysis, SEM images were taken (for a magnification of 1000 and 5000). This allowed visualizing the topography and the morphology of the existing pores and cracks in the samples, as well as their density of occurrence. Finally, the image analysis method applied on the facets of the tested samples made it possible to compare the mesoscopic surface state of the different rocks by introducing the concept of surface crack ratio. The methodology developed allowed us to classify the samples into three groups and to conclude that porosity is the most relevant factor in classifying their quality.
Since a long time, the Aggregates were commonly used in the production of concrete, coated stone, railway ballast and in general building and construction applications.
Especially, Aggregates form the skeleton of concretes (essential element of construction) and present about 80% of its weight. They govern both their mechanical characteristics and their costs. Mechanically, concrete derives most of its strength from aggregates and especially from coarse aggregates, due to their higher strength compared to than cement paste. (Added, 2005, Meddah et al, 2010, Wu et al, 2001, Achour, 2007, Pautre, 2011).
Protests over jobs in southern Tataouine and Kebili provinces hit oil and gas production in a region where French company Perenco and Austrian producer OMV operate. The deal calls for jobs in oil companies and development projects. The deal calls for 1,500 jobs in oil companies, a budget of 80 million dinars (USD 32.66 million) for a development fund and another 3,000 jobs in environmental projects.
This paper describes a detailed geochemical evaluation of the Paleozoic source rocks in the Chotts basin- Southern Tunisia. Cutting samples collected from Middle Ordovician Azzel Formation (Fm), Late Silurian-Early Devonian FegaguiraFm and Permian ZoumitFm were analysed using Rock-Eval pyrolysis, GC and GC/MS techniques.
The FegaguiraFm is the principal petroleum source rock (SR) in the basin with Total Organic Carbon (TOC) values ranging from 1 to 20%. The Petroleum Potential (PP) and the Hydrogen Index (HI) values average 8 kg HC/t rock and 225 mg/g of TOC respectively indicate that the sediments have oil and gas generating potential. The terpanes series are dominated by the tricyclic and tetracyclic terpanes comparatively to hopanes with C23, C24 and C21 tricyclic terpane as prominent compounds. The diasterane contents are relatively high confirming the shaly character of the SR.
The Azzel shales has poor to moderate, occasionally good, potential for sourcing oil and gas with TOC and PP values varying from 0.80 to 4.49 % and from 0.68 to 9.20 kg of HC/t rock respectively. The HI values of 95–165 mg S2/g TOC and Tmax value of 435–448°C indicate mainly mature oil-prone kerogen. The biomarker features are characterized by high proportion of tricyclic terpanes that are dominated by C23 and C21 tricyclic terpanes. The hopanes fraction is dominated by C29 and C30 hopanes. The diasterane content are relatively high supporting the shaly character of the SR.
The ZoumitFm shows fair to excellent TOC ranging from 0.06 to 6.84% and fair to good PP (reaching 4.77 kg of HC/t of rock) and both HI and Tmax values indicate mainly immature oil-prone kerogen. The biomarker analysis reveals a low content of trictyclic terpanes relative to pentacyclic terpanes. The content of C29 and C30 hopane is relatively high. The diasteranes are present in moderate to high proportions and are less abundant than regular steranes. These biomarker features indicate a marine OM associated with marly to argillaceous limestone SR, deposited in suboxic, normal salinity depositional environment.
Lower Reineche hydrocarbon-bearing limestones is subdivided into four different layers the first three ones (LRN1, LRN2, LRN3) belong to nummulite-rich unit and represent the main reservoir however the fourth layer (LRLs), which corresponds to an argillaceous limestones, is not considered as reservoir layer although its fair porosities. The sedimentological study based on CL description, USB, TS, and SEM analyses allowed the identification of eight facies. In the cored wells, the specified facies coupled to the FMI interpretation are used in order to recognize the specific response of each facies. Then the comparison of the FMI logs of the non-cored wells with those of the cored ones assists the prediction regarding facies and reservoir characteristics and helps to fill interpretive gaps when comprehensive formation evaluation data is not available. The CMR Logs show generally one modal T2 distribution illustrating the existence of only one fluid type except the LRN2 showing bimodal T2 distribution. In addition, this T2 signal is wide expressing a large pore size distribution (micro- to macroporosities). The sedimentological study proved the existence of matrix microporosity, an intergranular porosity between Nummulite tests and an intragranular porosity within Nummulites which is effective only when affected by microfractures (meso- to macroporosities). For Lower Reineche limestones, integration of sedimentological, RCA, FMI and CMR studies specified the different facies in addition to the porosity and permeability distribution in the reservoir. Nummulit biofabric and early diagenesis are the main factors that control the petrophysical characteristics of the Nummulit bearing limestones. The understanding of the heterogeneity and the distribution of the porosity and the permeability in this area is important for the reservoir modeling and the hydrocarbon (gas mainly) saturation.
The Oudna Field is located approximately 80 km. offshore Tunisia (Figure 1). Successful application and optimization of an artificial lift system for this field required a considerable amount of evaluation prior to implementation, in order to take into consideration three specific features of the prospect:
After extensive study of the various artificial lift alternatives available, the decision was made to install the first sub-sea hydraulic jet pump system, capable of producing 25,000 bpd, because it afforded the following advantages:
In this paper the authors explain the need for a long life system, the reasons for selecting jet pumps, the considerations in the design of the jet pump, its installation and operation. The process used for the optimization of the jet pumping system is discussed.
Initial field economics on Oudna was carried out based on a $27 / BBL pricing. With this oil price, under any circumstances the Field was likely to be Marginal. Although confidence existed that the Oudna reservoir modeling was sound this in turn had indicated that both reservoir pressure support and an artificial lift production mechanism would be required to keep oil production levels to that required.
Given that the field is in 270m of water and around 80km from shore then both the Production Handling and Artificial Lift options were going to be limited.