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Collaborating Authors
Abstract The Niger Delta Deep Offshore Basin has been the latest frontier within the Niger Delta for hydrocarbon exploration and production activities. Until the onset of drilling activities in the early 1990s, little was known about the biostratigraphy of this frontier setting. Thus, uncertainties existed in the ages ascribed to the various stratigraphic sequences. Presently, several wells have been drilled in the deep offshore Niger Delta and three-pronged biostratigraphic data and some sequence stratigraphic interpretations have become available. We have integrated biostratigraphic data comprising palynological, foraminiferal, and calcareous nannoplankton zonation and biofacies, wireline log information, and regional-3D seismic data, with simple basic sequence stratigraphic analysis for a detailed well correlation, regional mapping of hydrocarbon-bearing intervals, and evaluation of the thicknesses of promising stratigraphic intervals. Results indicate a significant effect on not only the earlier conceptualized age of the deepest prospective reservoirs, but also the ages of possible source rocks in the Paleogene of the Niger Delta offshore sequence. Our findings will help in the realistic assumptions of source rock characterization, charge modeling/prediction, and the stratigraphic thicknesses of the offshore sequences and their reservoirs. We examine the specific derivable age interpretations from the integration of at least six wells, biostratigraphic data with seismic, and the implications of these interpretations for hydrocarbon prospectivity of the Paleogene sequences. Furthermore, we document the biostratigraphy work done in the area, in all the structural belts where drilling has occurred including the deepest well drilled in the deep offshore Niger Delta, Bosi-006. The results of this study have a critical impact on the current regional geologic understanding of the deep offshore Niger Delta.
- Africa > Nigeria > Niger Delta (1.00)
- Africa > Niger (1.00)
- Geology > Geological Subdiscipline > Stratigraphy > Biostratigraphy (1.00)
- Geology > Structural Geology > Tectonics > Compressional Tectonics > Fold and Thrust Belt (0.70)
- Geophysics > Seismic Surveying > Seismic Processing (0.68)
- Geophysics > Seismic Surveying > Surface Seismic Acquisition (0.54)
- Africa > Nigeria > Niger Delta > Niger Delta Basin (0.99)
- Africa > Cameroon > Akata Formation (0.99)
- Africa > Nigeria > Gulf of Guinea > Niger Delta > Niger Delta Basin > OML 95 > Delta Field (0.98)
- (3 more...)
Abstract Since 2003 we have tested the use of benthic foraminiferal faunas as bio-indicators of highly biodegradable oil-based drill fluids and cuttings. In this paper we present data for 4 sites off western Africa (Angola, Congo and Gabon), with water depths varying from 30 to 670 m. A very similar faunal response to environmental perturbation is found in these different environmental settings. In the close vicinity of the oil drill mud and fluids disposal, the combination of lowered bottom water oxygenation, the presence of toxic compounds and a general ecosystem enrichment leads to strongly impoverished faunas. More sensitive taxa become very rare in these areas. Moderately impacted sites are characterized by high to very faunal densities, and a strong dominance of opportunistic taxa, that are favored by the increased amount of organic matter in the benthic environment, resulting from the introduction of hydrocarbons. Beyond 500 m of the disposal sites, the faunas progressively become similar to the natural faunas; the relative frequency of opportunistic and stress-tolerant taxa drops to background values. Two foraminiferal indices are proposed that allow a quantitative evaluation of the impact of the oil drilling activities. A first foraminiferal index, that is based on the cumulative percentage of opportunistic and stress-tolerant taxa, is very effective in continental shelf settings. Severely polluted sites contain more than 70% index species, moderately impacted area between 50 and 70%. In slightly to non impacted sites, the percentage of index species drops from 50 to 20%. A shallow, 30 m deep, area in front of the Ogoouรฉ estuary reveals a high percentage of marker species at all investigated stations. This elevated percentage is caused by the presence of naturally eutrophicated conditions due to the supply of important amounts of nutrients and continental organic matter by river outflow. In this a particular setting, oil exploration activities appear to have only a minor environmental impact. At the 670 m deep upper slope site, the impacted stations are characterized by the progressive disappearance of the taxa that are most sensitive to ecosystem perturbation. The cumulative percentage of these taxa strongly decreases at the most impacted areas, which provides a very useful additional quantitative monitoring tool. The present data show that foraminiferal faunas are extremely powerful in monitoring the environmental impact of oil exploration activities. In the near future, the proposed foraminiferal indices will be tested in other areas, and the selected marker species will be formalized for different types of environmental settings, with different water depths and climatic conditions. Introduction Oil well drilling operations are responsible for the disposal of large quantities of drill cuttings and fluids. In order to assess the impact of these products on the benthic ecosystem, since 2003 we have studied foraminiferal faunas around production sites off Angola, Congo and Gabon. In fact, foraminifera have several advantages over traditionally used macro- and meiofauna as bio-indicators of offshore drilling activities [1]:They appear with large densities, of several hundreds to thousands of individuals per 100 cm sea floor surface, which makes it possible to perform reliable analyses on the basis of very small samples. They have a high biodiversity, with up to 100 species living at a single site. These species occupy different ecological niches, and show large differences in tolerance to anthropogenic stress parameters, offering a large panel of marker species.
- Well Drilling > Drilling Operations (1.00)
- Health, Safety, Environment & Sustainability > Environment > Water use, produced water discharge and disposal (0.76)
- Well Drilling > Drilling Equipment > Offshore drilling units (0.60)
- Management > Strategic Planning and Management > Exploration and appraisal strategies (0.54)
Since the onset of offshore drilling, the drilled cuttings and their disposal have received much attention in the oil and gas industry. Numerous studies performed in the laboratory on the foreseeable fate of cuttings have led to the research for new formulations with the objective of achieving lower toxicity and better intrinsic biodegradability. The study of the marine environmental impact associated with the discharge of drilled cuttings has already given rise to numerous works and surveys related to the North Sea, but it is clear that knowledge is still limited. Further information is required on the monitoring of sediments contaminated with cuttings, especially in warm sea conditions. On this topic, research projects were conducted between 2000 and 2006 in West Africa (Congo, Gabon and Angola) in order to study the modes of regeneration of the benthic fauna and the recolonisation of the seabed after the discharge of cuttings. In addition to classical approaches concerning systematic study of the abundance and diversity of the macrobenthos ( 1 mm), physicochemical analyses on sediment, biodegradability and lixiviation, new methodologies based on toxicological tests and the study of foraminifers were applied. We show that these methodologies are adapted to extreme conditions such as deep and ultra deep environments and enable different sites to be compared at large scale conferring ubiquity of the methods. In a more general context of the environmental constraints of oil industry, our work demonstrated the geographically limited extent of the impacted zones, the absence of significant long-term modification of the adjacent ecosystems and the possible application to other discharge sites.
- Africa > Gabon (0.36)
- North America > United States > Texas (0.28)
- Africa > Angola (0.25)
- (6 more...)
Abstract Renewed interest in Mesozoic exploration, onshore and offshore, in the Gulf of Mexico (GOM) has precipitated a new look at Mesozoic biostratigraphy and how these age-diagnostic bioevents can help to establish a sequence-stratigraphic framework for the basin. We have developed a new chronostratigraphic framework, primarily founded on biostratigraphic age-diagnostic data, specifically developed for Mesozoic strata of the GOM basin. Our goal was to provide a systematic and consistent framework that serves as a reference for the order and timing of depositional sequences and key surfaces in the GOM Mesozoic stratigraphic section. The new chronostratigraphic framework was based on (1)ย our work delineating significant physical stratigraphic surfaces from seismic and well-log data in the GOM, (2)ย Mesozoic biostratigraphic data from 202 onshore and offshore wells in the GOM, and (3)ย published literature from the GOM and other studies. The chronostratigraphic framework was formalized in an online Mesozoic biostratigraphy table and summarized in a Mesozoic stratigraphy chart. The use of the framework was key to our ability to correlate within the GOM basin, and we evaluated several examples of seismic and well-log interpretation using the new chronostratigraphic framework, including onshore-offshore correlation, identification and correlation of source rocks, and interpretation of structural anomalies. These examples illustrated how the chronostratigraphic framework enabled us to reduce uncertainty in identifying and correlating Mesozoic units from land to the deepwater GOM basin. The framework also allowed us to better compare our work with other research groups, within academia and industry, and permitted a higher level of integration of work and comments from various applied industry workers.
- North America > United States > Texas (1.00)
- North America > United States > Louisiana (1.00)
- North America > Mexico (1.00)
- Phanerozoic > Mesozoic > Jurassic (1.00)
- Phanerozoic > Cenozoic > Neogene (0.93)
- Phanerozoic > Mesozoic > Cretaceous > Upper Cretaceous > Campanian (0.68)
- Phanerozoic > Mesozoic > Cretaceous > Lower Cretaceous > Albian (0.67)
- Geology > Geological Subdiscipline > Stratigraphy > Chronostratigraphy (1.00)
- Geology > Geological Subdiscipline > Stratigraphy > Biostratigraphy (1.00)
- Geophysics > Borehole Geophysics (0.88)
- Geophysics > Seismic Surveying > Surface Seismic Acquisition (0.46)
- Geophysics > Seismic Surveying > Seismic Processing (0.46)
Note in Figure 4 that the middle to outer of the outer shelf-upper slope area.
- North America > United States > Texas (0.52)
- North America > United States > Gulf of Mexico > Western GOM (0.16)
- Phanerozoic > Cenozoic > Neogene > Pliocene (0.69)
- Phanerozoic > Cenozoic > Quaternary > Pleistocene (0.41)
- Geology > Sedimentary Geology (1.00)
- Geology > Geological Subdiscipline > Stratigraphy > Biostratigraphy (0.66)
- Geophysics > Seismic Surveying (1.00)
- Geophysics > Borehole Geophysics (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Geologic modeling (1.00)
- Reservoir Description and Dynamics > Formation Evaluation & Management > Open hole/cased hole log analysis (1.00)