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Gaupp R.,Friedrich - Schiller University of Jena | Okkerman J.A.,Nederlandse Aardolie Maatschappij
SEPM Special Publications | Year: 2011

The Permian Rotliegend clastic reservoirs form the main gas-bearing intervals in the Netherlands, Northwest Germany, and the Southern North Sea. We review and summarise the results of more than thirty years of diagenesis and reservoir-quality studies in Rotliegend sandstones of the Netherlands and adjacent areas. The Rotliegend sediments were deposited in an alluvial-wadi-aeolian dune-sandflat-playa lake depositional setting, marked by an arid to semiarid climate, in which drier and wetter climatic cyclicity drove sedimentary processes. Present depths of Rotliegend reservoirs in the range of 2 to ca. 4.5 km, are often referred to as maximum burial depths. Rotliegend clastics were exposed to temperatures between 60°C and180°C. Structural uplift during Late Jurassic and Cretaceous times influenced the Rotliegend pressure and fluid-flow regime. The paragenetic sequence is spatially variable and comprises a wide variety of authigenic minerals, with several early cements typical of continental red-bed sequences. Characteristic of semiarid (to arid) environments is reddening and the presence of grain-coating metal (Fe, Al, Mn, and Ti) oxides as well as smectitic, illitic, and chloritic grain-coating clays. Early blocky and often pore-filling cements include dolomite, gypsum, anhydrite, and halite, but also quartz and K- and Na-feldspar overgrowths. Burial-related authigenic precipitates are Fe-dolomite, calcite, siderite, and quartz cements, kaolinite, dickite, chlorite, and mainly fibrous illitic clay. Dissolution of feldspar and volcanic rock fragments, of soluble pore-filling carbonate, sulphate, and halite cements, and the formation and destruction of secondary porosity are important factors in determining current reservoir properties. Most of the variance in porosity and permeability can be explained by a small number of significant variables: carbonate (and anhydrite) cementation, initial mineralogy, grain size, clay matrix content, diagenetic clay association, diagenetic quartz, and feldspar dissolution. Pore-blocking anhydrite and carbonate cements are the most pronounced phases that impacted on porosity. Impairment of permeability is due mainly to authigenic clays (illite, kaolinite, chlorite). Even after pronounced diagenetic alteration the depositional setting remains as an important control on overall reservoir quality. Aeolian dunes and dry aeolian sandflat deposits remain the best potential reservoirs even under deep burial. However, pore-occluding blocky cements, mechanical compaction, or clay growth can heavily impair reservoir quality in optimum depositional facies, particularly under extended exposure times to high temperatures. Long-term or continuous gas fills preserve favourable reservoir properties. The spatial proximity of Carboniferous source rocks to Rotliegend reservoirs in the Netherlands is considered to be a smaller risk for reservoir quality compared to northern German subsurface analogues. Reservoir characterisation studies spanning more than three decades clarified the mechanisms, controlling factors, and relative timing of many diagenetic processes, but uncertainties about the quantities of resulting products remain. The multitude of interfering factors that control Rotliegend reservoir properties and the geological heterogeneity in the area does not favour conceptual models of regional applicability. Evaluation of the existing concepts on Rotliegend reservoir quality indicates the necessity of combining all available data to constrain the complexities of depositional facies, diagenesis, structuration, and charge history in the specific cases. Copyright © 2011 SEPM (Society for Sedimentary Geology). Source


Van Gent H.,RWTH Aachen | Urai J.L.,RWTH Aachen | de Keijzer M.,Nederlandse Aardolie Maatschappij
Journal of Structural Geology | Year: 2011

We present a first look at the large-scale, complexly folded and faulted internal structure of Zechstein salt bodies in NW Europe using 3D reflection seismic reflection data from two surveys on the Groningen High and the Cleaver Bank High. We focus on a relatively brittle, folded and boudinaged, claystone-carbonate-anhydrite layer (the Z3 stringer) enclosed in ductile salt. A first classification of the structures is presented and compared with observations from salt mines and analogue and numerical models. Z3 stringers not only are reservoirs for hydrocarbons but can also present a serious drilling problem in some areas. Results of this study could provide the basis for better prediction of zones of drilling problems. More generally, the techniques presented here can be used to predict the internal structure of salt bodies, to estimate the geometry of economic deposits of all kinds and locate zones suitable for storage caverns. Structures observed include an extensive network of zones with increased thickness of the stringer. These we infer to have formed by early diagenesis, karstification, gravitational sliding and associated local sedimentation. Later, this template was deformed into large-scale folds and boudins during salt tectonics. Salt flow was rarely plane strain, producing complex fold and boudin geometries. Deformation was further complicated by the stronger zones of increased thickness, which led to strongly non-cylindrical structures. We present some indications that the thicker zones also influence the locations of later suprasalt structures, suggesting a feedback between the early internal evolution of this salt giant and later salt tectonics. This study opens the possibility to study the internal structure of the Zechstein and other salt giants in 3D using this technique, exposing a previously poorly known structure which is comparable in size and complexity to the internal parts of some orogens. © 2010 Elsevier Ltd. Source


Chinyelu A.G.,Nederlandse Aardolie Maatschappij
Society of Petroleum Engineers - SPE Offshore Europe Conference and Exhibition, OE 2015 | Year: 2015

Our industry is highly dependent on competent, innovative and motivated professional workforce to deliver the world energy needs now and years to come. Resourcing the business with the right numbers and skill level at all strata of the organization requires that we continue to develop our young professionals and also provide opportunities for the experienced professionals to continue to grow. This paper discusses current best practices deployed and the impact on the business, using the Production Technology (PT) Discipline as a case study. Development of young professionals is achieved through 3 key ways: In-role development, mentoring and coaching and formal learning. These 3 mode of training follow the 70:20:10 approach to maximize learning where it is expected that 70% of learning occurs through on-the-job experience and learning as you carry out tasks; 20% through interactions with others (coaching, demonstrations, peer-to-peer sharing, etc.); and 10% through formal learning (e-learning, classroom, etc.). Operator X Graduate Programme (SGP) and the Advanced Graduate Programme (SATP) are some of the recent modes deployed to ramp up the technical capabilities of new graduates. These have aided in cutting down the number of years to "autonomy" while maintaining the quality and efficiency of the technical professionals. For the more experienced staff, operator X has tailored their role specific needs through the technical learning portfolios which include the Project Academy and the Production Academy. The mode of delivery of the trainings is tailored toward the learning objective, for example-awareness training versus on-the-job learning support, etc. In many technical learning portfolios, the blended learning mode is more favored (with emphasis on adequate preparation prior to the classroom event (f2f), more hands-on during f2f and the continuation of learning after the f2f). The formation of Subject Matter Expert (SME) networks to address different subject areas in the Discipline has also helped in deepening the skills of the experienced staff while accelerating learning for the less experienced. The Production Technology career Path Plan provides a vehicle to deploy these tools and processes and consequently transform talented but in-experienced graduates to seasoned and motivated professionals. © Copyright 2015, Society of Petroleum Engineers. Source


Lohne A.,International Research Institute of Stavanger | Han L.,International Research Institute of Stavanger | Van Velzen H.,Nederlandse Aardolie Maatschappij | Twynam A.,British Petroleum | And 2 more authors.
SPE Journal | Year: 2010

In this paper, we describe a simulation model for computing the damage imposed on the formation during overbalanced drilling. The main parts modeled are filter-cake buildup under both static and dynamic conditions; fluid loss to the formation; transport of solids and polymers inside the formation, including effects of porelining retention and pore-throat plugging; and salinity effects on fines stability and clay swelling. The developed model can handle multicomponent water-based-mud systems at both the core scale (linear model) and the field scale (2D radial model). Among the computed results are fluid loss vs. time, internal damage distribution, and productivity calculations for both the entire well and individual sections. The simulation model works, in part, independently of fluidloss experiments (e.g., the model does not use fluid-leakoff coefficients but instead computes the filter-cake buildup and its flow resistance from properties ascribed to the individual components in the mud). Some of these properties can be measured directly, such as particle-size distribution of solids, effect of polymers on fluid viscosity, and formation permeability and porosity. Other properties, which must be determined by tuning the results of the numerical model against fluid-loss experiments, are still assumed to be rather case independent, and, once determined, they can be used in simulations at altered conditions as well as with different mud formulations. A detailed description of the filter-cake model is given in this paper. We present simulations of several static and dynamic fluidloss experiments. The particle-transport model is used to simulate a dilute particle-injection experiment taken from the literature. Finally, we demonstrate the model's applicability at the field scale and present computational results from an actual well drilled in the North Sea. These results are analyzed, and it is concluded that the potential effects of the mechanistic modeling approach used are (a) increased understanding of damage mechanisms, (b) improved design of experiments used in the selection process, and (c) better predictions at the well scale. This allows for a more-efficient and more-realistic prescreening of drilling fluids than traditional core-plug testing. Copyright © 2010 Society of Petroleum Engineers. Source


Steuber T.,The Petroleum Institute | Steuber T.,Nederlandse Aardolie Maatschappij | Schluter M.,Ruhr University Bochum
Earth-Science Reviews | Year: 2012

Numerical ages derived from strontium-isotope stratigraphy of 81 Late Turonian-Maastrichtian rudist localities from the Caribbean to Oman are used to establish stratigraphical ranges of readily identifiable taxa of rudist bivalves (Hippuritida). Based on these ranges, seven biozones for the Turonian-Maastrichtian of the central-eastern Mediterranean Tethys, and three biozones for the mid-Campanian-Maastrichtian of the Arabian Plate are established. Most of these are interval zones, each based on the first stratigraphical appearance of the nominal taxon. Micro-evolutionary patterns such as phyletic size increase have been demonstrated for some of the nominal species, as well as a trend of stratigraphical range expansion from the Turonian to the Maastrichtian. Implications of the geochronology of Late Cretaceous carbonate platforms for the biostratigraphy of other benthic fossils are briefly discussed.Three significant gaps in the stratigraphical distribution of rudist localities in the lower, middle, and uppermost Campanian, respectively, correlate with other records of sea-level change, indicating that they correspond to major eustatic sea-level falls. Only a limited number of rudist taxa is evaluated here, but the early and latest Campanian sea-level falls correspond to faunal turnover and extinction of characteristic associations of Late Cretaceous Hippuritida.The final extinction of the Hippuritida at the Cretaceous/Paleogene boundary is evaluated based on the available numerical ages of eighteen Late Maastrichtian localities. Eighteen genera are recorded at the six youngest localities, which thus have a species richness similar to older Late Cretaceous localities. While the ultimate cause for extinction of the Hippuritida must be evaluated on time scales beyond the resolution of strontium-isotope stratigraphy, the data set evaluated provides some insight into the pattern of their demise, which is considered to be the result of a high degree of endemism indicating limited exchange between increasingly isolated populations. This isolation was possibly related to the gradual decrease in the areal extent of Maastrichtian carbonate platforms due to a long-term cooling trend and local tectonics that affected carbonate platform growth in the regions studied. © 2012 Elsevier B.V. Source

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