Albian to Turonian agglutinated foraminiferal assemblages of the Lower Saxony Cretaceous sub-basins – implications for sequence stratigraphy and paleoenvironmental interpretation

Albian to Turonian carbonate deposits at three different locations of the Lower Saxony Cretaceous and thereby of the European mid-Cretaceous epeiric shelf sea were investigated for their fossil agglutinated foraminiferal fauna. In this study, 71 samples from two quarries and three drill cores were treated with formic acid, which enabled the study of agglutinated foraminiferal assemblages even in highly lithified limestones. In total, 114 species were determined and classified as belonging to nine morphogroups. In general, four agglutinated foraminiferal assemblages are distinguished: (1) an uppermost Albian–lowermost Cenomanian assemblage from the Wunstorf drill cores, with the dominant taxa Bathysiphon spp., Nothia spp., Psammosphaera fusca, Reophax subfusiformis, Bulbobaculites problematicus, Tritaxia tricarinata, Flourensina intermedia, Vialovella frankei, Arenobulimina truncata, and Voloshinoides advenus; (2) a Cenomanian assemblage from the Baddeckenstedt quarry and Wunstorf drill cores, with Ammolagena clavata, Tritaxia tricarinata, Vialovella frankei, Arenobulimina truncata, and Voloshinoides advenus; (3) an assemblage related to the Cenomanian–Turonian Boundary Event in Wunstorf and Söhlde dominated by Bulbobaculites problematicus; and (4) a Turonian assemblage in the Wunstorf and Söhlde sections with high numbers of Ammolagena contorta, Repmanina charoides, Bulbobaculites problematicus, Gerochammina stanislawi, and Spiroplectammina navarroana. The latest Albian–earliest Cenomanian assemblage consists of tubular, globular, and elongate foraminiferal morphogroups which are typical for the low- to mid-latitude slope biofacies. All other assemblages are composed of elongate foraminiferal morphogroups with additionally globular forms in the proximal settings of Baddeckenstedt and Söhlde or flattened planispiral and streptospiral forms in more distal settings of Wunstorf. For these assemblages, a new agglutinated foraminiferal biofacies named “mid-latitude shelf biofacies” is proposed herein. Changes in the relative abundance of different morphogroups can often be referred to single features of depositional sequences. Furthermore, classical macro-bioevents, which are often depositional-related, of the Lower Saxony Cretaceous seem to have a micro-bioevent or acme equivalent of the agglutinated foraminiferal fauna.

The Influence of Main Factors on Deepwater Sediments

Western Siberia is a unique petroleum basin with exclusive geological objects. Those objects allow us to test various methods of sequence stratigraphy, systematization and evaluation approaches for reservoir characterization of deep-water sediments. Different methods have potential to decrease geological uncertainty and predict distribution and architecture of deep-water sandstone reservoir. There are many different parameters that could be achieved through analysis of clinoform complex. Trajectories of shelf break, volume of sediment supply and topography of basin influence on architecture of deep-water reservoir. Based on general principles of sequence stratigraphy, three main trajectories changes shelf break might be identified: transgression, normal regression and forced regression. And each of them has its own distinctive characteristics of deepwater reservoir. However, to properly assess the architecture of deepwater reservoir and potential of it, numerical characteristics are necessary. In our paper, previously described parameters were analyzed for identification perspective areas of Achimov formation in Western Siberia and estimation of geological uncertainty for unexplored areas. In 1996 Helland-Hansen W., Martinsen O.J. [5] described different types of shoreline trajectory. In 2002 Steel R.J., Olsen T. [11] adopted types of shoreline trajectory for identification of truncation termination. O. Catuneanu (2009) [1] summarize all information with implementation basis of sequence stratigraphy. Over the past decade, many geoscientists have used previously published researches to determine relationship between geometric structures of clinoforms and architecture of deep-water sediments and its reservoir quality. Significant amount of publications has allowed to form theoretical framework for the undersanding sedimentation process and geometrical configuration of clinoforms. However, there is still no relationship between sequence stratigraphy framework of clinoroms and reservoir quality and its uncertainty, which is necessary for new area evaluation.

The geological framework for Hvideklint, south-east Denmark, using glaciodynamic sequence stratigraphy

Glaciodynamic sequence stratigraphy provides a practical model for grouping and classifying complex geological data to aid interpretation of past climatic and environmental development in Quaternary successions. The principles of glaciodynamic sequence stratigraphy are applied here to summarise the complex glacial geological framework of Hvideklint on the island of Møn, south-east Denmark. The framework of the superimposed deformed Hvideklint is presented in a reconstructed geological cross-section of Hvideklint. For the construction of the architecture of the glaciotectonic complex, the interpretation of structures below sea level was based on a detailed new survey of the cliff section combined with construction of successive approximation balanced cross-sections. The new description is supported by drill hole data from the Jupiter database. Where chalk is not glaciotectonically deformed, the constructed depth to the top-chalk-surface is generally located about 30 m below sea level. In Hvideklint, thrust sheets with chalk are exposed 20 m above sea level, and the balanced cross-section constructions indicate that the décollement surface for a Hvideklint glaciotectonic complex is located about 80 m below sea level. Between the décollement level and the top of the complex, two or more thrust-fault flat-levels and connecting ramps add to the complex architecture of Hvideklint.

Insights on Water Sources for Injection Development of Large Oilfields in Southeast Iraq and Appraisal of Paleogene Shallow Water Source Formation

As many large oilfields in southeast Iraq entered the final stage of depletion development, water injection appears to be the most economical and technically feasible method to enhance oil recovery. Considering the shortage of freshwater and huge investment in seawater supply project, it is very important to appraise and optimize the favorable shallow water source formation to ensure sufficient water injection supply. Based on regional seismic, well data, core analysis and production test data, Paleogene sequence stratigraphy was determined by integrating well and seismic interpretation. Under framework of sequence stratigraphy, the sedimentary evolution of main water source formations was characterized. Subsequently, combined with core analysis and special logging data, the petrophysical characteristics of the formations were evaluated, and the volume of the regional water source was estimated. The research shows that: 1) Dammam limestone and Ghar sandstone are the two main Paleogene shallow water source formations; 2) Dammama developed carbonate shelf, from southwest to northeast, the formation thickness decrease with the sedimentary evolved from inner slope to out slope. Expose and dissolution increased the porosity which is favorable for water storage; 3) Ghar developed alluvial and delta, from southwest to northeast, the formation thickness increase with the sedimentary evolved from alluvial fan, alluvial river to delta. Delta developed abundant and unconsolidated sandstone with high porosity and permeability; 4) The water sample analysis showed the water belong to Cacl2 type with total dissolved solids greater than 250,000 ppm which indicated well sealing condition. Production tests have shown that both Dammam and Ghar have a water supply capacity of 8,000-10,000 barrels per day. The preliminary evaluation of the water volume in the Ghar area can up to 1 trillion barrels. Paleogene shallow water formation is currently the most realistic and economic water source choice for water injection to enhance oil recovery in large oil fields in southeastern Iraq. Dammam formation and Ghar formation of Paleogene had the characteristics of shallow buried, good water quality and sufficient reserves. Thus, they are the preferred target water source formations for injection development of large oilfields in southeastern Iraq.