International audienceThe development of the Alpine mountain belt has been governed by the convergence of the African and European plates since the Late Cretaceous. During the Cenozoic, this orogeny was accompanied with two major kinds of intraplate deformation in the NW-European foreland: (1) the European Cenozoic Rift System (ECRIS), a left-lateral transtensional wrench zone striking NNE-SSW between the western Mediterranean Sea and the Bohemian Massif; (2) long-wavelength lithospheric folds striking NE and located between the Alpine front and the North Sea. The present-day geometry of the European crust comprises the signatures of these two events superimposed on all preceding ones. In order to better define the processes and causes of each event, we identify and separate their respective geometrical signatures on depth maps of the pre-Mesozoic basement and of the Moho. We derive the respective timing of rifting and folding from sedimentary accumulation curves computed for selected locations of the Upper Rhine Graben. From this geometrical and chronological separation, we infer that the ECRIS developed mostly from 37 to 17 Ma, in response to north-directed impingement of Adria into the European plate. Lithospheric folds developed between 17 and 0 Ma, after the azimuth of relative displacement between Adria and Europe turned counter-clockwise to NW SE. The geometry of these folds (wavelength = 270 km; amplitude = 1,500 m) is consistent with the geometry, as predicted by analogue and numerical models, of buckle folds produced by horizontal shortening of the whole lithosphere. The development of the folds resulted in ca. 1,000 m of rock uplift along the hinge lines of the anticlines (Burgundy Swabian Jura and Normandy Vogelsberg) and ca. 500 m of rock subsidence along the hinge line of the intervening syncline (Sologne Franconian Basin). The grabens of the ECRIS were tilted by the development of the folds, and their rift-related sedimentary infill was reduced on anticlines, while sedimentary accumulation was enhanced in synclines. We interpret the occurrence of Miocene volcanic activity and of topographic highs, and the basement and Moho configurations in the Vosges Black Forest area and in the Rhenish Massif as interference patterns between linear lithospheric anticlines and linear grabens, rather than as signatures of asthenospheric plumes

A B S T R A C TOutcrop studies reveal a common occurrence of tabular zones of significantlyincreased fracture intensity affecting otherwise well-lithified rocks. These zones, called fracture corridors, can have a profound effect on multi-phase fluid flow in the subsurface. Using standard geo-modelling tools, it is possible to generate 3D realizations of reservoirs that contain distributions of such fracture corridors that are consistent with observations, including the vertical frequency in pseudo-wells inserted into the model at random locations. These models can generate the inputs to flow simulation. The approach adopted here is to run the flow simulations in a single-porosity representation where the flow effects of fractures are upscaled into equivalent cellbased properties, preserving a clear spatial relationship between the input geology and the resulting cellular model. The simulated reservoir performance outcomes are very similar to those seen in real oilfields: extreme variability between wells, early water breakthrough, disappointing recoveries and patchy saturation distributions. Thus, a model based on fracture corridors can provide an explanation for the observed flow performance of a suitable field. However, the use of seismics to identify fracture corridors is not an easy task. New work is needed to predict the seismic responses of fracture corridor systems to be able to judge whether it is likely that we can robustly detect and characterize these flow-significant features adequately.

An enhanced oil recovery (EOR) pilot was conducted by Chevron North Sea Limited ("Chevron") at the Captain Field in the UK North Sea between 2011 and 2013. Results from the polymer injection are presented along with an assessment of incremental oil recovery. The polymer solution was selected and qualified using a combination of laboratory and yard tests to determine optimum specifications for injection. The selected polymer was initially tested in an injectivity test in 2010, followed by continuous polymer injection in 2011, after establishing a waterflood baseline. Continuous polymer injection was terminated in 2013 due to injectivity decline associated with polymer emulsion injection. An unambiguous response from the reservoir was observed with a significant uplift in oil production. The three mechanisms of a successful polymer flood were observed and evaluated: (1) acceleration of oil production, (2) incremental oil production due to improved polymer sweep, and (3) water production and injection minimization. Our results demonstrate that waterflood recovery can be accelerated by polymer flooding. Secondly, incremental oil was produced due to increased volumetric sweep by changing the displacing phase fluid mobility with the viscosified polymer. Finally, the reduction in water production translates into reduced water handling and thereby lower operating costs. Before and during the pilot chemical injection, production logging tools were run in the injector and producer to measure their respective outflow and inflow phase profiles along the horizontal completions. These logs confirmed that polymer promotes crossflow to make injection rates more uniform along the wellbore. We also drilled a post-polymer observation well in the swept zone between the pilot wells. Logs from this well established remaining oil saturations to polymer that we used to confirm our calculations for polymer flood volumetric sweep. The post-polymer flood oil saturations confirmed the performance of the polymer flood. We show a full suite of surveillance data and its use in quantitative interpretation. We also show innovative uses of the surveillance data in our interpretation methods. The results prove the subsurface and operational success of polymer flooding a heavy oil reservoir with horizontal wells, even in a harsh offshore environment such as the UK North Sea.

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