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Zanganeh M.N.,Xodus Group | Kraaijevanger J.F.B.M.,Royal Dutch Shell | Buurman H.W.,Royal Dutch Shell | Jansen J.D.,Technical University of Delft | Rossen W.R.,Technical University of Delft
Computational Geosciences | Year: 2014

We apply adjoint-based optimization to a surfactant-alternating gas foam process using a linear foam model introducing gradual changes in gas mobility and a nonlinear foam model giving abrupt changes in gas mobility as function of oil and water saturations and surfactant concentration. For the linear foam model, the objective function is a relatively smooth function of the switching time. For the nonlinear foam model, the objective function exhibits many small-scale fluctuations. As a result, a gradient-based optimization routine could have difficulty finding the optimal switching time. For the nonlinear foam model, extremely small time steps were required in the forward integration to converge to an accurate solution to the semi-discrete (discretized in space, continuous in time) problem. The semi-discrete solution still had strong oscillations in gridblock properties associated with the steep front moving through the reservoir. In addition, an extraordinarily tight tolerance was required in the backward integration to obtain accurate adjoints. We believe the small-scale oscillations in the objective function result from the large oscillations in gridblock properties associated with the front moving through the reservoir. Other EOR processes, including surfactant EOR and near-miscible flooding, have similar sharp changes and may present similar challenges to gradient-based optimization. © 2014 Springer International Publishing Switzerland. Source


Gooding S.,UTEC Geomarine | Allan P.,UTEC Geomarine | Errington P.,Cathie Associates | Hunt J.,Xodus Group
Frontiers in Offshore Geotechnics III - 3rd International Symposium on Frontiers in Offshore Geotechnics, ISFOG 2015 | Year: 2015

In the past, a ‘burial protection index’was used to provide a framework for selecting appropriate burial depths; however, this approach was relatively crude and did not take into account the probability of threats. This paper presents the results of a research study funded by the developers of offshore windfarms to provide a probabilistic framework for selecting a depth of lowering with an acceptable degree of risk. This can then lead to significant savings in installation costs. The methodology presented provides models for penetration of typical ship anchors and fishing gear into the seabed, and assesses the probability of them being deployed on a cable route. This then allows a statistical assessment of the relative benefits of increasing depth of lowering, and reducing probability of damage to be made. Thus an informed decision can be made when selecting appropriate depths. © 2015 Taylor & Francis Group, London. Source


Stephenson S.,Xodus Group
Acoustics Bulletin | Year: 2013

The combination of directivity and noise propagation effects which can potentially lead to high levels of noise at distances away from the exhaust stack is examined. Exhaust stacks, and other open ducts, have a relatively high degree of directivity. The sound power level of a stack can either be calculated or measured. There are several methods to do this, but each method will depend on the type of project. ISO 10494 presents a method for determining the sound power level of a stack exit. The standard is based on taking measurements at a defined angle of 20° above and below the lip of the stack (horizontal axis), integrating over an assumed surface area and then summing the upper and lower surfaces to derive a sound power level. Once the sound power level of the stack has been determined, it is then necessary to apply corrections to this level to account for directivity, as seen from the receiver position. Once this imission angle has been determined, it is then possible to attribute the correct directivity corrections to the stack exit sound power level. Source


Neill S.P.,Bangor University | Lewis M.J.,Bangor University | Hashemi M.R.,Bangor University | Slater E.,British Oceanographic Data Center | And 2 more authors.
Applied Energy | Year: 2014

The waters surrounding the Orkney archipelago in the north of Scotland are one of the key regions in the world suitable for exploitation of both wave and tidal energy resources. Accordingly, Orkney waters are currently host to 1.08. GW of UK Crown Estate leased wave and tidal energy projects, with a further 0.5. GW leased in the southern part of the adjacent Pentland Firth. Although several wave resource models exist of the region, most of these models are commercial, and hence the results not publicly available, or have insufficient spatial/temporal resolution to accurately quantify the wave power resource of the region. In particular, no study has satisfactorily resolved the inter-annual and inter-seasonal variability of the wave resource around Orkney. Here, the SWAN wave model was run at high resolution on a high performance computing system, quantifying the Orkney wave power resource over a ten year period (2003-2012), a decade which witnessed considerable inter-annual variability in the wave climate. The results of the validated wave model demonstrate that there is considerable variability of the wave resource surrounding Orkney, with an extended winter (December-January-February-March, DJFM) mean wave power ranging from 10 to 25. kW/m over the decade of our study. Further, the results demonstrate that there is considerably less uncertainty (30%) in the high energy region to the west of Orkney during winter months, in contrast to much greater uncertainty (60%) in the lower energy region to the east of Orkney. The DJFM wave resource to the west of Orkney correlated well with the DJFM North Atlantic Oscillation (NAO). Although a longer simulated time period would be required to fully resolve inter-decadal variability, these preliminary results demonstrate that due to considerable inter-annual variability in the NAO, it is important to carefully consider the time period used to quantify the wave power resource of Orkney, or regions with similar exposure to the North Atlantic. Finally, our study reveals that there is significantly less variability in the practical wave power resource, since much of the variability in the theoretical resource is contained within relatively few extreme events, when a wave device enters survival mode. © 2014 The Authors. Source


Tissen J.,Xodus Group | Buchan I.,GDP Suez e and P UK
Offshore Engineer | Year: 2014

Experts inform that a new approach to manage environmental issues aims at delivering increased alignment, engagement, transparency, and assurance in relation to managing environmental issues at the Cygnus gas field in he southern North Sea. This approach offers a better alignment with other business objectives and increased confidence in compliance with the existing existing legislative framework. It is being applied by GDF SUEZ E&P UK for the drilling program and operational phase of the southern North Sea Cygnus gas development project. The approach plays a key role in maximizing the benefits of prescriptive and goal setting regulation. This is done by creating a platform for open dialogue around important issues, which aims to achieve full integration of environmental management into the operation and maintenance of offshore exploration and production operations. Source

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