Assessment of zonal isolation risk to changes in design parameters

The Well Containment Screening Tool (WCST) focuses on well integrity evaluation after well control incident. The WCST favors a greater wall thickness and, hence, a narrower cementing annulus, potentially increasing the risk of cement loss. We develop a structured and systematic physical model to simulate and track formation damage. A simulation process is conducted to assess the sensitivity of zonal isolation risk as design parameters are changed. In this paper, a physical model involving wellbore, casing and cement fluid is developed to understand the interaction between cement fluid and the formation. Two failure metrics are defined that provide a comprehensive understanding of the zonal isolation risk. Quantitative risk assessment is implemented with Monte Carlo simulation to assess the risk of zonal isolation problems when design parameters are changed. Models of production casing and intermediate casing are studied to verify the generality of this analysis. Taking both failure metrics into consideration, sensitivity analysis for models of production casing and intermediate casing present common observations regarding changes of design parameters. Our analysis suggests that minor increases (within 0.05”) in casing thickness, due to increased outer diameter, has little influence on the risk of cement loss, as does slight decreases in mean open hole diameter (within 0.05”). To verify the generality of this approach, in addition to casing and wellbore parameters, the sensitivity to cement fluid flow rate is analyzed. We find that risk is not significantly affected by small increase of flowrate (e.g. from 40 to 100 gpm). This paper applies a novel quantitative risk analysis to assess the influence of different design parameters on zonal isolation problems. This approach, if well implemented, can help to assess the impact of changes in design parameters (e.g., casing length and depth, mud density and cement fluid density, etc.) on drilling safety. It can also help to inform drilling decisions by providing forecasts of zonal isolation risk for particular geological condition.Mechanical Engineerin

Computer simulation for tube-making by the cold roll-forming process

The conventional design of forming rolls depends heavily on the individual skill of roll designers which is based on intuition and knowledge gained from previous work. Roll design is normally a trial an error procedure, however with the progress of computer technology, CAD/CAM systems for the cold roll-forming industry have been developed. Generally, however, these CAD systems can only provide a flower pattern based on the knowledge obtained from previously successful flower patterns. In the production of ERW (Electric Resistance Welded) tube and pipe, the need for a theoretical simulation of the roll-forming process, which can not only predict the occurrence of the edge buckling but also obtain the optimum forming condition, has been recognised. A new simulation system named "CADFORM" has been devised that can carry out the consistent forming simulation for this tube-making process. The CADFORM system applied an elastic-plastic stress-strain analysis and evaluate edge buckling by using a simplified model of the forming process. The results can also be visualised graphically. The calculated longitudinal strain is obtained by considering the deformation of lateral elements and takes into account the reduction in strains due to the fin-pass roll. These calculated strains correspond quite well with the experimental results. Using the calculated strains, the stresses in the strip can be estimated. The addition of the fin-pass roll reduction significantly reduces the longitudinal compressive stress and therefore effectively suppresses edge buckling. If the calculated longitudinal stress is controlled, by altering the forming flower pattern so it does not exceed the buckling stress within the material, then the occurrence of edge buckling can be avoided. CADFORM predicts the occurrence of edge buckling of the strip in tube-making and uses this information to suggest an appropriate flower pattern and forming conditions which will suppress the occurrence of the edge buckling

Engineering Object-Oriented Semantics Using Graph Transformations

In this paper we describe the application of the theory of graph transformations to the practise of language design. We have defined the semantics of a small but realistic object-oriented language (called TAAL) by mapping the language constructs to graphs and their operational semantics to graph transformation rules. In the process we establish a mapping between UML models and graphs. TAAL was developed for the purpose of this paper, as an extensive case study in engineering object-oriented language semantics using graph transformation. It incorporates the basic aspects of many commonly used object-oriented programming languages: apart from essential imperative programming constructs, it includes inheritance, object creation and method overriding. The language specification is based on a number of meta-models written in UML. Both the static and dynamic semantics are defined using graph rewriting rules. In the course of the case study, we have built an Eclipse plug-in that automatically transforms arbitrary TAAL programs into graphs, in a graph format readable by another tool. This second tool is called Groove, and it is able to execute graph transformations. By combining both tools we are able to visually simulate the execution of any TAAL program

Evaluating the Impact of Critical Factors in Agile Continuous Delivery Process: A System Dynamics Approach

Continuous Delivery is aimed at the frequent delivery of good quality software in a speedy, reliable and efficient fashion – with strong emphasis on automation and team collaboration. However, even with this new paradigm, repeatability of project outcome is still not guaranteed: project performance varies due to the various interacting and inter-related factors in the Continuous Delivery 'system'. This paper presents results from the investigation of various factors, in particular agile practices, on the quality of the developed software in the Continuous Delivery process. Results show that customer involvement and the cognitive ability of the QA have the most significant individual effects on the quality of software in continuous delivery

Hunting for CDF Multi-Muon "Ghost" Events at Collider and Fixed-Target Experiments

In 2008 the CDF collaboration discovered a large excess of events containing two or more muons, at least one of which seemed to have been produced outside the beam pipe. We investigate whether similar "ghost" events could (and should) have been seen in already completed experiments. The CDF di-muon data can be reproduced by a simple model where a relatively light X particle undergoes four-body decay. This model predicts a large number of ghost events in Fermilab fixed-target experiments E772, E789 and E866, applying the cuts optimized for analyses of Drell-Yan events. A correct description of events with more than two muons requires a more complicated model, where two X particles are produced from a very broad resonance Y. This model can be tested in fixed-target experiments only if the cut on the angles, or rapidities, of the muons can be relaxed. Either way, the UA1 experiment at the CERN ppbar collider should have observed O(100) ghost events.Comment: 15 pages, 9 figure

Synoptic reorganization of atmospheric flow during the Last Glacial Maximum

A coupled global atmosphere–ocean model of intermediate complexity is used to study the influence of glacial boundary conditions on the atmospheric circulation during the Last Glacial Maximum in a systematical manner. A web of atmospheric interactions is disentangled, which involves changes in the meridional temperature gradient and an associated modulation of the atmospheric baroclinicity. This in turn drives anomalous transient eddy momentum fluxes that feed back onto the zonal mean circulation. Moreover, the modified transient activity (weakened in the North Pacific and strengthened in the North Atlantic) leads to a meridional reorganization of the atmospheric heat transport, thereby feeding back onto the meridional temperature structure. Furthermore, positive barotropic conversion and baroclinic production rates over the Laurentide ice sheets and the far eastern North Pacific have the tendency to decelerate the westerlies, thereby feeding back to the stationary wave changes triggered by orographic forcing

Numerical prediction and mitigation of slugging problems in deepwater pipeline-riser systems

Slugging involves pressure and flowrate fluctuations and poses a major threat to optimising oil production from deepwater reserves. Typical production loss could be as high as 50%, affecting the ability to meet growing energy demand. This work is based on numerical simulation using OLGA (OiL and GAs) a one- dimensional and two-fluid equations based commercial tool for the simulation and analysis of a typical field case study in West Africa. Numerical model was adopted for the field case. Based on the field report, Flow Loop X1 consisted of well X1 and well X2, (where X1 is the well at the inlet and X2 is the well connected from the manifold (MF)). Slugging was experienced at Flow Loop X1 at 3000 BoPD; 4MMScf/D and 3%W/C. This study investigated the conditions causing the slugging and the liquid and gas phase behaviour at the period slugging occurred. The simulation work involved modelling the boundary conditions (heat transfer, ambient temperature, mass flowrate e.t.c). Also critical was the modelling of the piping diameter, pipe length, wall thickness and wall type material to reflect the field geometry. Work on flow regime transition chart showed that slugging became more significant from 30% water-cut, especially at the riser base for a downward inclined flow on the pipeline- riser system. Studies on diameter effect showed that increasing diameter from 8” – 32” gave rise to a drop in Usg (superficial velocity gas) and possible accumulation of liquids on the riser- base position and hence a tendency for slugging formation. Depth effect study showed that increasing depth gave rise to increasing pressure fluctuation, especially at the riser- base. Studies on the Self-Lift slug mitigation approach showed that reducing the internal diameter of the Self-lift by-pass pipe was effective in mitigating slug flow. S3 (Slug suppression system) was also investigated for deepwater scenario, with the results indicating a production benefit of 12.5%. In summary, the work done identified water-cut region where pipeline-riser systems become more susceptible to slugging. Also, two key up-coming slug mitigation strategies were studied and their performance evaluated in-view of production enhancement