A new report from IOGP/IPIECA*, Guidance for computational fluid dynamics in well control (IOGP Report 596) offers advice on computer modeling of blowout modeling and mitigation. The Report discusses modeling of capping stack landing intervention, plume and gas dispersion analysis. Computational fluid dynamics is ‘a branch of fluid mechanics that uses numerical analysis and data structures to analyze and solve problems that involve fluid flows’. CFD is used in subsea well response pre-planning. The Report covers CFD workflows, models and factors that influence model reliability, quality checks and reporting requirements.
The report was prepared by the IOGP wells expert committee, set up in 2011 following the Deepwater Horizon disaster. Today the WEC is a ‘global voice of operators’ and an authority on the prevention and mitigation of high consequence well control events (blowouts to you and me). Oil country CFD practitioners from Boots & Coots, Siemens, Trendsetter Engineering and others provided input to the study.
The report advocates using a combination of models, sized to fit the engineering complexity of the problem and the acceptable level of risk. Four types of analysis are covered. Understanding the impact of a capping stack landing on a flowing well requires a model that predict how the stack behaves as it is progressively lowered until land-out. CFD is also used to model the behavior of the oil and gas plume in the water column as it interacts with ocean currents. Likewise analysis of the surface plume or ‘boil’ may be necessary as a blowout in shallow water may inhibit a vessel’s ability to work vertically above the source. CFD modeling has been successfully applied to non vertical slant-stack deployment.
The authors recommend the use of transient as opposed to steady state solvers. ‘Most capping stack landing simulations will use transient solvers [ which ] may be the only way to perform the simulation’. There are also situations where the blowout flow becomes a compressible flow problem particularly when flow exceeds Mach 0.7, another important consideration for the modeler.
In some extreme scenarios the flow in the well may be under-expanded when it reaches sea surface at which point it becomes increasingly complex, with shock and expansion wave structures. Such considerations need to be weighed against the ‘considerable effort’ required for compressible flow CFD.
Various CFD approaches are discussed, Volume of Fluid, Reynolds Average Navier Stokes, the role of spatial and temporal sampling and meshing paradigms. The 30 page report discusses in detail these and many other considerations as to what should be modeled and how. The report is, as it indicates, ‘guidance’. Unlike other work, notably from the IOGP’s geomatics committee, the report does not delve into the details of CFD modeling tools and code or their suitability for a particular task. No credits are given to the developers and vendors of the various illustrations of CFD tools in action.
* IOGP, the International Oil & Gas Producers Association. IPIECA, the International Petroleum Industry Environmental Conservation Association.
© Oil IT Journal - all rights reserved.