Espen Birger Raknes

Relief Well Drilling Using Surface Seismic While Drilling

Magnetic survey methods are used to locate the blowing wellbore when drilling a relief well. If no magnetic material is present in the openhole section of the blowing well, the last set casing shoe is the deepest possible intersection point. A deeper intersection point will increase the hydrostatic head, increase the frictional pressure drop and allow a lower density kill fluid to be used. A new potential method called surface seismic while drilling (SSWD), could make it possible to intersect the blowing well below the casing shoe. This method is not dependent of any casing or steel tubular present in the well to identify the relative wellbore positions. The SSWD method is based on a surface seismic source generator and a receiver array located on the seabed. Preliminary simulations indicate that it is possible to locate the wellpaths of the two wells on the seismic data. This method will allow real-time seismic monitoring of the well paths without interfering with the drilling operation. This can allow for more precise relative wellbore positioning. To investigate the benefits of a deeper intersection, a simulation model was prepared. A vertical offshore well consisting of 2000 meters of casing, and a 1000-meter openhole section were used. The well was killed dynamically by circulating seawater at high rates into the blowing wellbore. Compared to a casing shoe intersection, simulations show that a bottom hole intersection would reduce the flow rate and pump pressure by approximately 48% and 55%, respectively. The required kill mud weight was reduced by 24 %. The seismic method may also be used in conventional well killing operation to provide additional information of the position of the two wellbores and potentially reduce the time needed to drill the relief well. This paper presents the SSWD method and the potential improvements in relief well drilling and well killing. Introduction A blowout is by far the most severe consequence of loss in well control. Because of the tremendous powers at play, a blowout can rapidly become a disastrous event. Large volumes of hydrocarbons and toxic gasses can be released to the surface, potentially causing huge environmental damage and put human lives at jeopardy. Considering the resources required to stop the blowout, penalties imposed on the liable, reduction in share values, lost hydrocarbon resources, and destroyed reputation of companies involved, a blowout often becomes a dramatic and costly ordeal. If loss in well control escalates to a blowout, it is important that the well is brought under control fast and safely, and in a terminal manner. This might require a relief well to be drilled to intersect the blowing well at a certain depth, and kill it by pumping liquid into the blowing wellbore until overbalance is retained. Modern relief wells are drilled to directly intersect the blowing wellbore. The target is often smaller than 10 inches and the depth can be several thousand meters. Conventional surveying techniques do not offer the accuracy needed to accomplish this, and for that reason ranging tools that home in on steel tubular in the blowing well is used once the relief well is close enough. This often means that the last set casing shoe is the deepest point available for a relief well. If an extended openhole section

Towards fine-grained dynamic tuning of HPC applications on modern multi-core architectures

There is a consensus that exascale systems should operate within a power envelope of 20MW. Consequently, energy conservation is still considered as the most crucial constraint if such systems are to be realized. So far, most research on this topic focused on strategies such as power capping and dynamic power management. Although these approaches can reduce power consumption, we believe that they might not be sufficient to reach the exascale energy-efficiency goals. Hence, we aim to adopt techniques from embedded systems, where energy-efficiency has always been the fundamental objective. A successful energy-saving technique used in embedded systems is to integrate fine-grained autotuning with dynamic voltage and frequency scaling. In this paper, we apply a similar technique to a real-world HPC application. Our experimental results on a HPC cluster indicate that such an approach saves up to 20% of energy compared to the baseline configuration, with negligible performance loss.

Source Wavefield Reconstruction for Large-scale 3D Elastic Full-waveform Inversion

In elastic full-waveform inversion, the medium parameters are updated iteratively by incrementing them with the derivatives of the misfit functional with respect to each of the medium parameters. The efficient implementation of the derivative computations require large amount of computer memory storage. The large requirements in terms of storage is one the main barriers for the application of elastic full-waveform inversion to large scale 3D problems. In this paper, we propose and test a strategy based on reverse-time wavefield reconstruction using the Kirchhoff integral that effectively reduces the storage requirements, at the cost of a factor of two increase in the computational runtime.