Grunde Løvoll

Growth activity during fingering in a porous Hele-Shaw cell.

We present in this paper an experimental study of the invasion activity during unstable drainage in a two-dimensional random porous medium, when the (wetting) displaced fluid has a high viscosity with respect to that of the (nonwetting) displacing fluid, and for a range of almost two decades in capillary numbers corresponding to the transition between capillary and viscous fingering. We show that the invasion process takes place in an active zone within a characteristic screening length lambda from the tip of the most advanced finger. The invasion probability density is found to only depend on the distance z to the latter tip and to be independent of the value for the capillary number Ca. The mass density along the flow direction is related analytically to the invasion probability density, and the scaling with respect to the capillary number is consistent with a power law. Other quantities characteristic of the displacement process, such as the speed of the most advanced finger tip or the characteristic finger width, are also consistent with power laws of the capillary number. The link between the growth probability and the pressure field is studied analytically and an expression for the pressure in the defending fluid along the cluster is derived. The measured pressure is then compared with the corresponding simulated pressure field using this expression for the boundary condition on the cluster.

Influence of pore-scale disorder on viscous fingering during drainage

We study viscous fingering during drainage experiments in linear Hele-Shaw cells filled with a random porous medium. The central zone of the cell is found to be statistically more occupied than the average, and to have a lateral width of 40% of the system width, irrespectively of the capillary number Ca. A crossover length wf Ca−1 separates lower scales where the invaders fractal dimension D 1.83 is identical to capillary fingering, and larger scales where the dimension is found to be D 1.53. The lateral width and the large-scale dimension are lower than the results for Diffusion Limited Aggregation, but can be explained in terms of Dielectric Breakdown Model. Indeed, we show that when averaging over the quenched disorder in capillary thresholds, an effective law v (∇P)2 relates the average interface growth rate and the local pressure gradient.

COSSARC: Concept Selection for Shipping in the Arctic

Increased global demand for oil, gas and minerals combined with melting sea ice opens new opportunities for shipping companies, both in the form of new Arctic shipping routes and extended use of existing ones. It can be challenging for a ship owner to make informed decisions and plan for Arctic operations, as it requires complex techno-economical assessments of information that has a high degree of uncertainty. To aid ship-owners in making decisions for operation in the Arctic, DNV has developed a prototype decision support tool to assess strategic options: COSSARC — Concept Selection for Shipping in the Arctic. The tool integrates detailed models for ship performance both in ice and in open water with port and route alternatives to simulate travel time, fuel consumption, emissions and overall economics. The tool makes use of stochastic models for wave and ice conditions, but specific historical data or model data from climate models can also be taken as input. In this paper, the COSSARC tool is described, including a case study demonstrating the capabilities of the tool.Copyright