Experimental lost circulation and performance simulation studies of 60/40, 70/30, 80/20 and 90/10 OBMs

Master's thesis in Petroleum engineeringLost circulation has been and still is a cost factor for the drilling industry. By using lost circulation material in drilling fluid, it is possible to mitigate unnecessary loss of drilling fluid. This thesis presents characterization, performance simulation and lost circulation performances of four types of oil based mud systems. These are of 60/40, 70/30, 80/20 and 90/10 oil-water ratio. The characterization part deals with rheology measurement and modelling at various temperatures, and is based on direct experimental measurements. The performance simulation study deals with the hole cleaning efficiency of the drilling fluids. The lost circulation part deals with the bridging performance of the drilling fluids at various simulated fracture widths. For the experiment, 13.82 lb/bbl LC-lube (graphite) was used as lost circulation material. The results show that particle size distribution with a D50 at or higher than the fracture width gives a better performance in terms of bridge strength. Similar results have also been documented in previous works. For the studied mud systems, three rheological parameters also show good correlation with the bridge collapse pressure