Study On Water-Based Drilling Fluid System For Horizontal Well Of Daqing Oil Field

The currently used drilling fluids in horizontal wells of Daqing Oil Field are mainly oil-based drilling fluids, which are high cost and have a poor solid carry capacity and may result in environmental problems because of the ineffective dispose of drilling waste. Therefore, a study is commenced to develop a water-based drilling fluid system (MEG drilling fluid system) that can satisfy the needs of horizontal well of Daqing Oil Field. The study begins with the compare of shale inhibition abilities between methyl glucoside(MEG) and oil-based emulsion-drill ing fluid and brine waters. Then, the environmental effect of MEG is analyzed. Afterwards, the compatibility of MEG and the additives is tested and the optimal MEG drilling fluid composition is got through trials and errors. The laboratory experiment shows that MEG drilling fluid/shale interface can provide a semipermeable membrane like the one provides by oil-based drilling fluid/shale interface. Under the function of semipermeable membrane, a reasonable adjust of the drilling fluid activity to be less than formation water activity will transfer water from formation to drilling fluid because of the existence of osmosis pressure. This will prevent or reduce the negtive effect resulted from the transfer of drilling fluid to formation and benefit the wellbore stability. The reaction process between MEG drilling fluid and formation may include diffusion, absorption and osmosis. These three reactions play different roles during the whole process, but entangle to maintain the wellbore stability. Because the reactions are similar to those of oil-based drilling fluid, some researchers name the MEG drilling fluid as pseudo oil-based drilling fluid. The compare between MEG drilling fluid system and some commonly used water-based drilling fluids systems indicates that MEG drilling fluid system has evident advantages in cave in preventing, lubricity, solid carry capacity and formation damage controlling. The MEG drillling fluid system developed in laboratory is tested in Daqing Oil Field. The laboratory experiment and on-site trial show that the MEG drilling fluid system is stable in rheological property and can carry cuttings and clean wellbore effectively. Its lubricity is excellent and it can stabilize the borehole wall in a good condition. The MEG drilling fluid also can control formation damage and do no harm to environment. The above proves that MEG drilling fluid system is a qualified one to horizontal well of Daqing Oil Field.