Drilling Fluid Technology for Reservoir Protection in Offshore Thermal Production Well

Thermal recovery is presently the main method of producing heavy oil in Bohai oilfeld where heavy oil reserves are abundant. Drilling fluid technology aimed at reservoir protection in thermal production well has been developed in such a special thermal development environment to make the full use of the nonconventional heavy oil characteristics and the high temperature thermal injection technique, and to cut the operation cost. The thermal production heavy oil well Lvda5-2N in Baohai oilfeld is taken as an example in this paper. In developing a modifed drilling fluid suitable for drilling a thermal production horizontal heavy oil well, the unique physical properties of the reservoir were taken into account and the potential formation damage factors-all kinds of sensitivities-were analyzed. Selection of additives with strong inhibitive capacity, evaluation of thermal degradation of additives, optimization of the mud weight, optimization of plugging agents and evaluation of reservoir protection have all been performed through laboratory experiments. The drilling fluid developed has strong inhibitive capacity and good compatibility with formation fluids. The degradation product of the drilling fluid at high temperature is black carbon. The permeability recovery of a core flooded with this drilling fluid is greater than 85%, indicating that the drilling fluid has good reservoir protection capacity. Using this drilling fluid, the cost was reduced by 40%.