Drill-in Fluid Technology for Offshore Ultra-High Low-Permeability Reservoirs

The second member of the Huangliu Formation in the Dongfang F gas field in the western South China Sea is a reservoir with ultra-high temperature, low porosity and low permeability, the temperature which is as high as 205℃. The solid-free drilling fluid used in the previous drilling operations degraded at elevated temperatures, negatively affected field operations and caused water lock damage to the reservoir. To deal with this problem, a temperature-sensitive polymer viscosifier, a viscosity increasing filter loss reducer, and an ultra-high temperature modified starch were selected to formulate a new high temperature solid-free drill-in fluid. The three additives work synergistically in the new drilling fluid to resist the action of ultra-high temperature. The drill-in fluid is stable at 210℃, the filtration rate is less than 10 mL at 150℃, the permeability recovery of the core contaminated with the drill-in fluid is greater than 90%, and the filter cake is easy to break and remove. Meanwhile the selected supporting ultra-high temperature water lock inhibitor does not foam, and can reduce the gas-liquid surface tension and oil-liquid interfacial tension of the drill-in fluid filtrate to 27.7 mN/m and 5.9 mN/m respectively. The new ultra-high temperature solid-free drill-in fluid has been successfully applied on the X2 adjustment well in the Dongfang F gas field. During the operation, the viscosity and gel strength of the system were stable, the filtration rate was small, the hole diameter was regular, the operation was smooth, and the test and production effect was good. The skin factor of this well was only 0.13. The new ultra-high temperature solid-free drill-in fluid is of great significance for reducing the drilling and development risks of such offshore reservoirs and for ensuring the production capacity.