Low Damage Compound Salt Drilling Fluid for Low Permeability Beach Bar Sand Reservoirs

A low damaging drilling fluid formulated with compound salts has been developed to deal with production problems such as water sensitivity and water block taken place in production stage of "low production rate, low recovery factor and low water-cut" of the low permeability beach bar sand reservoirs in Block Bin425 in Shengli Oilfield. The development of the drilling fluid, based on the mechanisms of flow in porous media and reservoir protection, involved the optimization of key mud additives that functions synergistically in drilling fluid. The drilling fluid was evaluated quantitatively and analyzed with high-resolution CT and SEM for its damage to the permeability of cores taken from the reservoirs and the mechanisms of low damaging. It is concluded that the drilling fluid has high plugging capacity, being able to minimize the invasion of mud solids and filtrates into reservoirs. The surface tension of the filtrates is 26.2 mN/m, indicating low water block of the filtrates. Percent recovery of permeability of cores is greater than 90%. The low damaging compound salt drilling fluid has been successfully used on 26 wells in the Block Bin425, with average ROP of 22.80 m/h, and average drilling time saved by 11.23 d which meant that time for the wellbore to be contacted with drilling fluid was shortened. This drilling fluid is efficient in reservoir protection; the skin factors of the wall of newly drilled borehole were negative, meaning the new wells can be produced without the need for fracturing. This not only reduces the cost for a new well to begin production, it also enhanced the oil recovery of the well. It provides a new way of efficiently and economically developing reservoirs with low permeability.