用于滩坝砂低渗透油藏的复合盐低伤害钻井液技术

针对胜利油田滨425区块滩坝砂低渗透油藏低采油速度、低采出程度、低含水的“三低”开发阶段中的水敏、水锁损害为主的特点，结合渗流机理、储层保护原理，优选钻井液关键处理剂，通过“协同增效”作用，研发出一种复合盐低伤害钻井液体系。利用高分辨率CT扫描、扫描电镜SEM等微观评价手段，定量评价、分析了该体系对储层天然岩心的伤害程度和低伤害机制。结果表明，该体系封堵性能强，能最大程度地减少钻井液固相颗粒和滤液进入储层，滤液表面张力低至26.2 mN/m，水锁损害小，渗透率恢复值大于90%。复合盐低伤害钻井液在滨425区块应用了26口井，平均机械钻速为22.80 m/h，平均钻井周期提前11.23 d，有效减少了钻井液对低渗储层的浸泡时间。该体系油气层保护效果显著，所钻新井表皮系数为负数，新井不需要压裂就可直接常规射孔投产，不仅减少新井投产费用，而且增产效果明显，为低渗透油气藏的高效、经济开发提供了一种新方法。 

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.