琼东南盆地属于中孔低渗储层,储层易发生水化、水锁等伤害.当前区块系列井所用深水钻井液侵入损害类型、机理不明,且传统的钻井液伤害评价方法误差大,不能直观地量化损害程度.因此设计了以钻井液污染实验、扫描电子显微镜(scanning electron microscope,SEM)分析、计算机断层扫描(computed tomography,CT)结合的方式分析钻井液固相以及液相侵入损害储层的方法.结果表明,深水钻井液与地层水配伍性良好,储层水锁损害率处于19.8％～31.4％,液相侵入损害主要为水锁损害;岩心SEM扫描结果显示其孔隙连通性差,EDS测试结果中Ba2+、Ca2+含量较高,分析固相侵入损害主要由加重剂引起,且蒸馏水返排后岩心CT扫描结果显示孔隙度微幅上升表明固相堵塞很难通过自然返排的方式清除.于是通过研发降滤失剂和优选加重剂粒径配比的手段优化深水钻井液储层保护性能.根据理想充填理论,确定最佳配比为1 000目CaCO3、600目CaCO3和200目CaCO3的比例为5:11:9.优化后体系滤失量显著降低,固相颗粒中径在90 μm左右,滤饼致密程度明显提高;渗透率恢复值提高12.1％～19.68％,对该区块钻井液储层保护性能优化具有指导意义.
Comprehensive Analysis and Optimization of Drilling Fluid Invasion Damage in the Series Well Block of Qiongdongnan Basin
The Qiongdongnan Basin is categorized as a medium-porosity and low-permeability reservoir,making it susceptible to damages such as hydration and water blockage.The invasion damage type and mechanism caused by the deep water drilling fluid used in the current well series are not well understood.Additionally,traditional methods for assessing drilling fluid damage suffer from sig-nificant errors and an inability to quantitatively measure the extent of damage directly.Therefore,a method combining drilling fluid contamination experiments,scanning electron microscopy(SEM)analysis,and computed tomography(CT)was designed to analyze the solid-phase and liquid-phase invasion damage of drilling fluid to reservoirs.The results demonstrate that the compatibility between the deep water drilling fluid and formation water is good.The water blocking damage rate ranges from 19.8％to 31.4％,with water blockage being the primary liquid-phase invasion damage.SEM scanning of core samples reveals poor pore connectivity,and EDS tes-ting indicates elevated levels of Ba2+and Ca2+,suggesting that solid-phase invasion damage is mainly caused by weighting agents.Af-ter distillation water backflow,CT scanning of the core samples shows a slight increase in porosity,indicating that solid-phase plugging is not easily removed through natural backflow.To optimize the reservoir protection performance of the deep water drilling fluid,the de-velopment of a filtrate reducer and the optimization of weighting agent particle size distribution are proposed.According to the ideal fill-ing theory,the optimal ratio of 1 000 mesh CaCO3,600 mesh CaCO3,and 200 mesh CaCO3 is determined to be 5:11:9.Following op-timization,the filtrate loss of the system is significantly reduced,the median particle diameter of solid-phase particles is around 90μm,and the compactness of the filter cake is notably improved.The permeability recovery value increases by 12.1％to 19.68％,of-fering significant guidance for optimizing the reservoir protection performance of drilling fluid in this area.
formation damageCT scanningdrilling and completionwater-based drilling fluidregularity and degree
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