W/O型微乳酸前置冲洗液的制备及其性能研究

页岩气水平井钻井过程中,因使用油基钻井液而产生的油基泥饼往往难以被冲洗,进而造成固井时顶替效率低、固井二界面胶结强度差。为解决上述难题,基于前人的研究成果,提出了以土酸、长链季铵盐C-223、聚氧乙烯醚Z-15等为主要原料配制出W/O型柴油—土酸微乳固井前置冲洗液的设计及配方,并通过室内实验对其冲洗性能开展评价及微观机理分析。研究结果表明:(1)以C-223∶Z-15=3∶2的复配比作为主表面活性剂、正丁醇∶正辛醇=1∶2的比例作为助表面活性剂、柴油∶土酸=5∶4的比例配置的微乳酸稳定性良好,与油基钻井液相容性好,冲洗效率可达96.86%;(2)微乳酸冲洗后的界面接触角发生明显改变,套管壁的水相润湿性大幅度提高,套管无明显腐蚀现象;(3)微乳酸在形成过程中,随酸液浓度的不断增加,体系呈现由澄清向混浊的相态变化,增溶酸量多且预留油空间大;(4)微乳酸中布朗运动的微粒平均粒径在21.2 nm左右;(5)土酸、柴油的单相横向弛豫时间均为单一的时间峰,且土酸的弛豫时间分布在柴油的弛豫时间分布范围之内,有利于二者溶合成稳定的微乳酸。结论认为,该冲洗液体系能有效提高第一、第二界面的润湿性,将亲油性界面转变为亲水性界面,有利于提高固井顶替效率和固井质量。

Preparation and properties of W/O microemulsified acid preflush

During the drilling of shale gas horizontal wells, oil-based mud cakes generated from the oil-based drilling fluid can be hardly flushed down, and consequently the displacement efficiency of cementing is low and the cementing strength of the second interface is poor. In view of this problem, a formula of cementing preflush of W/O diesel–soil acid microemulsion was designed. This preflush is mainly composed of soil acid, long-chain quaternary ammonium salt C-223, and polyoxyethylene ether Z-15. Then, its flushing performance was evaluated and its microscopic mechanisms were analyzed by means of laboratory experiments. And the following research results were obtained. First, the microemulsified acid, with C-223∶Z-15 = 3∶2 as the primary surfactant, n-butanol∶n-octanol = 1∶ 2 as the co-surfactant and diesel∶soil acid = 5∶4, is stable and well compatible with the oil-based drilling fluid, and its flushing efficiency is up to 96.86%. Second, after it is flushed by the microemulsified acid, the interface contact angle alters greatly, the water phase wettability on the casing wall is increased significantly and no obvious corrosion occurs on the casing. Third, during the formation of the microemulsified acid, the system changes from a clear state to a turbid state with the increase of acid concentration. Besides, the volume of solubility improving acid is high and the reserved oil space is large. Fourth, the average diameter of the micro-particles involved in the Brownian movement in the microemulsified acid is about 21.2 nm. Fifth, the single-phase lateral relaxation time of both soil acid and diesel is distributed in the form of a single time peak and the relaxation time of soil acid is distributed within the range of diesel, so it is favorable for them to dissolve into a stable microemusified acid. It is concluded that this flush system can improve the wettability of the first and second interfaces effectively, altering the oil wet interface into the water wet interface, and thus it is favorable for the improvement of cementing displacement efficiency and cementing quality.