Wells drilled in the piedmont area in Kyche,Xinjiang have to penetrate thick salt and gypsum formations,which have complex geology,ultrahigh pressure saltwater with poor distribution patterns in length and breadth,highly varied formation pressures that are difficult to predict.Drilling fluid properties inevitably become deteriorated when high pressure saltwater cut is encountered.The deterioration of drilling fluid properties in turn results in frequent blowout,lost circulation,or pipe sticking,significantly affecting the progress of drilling operation.To resolve these problems,the entrapment nature of the high pressure saltwater and previous drilling practices were analyzed based on the drilling behavior in high pressure saltwater drilling.In laboratory study,simulating experiments were conducted to determine the limits of saltwater invasion to drilling fluid.Based on the research,a new technique has been developed to minimize the effects of high pressure saltwater.In this technique,the high pressure saltwater is allowed to go into the drilling fluid in annular space in a controlled manner by regulating choke valves and the flow rate of drilling fluid.Each time the volume of water allowed into the well should not exceed 10％ of the volume of the annular space.Many times of saltwater draining reduces formation pressure.In this way,the downhole troubles resulted from saltwater invasion can be minimized,thus mitigating the drilling difficulties resulted from the piedmont ultra-deep ultra-high pressure saltwater.Field application of this technique has shown that,using sound method to drain saltwater under controlled pressure is able to reduce saltwater formation pressure.A balance point between water kick and mud loss should be found to ensure the safety of well control.%库车山前深部巨厚盐膏层地质特征复杂,层间超高压盐水普遍发育,纵横向规律性差,地层压力变化大,预测难度高.盐膏层钻井过程中超高压盐水侵入井筒后,钻井液性能恶化,导致喷、漏、卡等复杂事故频发,严重影响安全快速钻井.结合超高压盐水层钻井特征,通过分析超高压盐水赋存的圈闭特点及实钻情况,在钻井液的盐水污染容量限实验模拟和评价的基础上,开展了超高压盐水层控压排水技术的探索与实践,形成了控压排水配套新技术,通过控制节流阀调节井口回压和钻井液排量等手段,让地层盐水按一定比例均匀侵入到环空钻井液中,单次放水量不超过环空钻井液量的10％,多次放出盐水,降低高压盐水层的地层压力系数.解决了库车山前超深超高压盐水层安全钻井难题.现场试验表明,采取合理的控压排水方法能够降低盐水层的压力,在溢流与井漏的矛盾中找到压力平衡点,有利于井控安全的井筒状态.
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