重力辅助井眼隔离在电缆取样作业中的应用低渗透率案例研究

G. Garcia, H. Dumont, T. Akindipe
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引用次数: 0

摘要

在阿拉斯加北坡的勘探中,一个常见的挑战是,当近井损害是由水基泥浆(WBM)造成时,如何对低渗透地层进行评价。本研究描述了现有技术在这些具有挑战性的条件下有效收集高质量碳氢化合物样品的新应用。该概念通过电缆地层测试器在一口井中进行了测试,该井的WBM造成了严重的地层损害。讨论了程序和所用硬件,并给出了该技术有效性的实例。由于流动性比不利,在低渗透岩石中尝试采油时,WBM滤液倾向于优先移动,导致电缆地层测试作业期间的站站时间较长。为了克服这一挑战,使用3D径向探头将目标相位移动到更靠近井筒的位置,从而使目标采样间隔承受较大的压降。一旦在流体分析仪中检测到碳氢化合物,就收回三维径向探头,重新定位管柱,用跨式封隔器组合覆盖同一段。跨式封隔器为恢复流动周期后的滤液和油气分离提供了井筒环空空间。当在流体分析仪中再次看到碳氢化合物时,同时使用双泵流来收集它们并丢弃滤液。3D径向探头和跨式封隔器的结合有助于取代泥浆滤液,将目标碳氢化合物带入井筒,并能够收集高质量的分离样品。在一个采样站使用3D径向探头进行泵送后,观察到的最大碳氢化合物分数为5%。当跨式封隔器位于同一井段时,流体分析仪显示,由于现有的密度对比,工具心轴和井筒之间的环空空间流速较低,从而使碳氢化合物从滤液中分离出来。当井筒中的碳氢化合物到达跨式封隔器入口时,下部泵将大部分滤液以高速向下流动。同时,碳氢化合物被“撇去”,并使用上部泵以更低的速率放置在样品容器中。实验室结果证实,传统取样方法采集的样品含有95%的滤液,而我们的技术采集的样品含有90%的碳氢化合物。使用单入口、电缆跨式封隔器和双泵作用的井下流体分离在文献中尚未发现。电缆地层测试的最新发展是在跨式封隔器模块中使用双进气口来实现井下隔离。我们认为,本文描述的技术创新地利用了当前地层测试器的能力,在低渗透条件下收集高质量的油气样品。只需稍作调整,该技术也可以应用于油基泥浆井的气或水取样。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Application of Gravity-Assisted Wellbore Segregation to Wireline Sampling Operations. A Low Permeability Case Study
A common challenge in exploration in the North Slope of Alaska is the formation evaluation of low-permeability formations when near-wellbore damage is caused by water-based muds (WBM). This study describes the novel application of existing technology to collect high-quality hydrocarbon samples efficiently in these challenging conditions. The concept was tested with a wireline formation tester in a well with severe formation damage caused by WBM. The procedure and hardware used are discussed and an example of the effectiveness of the proposed technique is shown. Due to the unfavorable mobility ratio, WBM filtrates tends to move preferentially while attempting oil sampling in low permeability rock leading to long station times during wireline formation testing operations. To overcome this challenge, a target sampling interval was subjected to high drawdown using a 3D radial probe to move the target phase closer to the wellbore. Once hydrocarbon was detected in the fluid analyzer, the 3D radial probe was retracted, and the string repositioned to cover the same interval with a straddle packer assembly. Straddle packers provide wellbore annular space for filtrate and hydrocarbon to segregate after the flow period is resumed. When hydrocarbons are again seen in the fluid analyzer, a simultaneous two-pump flow is used to collect them and discard the filtrate. The combination of 3D radial probe and straddle packer assists with displacing the mud filtrate, bringing the target hydrocarbons to the wellbore, and enables the collection of segregated samples with exceptional quality. After pumping at one sampling station using the 3D Radial probe, the maximum hydrocarbon fraction observed was 5%. When the straddle packer was positioned at the same interval, the fluid analyzer showed that the low velocity in the annular space between tool's mandrel and wellbore enabled hydrocarbon segregation from the filtrate due to the existing density contrast. When the hydrocarbon in the wellbore reached the straddle packer inlet, the lower pump was used to flow most of the filtrate in the down direction at high rate. Meanwhile, the hydrocarbon was "skimmed off" and placed in sample containers at a much lower rate using the upper pump. Laboratory results confirmed that the samples collected with the traditional sampling method contained 95% filtrate whereas the samples collected with our technique contained 90% hydrocarbon. Downhole fluid segregation using single-inlet, wireline straddle packer and dual-pump action has not been found in the literature. Recent developments in wireline formation testing use dual inlets in straddle packer modules to enable downhole segregation. We consider that the technique described here innovatively uses the capabilities of current formation testers to collect high-quality hydrocarbon samples in low permeability conditions. With minor adjustments, this technique can also be applied in gas or water sampling in wells drilled with oil-based muds.
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