注水作用下油藏注入传递率与衰减传递率的明显差异研究

N. Rahman, Omar H Obathani
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引用次数: 1

摘要

当向油藏注水时,根据各自的对数-对数图估计的流体传输率显示出注入量和脱落量模型之间的巨大差异。与生产井的情况相比,这一观察结果似乎是异常的,在生产井中,根据降压和累积模型估计的透射率没有明显差异。本研究探讨了从注入模型和脱落模型估计的流体传输率差异背后的原因。我们已经开发了高分辨率的数值模型,以说明在注入和衰减期间观察到的对数-对数图的差异。为了解释异常行为,我们回顾了特别适用于生产井的叠加基本原理。然而,我们发现,由于注入井周围渗透率分布缺乏静态平衡,在注入期间应用叠加原理时,叠加原理失效。相反,在注水一段时间后的下降期,叠加原理仍然适用。结果,在对数-对数图上出现了注入和衰减模型的差异。由于注入期间注入井附近透射率的变化,叠加原理对线性的要求被打破。这使得估计注入期间流体渗透率的方法失效。但在下降期,储层的透射率分布恢复到平衡状态。因此,在等温和非等温情况下,在对数-对数图上对下降期间模型的迁移率估计是有效的。这项研究是为了表明它是如何误导估计流动性从注入压力数据与传统的智慧相反。有了这些知识,油藏工程师将能够避开对瞬态压力数据进行错误分析的陷阱。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
An Investigation into Apparent Differences Between Injection Transmissibility and Falloff Transmissibility in Oil Reservoirs Subject to Water Injection
When water is injected into an oil reservoir, estimates of fluid transmissibility from the respective log-log plots show substantial differences between magnitudes out of injection and falloff models. This observation appears to be anomalous when compared to the cases of producing wells where there are no marked differences in transmissibility estimated from drawdown and buildup models. This study investigates the reason behind the differences in fluid transmissibility estimated from injection and falloff models. We have developed high-resolution, numerical models to illustrate differences in log-log plots observed in the injection and falloff periods. To explain the anomalous behavior, we have reviewed the fundamental principle of superposition which is particularly applicable in production wells. However, we have found that the principle of superposition falls apart while applying during injection periods due to a lack of static equilibrium of the transmissibility distribution around the injection wells. In contrast, the principle of superposition is still applicable during the falloff period following a period of water injection. As a result, differences in injection and falloff models appear on the log-log plots. The requirement of linearity on the part of the principle of superposition breaks down due to changing transmissibility in the vicinity of the injection wells during the injection periods. This invalidates the method of estimating the fluid transmissibility during the injection periods. But during the falloff periods, the transmissibility distribution in the reservoir gets back to its equilibrium condition. Hence the estimates of the mobility from the models during the falloff periods on the log-log plot are valid as demonstrated with isothermal and non-isothermal cases. This study is to show how it is misleading in estimating the mobility from injection-pressure data contrary to conventional wisdom. With this knowledge, reservoir engineers will be able to steer clear of the trap of wrongful analysis of transient-pressure data.
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