低渗油藏过渡带毛管力及相对渗透率曲线精确表征

The oil-water transition zone can be huge in low permeabile reservoirs with edge/bottom water, and the oil reserve and production in which takes great part of the total oil reserve and prodution of the whole reservoir. Formation of the oil and gas reservoir holds a different mechanism from the water flooding developing process. The drainage capillary pressure curve controls the oil/water distribution when the reservoir formates, while in the water flooding process the capillary pressure curve controls the oil/water distribution (supposing the formation rock is water wet). In addition, the capillary pressure curves and the relative permeability curves in the transition zone is related to the initial water saturation and the drainage velocity, which differs in the shape of the traditional capillary and relative permeability curves.The traditional capillary and relative permeability curves(the beginning water saturation is initial water saturation Swc) are commonly uesd in numerical simulation calculaitons, which brings great influence to the OOIP and production calculation. The innovative research of this subject focuses on: (1) Developing the neotype instrument for determining underground drainage capillary pressrure curves and the imbibition capillary pressure curves. (2) Determining the oil–water drainage capillary pressrure curves, the imbibition capillary pressure curves and relative permeability curves with different initial water saturation in reservoir condition of low-permeabile reservoirs with different permeabilities. (3)To study the influence of the drainage velocity on the capillary pressure curves. The purpose for this study is to give accurate drainage capillary pressrure curves, the imbibition capillary pressure and relative permeability curves based on gas permeability and initial water saturation etc. for reservoir simulation and calculation.

低渗透油藏大都具有边底水、油水过渡带较大，对储量及产量有重要影响。油气成藏与注水开发过程驱替机理不同，传统开发理论均没有考虑这些差异：一是油气成藏过程中驱替毛管力控制油水分布，注水开发过程（假设岩石亲水）吸吮毛管力控制油水分布；二是过渡带中毛管力和相对渗透率曲线与初始饱和度、驱替速度等有关，即过渡带中不同高度上毛管力和相对渗透率曲线不同，而传统计算只用初始饱和度下的毛管力及相对渗透率曲线，导致低渗透油藏数值模拟动态预测与实际差别较大。本课题创新性研究内容如下：(1)研制具有自主知识产权的地下驱替、吸吮毛管力曲线测试仪器；(2)研究地下不同渗透率岩心驱替毛管力曲线，不同渗透率、初始饱和度下的吸吮毛管力和相对渗透率曲线变化规律及特征；(3)研究驱替速度对毛管力曲线影响规律。构建考虑岩石渗透率、初始饱和度等因素影响的新型毛管力和相对渗透率曲线形式，为油藏数值模拟、油藏工程计算提供可靠数据支撑。

低渗透油藏大都具有边底水、油水过渡带较大，对储量及产量有重要影响。油气成藏过程中驱替毛管力控制油水分布，注水开发过程（假设岩石亲水）吸吮毛管力控制油水分布；过渡带中不同高度上毛管力和相对渗透率曲线不同，而传统计算只用初始饱和度下的毛管力及相对渗透率曲线，导致低渗透油藏数值模拟动态预测与实际差别较大。.本课题利用自主研制的地下驱替、吸吮毛管力曲线测试仪器，首先测试分析不同渗透率岩心水驱替毛管力曲线变化规律及特征，并总结数学描述方法；然后测试分析不同含水饱和度岩心油水吸吮毛管力曲线变化规律及特征，并总结数学描述方法。通过非稳态驱替法研究不同渗透率岩心不同初始含水饱和度相对渗透率曲线的变化规律及特征，并总结数学描述方法。自主设计动态毛管力曲线测试仪，研究分析驱替速度对吸吮毛管力曲线的影响规律。.研究结果表明：自主设计的岩石驱替—吸吮毛管力联测仪能够连续测定高温高压条件下的驱替毛管力曲线和吸吮毛管力曲线。实测油水毛管力曲线与压汞毛管力转化毛管力曲线差别较大，应以实测油水毛管力曲线为准。岩心渗透率减小，油水驱替毛管力曲线束缚水饱和度增加，残余油饱和度增加，平缓段变短。推导了同时使用于驱替和吸吮毛管力曲线的半解析模型，可应用于驱替吸吮毛管力预测。岩石初始含水饱和度对油水吸吮毛管力的形态影响显著，随初始含水饱和度增加，吸吮曲线整体向右移动，可动水流区域变窄。建立了考虑毛管力的非稳态相渗计算方法，岩石初始含水饱和度对相对渗透率的形态影响显著，随着初始含水饱和度增加，初始含水饱和度下油相渗透率降低，水相渗透率增加，残余油饱和度降低。动态毛管力曲线测试结果表明，动态毛管力表现为负的阻力，说明了在水驱油过程发生了润湿反转，且驱替速度越大，动态毛管力的绝对值就越大，动态效应逐渐增强。对影响拟动态系数的参数进行了无量纲分析，建立了拟动态系数τm的函数模型，继而确定了动态毛管力的数学表征模型。