特低渗储层不同渗流介质应力敏感特征及其评价方法研究

STUDY OF PERMEABILITY STRESS-SENSITIVITY CHARACTERISTICS AND ITS EVALUATION METHOD OF ULTRA-LOW PERMEABILITY RESERVOIR USING DIFFERENT TYPES OF FLUID MEDIA

地层岩石的渗透率应力敏感特征对于地下油气资源开发、核废料地下处置等具有极为重要的影响。选取大庆油田外围特低渗油藏及长庆油田某露头储层砂岩岩石进行不同渗流介质(氮气、盐水、煤油)渗透率应力性试验,分析岩样渗透率、孔喉变形、流体压缩性及流固耦合作用机制等因素对应力敏感性的影响。试验结果表明,特低渗储层岩石不同渗流介质渗透率应力敏感性具有明显的差异,气测渗透率与束缚水状态下的油相有效渗透率在有效应力增加初期(2～16 MPa变化区间)急剧减小,但有效应力增加后期水测与油测渗透率仍具有较为明显的减小趋势。1×10-3μm2是特低渗岩石气测与水测渗透率应力敏感性强弱对比发生变化的临界渗透率。有效应力作用下作为主要渗流通道的较大孔喉首先被压缩变形是导致渗透率在有效应力加载初期急剧减小的主要原因,不同渗流介质压缩性和流固耦合作用机制差异是导致气、液渗透率应力敏感性差异的主要原因。特低渗油藏储层应力敏感性评价中应以油相作为渗流介质进行评价试验。提出区分岩芯与油气储层2种不同的渗透率应力敏感性试验及其评价方法。在实际油藏储层有效应力变化范围内,特低渗储层渗透率应力敏感性较弱。

Understanding the permeability stress-sensitivity characteristics is vital for effective development of oil and gas reservoirs and nuclear waste underground disposal. Different types of fluid media（nitrogen, brine and kerosene） permeability stress-sensitivity have been comparatively studied in ultra-low tJermeability reservoir and outcrop sandstone rock samples obtained from Daqing oilfield and Changqing outcrop reservoir, respectively. Those factors including rock permeability, pore throat deformation fluid compressibility and fluid-solid coupling were also analyzed on the effect of permeability stress-sensitivity. The experimental results indicate that the magnitude of permeability stress-sensitivity of different types of fluid media is significantly different. Gas permeability and oil effective permeability at irreducible water saturation dramatically declined during the early increase of effective stress. The comparative results also suggest that water permeability stress-sensitivity is stronger than that of gas permeability when the rock gas permeability is larger than 1×10-3μm2. But the gas permeability stress-sensitivity is stronger than that of water permeability when the rock gas permeability is less than 1×10-3μm2. That the larger pore throats were firstly compressively deformed is the main factor causing the permeability dramatically decreased during the early increase of effective stress. Fluid compressibility and fluid-solid coupling differences among different types of fluid media cause different magnitudes of gas, water and oil permeability reduction. Oil phase should be used as the flow media in oil reservoir permeability stress-sensitivity evaluation. A clear distinction between rock core and petroleum reservoir permeability stress-sensitivity experiment and evaluation method were also proposed. The permeability stress-sensitivity of ultra-low permeability reservoir is weaker when the reservoir effective stress range is considered.