稠油油藏SAGD微压裂阶段储层压缩系数研究——以新疆风城陆相储层重1区齐古组为例

Study on compressibility during micro-fracturing in continental ultra-heavy oil sand reservoirs——Taking the Qigu Formation of Xinjiang Fengcheng Oilfield Z1 Block for instance

SAGD开采预热之前对稠油储层进行基于剪切扩容(剪胀)和张性扩容的微压裂改造有利于提高SAGD循环预热效率及蒸汽腔发育速度。微压裂阶段的稠油处于未流动状态,注水导致油砂骨架被剪胀或等向撑开,体应变变为负值,压缩系数(绝对值)增大,且压缩系数越大代表油砂储层具有更高的扩容量和更好的可注性。论文针对微压裂阶段储层压缩系数的定义、计算及测试等问题,以新疆风城陆相储层重1区齐古组为研究对象,通过油砂体积压缩实验,开展微压裂注水阶段储层压缩实验机理研究,评价考虑不同注压、注液温度等条件下油砂体积变形及压缩规律。实验结果表明,对于剪切扩容,油砂软化前的压缩系数随着平均有效应力增加而增加,软化后则正好相反;减小有效围压,降低注液温度,增加单向变形,压缩系数增大。对于张性扩容,平均有效应力越小,温度越低,压缩系数越大。该研究成果能够为评价微压裂过程中的储层可注性提供指导。

Micro-fracturing of the wells before preheating circulation phase can shorten the circulating preheating cycle and improve the propagation of steam chamber in SAGD(Steam Assisted Gravity Drainage) development. Injecting water to the immobile ultra-heavy oil sand reservoir during micro-fracturing phase will cause shear dilation and tensile parting dilation of the framework, which lead to volumetric expansion and increase in compressibility. A larger magnitude in coefficient of compressibility implies a greater volumetric dilation and an improved injectivity. In view of the built-in problems associated the definition, calculation and testing methods related to the compressibility under water injection, the core samples obtained from Middle Jurassic Qigu Formation of Xinjiang Junggar Basin were investigated. In this study, the volume compression/expansion tests were designed to study the compression mechanisms during micro-fracturing phase, based on which the volume change behavior under various pressure and temperature circumstances was investigated. It is revealed that the compressibility of oil sand under shear increases with increasing mean effective stress before softening, but displays an opposite trend after softening. Furthermore, the compressibility under shear dilation increases with decreasing effective confining pressure and temperature, as well as increasing uniaxial strain. The tensile dilation tests revealed that the compressibility is in inverse proportion to the mean effective pressure or temperature. The findings of this study can be used to estimate the injectivity of the reservoir for implementation of micro-fracturing in the field.