碎屑岩输导层内油气运聚非均一性的定量分析

THE INHOMOGENEITY OF PETROLEUM MIGRATION IN CLASTIC CARRIER BEDS

油气在以连通孔隙为流体储、流空间的碎屑岩输导层中的运移具明显的非均一性。在实际盆地中 ,输导层往往是非均质的 ,在宏观上表现为岩性、岩相在盆地范围内的频繁变化 ,在微观上则主要受粒度大小、胶结物含量、成岩作用等的影响。利用BasinMod所做的定量模拟试验发现 ,即便在宏观均质孔隙介质中 ,油气运移的动力也往往是非均一的 ,表现为受控于构造形态的空间变化。在非均质输导层中 ,运移动力的非均一性与所处的地质背景有关 :在毛细管力梯度小于浮力梯度时 ,流体势的梯度方向与浮力梯度方向相同 ,油气运移仍沿浮力降低的方向进行 ;当毛细管力梯度大于浮力梯度情况下 ,流体势梯度方向发生改变 ,岩性变化带成为油气运移的封挡层。将数值模拟分析的认识应用于准噶尔盆地腹部侏罗系三工河组 ,在假设输导层侧向延伸性良好的条件下 ,分析了输导层油气运移路线 ,认为石西 1井区、盆 4井区及陆 1井区等构造高部位为重要的油气运移指向区。

Migration behaviors of petroleum in clastic carriers seem to be inhomogeneous. Even for homogeneous carriers, the migration forces that controlled dynamically these behaviors are usually inhomogeneous, resulted generally from the topography of the upper surface of the carriers, the variation of hydraulic flows, etc. The heterogeneity of the migration may also be seriously influenced in actual basins by the heterogeneity of carriers that depends on sedimentary environment as well as the facies changes in macroscopic scale, and on grain size, cement content, degree of diagenesis, etc. in microscopic scale. A numerical basin model (BasinMod) was used to analyze the inhomogeneous characteristics of the migration behaviors in this paper. The modeled results show that driving force mainly caused by the buoyancy of oil or gas seems to lead a main migrating path along the “tectonic ridge” within the carrier, and such concentration of flows may be intensified or changed by the capillary pressure concerning to lithological variation. Based on these case studies and comprehension, the petroleum migration process happened in the Sangonghe Formation of the Junggar Basin in age of Jurassic was modeled and analyzed.