摘要：

曲流河点坝砂体内部岩相组合复杂，开发过程中受长期注水冲刷影响，储层物性及非均质性具有明显动态演化特征。以孤岛油田馆陶组点坝砂体为研究对象，基于岩心、压汞、核磁共振和驱替实验，结合地质建模与数值模拟，研究了点坝内部岩相分异、物性时变规律及其对非均质的影响。结果表明，点坝砂体可划分为点坝中砂岩相、细砂岩相和粉砂岩相，不同岩相在粒度大小、孔喉结构和孔渗上存在明显差异。水驱至 200 PV后，点坝中砂岩相20 μm以上大孔喉占比增加，点坝细砂岩相驱替后大于10 μm的孔喉与小于0.1 μm的孔喉占比均有所提高，点坝粉砂岩相驱替后小于等于4 μm孔喉占比明显升高。对应地，点坝中砂岩相和点坝细砂岩相渗透率分别增至初始值的1.42倍和1.30倍，而点坝粉砂渗透率降至初始值的0.86倍，表现出高渗岩相扩孔增渗、低渗岩相细化堵塞的差异化时变响应。受侧积层遮挡及岩相时变共同影响，过水高值区由底部向中上部缓慢扩展，渗透率级差由约6.4增至约7.3，突进系数由约2.69降至约2.53，变异系数表现为先升高后缓慢降低，储层非均质性经历了由快速增强到高位稳定的阶段性演化过程。动态孔喉重构及渗透率分异演化使注入水更加集中于高渗岩相，降低了低渗岩相及侧积层遮挡区的动用程度，剩余油主要富集于点坝粉砂岩相、弱波及点坝细砂岩相及侧积层遮挡区。与不考虑物性时变的模型相比，考虑物性时变后含水率拟合平均绝对误差及均方根误差降幅分别为33.33%和30.09%。研究认识可为高含水期曲流河点坝储层剩余油预测与开发调整提供依据。

关键词: 曲流河点坝, 岩相, 渗透率时变, 动态非均质性, 剩余油分布

Abstract:

The lithofacies assemblages within fluvial point-bar sand bodies are highly complex, and prolonged waterflooding induces pronounced dynamic changes in reservoir properties and heterogeneity. Taking the point-bar sand bodies of the Guantao Formation in the Gudao Oilfield as the study object, this study integrates core analysis, mercury intrusion porosimetry, nuclear magnetic resonance, and displacement experiments with geological modeling and numerical simulation to investigate lithofacies differentiation, time-dependent variations in petrophysical properties, and their effects on reservoir heterogeneity. The results show that the point-bar sand bodies can be subdivided into point-bar medium-sandstone, fine-sandstone, and siltstone facies, which differ markedly in grain size, pore-throat structure, porosity, and permeability. After waterflooding to 200 pore volumes (PV), the proportion of pore throats larger than 20 μm increased in the medium-sandstone facies. In the fine-sandstone facies, the proportions of pore throats larger than 10 μm and smaller than 0.1 μm both increased, whereas the proportion of pore throats no larger than 4 μm increased significantly in the siltstone facies. Correspondingly, the permeabilities of the medium- and fine-sandstone facies increased to approximately 1.42 and 1.30 times their initial values, respectively, whereas that of the siltstone facies decreased to approximately 0.86 times its initial value. These changes indicate contrasting time-dependent responses characterized by pore-throat enlargement and permeability enhancement in highly permeable facies, but pore-throat refinement and clogging in low-permeability facies. Under the combined effects of lateral-accretion-layer baffling and lithofacies-dependent property evolution, zones of high water throughput gradually expanded from the lower part of the point bar toward its middle and upper parts. The permeability contrast increased from approximately 6.4 to 7.3, the breakthrough coefficient decreased from approximately 2.69 to 2.53, and the coefficient of variation initially increased and subsequently declined slowly. Reservoir heterogeneity therefore underwent a staged evolution from rapid enhancement to stabilization at a relatively high level. Dynamic pore-throat restructuring and progressive permeability differentiation concentrated injected water increasingly within the high-permeability facies, reducing the displacement efficiency of the low-permeability facies and zones baffled by lateral-accretion layers. Consequently, the remaining oil was mainly enriched in the point-bar siltstone facies, weakly swept fine-sandstone facies, and lateral-accretion-layer-baffled zones. Compared with the model that neglected time-dependent petrophysical properties, the time-varying-property model reduced the mean absolute error and root mean square error of the water-cut history match by 33.33% and 30.09%, respectively. These findings provide a basis for remaining-oil prediction and development adjustment in fluvial point-bar reservoirs during the high-water-cut stage.

Key words: meandering-river point bar, lithofacies, permeability evolution, dynamic heterogeneity, remaining oil distribution

中图分类号: 

• P618.13

• TE341