基于图像法和流体法融合的致密砂岩全孔径孔喉表征及建模

Reservoir evaluation and percolation simulation of tight sandstone oil and gas have become hot point and the research focal point, and their precision relies on the fine pore-throat structure characterization and pore network modeling. Tight sandstone develops various pore types, multi-scale pore size distribution and complex pore and throat connectivity, which make the conventional method of pore characterization and modeling unavailable. From the integration of image and fluid methods perspective, the microscopic features of different scale pores and throats in full range, such as morphological characteristics and topology, size distribution and content, and connectivity of tight sandstone are comprehensively described, based on that the multi-scale pore network model of tight sandstone is reconstructed, and then the pore-throat combination characterizations and their effects on two phase flow are researched. Besides the complementary advantages of different type of methods, the integration characteristics also embody the following two aspects: (1) combining several fluid methods to obtain the pore and throat size distribution with seepage meaning; (2) calibrating the pore size calculated by fluid method based on pore morpholohy of image method. The integration of methods not only ensures the pore throat size distribution, content and connectivity of modeling result be consistent with cm level core’, but also its shape and topology similar to nano-mirco pores in image methods. The research results not only can deepen the cognition of tight sandstone’s pore and throat combination relationship and two phase flow features, but also can refine the methods and theories of pore structures quantitative characterization.

致密砂岩油气的储层评价及渗流模拟等已成为研究重点及热点，其精度依赖于全面精细的孔喉表征及建模手段。致密砂岩多样的孔隙类型、多尺度的孔径分布及复杂的孔喉组合，导致传统单一的孔喉表征及建模方法面临挑战。本申请拟从图像法及流体法测量结果融合的角度，全面刻画致密砂岩全孔径范围内不同尺度孔隙和喉道的形态及拓扑结构、大小分布及含量、连通关系等特征，以此构建致密砂岩多尺度孔隙网络模型，研究致密砂岩储层的孔喉组合特征及其对两相渗流的影响。除不同类测试方法的优势互补外，融合特色还体现在联合多种流体法刻画渗流意义上孔隙和喉道的分布，基于图像法的孔隙形态特征对流体法孔径大小进行校正。两类技术的融合既保证建模结果具有与厘米级岩心一致的孔喉分布、含量及连通关系，又具有与纳米-微米级孔隙相似的形态及拓扑结构。研究成果可以加深对致密砂岩孔喉组合关系和渗流特征的认识，同时也有助于完善孔喉结构定量表征的方法和理论。

我国油气对外依存度逐年递升，加快国内油气资源勘探及开发意义重大。我国非常规油气资源丰富，其中以致密油气最为现实。然而，油气赋存状态、渗流能力受微观孔隙结构的控制，揭示致密储层的微观孔隙结构及其对渗流能力的影响是正确认识致密储层成因机制、实现甜点分类及开发方案优化的基础。. 本项目以松辽盆地古龙凹陷高台子致密砂岩和徐家围子断陷沙河子组致密砂砾岩为研究靶区，基于低温氮气吸附、压汞法、核磁共振、微米CT及FIB-SEM等实验测试，研究致密储层微观孔隙分布、组合特征及影响，建立相应评价技术，基于图像法构建高分辨率三维数字岩心，并完成了渗流及驱替数字模拟。通过研究得出如下成果及数据：. （1）对比各类流体法及图像法表征结果，建立了一种联合低温氮气吸附和核磁共振表征多尺度孔隙分布的方法，将致密砂岩孔隙空间进行分区；致密储层发育大孔-细喉组合和类树形孔隙网络，粒间孔及粒间溶蚀孔越发育，大孔-细喉组合越发育，储层类型越好。. （2）利用恒速压汞实验会高估孔隙体大小及孔喉比，联合多尺度孔隙表征及恒速压汞实验，形成了一种全面刻画孔隙体和喉道大小分布、孔喉比的方法；揭示了压实作用及粘土胶结对致密储层孔喉结构演化过程的控制。. （3）以微米CT及FIB-SEM扫描技术为手段，联合孔隙组合关系认识，构建大孔-细喉型孔隙的数字岩心，并利用酸化及沉淀算法，反映溶蚀及胶结成因的微孔隙网络，进而形成一种高分辨率三维数字岩心构建技术，渗流模拟结果与实际岩心测试相当；. （4）通过基于LBM方法的驱油模拟，发现二氧化碳吞吐效率最高，水驱效率最低；随着注入速度和注入压力的增加，水驱、二氧化碳驱、水-二氧化碳交替驱和二氧化碳吞吐的驱替效率均得到提升，但不同驱替介质的提升幅度不同。. 本研究形成了一系列刻画孔隙分布及组合类型的技术方法，并建立考虑矿物、成岩作用的高分辨率数字岩心，联合LBM模拟了不同驱替条件下致密油可动用程度，不仅为深化研究致密储层形成机制及致密储层类型划分奠定基础，同时也为致密油开发提供了一种新的研究手段。