砂岩储层致密过程定量研究

Quantitative research on the sandstone reservoir densification process is of great importance to clear dense sandstone reservoir forming mechanism. Previous researches on the tight sandstone reservoir most focused on the qualitative description of the Characteristics of diagenesis, but lack of the research on diagenesis and sandstone reservoir densification process, the relationship between densification process and geological time, and the quantitative analysis of sandstone reservoir densification process. This study used Yanchang Formation of Ordos basin in Triassic as an example, selected the Chang6 Member of Ansai Area and Chang8 Member of Xifeng Area as the research objects, adopted the research methods on the combination of macro analysis and micro observation, get to know the diagenesis characteristics of tight sandstone reservoir in Yanchang Formation through the microscopic thin section observation, explore the diagenesis distribution and evolution characteristics in the sandstone reservoir densification process through combining with the borehole porosity profile; further synthesized the data statistics of microscopically thin residual intergranular pore volume and the volume of cement, secondary dissolution pore and the experiment simulation and mathematical model derivation of diagenesis, respectively established the function relationship between the compaction hole quantity reduction, cementation hole quantity reduction ,the dissolution hole volume between the geological time, thereby, due to the quantitative research of the sandstone reservoir densification process, get to simulate the densification process of sandstone reservoirs, reveal the formation process of dense sandstone reservoir, and provide the theoretical basis for the exploration and development of tight sandstone reservoirs.

定量研究砂岩储层致密化过程，对明确致密砂岩储层形成机理具有重要的意义。前人对致密砂岩储层的研究多集中在对成岩作用定性的特征描述方面，缺乏对成岩作用与砂岩储层致密过程、致密过程与地质时间关系以及砂岩储层致密化过程定量分析的研究。本次研究以鄂尔多斯盆地三叠系延长组为例，选取安塞地区长6段和西峰地区长8段为研究对象，采用宏观分析与微观观察相结合的研究方法，通过镜下薄片观察认识延长组致密砂岩储层成岩作用特征，并结合井孔孔隙度剖面，探讨成岩作用在砂岩储层致密过程中的分布及演化特征；进一步综合镜下薄片剩余粒间孔体积、胶结物体积、次生溶孔体积数据统计、成岩作用实验模拟与数学模型推导，分别建立压实作用减孔量、胶结作用减孔量和溶蚀作用增孔量与地质时间的函数关系，从而对砂岩储层致密过程进行定量分析，进而模拟砂岩储层致密化过程，揭示致密砂岩储层形成过程，为致密砂岩油气藏的勘探与开发提供理论依据。

为模拟典型陆相致密砂岩储层孔隙度演化的过程，本文以砂岩储层破坏性成岩作用（压实作用和胶结作用）与建设性成岩作用（溶蚀作用）作为切入点，对鄂尔多斯盆地延长组、四川盆地须家河组和松辽盆地登娄库组致密砂岩储层成岩作用特征进行了分析，并结合现今砂岩储层孔隙度剖面特征，探讨了砂岩储层成岩作用与孔隙度演化之间的关系，进而采用效应模拟原则，对致密砂岩储层孔隙度演化进行了数学推导与模拟。研究发现致密砂岩储层压实作用一直存在于砂岩中，胶结作用在储层埋藏到一定深度后才出现，此后一直存在于砂岩中，溶蚀作用只在一定的演化阶段才发生，具有窗口特征。与之对应的则是在现今砂岩储层孔隙度剖面上，成岩作用具有分段性，由浅到深分别为压实作用、压实作用和胶结作用以及溶蚀作用、压实作用和胶结作用，这样砂岩孔隙度演化可划分为正常压实段、酸化增孔段和溶蚀后正常压实段。研究结果表明，砂岩孔隙度演化可以分解为孔隙度减小模型和孔隙度增大模型，两种模型在三个阶段同一深度或同一地质时间的叠加，可构成砂岩储层总孔隙度演化模拟。通过模拟延长组、须家河组和登娄库组砂岩储层孔隙度演化过程，表明砂岩储层孔隙度演化过程类似、趋势接近，只是由于区域地层抬升或沉降幅度的不同以及埋深的差异，导致不同盆地致密砂岩储层孔隙演化存在差别。