应用物理模拟研究碎屑岩储层物性演化特征:以胜利油区古近系沙河街组为例

摘要

为定量恢复地质历史时期碎屑岩储层物性参数的演化特征,以胜利油区古近系沙河街组为例,采用物理模拟实验对纯压实作用下不同的粒度、分选、沉积相类型及不同地层流体性质的砂岩储层孔隙度和渗透率的变化规律进行研究.结果表明:物源相同时,分选、磨圆类似的岩石,随着粒度的增大,孔隙度减小、渗透率则增大;而对于粒径范围相同、分选不同的岩石,其孔隙度和渗透率均同分选呈现较好的正相关性,即分选越好物性也越好.在不同地层流体条件下,储层抗压能力不同,酸性水介质条件下岩石抗压能力最小,且随着埋深增加孔隙度减少的速率相对较快;而在碱性水介质下,其孔隙度随深度的变化速率则相对较慢;当地层流体介质发生改变时,即酸碱度降低至中性水介质条件时,抗压实能力则会得到一定程度的恢复.总体上,碎屑岩储层的孔隙度同埋深基本呈现对数关系,渗透率与埋深均呈指数关系.模拟实验结果与实际埋深相对较浅的碎屑岩储层(小于2500 m)孔隙度演化特征吻合度较高,表明在浅层影响储层物性的因素主要为压实作用;而中深层的储层物性影响因素较多,其定量化研究还需综合考虑其它参数.%Based on a case study in the Paleogene Shahejie Formation in the Shengli oil zone of the Bohai Bay Basin, the variation characteristics of physical property in clastic reservoirs with different grain size, sorting, sedimentary facies and formation fluid under pure compaction were analyzed by using physical simulation experiments. Results show that the larger the granularity of grain, the smaller the porosity and the higher the permeability when the reservoir has the same provenance rock and similar sorting and roundness. As for the reservoir rocks with same grain size range and different sorting, the better the sorting, and the higher the porosity and permeability. Under the condition of different formation fluids, the anti-compaction ability of reservoir is different. The reservoirs with acid fluids have the minimum anti-compaction ability, and the porosity decreases very quickly along with the increase of burial depth. Nevertheless, the change rate of porosity with depth is relatively slow in alkaline fluids. If the pH of the formation fluid is converted to the condition of neutral water medium, the anti-compaction ability of rock will be restored to certain extents. In general, the porosity basically has a logarithmic relationship with the buried depth, and the relationship between permeability and buried depth is exponential. The simulation experiment results are consistent with the porosity evolution characteristics of clastic reservoirs with relatively shallow buried depth (generally less than 2500 m), which indicates that the compaction is the main factor affecting physical property in shallow sandstone reservoirs. However, there are many factors affecting the physical property of moderately to deeply sandstone reservoirs, and the quantitative evaluation of physical property evolution needs to consider other parameters.