CO-盐水-砂砾岩作用机理与矿物成分、流体赋存及孔隙变化特征

Mechanisms behind CO-brine-Sandy Conglomerate interactions and resulting variations in mineral components， fluid occurrence， and pores： A case study of the Mahu Sag， Junggar Basin

杨柳 公飞 姜晓宇 刘朝阳 董广涛 蔡嘉伟

Liu YANG Fei GONG Xiaoyu JIANG Zhaoyang LIU Guangtao DONG Jiawei CAI

准噶尔盆地玛湖凹陷的致密砂砾岩储层具有极强的非均质性，CO驱后封存效果的矿场试验预测面临较大困难。CO-水-砂砾岩之间的相互作用机理对揭示CO在砂砾岩储层开发后的封存效果具有极为重要的意义。基于CO盐水饱和实验，综合运用QEMSCAN，Micro-CT，SEM和NMR测试等实验分析数据，研究了CO-盐水-砂砾岩作用机理与矿物成分、流体赋存及孔隙变化特征。研究结果表明：CO-水-砂砾岩的相互作用会导致岩石矿物发生溶蚀作用。矿物的溶解和迁移使得岩心的孔喉平均尺寸增大，连通性也随之增强。XRD分析结果表明，CO-水-岩石相互作用下，钠长石和伊利石的含量分别增加了3.20 %和2.32 %，CO对石英的影响非常小。SEM分析结果表明，CO作用后粒缘缝的数量和宽度增加，产生了新的侧向裂缝。碳酸盐和长石的溶蚀作用形成了大量微小粒内孔隙和微裂缝，且裂缝沿着解理方向扩展。核磁共振测试结果显示饱和水主要以黏土矿物束缚水、毛细管束缚水和可动水的形式赋存于岩心内部。经过CO浸泡后，孔隙中饱和水的赋存含量和范围均有所增加，其中大孔中可动水变化最为明显。研究结果强调了砂砾岩储层中CO相互作用的复杂性，对于指导玛湖凹陷砂砾岩储层CO驱后封存的矿场试验效果具有重要意义。

Tight Sandy Conglomerate reservoirs in the Mahu Sag， Junggar Basin exhibit extreme heterogeneity， posing significant challenges to the field tests and prediction of the CO sequestration performance following CO flooding. Understanding the mechanisms underlying CO-brine-Sandy Conglomerate interactions is crucial to evaluating the CO sequestration performance following reservoir development. Based on CO-brine saturation experiments and data from integrated quantitative evaluation of minerals by scanning electron microscopy （SEM）， SEM-based quantitative evaluation of minerals （QEMSCAN）， micro-CT scanning， and nuclear magnetic resonance （NMR） spectroscopy， we investigate mechanisms underlying CO-brine-Sandy Conglomerate interactions and resulting variations in the mineral components， fluid occurrence， and pores in tight Sandy Conglomerate reservoirs of the Mahu Sag. The results indicate that CO-brine-Sandy Conglomerate interactions led to the dissolution of rock minerals. This mineral dissolution and subsequent migration resulted in elevated average pore-throat sizes and enhanced pore connectivity in cores. The X-ray diffraction （XRD） analysis reveals that the interactions increased albite and illite contents by 3.20 % and 2.32 %， respectively， while producing minimal impact on quartz content. SEM analysis results demonstrate that CO soaking led to an increase in both the quantity and width of grain-edge fractures， as well as the formation of new lateral fractures. The carbonate and feldspar dissolution generates substantial intragranular micropores and microfractures， with these microfractures propagating along cleavages. NMR experiment results reveal that saturated water primarily occurs as clay-bound water， capillary-bound water， and movable water in the cores. CO soaking contributes to the enhanced content and expanded distribution range of saturated water in the pores， with movable water in macropores changing the most significantly. The research results highlight the complexity of CO interactions in Sandy Conglomerate reservoirs， which is of great significance for guiding the field test effectiveness of CO storage after flooding in the Mahu Sag Sandy Conglomerate reservoirs.

10.11743/ogg20250318