早期碳酸盐胶结作用对砂岩孔隙演化的影响——以塔里木盆地满加尔凹陷志留系砂岩为例

塔里木盆地满加尔凹陷志留系砂岩为无障壁的潮坪、滨岸及辫状河三角洲沉积的岩屑砂岩和岩屑质石英砂岩，对满北和满东、满南地区志留系砂岩成岩作用序次尤其是碳酸盐胶结的时间、方式和特征、物性的对比研究认为:砂岩中碳酸盐胶结的时间早晚对砂岩孔隙演化具有重要影响，满北地区志留系砂岩发育有大量早期泥晶碳酸盐胶结，显微镜下研究表明这种胶结作用发生在岩石受到充分压实之前，呈基底式胶结，岩石颗粒呈点接触或漂浮状分布于早期碳酸盐胶结物之中，这种胶结作用抑制了岩石后期的压实作用。尽管目前其埋藏达5 000～6 500 m，但其经历的压实作用并不强烈，粒间发育大量早期的碳酸盐胶结物，后来这些胶结物被溶蚀，形成了大量次生孔隙。而在满东和满南地区的志留系砂岩，碳酸盐胶结发生在岩石经过充分压实之后，晚期的碳酸盐胶结物仅分布于岩石经充分压实后的粒间孔隙中，含量较前者低，后期可供溶蚀的碳酸盐比前者少，因而溶蚀形成的次生孔隙有限。因此，尽管满东满南地区志留系埋藏比满北浅（3 700～5 000 m），碳酸盐胶结物含量也低，也发育晚期碳酸盐胶结物的溶蚀，但岩石的压实作用比满北强，物性比满北低差。这主要与碳酸盐胶结的早晚有关，早期碳酸盐胶结对孔隙演化具有明显控制作用，有利于岩石孔隙的保存，为后来的溶蚀形成次生孔隙提供了条件。

Influence of Early Carbonate Cementation on the Evolution of Sandstones:a case study from Silurian sandstones of Manjiaer depression, Tarim basin

Silurian sandstones of Manjiaer depression, Tarim basin deposited in the tidal, beach and braided delta environment, which are litharenite and quartzarenite. The study on the diagenesis, especially carbonate cementation history, sandstone porosity between northern Manjiaer and Eastern Southern Manjiaer indicates that the carbonate cementation time in sandstones has important influence on the porosity of sandstones. An abundant carbonate cements developed in sandstones in northern Manjiaer. These cements were formed before the thorough compaction of sandstones by the microscopical study because the sandstone grains are isolated in the carbonate cements. These cementations restrained the late compaction of sandstones. Although the buried depth of Silurian sandstones in northern Manjiaer only is 5 000～6 500 m, the compaction of sandstones is feeble, a great deal of carbonate cements exist in the sandstones around or between the grains of sandstones. The carbonate cements were dissolved lately and generated an abundant porosity. However, in the eastern and southern Manjiaer area, the cementation of carbonate took place after the thorough compaction of sandstones and carbonate cements were distributed in the limited space between sandstone grains. Thus late dissolution only generated less porosity compared with northern Manjiaer area although they were with shallow buried denpth（3 700～5 000 m）. This is related mainly to the time of carbonate cementation. Early carbonate cementation saved the intergranular space and provide the late dissolution, thus controles on the evolution of porosity of sandstone.