塔里木盆地奥陶系颗粒石灰岩埋藏溶蚀作用

Burial dissolution of Ordovician granule limestone in Tarim Basin

塔里木盆地奥陶系颗粒石灰岩的岩石学和地球化学综合研究表明,埋藏溶蚀作用可分为内源溶蚀和外源溶蚀两个作用阶段,这两种溶蚀作用的本质区别是酸性流体的来源和流体运移途径不同。埋藏溶蚀作用的流体来源于有机质在成熟作用和烃类热降解作用过程中产生的有机酸、CO2和H2S等酸性流体,内源溶蚀作用的流体来源于自身岩石颗粒中的有机质,而外源溶蚀作用流体则来源于颗粒石灰岩岩层之外的泥质烃源岩。埋藏溶蚀储层的形成是内源溶蚀和外源溶蚀共同作用的结果,早期颗粒石灰岩自身酸性流体的溶蚀作用主要形成彼此独立的小孔,后期外来酸性流体沿着不整合、断裂、裂缝和缝合线对围岩进一步溶蚀改造,地层中的矿物成分和流体的热对流是影响溶蚀储层形成的重要因素。

The comprehensive study of some samples from the Ordovician granule limestone in Tarim Basin showed that the burial dissolution could be classified as in-source dissolution and out-source dissolution based on the macro-microcosmic petrology and geo- chemistry features. There are different origin and migration path for the acid fluids in two stages of dissolution. The burial dissolu- tion fluids might be organic acid, CO2 and Ha S originated from the maturation of organic matters and decomposition of hydrocarbon. The fluid of in-source dissolution came from the organic matter in granule limestone, while the fluid of out-source dissolution mainly came from the shale source rocks far away from granule limestone strata. The burial dissolution reservoir was resulted from the actions of the in-source dissolution and the out-source dissolution. The granule limestone firstly formed the unattached pinholes under the action of in-source dissolution and afterwards suffered wide dissolution from the out-source fluid moving along the unconformities, seams, ruptures and associate fissures. The mineral composition of the stratum and the thermal convection of fluid are the important factors for forming the favorable reservoir.