济阳坳陷古近纪沙河街组页岩油储层中的藻纹层和藻生物层的发现及其意义

Salt weathering mechanism and climate response inNiujiaozhai Grottoes, Renshou, Sichuan

页岩油气是目前国内外的当采能源,受到了广泛的关注。我国页岩油气勘探开发起步较晚,但发展迅速。济阳坳陷古近系沙河街组页岩油气资源丰富,目前是国内单井产量最高,总产量最大的页岩油气勘探开发基地。但还有一些基础地质问题尚不清楚,给勘探开发带来了一定的困难。近期的研究发现,济阳坳陷古近系沙河街组页岩油储层发育良好的藻纹层(钙质纹层或亮晶纹层)和藻生物层,是页岩油气良好的储集层。

Objectives: Salt weathering is one of the important reasons of weathering deterioration of stone cultural relics,but its internal mechanism and process need to be further studied.Methods: In this paper, we collected the core and weathered samples of Buddha Grottoes from Niujiaozhai ofRenshou to do the study. Their mineral and chemical compositions were compared and researched, the compositionand crystallization state of soluble salt in samples are Focused.Results: Researches show that (i) the weathered samples have 16 times higher contents of SO3 than the coresamples;(ii) the core samples were detected to have trace amounts of gypsum only in the 0 ~ 22 cm surface,whereas the weathered samples contain 17. 5 times higher content of gypsum, and a few Na2SO4 and NaCl. Thisindicates that the weathering deterioration of grottoes is related to soluble salt, especially sulfate. Further studies onthe properties of Na2SO4, NaCl and gypsum show that Na2SO4 can undergo repeated crystallization reaction ofNa2SO4+H2O Na2SO4·10H2O in response to climatic conditions, the volume expansion during crystallizationis 416%, especially in humid climate, the secondary crystallization of Na2SO4 can cause more damage to rocks.NaCl can reduce the phase transition temperature (to 17. 6℃) and solubility of Na2SO4, and amplify its role in theprocess of rock weathering. CaSO4 has slight effect on rock weathering, but it can be used as an indicator for theaccumulation of soluble salts. Combined with the studies on the temperature and humidity monitoring data ofRenshou Giant Buddha, it was found that the changes of daily temperature and humidity with time naturally fit thetransition conditions of Na2SO4—NaCl system.Conclusions: Climate changes coupled with salt weathering is the main weathering mode of the sandstone inNiujiaozhai Grottoes.