碳酸盐岩中白云石有序度的控制因素——来自塔河下古生界和川东北三叠系的研究

Controlling factors of order degree of dolomite in carbonate rocks: A case study from Lower Paleozoic in Tahe Oilfield and Triassic in northeastern Sichuan Basin

作为矿物学特征的白云石有序度是白云岩形成机制和碳酸盐储层研究的重要手段之一。通过对塔河地区寒武系—奥陶系碳酸盐岩和川东北地区三叠系碳酸盐岩的X射线衍射分析,讨论了白云石有序度的主要控制因素。研究结果表明:①白云石的有序度与其结晶程度有关,自形程度好、晶体相对较大(如细—中晶)的白云石有序度好于泥晶或微晶白云石;②白云石的有序度与其CaCO3摩尔分数有关,CaCO3摩尔分数越低,白云石越接近理想组成,白云石有序度越好;③白云石有序度与碳酸盐岩白云石化程度有关,白云石化越彻底,白云石的有序度越高;④在控制白云石有序度(包括其它相应的矿物学因素)的各种因素中,结晶温度最为重要,相对较高温度条件下形成的白云石有序度好于相对低温条件下形成的白云石。因此认为,从白云石化的机理而论,与渗透回流、蒸发泵等准同生白云石化有关的白云石有序度较差,而与埋藏白云石化作用有关的白云石有序度较好,与大气水/海水的混合水白云石化作用有关的白云石的有序度可能在这二者之间。

As an important mineralogical characteristic, the order degree of dolomite is widely used in the study of dolomite formation mechanism and carbonate reservoir research. Based on the X-ray diffraction analysis of Cambrian- Ordovician carbonatite samples in Tahe Oilfield and Triassic earbonatite samples in northeastern Sichuan Basin, the controlling factors of the order degree of dolomite are discussed. The conclusions obtained as follows： （1）The order degree of dolomite is related to its crystallinity. For example, the order degree of the dolomite with ethereal and relatively large crystals is higher than that of mieritic dolomite.（2）The lower the molar percentage of CaCO3 in dolomite is, the higher the order degree of the dolomite is. （3） The order degree of dolomite undergone dolomitization completely is higher than that undergone incompletely dolomitization. （4） In all controlling factors, including other mineralogical elements, crystalline temperature is the most important one. For instance, the order degree of dolomite which formed in high temperature is higher than that formed in low temperature. As a result, in regard to dolomitization mechanism, the order degree of dolomite associated with penecontemporaneous dolomitization （seepage reflux dolomitization, evaporationpump dolomitization and so on） is low, while the order degree of dolomite connected with burial dolomitization is high and the order degree of dolomite concerned with dorag dolomitization maybe among the above two.