柴达木盆地膏盐层岩石物理特征及其对构造变形的影响

Petrophysical characteristics of the gypsum-salt layer in Qaidam Basin and its influences on tectonic deformation

柴达木盆地下干柴沟组发育膏盐层,膏盐层和柴达木盆地构造变形与油气成藏密切相关。对下干柴沟组的膏盐层、盐上层和盐下层进行岩石物理性质测试的结果显示,下干柴沟组膏盐层相较盐上层和盐下层的能干性弱,而相较于标准盐岩的能干性强。下干柴沟组膏盐为层状盐岩体,其构造变形行为与蒸发岩和盐间泥岩夹层在整个膏岩层段中的比例相关,蒸发岩含量高时膏盐层的变形以塑性蠕变为主,泥岩夹层含量高时膏盐层主要发生脆性变形。膏盐层的存在影响了柴达木盆地内的构造变形,导致盐上层和盐下层中构造样式不一致。在柴达木盆地西南地区,构造上表现为深层发育花状构造、浅层发育"Y"字形断层。在柴达木盆地北缘地区,构造上表现为深、浅层发育不一致的冲断构造。用盐构造耦合-解耦理论模型探讨深、浅层构造之间的联系,提出膏盐层的厚度是柴达木盆地构造解耦程度的主控因素,膏盐层厚度与构造解耦程度呈正相关。

Gypsum-salt layer developed in the Xiaganchaigou Formation has a close relation with tectonic deformation and hydrocarbon accumulation in Qaidam Basin.The petrophysical properties of gypsum-salt,supra-salt and pre-salt strata in the Xiaganchaigou Formation were tested.The results show that the competent of the gypsum-salt layer in the Xiaganchaigou Formation is weaker than that of the supra-salt and the pre-salt strata,but stronger than that of the standard salt rock.The gypsum-salt in the Xiaganchaigou Formation is a layered rock mass,of which the tectonic deformation is related to the proportion of evaporite and interbedded mudstone in the entire gypsum-salt stratum section.When the proportion of evaporite is high,the plastic creep deformation of the gypsum-salt layer is dominant,while when the proportion of interbedded mudstone is high,the gypsum-salt layer mainly occurs brittle deformation.The tectonic deformation in Qaidam Basin is influenced by gypsum-salt layer,resulting in inconsistent structural styles in the supra-salt and the pre-salt strata.In the southwestern Qaidam Basin,flower structures are developed in deep strata and Y-shaped faults are developed in shallow strata.In the northern margin of Qaidam Basin,the thrust structures developed in deep and shallow strata are inconsistent.The coupling-decoupling theoretical model of salt-structure is applied to explore the relationship between deep and shallow structures.It is proposed that the thickness of gypsum-salt layer is the main controlling factor for the degree of tectonic decoupling in Qaidam Basin.The thickness of gypsum-salt layer is positively correlated with the degree of tectonic decoupling.