川东北中—下三叠统流体动力场及成藏成钾耦合机理

川东北地区是近年来的找钾重点区。本文研究了三叠系嘉陵江组和雷口坡组的卤水储层特征、卤水化学特征和地下流体动力场,结果表明:川东北地区嘉陵江组和雷口坡组卤水储层主要为裂缝-溶孔型和白云岩型,属低孔低渗储层;宣汉—达州—开县—开江一带为中上扬子区的一个咸化凹陷,发育巨厚蒸发岩层,并且正好为流体越流浓缩成藏成矿区;该地区的卤水矿化度和钾离子含量较高,K+、Br+等离子含量达到卤水工业开采指标。综合分析川东北地区地下流体(气、水)的动力学特征,揭示地下流体动力场是二次富钾成矿的主要机制,在这一机制下,地层中封存的通过海水浓缩初始富钾形成的原始沉积水进一步浓缩富钾,并运聚至合适的构造-地层圈闭中,造就了该地区具备上气下水的耦合成藏成钾条件,有望成为"气钾兼探"的重要耙区。

Fluid Dynamic Field of the Lower Middle Trassic and Coupling Mechanism of the Potassic Formation in Northeastern Sichuan

Northeastern Sichuan is an important district for kalium mine exploration. In this paper, brine reservoir, brine chemical characteristics and underground fluid dynamic field of Jialingjiang and Leikoupo formations of the Triassic were studied. Results suggest that fractured dissolution pore reservoir and dolomite reservoir, with low porosity and low permeability, are the main reservoir for brine of Jialingjiang and Leikoupo formation in northeastern Sichuan. The Xuanhan Dazhou Kaixian Kaijiang area, a salt depression of middle and upper Yangtze region, develops a thick evaporite stratum and is also a leaky fluid area for gas reservoir formation and mine formation. Brine salinity and K+, Br+ abundance are high enough to reach the index standard for industrial exploration. Comprehensive analysis of underground fluid (gas, brine) dynamics in northeastern Sichuan reveals that underground fluid dynamic field was the main mechanism of second K+ enrichment for mine formation. In this mechanism, original sedimentary water sealed in the stratum, which experienced first K+ enrichment through sea water concentration, concentrated again, then migrated to the structure stratigraphy traps, and finally resulted in coupling with gas & mine formation characterized by upper gas and sub brine. Northeastern Sichuan would be an important target area for gas and kalium mine exploration simultaneously.