松辽盆地十屋断陷流体-岩石相互作用

Water-rock interaction in the Shiwu Depression, Songliao Basin, NE China

根据松辽盆地十屋断陷199个水化学分析测试数据,探讨该区地层水化学特征所反映的成岩作用过程,以揭示水化学特征的分布以及演化过程,示踪流体-岩石相互作用过程.水化学的空间分布特征受流体动力场控制:大气降水沿盆地的边缘及断层复杂的中央隆起带下渗,导致该地区盐度降低(小于4.5g/L),向盆地中心盐度逐渐增加到7～10g/L;垂向明显分为3个带:自由交替带(0～1250m深度)为NaHCO3型流体,交替阻滞带(1250～1650m深度)为Na2SO4型流体,交替停滞带(深于1650m)为CaCl2型流体.水化学的时间演化过程受流体-岩石相互作用的控制:地层水中Cl-与HCO3-和Na++K+与Ca2+的关系表明,地层水早期为富含HCO3-的低盐度流体,含钠矿物与碳酸盐矿物的溶解导致了流体中各种离子及盐度的增高,随后的钠长石化作用导致流体中富集Ca2+而Na+亏损,形成CaCl2型流体.十屋断陷水化学特征所反映的流体-岩石相互作用过程得到了其它地质观察的佐证.

Space distribution and evolution of the formation water chemistry in Shiwu Depression and its indication for the water rock interaction processes were discussed based on the 199 data collected from the Shiwu Depression, Songliao Basin, NE China. The space distribution of the water geochemistry was controlled by the hydrological conditions, the penetration of the meteoric water decreased the salinity at the basin margin and the severely faulted central ridge (below 4. 5g/L) and the salinity increased toward basin center to 7-10g/L. And the vertical change can be obviously subdivided into 3 zones: the free replacing zone (< 1250m) with the NaHCO3 type fluid, the obstructive replacing zone (12501650m) with the Na2 SO4 type fluid and the lagged zone (>1650m) with the CaCl2 type fluid. The time evolution of the formation water is governed by the water-rock interaction, the relationship between Cl- and HCO3-and relationship between Na+ +K+ and Ca2+ suggests that the initial water-rock interaction was the dissolution of NaCl and calcium-bearing carbonate, resulted in the increasing of ions and salinity. The succeeding water-rock interaction was albitization, which led to the decreasing of Na+ and the increasing of Ca2+ simultaneously and CaCl2 type fluid was formed. The analyzed water-rock interaction process has been proved by other geological observations.