柴达木西部南翼山构造富钾深层卤水矿的控制因素及水化学特征

Control Factors and Water Chemical Characteristics of Potassium-rich Deep Brine in Nanyishan Structure of Western Qaidam Basin

柴达木盆地西部南翼山地区深层卤水是经济价值极高的液体矿床,以富含钾、硼、锂和溴等为特征,前人认为南翼山背斜构造区地层的岩性控制着深层富钾卤水的分布。本次研究结果认为,该区卤水主要受控于背斜构造中发育的断层裂隙,深度范围为上新统上油砂山组至渐新统下干柴沟组。本文着重以青藏高原柴达木盆地西部南翼山背斜构造E3g–N1y地层富钾深层卤水的形成机制及水化学特征为研究对象,在野外观察、取样及室内分析的基础上,综合分析地质及石油等相关部门地质、水文、物探等方面资料,及对青海油田公司老井最新的卤水层射孔资料,结合储卤层沉积环境、地质构造,富钾深层卤水水文地质及地球化学特征,认为柴达木盆地西部南翼山背斜构造从渐新世至上新世经历了深湖相—半深湖相—浅湖相—潮坪相沉积。沉积环境决定着原始深层卤水的水性与水质,南翼山背斜褶皱构造形成的同时,产生了一系列纵向、横向及顺层等断层及相应的构造裂缝(隙),构成了富钾深层卤水的储水空间。大量的化学分析资料显示,南翼山背斜构造区深层卤水是封闭程度高的还原环境下沉积变质作用的产物。

The deep brine in Nanyishan area in the western part of the Qaidam Basin is a liquid deposit with extremely high economic value, characterized by enrichment of potassium, boron, lithium and bromine. Previous workers considered that the lithologic character of the strata in Nanyishan anticlinal structural area controls the distribution of deep potassium-rich brine. The study conducted by the authors reveal that the brine in this area is controlled by fault fissures developed in the anticlinal structure, with the depth range from Pliocene Shangyoushashan Formation to Oligocene Lower Ganchaigou Formation. With the formation mechanism and hydrochemical characteristics of the potassium-rich deep brine in E3g–N1y strata of Nanyishan anticlinal structure as the emphatic study objects and on the basis of field observation and sampling as well as indoor analysis, the authors made an integrated analysis of geological, hydrological and physical data provided by related geological and petroleum departments as well as the newest brine bed perforation data of old drill holes provided by Qinghai Oilfield Company in combination with sedimentary environment and geological structure of the brine-storage reservoir as well as hydrogeological and geochemical characteristics of potassium-rich deep brine. The results show that Nanyishan anticlinal structure in the western part of the Qaidam Basin experienced the evolution of deep lacustrine facies-semi-deep lacustrine facies-shallow lacustrine facies-tidal flat facies from Oligocene to Pliocene. The sedimentary environment decided the water character and water quality of the primary deep brine. Simultaneously with the formation of Nanyishan anticlinal structure, a series of longitudinal, transverse and bedding faults as well as corresponding structural cracks（fissures） were formed to serve as water-storage space for potassium-rich deep brine. Large quantities of chemical analytical data demonstrate that the deep brine in Annyishan anticlinal structure resulted from sedimentary metamorphism in a highly-closed reduction environment.