地学前缘 ›› 2021, Vol. 28 ›› Issue (6): 79-94.DOI: 10.13745/j.esf.sf.2021.1.43

• 钾盐成矿新认识 • 上一篇    下一篇

同层型气钾复合矿藏的形成机理浅析:以四川盆地磨溪背斜中三叠统雷口坡组富钾卤水矿为例

陈小二1,2, 张兵3,*, 范昆4, 杨凯3, 张赛民3   

  1. 1.成都理工大学 沉积地质研究院, 四川 成都 610059;
    2.中石油东方地球物理勘探有限公司 物探技术研究中心, 四川 成都 610213;
    3.成都理工大学 地球勘探与信息技术教育部重点实验室, 四川 成都 610059;
    4.中石油东方地球物理勘探有限公司 西南物探研究院, 四川 成都 610213
  • 收稿日期:2020-12-05 修回日期:2021-01-27 出版日期:2021-11-25 发布日期:2021-11-25
  • 通讯作者: *张 兵(1981—),男,博士,副教授,主要从事储层沉积学的教学与科研工作。E-mail:zb4819890@qq.com
  • 作者简介:陈小二(1983—),男,博士研究生,沉积学专业。E-mail:chenxiaoer1983@126.com
  • 基金资助:
    国家自然科学基金项目(41972154); 国家重点研发计划项目“重点含钾盆地富钾规律、战略选区与深部探测技术示范(2017YFC0602806)”; 中石油东方地球物理勘探有限公司项目“多道瞬态面波与纵波各向异性近地表建模及静校正方法软件研发项目(01-02-2020)”

Metallogenic model for the coexistence of potassium-rich brine and natural gas in the same strata: An example from the Middle Triassic Leikoupo Formation in the Moxi Anticline, Central Sichuan Basin, Southwest China

CHEN Xiao'er1,2, ZHANG Bing3,*, FAN Kun4, YANG Kai3, ZHANG Saimin3   

  1. 1. Institute of Sedimentary Geology, Chengdu University of Technology, Chengdu 610059, China;
    2. Geophysical Technology Research Centre, BGP, CNPC, Chengdu 610213, China;
    3. Key Laboratory of Earth Exploration and Information Technology of Ministry of Education, Chengdu University of Technology, Chengdu 610059, China;
    4. Southwest Geophysical Research Institute, BGP, CNPC, Chengdu 610213, China
  • Received:2020-12-05 Revised:2021-01-27 Online:2021-11-25 Published:2021-11-25

摘要: 四川盆地中三叠统雷口坡组中发育多种类型的钾盐矿藏,是我国找钾的重点目标层系。磨溪气田雷口坡组地层卤水富含K、Li、Br、B元素,定性为中低矿化度KCl、LiCl、Br-、B2O3等超标的优质化工原料水,显示出较好的钾盐勘探前景。地震资料解释结果表明,磨溪气田雷口坡组一段的第一亚段(雷一1)顶面表现为一个完整的长轴背斜形态,断层不发育。富钾卤水发育在背斜的翼部,而天然气则占据了背斜的核部,二者共同贮存在雷一1亚段溶蚀孔洞发育的滩相白云岩中,构成了典型的同层型气钾复合矿藏。借鉴含油气系统的概念,将富钾卤水的形成、聚集及后期保存等影响卤水型钾矿形成全过程的各种因素总结归纳为6大关键要素,即钾的物质来源,储层物性、封盖条件、圈闭条件、运移方式和保存条件。在乐山—龙女寺古隆起形成和演化的背景下,确定构造圈闭形成时间,分析优质储层发育有利因素以及后期保存条件,并按照各要素在时空上的搭配关系,动态地分析雷口坡组同层型气钾复合矿藏的形成过程。烃类物质和卤化物都是地下水所含的特殊物质,在地下水动力场的作用下,地层水在雷口坡组内部向着川中地区的继承性发育的古构造高点——磨溪背斜持续运移。被运移而来的由蒸发浓缩的古海水和石膏脱水形成的初始富钾地层水不断捕获下伏绿豆岩释放的钾离子,使得钾离子二次富集成藏。在地层水运移和气藏压力的共同作用下,形成气在上、富钾卤水在下的复合矿藏。长期继承性发育的古隆起不仅是油气聚集的有利部位,亦是二次运移、聚集的富钾卤水矿藏发育部位。本次研究成果为四川盆地及其他类似盆地的“气钾兼探”工作提供了一种新的方法和思路。

关键词: 四川盆地, 雷口坡组, 富钾卤水, 同层型气钾复合矿藏, 磨溪背斜

Abstract: Various types of Middle Triassic potash developed in the Leikoupo Formation in the Sichuan Basin, a key target strata for potassium prospecting in China. Brine from the Leikoupo Formation in the Moxi gas field is rich in K, Li, Br and B and has been classified as high-quality industrial grade saline solution, with its contents of minerals including KCl, LiCl, Br- and B2O3 exceeding the grade standards. The brine deposit in Leikoupo Formation shows great prospects for potash exploration. The seismic data interpretation results show that the top-boundary of the Leikoupo Formation appears as a complete anticline with few faults. Potassium-rich brine occurs in the wings of the anticline, while natural gas occupies the upper part of the anticline, both are stored together in the shoal dolomite with dissolved pores in the first member of the Leikoupo Formation, constituting a combined resources of nature gas and potassium-rich brine. Analogous to the concept of petroleum systems, we summarized the key factors affecting the formation, accumulation and preservation of potassium-rich brine into six key elements, namely the source of potassium, reservoir, sealing and trap conditions, transportation, and storage conditions. According to the collocation of these elements in time and space, we performed dynamic analysis of the formations of gas and brine in the same strata of the Leikoupo Formation. Hydrocarbons and halides are unusual substances found in groundwater. Controlled by groundwater dynamics, brine in the Leikoupo Formation continues to move towards the inherited palaeo-uplift upper part—the Moxi Anticline. Under the combined effects of formation water migration and gas reservoir pressure, the initial potassium-rich formation water, formed by gypsum dehydration and ancient seawater evaporation, continuously captures the potassium ions released by the underlying ‘green bean rock’, producing a secondary K+ enrichment, and finally forms the gas-potassium combined resources in the Moxi Anticline. The long-term inherited paleo-uplift is a favorable site not only for hydrocarbon accumulation, but also for secondary migration and accumulation of potassium-rich brine. The result of this research represents a novel approach for “simultaneous exploration of gas and potassium” in the Sichuan Basin and other basins alike.

Key words: Sichuan Basin, Leikoupo Formation, potassium-rich brine, combined resources of natural gas and brine, Moxi Anticline

中图分类号: