羌塘盆地膏盐岩及其与油气勘探的关系

The gypsolith and its bearings on the oil and gas exploration in the Qiangtang Basin in northern Xizang and southern Qinghai

关键词:  羌塘盆地  膏盐岩  油气勘探

Key words:  Qiangtang Basin  gypsolith  oil and gas exploration  northern Xizang and southern Qinghai

摘要:

羌塘盆地有较广泛的膏盐岩层分布,主要赋存于中侏罗统雀莫错组、布曲组、夏里组和上侏罗统索瓦组中,具有亮晶鲕粒灰岩→白云岩(云灰岩)→膏盐岩层、粉砂岩(或泥岩)→膏盐岩→粉砂岩(或泥岩)→膏盐岩层和膏质白云岩(或泥岩)→膏盐岩层三种沉积层序,分属湖-海湾型、潮坪和萨布哈型三种成因类型与沉积模式。湖型膏盐层较厚且展布稳定;潮坪型膏盐层较薄、变化快、层数多;萨布哈膏盐层呈薄层、极薄层夹于泥岩、白云岩中,也呈结核状、眼球状等,多发生表生水化变形。膏盐岩层除层状产出外,也呈盐丘产出,已在赤布张错、雁石坪、温泉等地多处发现盐丘构造,直径一般为100~1000m,并见有油气显示。因此,根据盐丘的发育情况,结合沉积相展布,在有利的构造部位寻找刺穿油气藏是大有可为的,应作为羌唐盆地油气早期勘探的突破点。

Abstract:

The gypolith deposits crop out over a wide area of the Middle Jurassic Quemocuo Formation, Buqu Formation and Xiali Formation, and the Upper Jurassic Suowa Formation in the Qiangtang Basin in northern Xizang and southern Qinghai. These deposits may be arranged into three types of sedimentary sequences:(1) oosparite-dolostone (dolomitic limestone)-gypsolith, (2) siltstone (or mudstone)-gypsolith-siltstone (or mudstone)-gypsolith, and (3) gypeous dolostone (or mudstone)-gypsolith sequences, which are assigned to the lagoon-gulf, tidal-flat and sabkha sedimentary environments, respectively. The lagoon-gulf gypolith deposits are commonly larger in thickness and laterally extensive. The tidal-flat gypolith deposits become apparently thinner and laterally inextensive. The sabkha gypolith deposits occur as thin and very thin beds or as nodules and augens in the mudstone and dolostone of the basin. The gypolith deposits cited above have also been found to occur as salt-dome structures 100 to 1 000 m in diameter in Yanshiping, Wenquan and Chibuzhang Lake, where oil shows have been identified. It is possible, judged from the development of the salt domes and distribution of sedimentary facies, to search for piercement oil pools in favourable structures of the basin.