摘要：

羌塘盆地地处藏北高原，其南北界分别为班公湖－努江缝合带与拉竹龙-金沙江缝合带，盆地面积约160,000km2。盆地内发育古生代～中生代海相沉积地层，其中尤以侏罗系分布最广、发育最为齐全。在侏罗系的中统和上统下部广泛发育白云岩，并构成最具潜力的油气储层。这些白云岩按其成因与岩矿特征可归为两类即I型和II型白云岩。I型白云岩是在蒸发条件下由毛细管浓缩作用形成，故与膏岩层关系密切。它具有白云石晶粒细小、化学组成中相对富Ca2＋、晶体有序度相对偏低等特点；II型白云岩则是在海水与大气淡水的混合水中生成，因而与膏岩层无关。与I型白云岩相比，其具有白云石晶粒较粗且自形程度较高、化学组成相对富Mg2＋及晶体有序度较高的特点。I型白云岩在形成之后基本无明显后期改造，因而其在储集物性上保持了原始的中低孔和低渗的特点，可构成区内的II～III级油气储层；而II型白云岩则在形成后的晚成岩～表生阶段，经历了明显的重结晶、溶蚀和方解石充填交代等后期改造，由于其(尤其是地下未经表生改造的部分)具有较好的孔渗条件，因而常构成区内的I～II级油气储层。

Abstract:

Qiangtang Basin is situated in the North Tibet plateau. Its north and south boundaries are Lazhulong-jinshajiang suture belt and Bangonghu-nujiang suture belt respectively. The area of the basin is about 160,000km2. Paleozoic to Mesozoic (especially Jurassic) marine strata is well developed in the basin. Dolostones are widely distributed in the middle series and the bottom of upper series of Jurassic. They are the most potential oil & gas reservoir rocks. The dolostones can be classified into two types (i.e. type 1 and type 2) according to their origin and the characteristics of rocks & minerals. Type 1 dolostone was formed in the evaporation condition by way of capillary concentration dolomitization. It is associated closely with gypsum (anhydrite). Dolomite crystals in the dolostone are very thin or little. Its chemical composition is relatively rich in Ca2+.  The degree of order of its crystals is fairly low. Type 2 dolostone was formed in the mixed waters of marine water and meteoric fresh water. It is not associated with gypsum (anhydrite). Dolomite crystals in it are thicker and more euhedral than that in type 1 dolostone. The chemical composition of type 2 dolostone is relatively rich Mg2+. The degree of order of its crystals is fairly high. Type 1 dolostone was not obviously remade after it was formed. It keeps low to mid porosity and very low permeability as it was in original. Type 1 dolostone can form oil and gas reservoir with ranks II-III in the basin. After it was formed, type 2 dolostone underwent clear recrystallization and dissolution, and filling and replacement by calcite in late-diagenetic to epidiagenetic stages. Type 2 dolostone, especially that was not remade by epidiagenesis, can form oil and gas reservoir with ranks I-II in the basin because of its fairly good conditions of porosity and permeability.