鄂尔多斯盆地东部上三叠统含油砂岩的古地温及成岩阶段

PALAEOTEMPERATURES AND DIAGENETIC STAGE OF THE UPPER TRIASSIC OIL SANDSTONES IN THE EASTERN ORDOS BASIN

本文采用镜质体反射率、流体包裹体、磷灰石裂变径迹、伊利石结晶度、绿泥石多型及自生矿物的成岩变化等多种方法,对鄂尔多斯盆地东部上三叠统含油砂岩所经历的最高古地温进行了测定和对比。中生代晚期本区古地温梯度为2.9—3.0℃/100m,上三叠统在此期间进入有机质成熟阶段,开始生烃和运聚过程。含油砂岩段的古温度为88—110℃,油的生成和运移的温度为112—122℃。上三叠统上覆地层的剥蚀厚度为2465—2750m。含油砂岩段现埋深一般为400—1200m,埋深1900m左右温度达140℃,此深度带以下以产天然气为主,进入有机质超成熟阶段。

The maximum palaeotemperature of oil sandstones in the Upper Triassic in the eastern Or-dos basin has been determined and correlated by using many ways including the vitrinite reflectance, fluid inclusions, apatite fission track, illite crystallinity, chlorite polytypes and diage-netic changes of authigenic minerals. The temperature gradient in the Late Mesozoic was about 2. 9-3. 0℃/100 m. The Late Jurassic was a stage of maturation of organic matter in the Upper Triassic oil sandstones and hydrocarbon began to be produced and migrate in this stage. The palaeotemperatures of oil sandstones is in the range of 88-110℃ those for the generation and migration of oil range from 112 to 122 ℃. The thickness of the denuded strata overlying the Upper Triassic is about 2465-2750 m. The present burial depth of oil sandstones is generally 400 to 1200 m. At the depth of ca. 1900 m, the temperature may reach 140 C. Below this depth, rocks are overmature and yield mainly gas.