鄂尔多斯盆地上三叠统延长组含气页岩地质特征及资源评价

Geological characteristics of gas-bearing shales in the Yanchang Formation and its resource assessment in the Ordos Basin

为了摸清鄂尔多斯盆地上三叠统延长组页岩气的勘探潜力,通过野外露头调查、钻井岩心观察、老井资料复查,结合有机地球化学和岩石学分析、含气量现场解析测试等手段,系统开展了延长组含气页岩段展布特征、岩石矿物学特征、有机地球化学特征、储层特征、含气性等地质特征分析,明确了该区中生界含气(油)页岩的主要赋存层段为延长组长4+5、长7、长9段,其中长7段页岩品质条件最好;延长组湖相页岩分布面积较广,厚度大,干酪根类型为腐泥型,有机碳含量高、分布差异性大,吸附能力强,含气量值与海相页岩相当。在地质评价基础上,以含气泥页岩段作为评价单元,采用体积法计算出长9段含气页岩段的地质资源量为0.4145×1012m3,长7段为1.1506×1012m3,长4+5段为0.255 1×1012m3;其中长7段资源量占延长组总资源量的,可作为盆地页岩气勘探开发的优先选择层段。结论认为:鄂尔多斯盆地延长组页岩气资源量巨大,是未来值得重视的天然气勘探开发新领域。

This paper aims to make clear the shale gas exploration potential of the Yanchang Formation in the Ordos Basin. Based on outcrop investigation, core sample analysis, and old well data reexamination and in combination with organic geochemistry and rock analysis, gas content measurement, and isothermal adsorption curves, etc. , a systematic evaluation was conducted of formation dis- tribution, petrological characteristics, geochemical eharacteristies, reservoir characteristics and other geological features like gas bearing in this study area. The following results were achieved. （1） The major target pay zones in this area are the members of Chang 4＋5, Chang 7, Chang 9 in the Mesozoic Yanehang Formation, among which Chang 7 has the best quality in shales. （2） There is a wide distribution area of the lacustrine shales with great thickness, the sapropelic as the kerogen type, high TOC content, big distributional difference, strong adsorption ability, and the gas content of lacustrine shales is equivalent to that of marine shales. （3） By use of the volumetric method, the gas iwplace in the member of Chang 9 is calculated to be 0. 4145 trillion m^3 , that of Chang 7 is 1. 1506 trillion m^3 , that of Chang 4＋5 is 0. 2551 trillion m3 ; the resource reserves in the Chang 7 accounts for 63% of the total in the Yanchang Formation so that it can be seleeted as the first target zone in the shale gas exploration and development in this ba sin. In conclusion, it is considered that the shale gas resources are rich in the Yanchang Formation, Ordos Basin, which will be a new area for natural gas exploration and development in the future.