准噶尔盆地阜康凹陷侏罗系烃源岩特征与页岩气勘探潜力分析

Characteristics of the Jurassic Source Rocks and Their Shale Gas Exploration Potential in the Fukang Sag of the Junggar Basin

页岩油气正在成为中国油气勘探的重要对象之一。准噶尔盆地是中国西部最大的叠合盆地之一,盆地中是否存在页岩油气是能否打开油气勘探新局面的关键问题。本文通过对比其最大的生烃凹陷（阜康凹陷）的侏罗系烃源岩特征与Barnett页岩,来评价准噶尔盆地页岩油气的勘探潜力。阜康凹陷侏罗系烃源岩与Barnett页岩有以下相似性：①烃源岩规模稍大。阜康凹陷侏罗系主要发育八道湾组、三工河组和西山窑组三套泥质烃源岩层,累计厚度（最大950m）大于Barnett页岩;②干酪根类型相当。阜康凹陷干酪根类型在纵向上表现出一定的差异,下部八道湾组以Ⅱ型—Ⅲ型为主,中上部以Ⅲ型为主。③有机质的丰度偏小,但是存在厚层的煤。阜康凹陷有机质丰度分布符合正态分布,主要分布在1.2%~2.5%,与Barnett页岩相比略微偏小。但是从页岩气的角度来看,阜康凹陷发育多层单层厚度〉5m的煤层,总厚度超过50m,最大单层厚度超过20m,弥补了泥岩丰度不足的缺憾;④烃源岩已经进入中—高成熟阶段。表征烃源岩成熟度的Ro=1.6%,与Barnett页岩相当。上述对比结果表明阜康凹陷具有生成页岩油气的潜力。在此基础上,本文试图通过生烃潜力法的残留烃量评价本区页岩油气的勘探潜力,评价结果表明残留烃的规模为874.6亿吨,展示出阜康凹陷良好的页岩油气勘探潜力。

The shale oil and gas resources are becoming one of the most important oil and gas exploration targets in China. The Junggar Basin is a classical example of the overlapped basins that developed in northwest China. The Jurassic source rock that developed in its main hydrocarbon generating depression is studied and compared with the typical Barnett shale that developed in the Fort Worth Basin, North America, to show its shale gas exploration potentials. All of them are comparable with the Barnett shale in the following four aspects： ①The scale of source rocks is slightly larger. Three sets of source rocks were recognized in Fukang Sag, namely, the Badaowan Formation of the lower Jurassic （J1b ）, the Sangonghe Formation of the lower Jurassic, and the Xishanyao Formation of the middle Jurassic. The total thickness is 〉 950 m, which is greater than that of the Barnett shale. ② All of them are characterized by humic prone organic type that falls within type 112 and type 111 source rocks. ③ The abundance of organic matter measured in TOC falls within 1.2 % ~ 2.5 %. The lower limit is a little bit lower than that of the Barnate shale, but the abundant coal beds （ thickness 〉 20 m for a single bed） seems to compensate for that.④ The maturity falls within the window of gas generating with the Ro = 1.6 %. Based on the above geologic evidences, the total residual hydrocarbon in the source rock is estimated to be 87.46 billion tons, indicating a great shale gas exploration potential in the Junggar Basin.