羌塘盆地半岛湖—东湖地区主力烃源岩及油气资源潜力

Main source rock and oil resource potential of the Bandaohu-Donghu area in the northern Qiangtang Basin

羌塘盆地中部新发现很多液态油苗,生物标志化合物指示这些液态油苗和BAPS古油藏的原油来自早侏罗世Toarcian油页岩。下侏罗统海相油页岩TOC含量高、生烃潜量大、有机质成熟度适中,是羌塘盆地侏罗系优质烃源岩和主力生油层。地震反射剖面结合钻探标定揭示,下侏罗统Toarcian油页岩稳定分布于北羌塘凹陷,厚度110~150m,大部分地区埋深4500~3000m,半岛湖背斜两翼埋深3000~1000m。由于逆冲推覆及构造改造,下侏罗统Toarcian富碳页岩在半岛湖背斜核部埋深变浅为522~675m,在比洛错、胜利河、长蛇山、托纳木藏布等地表形成油页岩露头。应用氯仿沥青法和成烃率法,采用不同地点Toarcian油页岩及生烃参数,估算面积2万km^2半岛湖-东湖地区初次生烃形成原油资源量为50~100亿吨,新生代二次生烃形成原油资源量为24.4亿吨。北羌塘凹陷Toarcian海相油页岩经过初次生烃和二次生烃形成了巨量油气资源,具有巨大的油气勘探前景。

Several liquid oil seeps were discovered recently in the central Qiangtang block. Biomarker parameters indicate that crude oil of the seeps and the Beileico-Andarco Petroliferous Sequence(BAPS) are both derived from the Early Jurassic Toarcian oil shale. The Lower Jurassic oil shale characterized by high content of TOC, large potential of hydrocarbon generation and lower maturity of organic matter is the main source rock and major oil generating strata in the Qiangtang basin. Seismic reflection profile and drilling logs reveal that the Toarcian oil shale as thick as 110~150 m covers all over the Northern Qiangtang Depression(NQD). Depth of the Toarcian oil shale ranges from 4500~3000 m in most areas of the NQD to 3000~1000 m in both wings of the Baodaohu anticline. Early Cenozoic thrust and deformation caused uplift of the Toarcian oil shale, which forms oil shale outcrops in the Bilog Co, Shenglihe, Changsheshan and Tuonamu Zangbu, and the Toarcian oil shale rise to as deep as 522~675 m at core summit of the Bandaohu anticline. Methods of chloroform bitumen "A" and hydrocarbon generation rate of Toarcian oil shale sampled from different areas were taken for evaluation of oil resource in the focused region of NQD. It is estimated that the crude oil as much as 5000~10000 million tons occurs in the Bandaohu-Donghu area as large as 20000 km^2 after first time hydrocarbon generation of the Toarcian oil shale, and second time hydrocarbon generation of the oil shale forms 2440 million dons crude oil in the Cenozoic. The NQD contains mega volume of crude oil after two times hydrocarbon generation and is of prospective for oil exploration in the Qiangtang basin.