摘要:
针对西藏羌塘盆地中生界海相烃源岩地面样品风化严重等实际情况,利用大量露头剖面点样品的有机地球化学测试数据和前人研究资料,在对有机质丰度、类型和成熟度有效性分析及评价标准建立的基础上,采用综合地球化学剖面方法,对盆地不同构造单元的烃源岩进行了综合评价研究,预测了有利生烃区。结果表明,有机碳含量与生烃潜力(S1+S2)、氯仿沥青"A"和总烃(HC)含量之间相关性良好,总体呈正向线性关系,受岩性的影响,灰岩和油页岩的关系曲线一般高于泥岩和煤;地表风化作用虽然对地面样品尤其是灰岩样品的有机碳含量影响较小,但对生烃潜力、氯仿沥青"A"和总烃含量等指标的影响不容忽视;中生界海相烃源岩在各构造单元内的发育不同,蒂让碧错-土门凹陷的索瓦组台地相泥灰岩和肖茶卡组三角洲相泥岩为好生油岩;帕度错-纳江错凹陷比洛错地区肖茶卡组外陆棚相油页岩或页岩为极好生油岩,深水陆棚相或开阔台地相灰岩为中等烃源岩;洞错-葫芦湖较深凹陷和吐坡错-白滩湖深凹陷的布曲组和索瓦组台地相灰岩及肖茶卡组上部灰岩为中等生油岩。有机质类型以Ⅱ型为主,各地区成熟度差异明显,总体以成熟~高成熟为主,在同一剖面上自上而下成熟度逐渐增高。沉积环境是优质烃源岩发育的主控因素,上三叠统肖茶卡组(T3x)广泛发育的半深海盆地相黑色泥页岩是盆地最重要的烃源层,泥岩有利生烃区分布面积大,侏罗系布曲组(J2b)和索瓦组(J3s)碳酸盐岩台地相台内凹陷较闭塞的静水沉积的泥灰岩为重要烃源岩层,灰岩有利生烃区分布面积大,对进一步明确羌塘盆地不同构造单元主力烃源岩特征与分布及下一步油气勘探具有重要参考价值。
Abstract:
The comprehensive geochemical cross section in the main structures of the Qiangtang basin was established to evaluate the source rock and predict the favorable hydrocarbon generation areas, based on the data of organic abundance, type and maturity from a large number of outcrop samples in the Mesozoic marine mudstone and carbonate source. The results show that relation between TOC and hydrocarbon potential (S1+S2), chloroform bitumen "A" and total hydrocarbon content (HC) has good correlation, generally in positive liner, of which in carbonate and oil shale is higher than that in the mudstone and coal, dependent on their lithology to some extent. Subaerial weathering has small impact on organic abundance, but has significant impact on hydrocarbon potential, chloroform bitumen "A" and total hydrocarbon content (HC). The Mesozoic marine source rocks development varies in different structural unit, for example, carbonate rocks in the Suowa Formation and Delta mudstone in the Xiaochaka Formation of Dirangbicuo-Tumen sag are of good quality source rock. Oil shale and shale in the Xiaochaka Formation of Paducuo-Najiangcuo sag are of extreme good quality source rock, deep water shelf and platform carbonate rock are middle class source rocks. And platform carbonate rock in the Buqu Formation and Suowa Formation buried deep in the Dongcuo-Huluhu and platform carbonate in the Buqu Formation and upper carbonate in Xiaochaka Formation buried deep in the Tupocuo-Baitanhu are middle class quality source rock. Organic matter,is mainly Ⅱ type, with maturity various in different areas, ranging from mature to over-mature, most mature-high mature and increasing from top to bottom in a single cross section. Sedimentary environment is the main controlling factor of source rocks quality. Middle deep marine black shale or mudstone in Upper Triassic Xiaochaka, with wide hydrocarbon generation area, are the most important source rocks. While the still water mud-carbonate rocks in water closed carbonate plateform in the Jurassic Buqu Formation (J2b) and Suowa Formation (J3s) are important source rocks, with wide carbonate hydrocarbon-generation. Further study on the source rock characteristics and major source rock has significance for future oil and gas exploration.
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