鄂尔多斯盆地延长组湖相黏土岩分类和沉积环境探讨

鄂尔多斯盆地三叠系延长组长7油层组沉积了区域分布的大套湖相黏土岩,它不但是鄂尔多斯盆地中生界最重要的烃源岩,同时也是目前致密油/页岩油勘探的主要领域.作者在对国内外黏土岩分类及其成因机制等系统调研基础上,通过对工区25口连续取芯井的岩芯描述和400余块典型黏土岩薄片观察,并充分应用X衍射、有机地球化学等分析测试资料,提出了湖相黏土岩的分类方案与基本特征,探讨了不同类型黏土岩形成的沉积环境.根据岩石组分、沉积构造等特征,鄂尔多斯盆地延长组长7油层组黏土岩主要发育5种类型:①块状泥岩;②粒序层理泥岩;③波状纹层页岩;④平直纹层页岩;⑤似块状页岩.该成因分类方案将黏土岩类型与沉积环境相结合.指出受三角洲前缘影响的浅湖区以块状泥岩为主;受湖流和波浪影响的浅湖—半深湖环境以波状纹层页岩为主;深湖静水区以平直纹层状页岩为主;深湖坳陷区以粒序层理泥岩为主;火山灰爆发时期以似块状页岩为主.粒序层理泥岩是致密油赋存的主要类型,有机碳平均含量为6%;似块状页岩是页岩油赋存的主要类型,有机碳平均含量为17.17%.

The Classification of Lacustrine Mudrock and Research on Its' Depositional Environment

The deep lacustrine mudrock are the important source rock as well as self-stored reservoirs. The exploration of unconventional resources has been a hot topic at present. Being the main target of tight oil and shale oil, it's characteristics and formation mechanism have been paid great attention. Chang 7 member of Yanchang Formation, which is deposited in the late Triassic, is the main source rock of Ordos Basin.A classification scheme based on the constituents and texture is proposed. The research of the lacustrine mudstone of Chang 7 member indicates that the deep lacustrine mudstone comprises at least 5 lithofacies: massive mudstone, graded laminated mudstone, wavy laminated shale, even laminated shale, and block-like laminated shale. These mudstone facies assemble two categories on the basis of self-generating characteristics, i.e. allogenous mudrock, including massive mudstone, graded laminated mudstone; autogenic mudrock, including wavy laminated shale, even laminated shale, block-like shale.This classification is associated with sedimentary environment. Shallow lake which is influenced by delta is dominated by massive mudstone; shallow-semi shallow lake being influenced by lake currents and waves is mainly deposited with wavy laminated shale; deep quite lake is associated with even laminated shale; deep lake depression is dominated by graded mudstone; block-like shale mainly appears in the period of volcano eruption.However, the mudstone lithology is changing with the evolution of the lake and thus one interval has different types of mudrock. The lithology can be changed within centimeters. We can conclude in this way that the mudrock interval is highly heterogeneous, which makes our prediction much more difficult. As a whole, graded mudstone is the interval of tight oil and the block-like shale is the main source rock and contains shale oil.