塔里木盆地塔中隆起志留系油气成藏及分布特点

Hydrocarbon accumulation and distributional characteristics of the Silurian reservoirs in the Tazhong uplift of the Tarim basin

塔里木盆地塔中隆起志留系油气成藏具有两源三期的成藏特点,"两源"是指油气来源于寒武系、中、上奥陶统两套烃源岩;"三期"是指从沥青到可动油的形成经历了加里东晚期、海西晚期、燕山—喜山期三个成藏期,沥青的形成是早期油气运移聚集过程中遭破坏的结果,目前所发现的可动油是以中、上奥陶统油气源为主的晚期成藏的结果。发育三种油气藏类型,即背斜构造、地层岩性以及火山岩遮挡型。塔中隆起志留系油气聚集受三大因素控制,一是隆起构造背景,围绕古隆起构成多种圈闭类型组合的复合油气聚集区;二是有效盖层,志留系中的油气显示十分活跃,包括沥青、稠油和正常油,沥青和稠油分布在红色泥岩段以下,而可动油集中分布在灰色泥岩段之下;三是优质储层,砂岩储层分布广泛,储层储集空间有次生-原生孔隙型、原生-次生孔隙型、微孔隙型三种类型,孔隙度3.3 %～17.4 %,渗透率(0.1 ～667.97)×10-3μm2。

Hydrocarbon accumulation of the Silurian in the Tazhong uplift of the Tarim basin is characterized by the ＂two sources and three periods＂. The ＂two sources＂ means that the hydrocarbons were derived from two source rocks of the Cambrian and middle-upper Ordovician. The ＂three periods＂ means that asphalt and movable oil experienced three hydrocarbon accumulation stages in the late Caledonian, late Hercynian and Yanshanian-Himalayan. The formation of asphalt resulted from the destruction of the accumulation and migration of hydrocarbons in the early stage. The present movable oil, mostly derived from middle-upper Ordovician source rock, resulted from the accumulation of hydrocarbons in the late stage. There are three types of reservoirs, namely anticline structural, stratigraphic lithological and lava-shielded reservoirs in the Tazhong uplift. Hydrocarbon accumulation of the Silurian in the Tazhong uplift is controlled by the following three factors. The first is the background of uplift structure; around the ancient uplift, the combination of many types of traps made up the composite hydrocarbon accumulation areas. The second is the effective cover; the show of oil and gas including asphalt, heavy crude oil and normal oil is quite active in the Silurian; asphalt and heavy crude oil are distributed under the red mudstone member, and movable oil is distributed under the gray mudstone member. The third is the high quality reservoir bed; sandstone is distributed widely in the Tazhong area. Reservoir pore space may be divided into three types： the secondary origin-primary origin pore space, the primary originsecondary origin pore space, and the micropore space. The porosity is 3.3%-17. 4%, and the permeability is （0. 1-667. 97） × 10 ^-3μm^2.