IDENTIFICATION OF CONDENSED SECTION AND ITS IMPLICATION FOR EXPLORATION OF TIGHT SANDSTONE GAS: EXAMPLES FROM XUJIAHE 3 AND XUJIAHE 5 MEMBERS, SICHUAN BASIN
【摘要】 以四川盆地须家河组三段和五段为例,分析凝缩段识别及如何指导致密砂岩气勘探。分析认为:1凝缩段是最大湖泛面时沉积产物,岩性主要为质纯的暗色泥岩或黑色页岩,测井曲线上表现为高自然伽马,对应于△log R高值段,地震上为强连续反射,为高位体系域的下超面;2须三与须五段属于致密砂岩气藏,具有近源成藏的特点,而非源内成藏,可形成经济型致密气资源,而凝缩段发育优质烃源岩,有机碳含量高,生烃能力强,与之紧密接触的规模储集砂体最具勘探潜力。综合研究指出,寻找致密砂岩气勘探"甜点区"首先寻找凝缩段,其上直接接触的规模储集砂体就是最有利勘探区。
【Abstract】 Taking Xujiahe 3(T3x3)and Xujiahe 5(T3x5)members in Sichuan Basin as examples, we analyze how to identify condensed section and how to guide an exploration of tight sandstone gas by means of its identification. Results show that(1)the condensed section, a product of the maximum flooding surface during deposition, is mainly composed of pure dark mudstone and shale. In well-logging curve, it represents high natural gamma ray, corresponding to a high △log R value. In seismic appearing a strongly continuous reflection, it is a downlap interface at HST;(2)characterized by near-source accumulation, the sandstone reservoirs of both T3x3 and T3x5, can form economic tight gas resources; and(3)in the condensed sections of these two members, there are developed high-quality source rocks with rich organic carbon and strong hydrocarbon-generating capacity, all resulting in a high exploration potential for its closely adjoining sandbody. In addition, our comprehensive study demonstrates that to search for sweet spot of tight sandstone gas must find out some condensed sections at first just because the closely upper large-scale reservoir sandbody is the most favorable exploration zone.
【Key words】 Sichuan Basin； Xujiahe 4 and Xujiahe 5 members； condensed section； tight sandstone gas； △Log R； near-source accumulation；
- 【文献出处】 天然气勘探与开发 ,Natural Gas Exploration and Development , 编辑部邮箱 ,2015年02期