王府断陷断裂特征及其对深层火山岩气藏的控制作用研究

The fault characteristics of the Wangfu fault depression and its controlling effects on deep-seated volcanic gas reservoir

松辽盆地深层火山岩天然气藏勘探获突破进展,表明火山岩成藏条件良好。在火山岩天然气成藏研究方面前人做了很多工作,但对于断层在成藏控制作用方面研究较少。本文以松辽盆地东南部王府断陷为研究对象,利用地震资料进行构造、断裂精细解释,总结了断裂发育特征,并系统分析了断裂体系对成藏的控制作用,认为该区断裂体系是火山岩气藏最为根本和关键的控制因素,具体表现在不同级别、不同期次的断层对油气成藏的控制作用不同。王府西断裂为铲式断裂,是控制洼陷形成的边界大断层。王府1东基底断裂与城深2东基底断裂控制了山东屯与小城子两个二级构造带的形成,还直接控制火山岩储集体的分布。本区火山口大多发育于两条或多条断裂的交汇处,其四周依次发育爆发相、溢流相、火山通道相、火山沉积相,其中最有利的火山岩储集体主要发育于爆发相与溢流相。利用地震技术能够对火山岩储集体进行有效识别。储层研究表明,山东屯构造带火山岩储集体发育,西邻沉积中心与烃源岩构成良好的生储盖组合,是王府断陷深层天然气成藏最为有利的地区。断裂体系对火山口与火山岩相及储集体的分布具有重要的控制作用,对研究区火山岩成藏至关重要。这些认识对类似地区的勘探有一定指导作用。

Recent breakthroughs on the exploration of deep volcanic gas reservoirs in the Songliao Basin indicate that volcanic rocks have favorable conditions for reservoir forming. So far,previous studies are mainly concentrated on the volcanic gas reservoir forming of this basin; however,few works have been done on the control effects of the fault system on its reservoir forming. This paper took the Wangfu depression in southeastern Songliao Basin as an example,and by using seismic data,to conduct a fine interpretation on its structures and fault system by summarizing the characteristics of the fault system developed there,and to systematically analyze the control effects of the fault system to reservoir forming. It can be concluded that the fault system in the study area is the most fundamental controlling factor for the formation of the volcanic gas reservoirs,and the controlling effects of faults on reservoirs are different with their different grades and stages. The Wangfu west fault is a listric fault,and controlled the formation of the sag as the boundary fault. The Wangfu No. 1 basement fault and the Chengshen No. 2 east basement fault controlled the formation of two secondary tectonic belts（ Shandongtun and Xiaochengzi） and directly controlled the distribution of volcanic reservoirs. The volcanic craters always occurred at the intersections of two or more groups of faults,and four types of lithofacies successively developed around the craters,namely the eruption facies,the overflow facies,the volcanic conduit facies and the volcanic sedimentary facies. The most favorable volcanic reservoir is chiefly developed in the eruption facies and the overflow facies. Seismic technology can effectively identify volcanic reservoirs. Studies on reservoirs show that the Shandongtun tectonic zone has well-developed volcanic reservoirs; moreover,it is adjacent to the depocencer in the west,and constitutes a good combination of source-reservoir-caprock with source rocks,thus it is the most favorable area for natural gas accumulation in deep of the Wangfu depression. The fault system has an important controlling role on the distribution of volcanic craters,volcanic phases and reservoirs,and as a result,it is critical for volcanic reservoir forming. The results of this paper have some guiding significance for oil and gas exploring in similar areas.