松辽盆地无机成因气藏形成分布特征及勘探方向

FORMATION AND DISTRIBUTION FEATURES OF THE ABIOGENIC GAS POOLS AND THEIR EXPLORATION STRATEGIES IN THE SONGLIAO BASIN

松辽盆地特有的深部物质组成及其弧后走滑拉张盆地的区域构造背景,使之发育大量无机成因气藏。无机成因气藏主要发育在NNE、NWW向两组深大断裂周缘,火山活动较强烈,有较充裕无机成因气供给的区域。无机成因烃类气藏主要分布在地壳深部氧逸度低,氢元素丰富的有利区带。无机与有机成因天然气均有相似的流体运移通道,有相似的富集带——NNE向坡折带、坡垒带与洼陷间隆起带及NEE—EW向鼻状隆起带相交接部位。在富含无机成因气的深部热液作用下,形成溶蚀孔隙极为发育的各类储层。同时,CO2气体对烃源岩中烃类的强烈溶洗及萃取,形成油气混合流体,为油气运移提供了动力,提高了油气运聚效率。由此,常形成有机与无机成藏共生组合。下一步既要继续开展有机与无机成藏共生组合均发育深断陷的勘探,又要积极探索断陷基底的中古生界碳酸盐岩和火山活动较强浅断陷中的无机成因天然气。

Abundant abiogentic gas pools were developed in Songliao Basin due to its unique deep litho- sphere, crustal structure and regional structure background of rear arc strike-slip ＆ pull-apart basin. The abiogenie gas pools are mainly located around the NNE and NWW trend major faults in deep crust, where there is plenty of abiogenic natural gas supply because of intense volcanic activities. Abiogentic hydrocarbon gas pools are mainly located in low-oxygen-fugacity and hydrogen abundant zones in deep crust. Organic and abiogentic pools are mutually accelerated and effected. They share similar migration pathways and their accumulation belts are both located in strike-slip ＆ pull-apart related NNE slope breaks and horsts as well as central fault uplifts, strike-slip thrusting related uplifts between sags, big structures connected to NEE--EW nose uplifts, and structure-lithology-layer combined traps. Deep abiogentic hydatogenesis causes corrosion reservoir beds. In the meanwhile, the strong corrosion of CO2 fluid helps the extraction of organic substance, generating oil and gas combined flow, and there＇s a good chance of the coexistence of organic and abiogentic hydrocarbon pools. Work for the next phase is to go on exploring the abiogentie gas and combined generated gas in deep fault depressions, and to find the abiogentie gas both in Mesozoic--Paleozoic carbonate sequences in the base of fault depression and in shallow fault depression with intense volcanic activities.