火山岩期次划分及分布预测方法——以松辽盆地徐家围子断陷安达凹陷为例

安达凹陷位于松辽盆地徐家围子断陷北部,其烃源岩品质优越,下白垩统营城组火山岩储层致密,以岩性气藏为主要类型。该区火山机构类型多样,具有多期喷发、叠置分布的特征。目前该凹陷天然气勘探程度相对较高,储层相对发育的明显火口区目标己基本钻探完毕,亟须寻找新的勘探目标。为此,通过岩心、测井响应和地震反射的标志建立起了火山喷发期次划分标准,结合井—震骨架剖面分析,认为该凹陷存在3期火山喷发,并利用地震相干体和趋势面分析等技术,对各期次火山机构和相带展布进行了预测。结果表明:岩相和岩性分布特征决定了该区火山岩储层呈现出西好东差、南好北差的分布格局,西部以岩性构造气藏为主,东部为致密岩性气藏。最后依据研究成果,落实有利勘探面积950 km~2,新识别出超过30个火口区、近火口区,落实了1000×10~8m~3天然气资源潜力。

Methods of phase division and distribution prediction of volcanic rocks in the Xujiaweizi Fault Depression,Songliao Basin : A case study of the Anda Sag

The Anda Sag, the northern part of the Xujiaweizi Fault Depression in the Songliao Basin, contains high-quality source rocks and tight, lithologic gas deposit-dominated volcanic reservoirs of the Lower Cretaceous Yingcheng Formation. This area is known to have a variety of volcanic edifices that are characterized by multi-phase eruption and superimposed distribution. Currently, the sag has been highly explored, and drilling of targets in the critical crater areas with reservoirs relatively developed has basically finished. So, additional targets will be defined. Thus, a criterion for dividing the volcanic eruption phases was established based on core, well log and seismic response marks. Through a well-seismic skeleton section analysis, it was believed that three volcanic eruption phases (Ⅰ, Ⅱ and Ⅲ) occurred in the Anda Sag. Finally, the volcanic edifice and facies belt distribution of each phase were predicted by using seismic coherence body and trend-surface analysis techniques, with over 30 new volcanic crater targets identified, the predicted results show that the distribution of lithofacies and lithologies determines the framework of better volcanic reservoirs in the west and south than that in the east and north respectively – lithologic-structural gas reservoirs are dominant in the west, while tight lithologic gas reservoirs are dominant in the east. Based on the study results, the favorable exploration area is finalized as 950 km², a potential of 100 billion m³ gas resources has been implemented.