黄金坝地区断层特征及其对页岩气富集的影响

Fault characteristics in Huangjinba area and their influences on shale gas enrichment

昭通国家级页岩气示范区黄金坝地区不同区块或平台的页岩气井产能差异显著,断层发育与否是引起产能差异的重要原因之一。为了实现对该区页岩气更有效地商业开采,通过构造分析和断层刻画,剖析黄金坝地区断层发育的特征;依据断层发育规模进行分类和特征描述,开展断层与页岩气赋存关系的研究,明确不同类型断层对于页岩气富集的影响规律,近而选定页岩气勘探开发的有利区块。研究结果表明:(1)黄金坝地区断层具有分层性,以中上寒武统膏岩层为界,发育上、下两套断裂系统;(2)黄金坝地区背斜核部和构造转换部位是Ⅰ、Ⅱ类断层的主要发育区,向斜内断层较不发育,仅发育少量的Ⅲ类断层或裂缝;(3)Ⅰ、Ⅱ类断层不利于页岩气的保存,在距Ⅰ、Ⅱ类断层1 km以内、距大型断层破碎带发育区3 km以内,页岩气的富集程度通常较低。结论认为,该项研究成果可以为黄金坝及其他探区页岩气区带优选提供依据;区内沐爱向斜和建武向斜区五峰组—龙马溪组页岩气保存条件较好,是该区页岩气的有利富集区,可以作为现实的开发区。

The productivity of shale gas wells at different blocks or platforms in Huangjinba area of Zhaotong National Shale Gas Demonstration Area is significantly different.And fault development is one of the important factors causing the productivity difference.In order to realize commercial production of shale gas more effectively in this area,this paper analyzed the fault development characteristics in Huangjinba area based on structural analysis and fault description.Then,fault classification and characteristic description were carried out according to its development scale.In addition,the relationship between faults and shale gas occurrence was studied and the influence laws of different types of faults on shale gas enrichment were clarified.Finally,the favorable shale gas exploration and development blocks were determined.And the following research results were obtained.First,the faults in Huangjinba area are stratified,and bounded by the Middle-Upper Cambrian gypsum layer,there are two sets of fault systems,i.e.,the upper fault system and the lower fault system.Second,the anticline core and the structural transition belt in Huangjinba area are the main development areas of Class I and II faults.In the syncline,faults are less developed and only a small number of Class III faults or fractures are developed.Third,Class I and II faults are not beneficial to the preservation of shale gas.The shale gas enrichment degree within 1 km from Class I and II faults and 3 km from large fractured zones is usually lower.In conclusion,the research results provide a basis for the selection of shale gas zones in Huangjinba area and other exploration areas.What’s more,the Wufeng-Longmaxi Formation in Muai syncline and Jianwu syncline zone of this area has better conditions for the preservation of shale gas and it is a favorable shale gas enrichment zone,so it can be taken as a practical development zone in this area.