燕山运动对页岩气保存条件的控制作用——以滇黔北地区太阳—海坝区块龙马溪组页岩气为例

Control of Yanshanian movement on shale gas preservation conditions: a case study on the Longmaxi Formation shale gas in Taiyang-Haiba Block of northern Yunnan and Guizhou

滇黔北地区昭通国家级页岩气示范区太阳—海坝地区上奥陶统五峰组—下志留统龙马溪组发育优质页岩气储层,现已进行规模开采,但对页岩气保存条件尚未进行系统性分析。为了落实该区页岩气开发潜力、明确有利勘探区带,基于地震资料,结合区域地质认识,对区内构造演化、断裂期次、地层变形特征及其对龙马溪组页岩气保存条件的影响进行了研究。研究结果表明:(1)太阳—海坝地区受多期构造运动作用,其中燕山期两幕构造运动对构造形态及断裂发育影响最大,形成北东、近南北、北西三组走向断裂,对龙马溪组页岩气的保存条件有着不同程度的影响;(2)燕山早期为北西方向应力作用,形成北东走向逆断层及近南北走向走滑断层,其中北东走向逆断层上盘地层较破碎,页岩气保存条件变差,断层下盘地层完整,保存条件较好,近南北走向走滑断层多断至地表,早期对保存条件具有一定破坏作用;(3)燕山晚期为北东东方向应力作用,形成北西走向逆断层,与早期形成的逆断层相似,保存条件断层下盘比上盘更好,同时早期形成的走滑断层走向与本期应力方向垂直,断层闭合,对页岩气保存条件影响变小。结论认为,燕山运动控制了该区整体构造形态及主要断裂空间展布、不同性质的断裂及断层上下盘地层的完整性,对页岩气保存条件的影响存在着较大的差异。

High quality shale gas reservoirs are developed in the upper Ordovician Wufeng Formation and Lower Silurian Longmaxi Formation of Taiyang-Haiba area,Zhaotong national shale gas demonstration area in northern Yunnan and Guizhou,and have been exploited on a large scale,but the preservation conditions of shale gas have not been systematically analyzed.In order to realize the development potential of shale gas in this area and identify the favorable exploration zones,based on seismic data and combined with regional geological knowledge,the structural evolution,fault periods,strata deformation characteristics and their influence on shale gas preservation conditions of Longmaxi Formation in this area are studied.The results show that:(1)Taiyang-Haiba area is affected by multi-stage tectonic movement,in which the Yanshanian two-stage tectonic movement has the greatest influence on the structural morphology and fault development,forming three groups of strike faults,namely NE,nearly SN and NW,which have different degrees of influence on the preservation conditions of Longmaxi Formation shale gas;(2)In the early Yanshanian period,the stress action was NW,thus forming reverse faults with strike of NE and strike slip faults with strike of nearly NS.The hanging wall strata of reverse faults with strike of NE were relatively broken,and the shale gas preservation conditions became worse.The footwall strata of faults were complete,and the preservation conditions were good.The strike slip faults with strike of near NS were mostly broken to the surface,which had a certain destructive effect on the preservation conditions in the early period;(3)The stress action of late Yanshanian is NEE,forming reverse fault with strike of NW,which is similar to that of early Yanshanian.The preservation condition of footwall is better than that of hanging wall.At the same time,the strike slip fault formed in early Yanshanian is perpendicular to the stress direction of this period,and the fault is closed,which has less influence on shale gas preservation condition.It is concluded that the Yanshanian movement controls the overall structural shape and the spatial distribution of major faults in the area,and the faults with different properties and the integrity of the strata in the upper and lower walls of the faults have great differences in their effects on the preservation conditions of shale gas.