渤海湾盆地东营凹陷南斜坡断裂趋势带形成机制与控藏作用

Formation mechanism of covert fault zone and its control of reservoir in the south slope of Dongying Sag,Jiyang Depression,Bohai Bay Basin

断裂趋势带是指盆地基底断裂继承性活动或盖层受到剪切作用影响而产生在盖层中的弱变形构造带,是主断裂面形成前的变形程度较弱的构造带。研究发现,东营凹陷南斜坡王家岗和八面河断裂趋势带是由一系列雁列式排列小断层带组成的,具有上宽下窄,下部收敛于主走滑断裂的特点。由于浅层没有主断层显现,故也称这种构造带为隐性断裂带,其形成机制和变形程度不同,发育的圈闭数量、圈闭性质等特征不同,富集油气的能力也有差异。构造物理模拟实验表明,王家岗和八面河断裂趋势带都形成于基底断裂走滑—伸展双重作用,前者走滑—伸展运动方向夹角为40°~50°,后者夹角为20°左右。前者处于断裂带发育的幼年期,变形程度较弱,趋势带宽度小,断裂密度小;后者处于断裂带发育的青年期,变形程度强,趋势带宽度大,断裂密度大,形成与断裂相关的圈闭数量多,油气聚集能力高于前者。根据断裂趋势带演化阶段、发育特征和源藏匹配关系,认为断裂趋势带变形强度是控制油气富集程度的关键因素。王家岗断裂趋势带成藏模式为“幼年期弱变形—单洼供烃成藏模式”,八面河断裂趋势带成藏模式为“青年期强变形—双洼供烃成藏模式”。

Objective: Covert fault zone refers to the weak deformation structural zone in the cap rock caused by the inherited activity of the basement fault or the shear effect of the cap rock. It is a weak deformation structural zone before the formation of the main fault plane. The formation mechanism and evolution degree of covert fault zone are different,and its structural characteristics and structural types are also different. This paper attempts to reveal the differences in characteristics,formation mechanism and reservoir control between Wangjiagang covert fault zone and Bamianhe covert fault zone located in the south slope of Dongying Sag,Bohai Bay Basin.Methods: In this paper,by using fault distribution maps in different periods and 3-dimensional seismic profiles,the deformation characteristics of Wangjiagang covert fault zone and Bamianhe covert fault zone on plane and section are analyzed. In addition,the structural physical simulation experiment of extension-strike slip movement of basement fault at different direction angles α( the angle between extensional movement and strike slip movement in the horizontal direction) is designed to study the included angle α of their respective extension-strike slip movement directions,so as to analyze the difference between the formation mechanism of Wangjiagang and Bamianhe fault trend zone.Results: The Wangjiagang and Bamianhe covert fault zones in the south slope of Dongying sag are composed of a series of small en echelon faults,which are characterized by wide upper and narrow lower parts,and converging to the main strike slip faults in the lower part. Because there is no main fault plane in the shallow layer,it is also called recessive fault zone. Its formation mechanism and deformation degree are different,the number and nature of traps are different,and the ability to enrich oil and gas is also different. The results of structural physical simulation show that both Wangjiagang and Bamianhe covert fault zones are formed by strike slip-extension dual activity of basement faults. The angle between strike slip-extension direction is different: the former is 40° to 50° and the latter is about 20°. The Wangjiagang covert fault zone is in juvenile stage of fault zone development,with weak deformation,small fault zone width and small fault density;Bamianhe covert fault zone is in the young stage,with strong deformation degree,wide fault zone,high fault density,a large number of fault related traps,and higher oil and gas accumulation capacity than the former.Conclusions: According to the evolution stage,development characteristics and source-reservoir matching relationship of covert fault zone,it is considered that the deformation intensity of covert fault zone is the key factor to control the degree of hydrocarbon enrichment. The hydrocarbon accumulation model of Wangjiagang covert fault zone is “ juvenile stage weak deformation-single source depression hydrocarbon accumulation model ”,and Bamianhe covert fault zone is“young stage strong deformation-double source depressions hydrocarbon accumulation model”.