东营凹陷基底断裂走滑活动对油气成藏的影响

Effect of Strike-Slip Activity of Basement Faults on Hydrocarbon Accumulation in Dongying Sag

弱变形构造带是沉积盆地盖层中客观存在的构造现象,并且与油气聚集关系密切,一般可以通过不同地质单元(次级断层、油藏、圈闭、相带、凹陷、岩体、潜山等)的有规律排列等现象进行识别.为了初步揭示盖层变形带变形强度与油气聚集规模这一问题,首先在渤海湾盆地初步识别出40条盖层变形带,然后应用变盖层厚度和变剪切强度的构造物理模拟实验方法研究基底断裂走滑活动对盆地沉积盖层产生断层的过程.应用SPSS软件,对基底走向滑动量、横向滑动量、实验盖层厚度、雁列缝长度等参数进行了多元二次函数拟合.根据东营凹陷八面河、王家岗地区古近系各时期地层厚度、构造图R剪切长度、实验估算的张扭角度,计算出了各个时期的基底断裂走滑量;在模拟实验各阶段充注染色石油,结合凹陷实例建立了基底断裂走滑早期R剪切单一通道运移‒孤立聚集、早中期R剪切主通道运移‒雁列串珠状聚集(王家岗)、P剪切主通道运移‒断续带状聚集、全通道运移‒连续带状聚等成藏模式(八面河);最后指出盖层变形带上的R剪切增压变形段,R、P剪切交汇段是油气勘探有利目标区.

The development stage of the fault deformation zone refers to the weak deformation(strong concealment)zone developed in the sedimentary cover of the basin,which is the product of the early and middle stages of the formation and evolution of the fault zone.It is difficult to identify because of the lack of obvious fracture surface(zone)and significant displacement.It has been found that the weakly deformed tectonic belt is an objective tectonic phenomenon in the sedimentary basin cover,and is closely related to oil and gas accumulation.It can be recognized by regular arrangement of different geological units(secondary faults,oil reservoirs,traps,facies belts,depressions,rock masses,buried hills,etc.).In order to reveal the deformation intensity and hydrocarbon accumulation scale of cap cover deformation zone,the key issue of oil and gas geology,this paper takes the Dongying Sag as the research object and applies variable caprock thickness and the structural physical simulation experiment method in which variable shear strength is used to study the process of basement fault strike-slip activity on the formation of faults in the sedimentary caprock of the basin.Using SPSS software,taking the sliding amount of the basement/the thickness of the experimental cover layer(D_(NBD))as the independent variable x1,the amount of lateral sliding/the thickness of the experimental cover layer as the independent variable x_(2)(x_(2)=x_(1)×tanα)and the length of the echelon seam/the thickness of the experimental cover as the dependent variable y,multivariate quadratic function fitting was performed.According to the strata thickness,shear length of structural map R and experimentally estimated tensional and torsion angles by experiment in different periods of Paleogene in Bamianhe(strong strike slip)and Wangjiagang(weak strike slip)areas of Dongying Sag,the strike-slip amounts of the basement faults of Bamianhe and Wangjiagang fault zones in each period were calculated.At each stage of the simulation experiment,dyed oil was charged,and combined with the sag examples,the accumulation models of the basement faults were established,such as Early R shear single-channel migration-isolated aggregation,Early and mid-term R shear main channel migration-geese and beaded aggregation,P shear main channel migration-intermittent zonal aggregation,full channel migration-continuous belt aggregation,etc..Finally,it is pointed out that the R shear pressurized deformation section and the R and P shear intersection section in the deformation zone are favorable target areas for oil and gas exploration.