塔里木盆地的三维电阻率结构

Three Dimensional Electrical Resistivity Structures of the Tarim Basin

塔里木盆地内油气资源非常丰富,但是深层勘探程度低,需要开展深入的地球物理调查。经过在盆地内大地电磁测站的数据采集、资料处理和三维反演,取得盆地三维电阻率模型,从电性结构角度刻划了盆地的三维构造。塔里木盆地的碎屑岩和碳酸盐岩的电阻率变化范围很大,主要受其中的孔隙裂隙发育程度控制。在同一深度的平面上,盆地侏罗纪以前地层的构造隆起显示为相对高阻区,而深层低阻带主要反映古生代碳酸盐岩中的裂隙和流体汇聚,提供了油气储层分布的信息。从6km到10km深度,低电阻率区面积向下缩小,但沉积盆地总面积仍有近20万km^2。由于油气成藏伴随着活跃的流体活动,而孔隙流体呈现低电阻率,可以认为低电阻率区分布范围和产状指示深层流体活动及可能的油气储层的分布范围。深层电阻率平面图显示的低电阻率区包括:满加尔坳陷中北部到塔北隆起西段,塔西南的和田坳陷与莎车坳陷。于田-民丰坳陷以及唐古孜巴斯坳陷在深度6~10km的平面图也显示为较低电阻率,也是深层油气勘探的有利区段。塔里木盆地结晶基底可分为三种类型:正常的克拉通结晶基底呈现高电阻率,玄武岩浆侵位的基底对应高电阻率区,而含裂隙水的变质基底呈现低电阻率。对比大地电磁法和反射地震结果认为,地球物理调查资料不支持塔里木盆地二叠纪"大火成岩省"的猜测。

Although the Tarim basin contains rich oil/gas resources,the exploration of oil/gas buried in its deep layers is just beginning,requiring detailed geophysical investigations.This paper presents the results of magnetotelluric investigation for 3Dstructures within the Tarim Basin.We completed the survey at 701 stations and performed data processing and 3Dinversion,obtaining 3Delectrical resistivity model of the basin,which shows structures of sedimentary layers from viewpoint of electrical properties.Electrical resistivity of clastic and carbonate rocks in the basin varies in a large range and is mainly controlled by fluid contents contained in pores and cracks.On a plane with a certain depth,structural highs beneath the Jurassic strata usually shows higher electrical resistivity,while lower electrical resistivity zones show information of fluid convergence and strata containing possible oil/gas reservoirs,as oil/gas reservoirs are usually accompanied with vivid fluid motion and fluid is of low electrical resistivity.The inversed 3D electrical resistivity model indicates that the most areas of the upper-part of the basin are of low electrical resistivity,caused by the Mesozoic and Cenozoic water-bearing clastic rocks.Some local areas with high electrical resistivity coincide with positions of low geothermal heat flow and high density disturbance,reflecting local structural highs.In the lower-part of the basin with depth from 6km to 10 km,the area of low electrical resistivity is reduced downward,but remains at least 200,000km^2 on the plane of depth 10 km.Based on the idea that lower electrical resistivity zones show fluid convergence and strata containing possible oil/gas reservoirs,the lower electrical resistivity zones revealed on the inversed images from 6km to 10 km demonstrate the prospect areas in the deep layers of the basin oil exploration.The prospect areas include the northern Manjar depression to western Tarbei uplift,the Hetain and Sache depressions,as well as the Yutain-Mingfeng and Tangguzibas depressions that shows relatively low electrical resistivity on the plane of depth 6-10km.The crystalline basement can be divided to 3types as follows：the normal craton basement of high electrical resistivity,the water-bearing cracked metamorphic basement with low electrical resistivity,and the basalt intrusive basement with high electrical resistivity.