天津东丽湖深部岩溶热储时频电磁法探测及有利区预测

Research on time-frequency electromagnetic method detection of deep karst thermal reservoir and prediction of favorable area in Dongli Lake of Tianjin

天津市地热资源储量丰富,蓟县系雾迷山组作为主力热储,是典型的碳酸盐岩型热储层。为查明天津东丽湖5 km以浅的地层结构和隐伏断裂、重点查明深部主力热储层空间分布及结构特征、预测地热有利区,笔者首次将主要用于深部油气勘探的时频电磁法应用于东丽湖深部地热资源探测。通过高标准的数据采集、精细化数据处理和电阻率约束反演,结合地震和钻孔资料进行层位标定,精细刻画了地层结构:推断了7条隐伏断裂,均为NNE与NWW向的拉张性正断层,其中沧东断裂F1作为区内主要热流体的必要通道,导热、储热并控制着地热异常区的分布和形态;雾迷山组热储层主要分布在沧东断裂西侧,顶界面埋深海拔约-2200~-2400 m,在电阻率剖面上显示为连续递增的A型电性特征,三、四段岩溶裂隙较发育时,热水在裂隙或断裂处的聚集引起局部低电阻率异常,出现H型电性特征,指示了目标深度内地热有利区的发育部位。据此,本文圈定地热有利区4处,为后续地热资源的开发利用提供了重要的基础资料和支撑。

Tianjin is abundant in geothermal resources.As the main geothermal reservoir,Wumishan Formation of Jixian System is a typical carbonate reservoir.In order to find out the stratigraphic structure and concealed faults within 5 km of Dongli Lake in Tianjin,focus on the spatial distribution and structural characteristics of the main deep thermal reservoirs,and predict the favorable geothermal areas,the author first applied the timefrequency electromagnetic method,which is mainly used for deep oil and gas exploration,to the deep geothermal resources exploration of Dongli Lake,through high-standard data acquisition,fine data processing and resistivity inversion.Seismic and borehole data are used to calibrate the horizon and finely depict the stratigraphic structure.Seven concealed faults are inferred,all of which are NNE and NWW tensional normal faults.Cangdong Fault(F1)as the necessary channel of the main thermal fluid in the area,conducts heat,stores heat and controls the distribution and shape of geothermal anomaly areas;The thermal reservoir of Wumishan Formation is mainly distributed on the west side of Cangdong fault,the buried depth of the top interface is about-2200~-2400m,and the resistivity profile shows a continuous increasing A-type electrical characteristics.When the karst fissures in the third and fourth sections are relatively developed,the accumulation of hot water in the fissures or faults causes local low resistivity anomalies and H-type electrical characteristics.It indicates the development position of the favorable geothermal area in the target depth,and four favorable geothermal areas are delineated in this paper,which provides important basic data and support for the subsequent development and utilization of geothermal resources.