Study On The Development Law And Main Control Factors Of Carbonate Fractures In Ma Jiagou Formation Of The West Shandong Uplift

The Ordovician Ma Jiagou Formation in Luxi Uplift has rich fissured geothermal resources and great exploration potential.As an important reservoir space and seepage channel in carbonate reservoir,natural fractures play an important role in geothermal storage and migration.Based on the basic geological data such as outcrop,core,thin section and conventional or imaging log,the geostatistical method is used to make statistics on the fracture direction,geometric parameters and effectiveness of the Ordovician Ma Jiagou Formation carbonate rock in the Luxi Uplift and analyze its development and main controlling factors.And through finite element simulation method,using COMSOL software,the paleotectonic stress is imitate to predict the fracture development.The results indicate that there are three types of fractures in Luxi uplift,including structural fractures,diagenetic fractures and weathering fractures,and mainly composed of structural shear fractures with an angle of 45°-85°.The dominant strike of fractures is NNE-SSW,NEE-SWW,EW and NE-SW.Combined with the characteristics of tectonic evolution in the study area,it is believed that the fractures in the study area were formed under the Indosinian,Yanshanian and Himalayan tectonic movements,and the Yanshanian and Himalayan periods are the most effective.Using known data to analyze the main controlling factors of fractures,it is believed that the development is mainly controlled by lithology,layer thickness,paleotectonic stress,faults and folds.The development of dolomite fractures is the highest,followed by limestone,and marlstone is the lowest;the thinner the stratum is,the higher the development degree is;Under the same regional tectonic stress condition,the linear density of fractures in the tectonic active plate and the tectonic turning end is large.According to the longitudinal statistics of the fracture development degree of different layers,it is found that the O2 b and O2 d have the best fracture development,but the filling is high,and the effectiveness is poor.O2-3b and O2 g have low development degree,but most of them are unfilled fractures,and the effectiveness is good.According to the simulation of the paleotectonic stress field in the study area,the fracture values are concentrated in 0.5-1.2 during the Yanshanian period and 1-3 during the Himalayan period.The larger fracture values are developed at the end of the fault or at the area with dense fractures.