Concentration Mechanism of Fluorine, Arsenic, and Uranium in Groundwater of the Hailar Basin, China

Located in semi-arid regions of Hulun Buir League in China Inner Mongolia Autonomous Region, Hailar Basin is a region with less precipitation, where groundwater is the most important source for water supply. It is very important to study groundwater characteristics and hydrogeochemical processes for better management of the groundwater resource.The current status of fluorine (F), arsenic (As), and uranium (U) co-contamination exists in groundwater of the Hailar Basin, China. To understand the concentration mechanism of F, As, and U in groundwater in the study area, groundwater samples were collected for detection and analysis. The results showed that the main hydrochemical types were Cl-Na, HCO3-Na, and HCO3-Ca in the study area. The average values of F, As, and U were 3.94 mg/L, 0.04 mg/L, and 0.07 mg/L, respectively, which all exceeded the World Health Organization(WHO) guidelines. Through the Gibbs diagram and the end member diagram, it can be seen that the groundwater in the study area is mainly affected by the hydrogeochemical effects of evaporative crystallization, rock weathering mechanism, and the dissolution of silicate rock and evaporative salt rock minerals. Mineral dissolution, cation exchange, and weakly alkaline environment are important factors affecting F concentration; Low NO3ˉ and SO42- will cause a reducing environment and the competitive adsorption of HCO3ˉ will promote As pollution; The concentration of Ca2+,Mg2+, SO42-,and NO3ˉ have a great influence on the concentration of U.

Reservoir characteristics and control factors of Tongbomiao formation in Hongqi sag

Hongqi sag is located in the north of Beiehur depression in Hailar Basin, which is a secondary structural unit in the peripheral depression of Hailar Basin, with great exploration potential. Based on SEM, conventional thin sheet, cast thin sheet, mercury pressure and physical property data, this paper discusses the reservoir characteristics, types and control factors of high quality reservoir in Tongbomiao formation, Hongqi sag, so as to provide a strong geological basis for the exploration of oil and gas in this area. The reservoir space of Hongqi sag is mainly composed of four types: primary intergranular pore, micro fracture, feldspar dissolution pore and debris dissolution pore. It is of the type of ultra low porosity and low permeability. Although Tongbomiao formation in Hongqi sag is of very low porosity and low permeability type, high quality reservoir is still developed, and its reason is mainly controlled by sedimentary environment, diagenesis and structural fracture.