The Characteristics Of The Middle Ordovician Shale Reservoirs In The Western Ordos Basin

The detailed study of petrophysical characteristics of shale is the basis for evaluating shale gas reservoirs,which can better explain the complex nature of shale reservoir parameters and provide support for subsequent research work,which is of great significance to the exploration and development of shale gas.In this paper,the Middle Ordovician Lashenzhong Formation and Wulalike Formation shale in the western margin of the Ordos Basin are studied.System collects and analyzes the basic geological data,conducts field observations and drill core observations,and comprehensively studies the features of mineral components,organic geochemical parameters,shale properties,pore structures,etc.to study shale reservoir characteristics,The results show:The brittle mineral components of shales in the Lashenzhong Formation and Wulalike Formation are mainly quartz,potash feldspar and calcite,Quartz content was 23.6% in the Lashenzhong Formation and 65.7% in the Wulalike Formation,The Wulalike Formation's mineral brittleness index reached 76.5%;According to the "quartz + feldspar + pyrite" "carbonate minerals" "clay minerals" the relative content of shale types,dividing the type of shale.The organic geochemical parameters test showed that the TOC content of organic carbon in shale of the Lashenzhong Formation and Wulalike Formation was 0.12-8.89% with an average content of 1.121%,The degree of thermal evolution is mostly in the high-overmaturation stage,Ro is mainly in the range of 0.55% to 2.01%.The clay minerals are mainly illite,chlorite and montmorillonite.the development of micro-nanopore pores in the shale reservoirs of the Lashenzhong Formation and Wulalike Formation in the study area mainly includes dissolution pores,intergranular pores,intragranular pores,and a small amount of microcracks.The dissolution hole is the most developed,followed by the intergranular pores.The pore structure parameters were analyzed by the specific surface adsorption method.The average pore size of 3.5 to 10 nm in the Wulalike Formation was positively correlated with the specific surface area,and the specific surface area of the shale in the Lashenzhong Formation was greatly influenced by pore sizes above 10 nm.The physical properties of the shales of the Lashenzhong Formation and the Wulalike Formation were tested by the alcohol method,and their properties were characterized by low porosity and low permeability.Comprehensively evaluate shale gas reservoir evaluation parameters such as Shale distribution and organic geochemical parameters in the Middle Ordovician,combined with data on shale reservoir gas production in the study area.It is predicted that the shale gas reservoirs of the Middle Ordovician are mainly distributed in the lower organic-rich shale section of the Wulalike Formation,and the favorable areas are located in the area around the Wuzhong district Yutan 1-Zhong 4-Huitan1.