Objective The reservoirs of the fifth member of the Ordovician Majiagou Formation in the southeastern part of the Sulige Gas Field are mainly carbonate reservoirs. During the production process, the formation water produced seriously, the gas−water relationship was complex, and the main controlling factors were unclear. Restricting natural gas production in the area.

Methods Based on the analysis of the chemical characteristics of formation water, this paper uses parameters such as chlorine−sodium coefficient, desulfurization coefficient, and sodium−calcium coefficient to analyze the formation environment of formation water; then, it studies the formation environment of formation water through single well identification, continuous well comparison, and plane distribution characteristics. The distribution rules of gas and water; finally, the main controlling factors of gas and water distribution and their impact on oil and gas production were studied based on the structure, ancient landforms and reservoir physical properties.

Results The results show that the formation water in the Ma5₁ subsection in the southeastern part of the Sulige gas field has high salinity, with an average of 148905.46 mg/L, PH shows weak to medium acidity, the water type is CaCl₂ type, and the formation water overall is low chlorine The characteristics of sodium coefficient, sodium−calcium coefficient and desulfurization coefficient, high chlorine−magnesium coefficient, metamorphism coefficient and salinization coefficient make the formation sealing better, which is beneficial to the preservation of gas reservoirs. Vertically, the formation water is divided into structural low water, isolated lenticular water and low permeability zone retained water based on the differences in origin and spatial distribution. Water in structural low parts is common in the relatively low structures in the west of the study area and in the relatively high structures in the southeast. Low nasal recess; isolated lenticular water is less developed. On the plane, water−producing wells are mainly concentrated in five areas including G4−8 and S158. The eastern part has a larger water−bearing area and is mainly a gas−water mixing area.

Conclusions The distribution of formation water is controlled by three factors: structure, pre−Carboniferous paleo−geomorphology and reservoir heterogeneity. Structural highs control the vertical gas−water differentiation, making it easier to produce water. Karst paleo−geomorphology controls the lateral distribution heterogeneity of gas and water, making the permeability of some areas low, affecting the development effect. Reservoir characteristics control the efficiency of gas−driven water. Reservoirs with better physical properties are rich in natural gas, and blocks with poor physical properties retain more water, affecting production.