The chemical features

genesis

spatial distribution characteristics and controlling factors of the formation water in Shenmu gas field

northeastern Ordos Basin

were studied by the analysis of seismic

drilling and logging

as well as performance data combined with test analysis of mercury injection

gas-water relative permeability

physical and hydrochemical properties.Since the studied area is located in the transitional area from water to gas

the formation water herein is of "V-shaped" CaCl

2

type

with low salinity"acid water" and high salinity conventional formation water being dominant.Vertically

the differential distribution of formation water are mainly caused by the differences of deposition

lithofacies and distance from gas source for various formations.Multiple tight limestones distributed in the Benxi and Taiyuan Formations have blocked the entry of hydrocarbons into reservoirs

leading to a low degree of gas charging for the original reservoirs and relatively high enrichment of formation water.The Shiqianfeng Formation

located far away from gas source

is in short of hydrocarbon supply with incomplete gas displacement of water.The Shanxi Formation is a self-sourced indi-genous play

which has a high degree of gas charging and low quantity of water produced.Horizontally

influenced by the "west-dipping" structural movement of the basin in the Late Cretaceous

the northeastern Ordos Basin uplifted as a whole along with the secondary adjustment of water/gas contact

producing more gas-bearing horizons and continuously increa-sing the height of gas columns; meanwhile

the pressure in the gas reservoir decreased

and the formation water at the basin margin invaded into bed laterally

leading to the pattern of "multiple gas layers

low gas yield and water-gas co-production"

characterized by the ever-increasing formation water scale and water production from west to east with a gradual increase of salinity.The results provide some basis for prediction of the spatial distribution and genesis of gas and water at the margin of the Ordos Basin.