Study On The Distribution Regulation Of Gas And Water In The North Tianhuan Depression,Ordos Basin

The Upper Paleozoic in the Tianhuan Depression is an important replacement area for natural gas exploration in the Ordos Basin.However,there is little knowledge about its complicated gas-water relationship,which restricts the development of oil and gas exploration.Therefore,this paper,by using drilling and logging data,Nuclear Magnetic Resonance,geochemical test and other technical means,Based on the study of source rocks and sedimentary reservoirs,this paper analyzes the macro-distribution and micro-occurrence of formation water and the controlling factors of gas-water distribution in the study area,so as to provide geological basis for the exploration of natural gas in the next stage.It is concluded that the lithology of Upper Paleozoic source rocks in Tianhuan Area mainly includes coal and dark mudstone.Integral in high maturity stage,give priority to with thermal cracking raw moisture.In the northern part of Tianhuan,there are the least wells producing water in Shan1,the most wells producing water in the Lower He8,and the least wells producing gas in the Upper He8.The gas layer,gas-water layer and water layer are intersected in the plane,and there is no uniform distribution boundary of gas and water layer.Vertically,the relationship between gas and water distribution is complicated,but the gas-water relationship in the same connected sand body unit is normal,with gas at the top and water bottom.The occurrence of formation water in the North Tianhuan can be divided into free water capillary water and adsorbed water.Nuclear magnetic resonance experiments showed that large pores with pore radius greater than 0.23?m controlled the distribution of free water,pore radius ranging from 0.05 to 0.23?m controlled the distribution of capillary water,and less than 0.05?m controlled adsorbed water.The formation water show property of weak acidity with high salinity.Cl^-,Na⁺+K⁺and Ca²⁺are dominant,The calcium chloride?-type and?-type water are predominant.Formation water is closed to water-rock interaction effect,fluid mixing effect,evaporation and concentration effect,the formation water is original sedimentary water,having undergone strong condensation and metamorphism effect.The gas accumulation mechanism of tight sandstone with low hydrocarbon generation intensity in Tianhuan area is mainly hydrocarbon generation intensity determines the size of the gas reservoir in essence,local structure is conducive to gas water differentiation,advantageous to the gas flow and aggregation.The superposed sand body has been scoured by multi-stage distributary channel,forming good lithological and physical combination in vertical direction,which is conducive to natural gas enrichment.The sand layer with relatively good physical property is easy to charge natural gas.In addition,good capping and sealing conditions are beneficial to the accumulation and preservation of gas reservoirs to some extent.