The Study Of Physicochemical Mechanism Of Nature Gas Dissolution And Exsolution In Xujiahe Formation In West Sichuan Depression

Water soluble natural gas is the potential unconventional resource.Because of the especial condition of temperature,pressure and geology,Upper Triassic Xujiahe Formation in West Sichuan depression contains the abundant water soluble natural gas. Along with the additional exploratory development in West Sichuan area,the exploratory development of water soluble natural gas will become extraordinary important.So far,the study of physicochemical condition and mechanism of nature gas dissolution and exsolution in Xujiahe Formation in West Sichuan depression isn't reported in detail.The method which is not only fit for evaluation of gas solubility but also plays an important role in evaluating conventional gas reservoir in Xujiahe Formation in West Sichuan area isn't found.Based on the information of geology, testing and production in Xujiahe Formation in West Sichuan depression and achievements of the study of gas solubility in water at home and abroad,the thesis deduces the gas dissolving equation in water under high pressure and temperature, using the theory of phase equilibrium.Then the paper generalizes two gas dissolving mechanisms in brines,namely,interstitial filling and hydration,and analyzes detailedly influential factors of gas solubility in brines,which include composition of nature gas,formation temperature,formation pressure,chemical character of formation water and so on.After that,through considering the structural and formation evolutionary characters of West Sichuan depression,we analyze the characters of physicochemical condition in Xujiahe Formation in Cretaceous period and at present,including formation pressure,temperature and chemical character of formation water.Considering the information of formation,structure and production, two exsolution patterns of water soluble natural gas are evolved gas created by temperature and pressure falling after formation uplifting and by quake.And then,the thesis calculates the natural gas solubility in formation water in depression region by four methods,and chooses the result of phase equilibrium to calculate and evaluate the volume of dissolved and evolved gas in the second and forth member of Xujiahe formation.At last,under taking the distribution of reservoir porosity in consideration, we divide the favorable rich zone of water soluble natural gas and evolved gas,the former are the zones of Xiaoquan and Hexingchang in West depression,and around Shuangyushi,the latter is the zone of Zhebachang and Laoguanmiao.In addition,the thesis provides some exploiting proposals for water soluble natural gas pool.