致密砂岩气藏近井地带含水饱和度变化规律

致密砂岩气藏普遍含水,近井地带极易形成积液,从而导致气井减产甚至停产,因而研究近井地带含水饱和度变化规律对于认识气井产水机理具有重要的意义。为此,根据气井径向渗流原理设计了一套近井地带储层含水饱和度变化物理模拟实验流程,运用直径分别为10.5 cm、3.8 cm、2.5 cm的致密岩心由远及近串联以模拟气藏中直井压裂后的生产状况;基于气井降压生产方式,分别用20μm、30μm、40μm、50μm的微管来模拟气井油管以控制产气量,研究气藏衰竭开采过程中近井地带含水饱和度的变化及其影响因素,结合现场生产井资料计算气井近井地带及不同区域、不同微管直径下的含水饱和度及产水量,并分析其变化情况。研究结果表明:(1)不同采气速率各自对应一个临界含水饱和度,当原始含水饱和度低于临界值,近井地带和中部区域流动的地层水会随气体的采出而携出,近井地带不会产生积液;(2)当原始含水饱和度高于临界值时,由远端运移的地层水大量聚集在近井地带导致近井地带积液;(3)含水饱和度相同时,采气速率越大,越容易导致近井地带积液;(4)同一含水饱和度下,采气速率越大,产水越严重,采收率越低。结论认为,由物理模拟实验新方法计算得到的气井累计产水量图版与对应气井的产水动态具有较好的一致性,该研究成果可以有效预测气井产水量,对于气井采取合理的治水措施具有指导作用。

Change of water saturation in tight sandstone gas reservoir near wellbores

Tight sandstone gas reservoirs commonly contain water, so liquid loading often appears near wellbores, leading to production decline and even shutdown of gas wells. Therefore, the study on the change of water saturation near wellbores is of great significance to understanding the water production mechanisms of gas wells. In this paper, a set of physical simulation experiment procedures of identifying the change of water saturation near wellbores was designed according to the principle of radial well seepage of gas wells, and the production performance after vertical well fracturing in gas reservoirs was simulated by connecting tight cores with a diameter of 10.5 cm, 3.8 cm and 2.5 cm in series in a descending order of distance. According to the depressurizing production mode of gas wells, tubes with small diameters of 20, 30, 40 and 50 μm were used to simulate gas well tubing to control the gas production rate. And the change of water saturation near wellbore in the process of depletion production and its influencing factors were investigated. Finally, combined with actual data of production wells, the water saturation and water production of gas wells near wellbores and in different zones were calculated at the above four different small diameters of tubes and the changes thereof were also analyzed. The following results were obtained. First, each gas production rate corresponds to a critical water saturation. When the initial water saturation is lower than the critical value, the formation water flowing near the wellbore and in the middle zone can be carried out along with the production of gas and no liquid loading is formed. Second, when the initial water saturation is higher than the critical value, a large amount of formation water migrating from the distal zones accumulates near the wellbore, and thus liquid loading occurs at the bottom hole. Third, when the initial water saturation is equal to the critical value, the higher the gas production rate is, the more easily liquid loading tends to form near the wellbore. Fourth, for the same water saturation, water production increases and recovery factor decreases with the increase of gas production rate. In conclusion, the cumulative water production chart of a gas well generated by the physical simulation experiment method proposed in this paper agrees well with the water production behavior of the corresponding gas well. The research results are conducive to the effective prediction of gas well water production and can be used as guidance for the reasonable gas well water control.