致密砂岩孔隙内水的赋存特征及其对气体渗流的影响——以松辽盆地长岭气田登娄库组气藏为例

致密砂岩储层岩石孔隙结构复杂,孔隙内水的赋存状态和可动性难以确定,影响气井的产能确定和生产动态预测。为了认识该类储层气水渗流特征,根据铸体薄片和压汞等实验资料,分析了松辽盆地长岭气田下白垩统登娄库组气藏储层的孔隙结构,选取具有代表性的岩样,通过核磁共振、气驱水等实验,研究了岩石孔隙中水的赋存特征及其流动性,进而研究储层岩石在不同含水条件下对气体渗流的影响。结果表明:致密砂岩细小孔喉内的水流动性差,残余水饱和度较高,其大小不仅与岩石孔隙结构和物性相关,而且还与其中的气体流动有关;气体在含水孔隙内的流动受毛细管压力和滑脱效应影响存在非达西渗流特征,启动压力梯度的大小与储层渗透率和含水饱和度密切相关,登娄库组储层Sw/K值大于1 000mD-1以后,启动压力显著增大。该成果为该类气藏合理开发技术政策的制定提供了依据。

Occurrence characteristics of tight sandstone pore water and its influence on gas seepage:A case study from the Denglouku gas reservoir in the Changling Gas Field,southern Songliao Basin

The complex structure of rock pores in a tight sandstone reservoir makes it more difficult to determine the occurrence and mobility of pore water, which will have a great impact on the productivity determination and dynamic performance prediction of a gas well. This paper aims to know about the water and gas seepage characteristics of a tight sand gas reservoir. According to the experimental data of casting thin sections and mercury penetration, we first analyzed the pore structure of the Denglouku gas reservoir in the Changling Gas Field, southern Songliao Basin. Then, with some representative samples selected there, we studied the occurrence characteristics and mobility of rock pore water through experiments of nuclear magnetic resonance and gas drive water, etc. On this basis, we finally discussed the impact of reservoir rocks on gas seepage under different aquiferous conditions. The following results were achieved. First, the water in the small pore throat of tight sandstones is difficult to flow so the residual water saturation is becoming higher and its value depends not only on the pore structure and physical properties of rocks, but on gas flow in the pore throat. Second, because of the influence of capillary pressure and slippage effect, there is non Darcy gas seepage in aquiferous pores. The level of starting pressure gradient relates to permeability and water saturation in the reservoir. When the value of S_w/K is greater than 1 000 mD^-1, the starting pressure gradient will increase significantly. This study provides the reference in the development of more rational technologies to explore and exploit such type of gas reservoirs.