低渗透砂岩气藏渗流特征及渗透率下限研究

针对川中须家河组低渗气藏含水饱和度高、气井单井产能低、稳产困难的现状,急需优化调整生产方案提高产能。为此,通过计算机断层扫描(computed tomography, CT)技术分析了不同类型储层的孔隙结构特征及其影响;其次,在地层条件下进行实验研究了不同类型岩心的气-水两相、气相单相的渗流特征,并确定了气藏开发的渗透率下限。研究表明,与孔隙度、孔喉半径相比,孔隙类型对渗透率的影响程度更高;随着含水饱和度的提高,气相流动能力大幅降低;束缚水条件下,孔隙型岩心内的气相流动存在启动压力梯度;当生产压差为16 MPa和20 MPa时,对应的渗透率下限分别为0.34、0.27 mD。实际生产过程中,可以通过控制含水饱和度、提高储层渗透率或生产压差的方式提高气井产能。该研究对掌握低渗气藏的气相流动特征、优化调整生产方案具有借鉴意义。

Study on Percolation Characteristics and Permeability Lower Limit of Low Permeability Sandstone Gas Reservoir

The low permeability gas reservoir of Xujiahe Formation in central Sichuan is facing the situation of high water saturation, low single well productivity and difficulty in stabilizing production. It is urgent to optimize and adjust production plan to improve productivity. Therefore, the pore and permeability characteristics of different types of reservoirs are analyzed by CT scanning. Secondly, the gas-water two-phase and gas-phase single-phase percolation characteristics of different types of cores are experimented under formation conditions. The results show that the core type has a higher influence on permeability than porosity and pore throat radius; with the increase of water saturation, the gas flow ability decreases greatly; under the condition of irreducible water, the gas flow in porous cores has a starting pressure gradient, and when the production pressure difference is less than 16 MPa, the gas flow is in the same state. In the low-speed non-Darcy stage, the lower limit of permeability is 0.32mD under this differential pressure. In actual production process, gas well productivity can be improved by controlling water saturation, improving reservoir conductivity or increasing production pressure difference. This study has reference significance for grasping the gas flow characteristics of low permeability gas reservoirs and optimizing and adjusting production schemes.