基于油气藏形成的毛细管平衡理论的传统观念认为，油气层初始含水饱和度几乎等于束缚水饱和度。随着致密气藏开发的进行，这一传统认识逐渐受到质疑。通过鄂尔多斯盆地和四川盆地西部典型致密砂岩气藏测井、密闭取心和岩心分析资料证实，气藏初始含水饱和度低于束缚水饱和度，即存在超低含水饱和度。毛细管自吸、气驱水及气体传质实验研究表明，具有超低初始含水饱和度的气藏更易发生毛细管自吸，导致近井带或裂缝面含水饱和度增加，诱发水相圈闭损害，降低气体有效渗透率，同时诱发流体敏感性，加剧应力敏感性。测井资料及气体传质实验表明，发生水相圈闭后，近井带或裂缝两侧储集层气相渗透率很低甚至为零，影响气体的顺利产出，导致测井解释含气饱和度偏低，测试为低产甚至没有产量，漏判或低估高产气藏。抑制毛细管自吸或促使近井带或裂缝气层水相快速排出是超低含水饱和度气藏高效开发的关键。%With the development of tight gas, traditional capillary-equilibrium theory that initial water saturation is almost equal to irreduc- ible water saturation is questioned. Taking the typical tight gas reservoirs in northern Ordos basin and western Sichuan basin for examples, their well logs, sealed coring and core lab analyses indicate that the initial water saturation is lower than the irreducible water saturation, namely, there exists ultra-low water saturation for such a reservoir. The reservoirs with low initial water saturation have high spontaneous imbibition potential, leading to the increase of water saturation nearby the wellbore and fractures, and the decrease of gas permeability, which is water phase trapping damage. The analysis of well logging data and the gas transfer experiments show that water phase trapping damage could induce fluid sensitivity damage and aggravate stress sensitivity damage. Water phase trapping impairs gas permeability near- by the wellbore and fractures, prevents from the gas production, obtains low gas saturation from well logging, no gas rate during the well test, and causes to undervalue such a gas reservoir. It is crucial for effective development of tight gas with abnormal low water saturation nearby the wellbore and fractures to prevent from capillary imbibition and aqueous retention.
展开▼
