四川盆地孝泉—丰谷构造带须家河组气藏气水分布控制因素及勘探潜力

Factors controlling gas-water contact and the exploration potential of the Xujiahe Fm gas reservoirs in the Xiaoquan-Fenggu structural zone,Sichuan Basin

孝泉—丰谷构造带位于四川盆地川西坳陷中段,同一构造带内上三叠统须家河组气藏气、水、干层共存,气水关系异常复杂。为弄清须家河组气藏气水分布的控制因素,利用气井历年地层水分析资料,结合生产动态数据研究了该区地层水的特征,认为钻井生产过程中产出水包含了凝析水以及地层水与凝析水的混合水,地层水的产出与气藏含气丰度密切相关。在此基础上,采用洛瓦克相图分析了气水分布的控制因素。结果表明:①须家河组气藏同一局部构造范围内底水、边水并存,地层水分布横向连通性差,平面上分布规模较小,为各自独立的气水系统;②古、今构造高部位均有利于水溶气脱溶成藏,但成藏期古构造起到了决定性作用;③高地层水矿化度、低地层压力区更有利于游离气气藏的发育。最后,分析了须二段、须四段的油气勘探潜力,结论认为:须二段、须四段游离气、溶解气共存,须二段水溶气脱溶程度高于须四段,勘探潜力更大;合理利用及开采水溶气有利于扩大气藏规模。

The Xiaoquan Fenggu structural zone is located in the central section of Western Sichuan Depression. Gas, water and dry layers coexist in the Upper Triassic Xujiahe Fm in this structural zone and the gas-water contract is very complex. In order to make clear the factors controlling gas-water contact in the Xujiahe Fm gas reservoirs, the produced water analysis results obtained over the years were integrated with the dynamic production performance data to study the characteristics of formation water. It is believed that the produced water during drilling operation and production is a mixture of condensate water and formation water. The produc- tion of condensate water is closely related with gas reservoir abundance. The Nvok phase diagrams were used to analyze the factors controlling gas water contract. The following conclusions were obtained. （1） Edge water and bottom water coexist in a single local structure in the Xujiahe Fm gas reservoir. The lateral continuity of formation water is poor and its areal distribution is limited. Each local structure has a separate gas-water system. （2） Both the ancient and modern structural highs are favorable for the degassing and accumulation of wate^dissolved gas. However, the palaeo-structure of reserv for oiring stage plays a decisive role. （3） Such areas with high formation water salinity and low formation pressure are more favorable the accumulation of free gas. Finally, the explora- tion potential of the 2nd and 4th members of Xujiahe Fm was analyzed. It is believed that free gas and dissolved gas coexist there, but in the 2na member of Xujiahe Fm the degassing degree of water soluble gas is relatively higher, and this brings about a higher explo ration potential there. Rational utilization and recovery of water dissolved gas is favorable for enlarging the scale of a gas reservoir.