致密砂岩气藏地层水水化学特征及其地质意义——以川西坳陷新场气田为例

四川盆地侏罗系沙溪庙组及三叠系须家河组作为陆上致密气资源增储上产重点的接替区,保有大量的难动用储量,具有较大的勘探开发潜力。然而随着深入的滚动勘探开发,中浅层沙溪庙组气藏和深层须家河组气藏气井产水已严重制约了气井产能,部分气井甚至因水淹而停产。本文对研究区不同层位34口气井的地层水进行了主量、微量元素和气藏成藏演化特征分析,结果显示沙溪庙组气藏和须家河组气藏经历了先成藏后致密再改造的成藏演化过程,断层的沟通导致深层须家河组地层水的大量上涌,使断层附近高渗的砂体被充注,在水动力等驱动作用下,天然气以游离相或水溶相沿断裂带进行垂向高效运移。垂向上大部分离子含量都随着埋深逐渐增大,深层须家河组地层水气藏具有较好的油气保存条件,并且经历了更为复杂的水岩相互作用,不同程度地使K、Ba、Sr、Li、Rb等元素更加富集。

Hydrochemical characteristics of formation water in tight sandstone gas reservoirs and their geological significance: A case study of the Xinchang Gas Field in Western Sichuan Depression

The Jurassic Shaximiao Formation and Triassic Xujiahe Formation in the Sichuan Basin serve as key replacement areas for increased storage and production of onshore tight gas resources. They possess substantial reserves that are challenging to exploit and hold significant exploration and development potential. However, extensive and ongoing exploratory drilling and development have led to significant water production from wells in both the shallow Shaximiao Formation and the deeper Xujiahe Formation gas reservoirs. This water production has severely constrained the gas production capacity of these wells, with some wells even ceasing production due to water flooding. This study conducted an analysis of the formation water from 34 gas wells at various stratigraphic levels in the study area, focusing on major and trace elements, as well as the evolutionary characteristics of the reservoirs. The results indicate that both the Shaximiao Formation and the Xujiahe Formation gas reservoirs underwent an evolutionary process of initial formation, subsequent compaction, and subsequent modification. Fault connectivity resulted in significant upwelling of formation water from the deep Xujiahe Formation, leading to substantial infiltration into highly permeable sand bodies adjacent to faults. Under the influence of hydrodynamics and other driving forces, natural gas efficiently migrated vertically along fault zones in either a free or dissolved phase. Vertically, the majority of ion concentrations increased progressively with depth. The deep Xujiahe Formation gas reservoirs exhibit favorable conditions for oil and gas preservation and have undergone more complex water-rock interactions, causing varying degrees of enrichment in elements such as K, Ba, Sr, Li, and Rb.