水溶—释放作用对气藏形成的影响——以克拉2气田为例

INFLUENCE OF SOLUTION-RELEASING ON GAS RESERVOIR FORMATION——TAKING KELA-2 GAS FIELD AS AN EXAMPLE

以克拉 2气田为例 ,讨论了天然气在地层水中溶解—释放作用对气藏形成的影响 ,估算了因地层抬升所导致的水溶气释放为游离气的量 ,分析了影响水溶气与气藏中游离气组分分馏的主要因素。研究表明 ,天然气在地层水中的溶解—释放作用对克拉 2气田天然气组分分馏起重要的作用 ,主要表现为 :①在地层沉降和抬升过程中 ,由于地层温度、压力的变化 ,地层水选择性溶解和释放天然气组分 ;②在大规模水平挤压过程中 ,C2 + 烃类气体随着边底水的迁移而流失 ;③地层异常高压导致大量C2+ 烃类溶解于地层水中 ,致使气藏中甲烷相对富集。此外 ,水溶气释放对克拉 2气田异常高压的形成也有一定的贡献作用。文章还通过天然气在水中溶解—释放模拟试验 ,分析了甲烷气体在地层水中因压力变化而释放的过程中碳同位素分馏状况。总结了克拉 2气藏水溶气成藏过程及其成藏模式。

By taking Kela-2 gas field as an example, the influence of the solution-releasing of natural gas in formation water on gas reservoir formation is discussed; the amount of the free gas released from formation water due to strata uplift is estimated; the principal factors affecting the component fractionation of water-soluble gas and free gas in gas reservoir are analyzed in the paper. Through investigation it was indicated that the solution-releasing of natural gas in formation water played an important role in fractionating the gas components of Kela-2 gas field. The main manifestations include: 1 gas components' being selectively solved and released by formation water because of the changes in formation temperature and formation pressure in the process of stratigraphie subsidence and uplift; 2 C2+ hydrocarbon gas' being lost with the edge and bottom water migration in the process of large scale horizontal compression;and 3 C2+ hydrocarbon gas' being greatly solved into formation water by the action of abnormally high formation pressure) thus causing the methane's being relatively enriched in the gas reservoir. In addition, the free gas released from formation water played also a certain role in forming the abnormally high formation pressure in Kela-2 gas field. According to the simulation test results of the solution-releasing of natural gas in formation water, the methane carbon isotopic fractionation in the process of methane's being released from formation water due to the change in pressure is analyzed and the process of forming the water-soluble gas reservoir in Kela-2 gas field and its reservoiring mode are summarized in the paper.