断层输导型天然气成藏模式的动态成藏过程——以川西坳陷新场构造带上三叠统须二段气藏为例

Dynamic accumulation process of fault-translocation natural gas accumulation model:A case study on the gas reservoir of the second Member of Upper Triassic Xujiahe Fm in the Xinchang structural zone of the Western Sichuan Depression

上三叠统须家河组二段气藏是四川盆地川西坳陷致密砂岩气勘探开发的重要区块,但须二段气藏气水分布关系复杂、勘探开发难度较大。为了给川西坳陷须家河组气藏的高效勘探提供新思路,以新场构造带须二段气藏为研究对象,根据地层水化学特征,结合构造、断层输导体系特征及单井生产动态分析,探讨了SN走向断层对须二段气藏天然气成藏及气水分布的影响。研究结果表明:①新场构造带须二段气藏油气高产富集区主要表现为断层输导型天然气成藏模式,该类成藏模式具备良好的构造—断层—储层配置条件,含气性好;②断层输导型成藏模式的气藏高产富集主控因素为“古今构造高位+断层通源输导+优质储层聚气”,构造—断层—储层时空配置是控制气水分布的关键;③根据构造—断层—流体—成岩—成藏时空配置的差异性,结合单井生产数据,将断层输导型天然气成藏模式细分为“高产稳产、气水同产”“中产稳产、低产水”“低产气、高产水”3种气水产出特征;④具有“高产稳产、气水同产”生产特征的钻井,表现出“断层、储层在构造高部位相接”的特征,而具有“中产稳产、低产水”生产特征的钻井,普遍具有“断层、储层在构造高部位、低部位均相接”的特征,单井以产气为主,天然气产量稳定,仅产少量低矿化度地层水,可以通过实施水平井钻井来提高单井产量,以获得较好的经济效益。

The gas reservoir in the second Member of Upper Triassic Xujiahe Fm (Xu 2 Member) is an important exploration and development block of tight sandstone gas in the Western Sichuan Depression of the Sichuan Basin, but its gas and water distribution relationships are complex and its exploration and development is more difficult. In this paper, the Xu 2 Member gas reservoir in the Xinchang structural zone was taken as an example in order to provide a new idea for efficient exploration of the Xujiahe Fm gas reservoir in the Western Sichuan Depression. The effects of SN striking faults on the hydrocarbon accumulation and gas and water distribution in the Xu 2 Member gas reservoir were discussed based on the chemical characteristics of formation water, combined with the analysis on structures, fault translocation system characteristics and single-well production performance. And the following research results were obtained. First, high yield and enrichment area of Xu 2 Member gas reservoir in the Xinchang structural zone mainly presents a hydrocarbon accumulation pattern of fault-translocation type, which is good in structure–fault–reservoir configuration conditions and gas bearing property. Second, as for the hydrocarbon accumulation pattern of fault-translocation type, the factors controlling the high yield and enrichment of gas reservoir are "high positions of ancient and modern structures + fault translocation by connecting with the source + gas accumulation in high-quality reservoirs", and the key to control gas and water distribution is the spatial and temporal configuration of structure–fault– reservoir. Third, based on the difference of spatial and temporal configuration of structure–fault–fluid–diagenesis–accumulation, combined with single well production data, the hydrocarbon accumulation pattern of fault-translocation type is divided into 3 gas and water production characteristics, i.e.,"high and stable gas production, gas and water production simultaneously","medium and stable gas production, low water production" and "low gas production and high water production". Fourth, the wells with the production characteristics of "high and stable gas production, gas and water production simultaneous" present the characteristic that "faults and reservoirs are connected at structural highs", while the those with the production characteristics of "medium and stable gas production, low water production" present the characteristic that "faults and reservoirs are connected at structural highs and lows", which means that this kind of single well dominantly produces gas at a stable production rate with a little low-salinity formation water. Therefore, single well production can be improved by applying horizontal well drilling, so as to realize better economic benefits.