琼东南盆地深水区中央峡谷天然气藏输导模式研究

琼东南盆地晚期构造活动较弱，为了阐明该盆地深水区深层古近系烃源岩生成的天然气如何运移至浅层新近系中央峡谷储集体聚集成藏这一问题，利用地震分频处理技术提高3D地震资料分辨率，开展断裂输导体系识别，结合区域断裂发育特征建立天然气输导模式。琼东南盆地深水区发育4期断裂活动，且断裂活动具有明显的周期性，基于此，提出了断裂旋回的概念——一个断裂旋回包括了较短时间的断层活动期和较长时间的断层静止期。通过对比断裂旋回不同阶段断层输导天然气的差异特征，提出断层活动期高效涌流输导模式和断层静止期有效渗流输导模式，并指出超压断陷盆地涌流和渗流交替输导可以增强天然气输导效率。中央峡谷陵水段下方深层发育一系列沟通烃源岩的阶梯状断层，浅层发育许多高角度小断层，其是深部天然气运移至浅层的重要通道。建立了中央峡谷天然气"多期断裂-多断层"接力输导模式。

Gas migration mode for the central canyon in deep-water Qiongdongnan Basin

Exploration results showed that the gas in the shallow Neogene central canyon reservoirs of the Qiongdongnan Basin mainly came from the deep Paleogene source rocks in the deep-water area. However, given that the late tectonic activity in the basin was weak, how did the gas in the deep formations migrate to the Neogene reservoirs? Using seismic frequency division technology, the resolution of 3D seismic data was improved. A fracture system below the central canyon was identified, and a gas transport mode was established by combining this interpretation with the development characteristics of regional faults. There were four stages of fault activity in the deep-water area of the basin, with pronounced periodicity. The activity and stationary periods happened alternately. Based on this, this paper proposed a concept of fracture cycle, which includes a shorter activity period and a longer stationary period. A fracture activity corresponds to a fracture cycle, and multiple fracture activities can be superimposed to form a stacking pattern of fracture cycles. Then, studying the difference of the migration mode for fractures in different periods, this paper proposed a fast inflow migration mode during the fault activity period and an effective seepage migration mode during the stationary period, and pointed out that it could enhance the efficiency of gas migration in a overpressure rift basin, if the inflow migration mode and seepage migration mode occurred alternately. In the Lingshui Depression, a series of ladder-like faults developed, connecting source rocks in the deep formations with many high-angle small faults in the shallow formations, which allowed deep natural gas migrate to shallow reservoirs. Thus, a relayed transport mode of “multi-stage fracturing and multiple faults” for gas migration in the central canyon was proposed.