阿姆河右岸东部侏罗系盐下断层发育特征及其对天然气富集影响

Characteristics of subsalt Jurassic faults and the influence on natural gas enrichment in the eastern part of the right bank of Amu Darya River

中亚阿姆河盆地天然气资源丰富,断层对侏罗系盐下天然气聚集有着重要影响。通过对阿姆河右岸区块东部三维地震、岩心和生产资料分析,系统研究了不同尺度断层对卡洛夫阶—牛津阶碳酸盐岩储层发育和天然气成藏的控制作用。结果表明:盐下碳酸盐岩主要发育NE、NEE向两组逆断层和NWW、EW、NNW、SN向四组走滑断层,构造样式以基底卷入的逆断层相关褶皱和压扭性的正花状构造为主;断层主要形成于新近纪,NEE向逆断层在喜马拉雅早期挤压作用下形成,NE向逆断层和走滑断层形成于喜马拉雅中晚期的压扭应力场;断层分布具有分带性,南北方向以阿高左行走滑断裂带为界,南侧逆断层以NE向为主、北侧逆断层逐渐过渡为NEE向,SN向走滑断层则主要分布于玛霍断裂带以东。根据规模可划分为控构造带断层、控圈断层、改造断层和微断层4类,前3类多从基底断至盐膏岩,控制了缝洞储层的发育和天然气运移,断层的活动强度越高,缝洞储层越发育,天然气富集程度越高。根据断层特征划分为3类有利区带:Ⅰ类为临近控构造带断层和控圈断层的强充注规模缝洞型气藏发育区;Ⅱ类为临近改造断层的局部低充注的缝洞型气藏发育区;Ⅲ类为临近微断层的裂缝—孔隙型或裂缝型气藏发育区,其中Ⅱ类气藏发育区是下一步勘探的重点区带。

Natural gas resources are abundant in Amu Darya Basin in the Central Asia, and faults play an important role in subsalt Jurassic gas enrichment. By analyzing 3D seismic data, core samples and production performance in the eastern part of the right bank of Amu Darya River, the control effects of faults with different scales on the reservoir development and gas enrichment in the Callovian-Oxfordian carbonate reservoirs are systematically studied. The result shows that two groups of reverse faults in NE and NEE directions and four groups of strikeslip faults in NWW, EW, NNW and SN directions are developed in subsalt carbonate rocks, with structural types characterized by reverse faults related folds involved by basement and the compression-torsion related positive-flower structures. Faults were mainly formed in the Neogene,of which the NEE direction reverse faults were developed by the compression in the early Himalayan stage, and the NE direction reverse faults and strike-slip faults were formed in compression-torsion stress field in the middle-late Himalayan movement. Faults are distributed in zones in N-S direction bounded by A-Gao sinistral strike-slip fault belt. Among them, reverse faults are dominated by NE direction in the south side,while they gradually change to NEE direction in the north side. The SN trending strike-slip faults are mainly distributed to the east of Ma-Huo fault belt. Based on the scale, faults are divided into four categories, i.e., fault controlling structural belts, fault controlling traps, secondary fault in structures and micro fault. Faults of the first three categories mostly extend from basement to salt-gypsum rocks and control the development of fractured-vuggy reservoirs and the migration of natural gas. The higher the activity intensity of faults, the more developed the fracturedvuggy reservoir and the higher degree of gas enrichment. Three types of favorable zones are classified according to fault characteristics. Type Ⅰ is the large-scale fractured-vuggy gas reservoir development zone with strong gas-charging adjacent to fault controlling structural belts and fault controlling traps. Type Ⅱ is the fractured-vuggy gas reservoir development zone with partial weak gas-charging adjacent to the secondary faults in structures. Type Ⅲ is the fractured-porosity type or fractured gas reservoir development zone adjacent to micro faults. Among them,Type Ⅱ gas reservoir development zone is the key exploration target in the near further.