川中地区震旦系古岩溶微地貌对气藏储层及产能的控制作用

Controls of Sinian karst micro-paleogeomorphology on gas reservoir and productivity,central Sichuan Basin

四川盆地川中地区震旦系顶部受桐湾运动Ⅱ幕的影响,存在区域性不整合面,形成复杂的岩溶古地貌,研究基于数据驱动高精度三维空间层位追踪技术,采用印模法对川中地区震旦系顶部岩溶古地貌进行了恢复。根据现代岩溶地貌划分方案,将研究区划分出丘丛、残丘平原、滨岸平原、古水道、岩溶湖等五类四级微古地貌单元,并绘制四级微古地貌单元的平面分布图,详细对比分析不同微古地貌单元实钻井储层发育情况及气井产能情况,明确岩溶微地貌对气藏储层及产能的主控作用。研究结果表明:①四级微古地貌单元中滨岸平原的储层最发育,平均储层厚度为44.2m,气井优质储层钻遇率为15%,以裂缝—孔洞型和孔洞型储层为主,气井产能最高,稳产能力强;②古水道的储层发育,平均储层厚度为31.5m,气井优质储层钻遇率为12%,以孔洞型储层为主,气井产能高;③残丘平原储层较发育,平均储层厚度为25.0m,气井优质储层钻遇率为10%,以孔洞型储层为主,在断层分布区发育裂缝—孔洞型和裂缝—孔隙型储层,气井产能较高;④而丘丛和岩溶湖优质储层发育程度低,平均储层厚度10m以下,气井优质储层钻遇率低于5%,储集类型主要为孔隙型储层,天然气难以有效富集,气井多为低产井或无效井。

There exists regional unconformity caused by the second episode of the Tongwan movement in the top area of the Sinian in the central Sichuan Basin,forming a complex karst paleogeomorphology.Based on a data-driven high-precision 3-D spatial horizon tracking technology,the karst paleogeomorphology of the Sinian top was restored by using the impression method.According to the classification of modern karst geomorphology,the study area was divided into five fourth-order micro-paleogeomorphological units,i.e.hill cluster,residual hill plain,shoreland plain,ancient water channel,and karst lake.The planar distribution of the fourth-order units was mapped,and a comparative analysis was conducted on the reservoir development and well productivity in different units,to figure out the controls of karst microgeomorphology on gas reservoir and productivity.The research results are as follows:(i)Among the fourth-order units,reservoirs of the shoreland plain are the most developed,with an average thickness of 44.2 m.The ratio of drilled high-quality reservoir achieves 15%.Dominated by fractured-vuggy and vuggy reservoirs,the unit exhibits the highest well productiv-ity and stable production.(ii)Reservoirs are well-developed in ancient water channel,with an average thickness of 31.5 m.The ratio of drilled high-quality reservoir is 12%.Dominated by vuggy reservoirs,the unit shows high well productivity.(iii)Reservoirs are developed in residual hill plain,with an average thickness of 25.0 m.The ratio of drilled high-quality reservoir is 10%.Dominated by vuggy reservoirs,followed by fractured-vuggy and fractured-porous reservoirs in fault zones,the unit exhibits the relatively high well productivity.(iv)High-quality reservoirs are underdeveloped in hill cluster and karst lake,with an average reservoir thickness<10 m.The ratio of drilled high-quality reservoir is<5%.The units are dominated by porous reservoirs,gas cannot be effectively accumulat-ed,resulting in low-yield or non-productive wells.