“改造型”致密砂岩气藏特征:以吐哈盆地巴喀气田下侏罗统八道湾组为例

Characteristics of “Subsequent” Tight Gas Accumulation:A Case from Badaowan Formation of Lower Jurassic in Baka Gas Field,Tuha Basin

受后期多阶段构造活动的影响,原生致密砂岩气藏或后期储层致密化的常规天然气藏经多期改造调整可形成"改造型"致密砂岩气藏。根据烃源岩排烃天然气充注期同砂岩致密化期的先后顺序和后期构造活动影响两个因素,"改造型"致密砂岩气藏可划分为A、B两种类型;A类的储层先致密,后成藏,再改造,B类则是先成藏、后致密、再改造。受北部博格达山多阶段造山运动的影响,吐哈盆地巴喀气田发育A类"改造型"致密砂岩气藏;甜点分布受局部构造高部位的控制明显,物性甜点和裂缝型甜点是主要的甜点类型。"改造型"致密砂岩气藏的形成可划分为物性圈闭的形成和初期充注阶段、差异聚集阶段、初始改造阶段、强烈改造及残存阶段共4个阶段。由于经受多期构造活动的改造,最终形成复杂多期叠合的"改造型"致密砂岩气藏,总体表现出受构造高部位主导的甜点型富集的特征。

Primary tight gas accumulation or normal gas accumulation reservoirs that experienced later reservoir densification can form the ＂subsequent＂ tight gas accumulation after multistage readjustment influenced by multistage tectonic movements. According to these two factors, sequence between gas charging and reservoir compaction and influence from later tectonic movements, ＂subsequent＂ tight gas accumula- tion can be divided into A and B type. Type A reservoir experience disification first, then gas accumulation and after that experience structural reworking, however B type develop with the sequence of gas accumulation, densification and reworking. Due to multistage orogenic movements of Bogda Mountain, ＂subsequent＂ tight gas accumulation occurred in Baka gas field of Tuba basin. The distribution of sweet spots is obviously controlled by local high structural locations. Main sweet spot types are ＂physical-property＂ sweet spots and ＂fracture＂ sweet spots. The formation of ＂subsequent＂ tight gas accumulation can be divided into four stages： physical-property trap formation and initial charging; differential accumulation; initial preservation and destruction; intensive destruction and residual. The complicated and multistage stacked ＂subsequent＂ tight gas accumulation formed finally after later multistage tectonic movements in Baka gas field.