地球化学动态示踪油气成藏过程初探——以库车坳陷大宛齐构造为例

塔里木盆地库车坳陷大宛齐油气藏中³⁸Ar的富集与缺氧流体及挥发分沿大断裂运移有关,吐孜玛扎断裂是流体活动形成的³⁸Ar运移至油气藏的主要通道;而大北油气藏低的³⁸Ar丰度显示了气源就近成藏的特征。大宛齐油气田为原生油气藏,并非后期气侵作用形成。油气藏形成后期,因圈闭封闭能力弱造成气体轻组分沿破裂部分散逸,形成现今饱和程度较低的凝析气藏。大宛齐油气田为下生上储型成藏,三叠系和侏罗系为其主生油层系。在大宛齐油气田的形成过程中,烃类先沿吐孜玛扎断层运移,再从北向南进入大宛齐构造。大宛齐油气藏中的液态烃为中生界淡水湖相沉积有机质在成熟-高成熟演化阶段的产物。大宛齐油气田经历了早期与晚期两个充注过程,晚期充注的高-过成熟天然气密度较小因而主要聚集在上方,早期形成的相对高密度的天然气主要聚集在下方。

A preliminary discussion on geochemical dynamic tracing of oil/gas reservoiring process-taking Dawanqi structure in Kuqa depression as an example

In Dawanqi oil/gas pool in Kuqa depression, Tarim basin, the enrichment of ^38Ar was related to the migration of anoxic fluids and volatile constituents along large faults. Tuzimazha fault is the major pathway, through which ^38Ar generated from fluid activities would have migrated to the oil and gas reservoirs. The low concentration of ^38 Ar in Dabei reservoir reveals that gas would have been reservoired near the source rocks. Dawanqi oil/gas field is not an oil/gas pool as a result of later gas invasion, but is a primary oil/gas pool. The light components of gas partially dispersed along the fault due to the poor sealing ability of the trap at later reservoiring stage, leading to the formation of the current condensate gas reservoir with relatively low saturation. Hydrocarbons were generated from the Triassic and Jurassic major source rocks below, and were accumulated in the reservoir rocks above, i.e. , hydrocarbons have been generated from the organic matters in the Mesozoic fresh lake facies sediments during mature to high-mature evolutional phases. During the reseroviring process of Dawanqi oil/gas pool, hydrocarbons first migrated upward along Tuzimazha fault, and then entered Dawanqi structure from north to south. Dawanqi oil/gas pool has experienced early and late charging processes. The high-mature to over-mature natural gas charged in later stage would have mainly accumulated in the upper part, due to their relatively low density; while the relatively high density natural gas generated in early stage would have accumulated in the lower part.