海相叠合盆地构造演化与油裂解气晚期成藏关系

The Relationship between Tectonic Evolution and Oil-cracking Gas Accumulation in Late Stage for Marine Superimposed Basins

海相叠合盆地蕴含丰富的油裂解气资源,其晚期成藏过程经历了早期古油藏成藏与晚期油裂解成气阶段,受构造演化控制作用明显。探索构造演化与晚期油裂解气成藏的关系,对油裂解气藏的勘探具有指导意义。以四川盆地蜀南地区构造演化与晚期油裂解气成藏关系为研究实例,通过分析构造演化与沉积响应,研究古老烃源岩生烃演化过程、原始油气聚集、原油裂解与天然气晚期成藏关系。蜀南地区寒武系筇竹寺组烃源岩存在3次生烃期和2次生烃停滞期,筇竹寺组烃源岩在加里东期和海西期发生的沉积埋藏和抬升剥蚀事件出现了2次生烃和2次停滞,印支期和燕山期上覆巨厚沉积地层使得筇竹寺组烃源岩持续生烃;龙王庙组古油藏内原油存在一次油裂解生气过程,印支期后三叠系埋藏深度足够大并激发了龙王庙组古油藏内原油的裂解成气,持续到燕山晚期,提供充足的气源。研究得出以下结论:1海相叠合盆地的构造沉积演化控制了油气基础地质条件的发育;2构造沉积演化控制了古老烃源生烃过程;3构造沉积演化控制了古构造发育、古油藏聚集与保存;4构造沉积演化控制了古油藏的原油裂解与晚期聚集成藏;5建立了古老海相烃源层系晚期油裂解气成藏的研究思路,以期对同类古油藏研究起到借鉴作用,扩大油裂解气藏勘探的规模。

The marine superimposed basins are rich in oil-cracking gas resources. Their hydrocarbon accu- mulation processes of late stage have experienced early paleo-oil reservoir accumulation period and late oil- cracking gas period, which are apparently controlled by tectonic evolution. Studying the relationship be- tween tectonic evolution and oil-cracking gas accumulation of late stage has great significance to guide the exploration of oil-cracking gas reservoirs. Taking the relationship between tectonic evolution and oil-crack- ing gas accumulation of late stage for the Shunan area in the Sichuan Basin as an example, through the anal- ysis on the responds of structural evolution to deposition, the relationship between hydrocarbon generation process of ancient source rocks, initial hydrocarbon accumulation, oil cracking and gas accumulation of late stage was studied. The source rocks of the Cambrian Qiongzhusi Formation in the Shunan area experienced three periods of hydrocarbon generation and two lag periods of hydrocarbon generation. During the large- scale tectonic uplift and thick erosion event in the periods of the Caledonian and the Hercynian, source rocks of the Qiongzhusi Formation had experienced two periods of hydrocarbon generation and two lag pe- riods of hydrocarbon generation. The overlying super-thick strata deposited during the Indosinian and Yan- shan periods made the source rocks of the Qiongzhusi Formation continuously generate oil and gas. The crude oil in the paleo-reservoir of the Longwangmiao Formation experienced one time of oil-cracking gas process. After the Indo-Chinese Epoch, the burial depth of the Triassic was deep enough to promote the crude oil in the paleo-reservoir of the Longwangmiao Formation to crack into gas. This process continued to the Late Yanshan Period,providing sufficient gas source. The following five conclusions are obtained ： （1） The tectonic and depositional evolution of the marine superimposed basins controlled the development of the basic hydrocarbon geological conditions （2）The tectonic and depositional evolution controlled the hy- drocarbon generation process of the ancient source rocks; （3）The tectonic and depositional evolution con- trolled the development of the paleo-structures,accumulation and preservation of the paleo-oil reservoirs; （4）The tectonic and depositional evolution controlled the crude oil cracking of paleo-reservoirs and their ac- cumulation in the late stage; （5）The research idea on oil-cracking gas accumulation of late stage of ancient marine source rocks was established,which could provide references for the paleo-oil reservoirs of the same type in order to expand the exploration scopes of oil-cracking gas reservoirs.