四川盆地川中古隆起震旦系—下古生界天然气勘探新认识及勘探潜力

四川盆地川中古隆起安岳气田被发现后,在与其具有相似沉积背景的现今古隆起北斜坡震旦系—下古生界寻求天然气勘探发现便成为努力的目标。随着风险探井PT1井于川中古隆起北斜坡(以下简称北斜坡)上震旦统灯影组二段获得天然气勘探突破,以及JT1井在灯四段和下寒武统沧浪铺组发现天然气勘探新苗头,证实了北斜坡同样具备形成规模大气区的优越条件。为了进一步明确川中古隆起震旦系—下古生界天然气勘探潜力并指导后续勘探部署,对北斜坡震旦系—下古生界含油气地质条件进行了分析。研究结果表明:①北斜坡震旦系灯二段、灯四段两期台缘带在平面上基本分离,并且无论是台缘宽度还是沉积厚度均优于高磨地区,具备天然的沉积优势;②北斜坡震旦系灯影组储层储集条件较高磨地区更优,并且震旦系—寒武系纵向上发育多套优质储层;③北斜坡震旦系灯影组天然气成藏要素配置关系较好,岩性圈闭发育且累计面积较大,JT1井、PT1井已分别证实灯四段、灯二段岩性圈闭内含气,发育斜坡背景下的大型岩性圈闭气藏。结论认为,北斜坡震旦系—下古生界含油气地质条件比高磨地区更佳,并且具备纵向上多层系立体勘探的优势,展现出巨大的天然气勘探潜力和广阔的勘探前景,是该盆地常规天然气勘探的重要战略新区带。

New understandings and potential of Sinian–Lower Paleozoic natural gas exploration in the central Sichuan paleo-uplift of the Sichuan Basin

Since the Anyue Gasfield, located in the central Sichuan paleo-uplift of the Sichuan Basin, was discovered, great efforts have been made to work on natural gas exploration and discovery in the Sinian–Lower Paleozoic in the north slope of present paleo-uplift which has similar depositional settings. It is verified by the breakthrough of natural gas exploration in the second Member of Upper Sinian Dengying Formation in the north slope of central Sichuan paleo-uplift by wildcat well PT1 and the new sign of natural gas exploration in the Canglangpu Formation of Lower Cambrian and the fourth Member of Dengying Formation by Well JT1 that there are also favorable conditions for the formation of large-scale gas province in the north slope. In order to determine the natural gas exploration potential of Sinian–Lower Paleozoic in the central Sichuan paleo-uplift and provide the guidance for the following exploration deployment, this paper analyzed the petroleum geological conditions of Sinian–Lower Paleozoic in the north slope. And the following research results were obtained. First, the marginal platform belts in the second and the fourth Member of Sinian Dengying Formation in the north slope are basically separated areally, and they are superior to the Gaomo area in terms of marginal platform width and sedimentary thickness and are intrinsically advantageous in sedimentation. Second, compared with the Gaomo area, the reservoirs of Sinian Dengying Formation in the north slope are better in reservoir conditions, and many sets of quality reservoirs are developed vertically in Sinian–Cambrian. Third, hydrocarbon accumulation elements of Sinian Dengying Formation are better allocated in the north slope. Lithological traps are developed with a larger cumulative area. Wells JT1 and PT1 verify that there is gas in the lithological trap of the fourth and the second Member of Dengying Formation and large-scale lithological gas reservoirs are developed in the slope setting. In conclusion, compared with the Gaomo area, the Sinian–Lower Paleozoic in the north slope is superior in petroleum geological conditions and has the advantage of multi-layer stereoscopic exploration vertically, presenting a great natural gas exploration potential and promising exploration prospects, so it is a new important strategic zone of conventional natural gas exploration in the Sichuan Basin.