四川盆地寒武系沧浪铺组油气勘探重大发现及其启示

Great discovery of oil and gas exploration in Cambrian Canglangpu Formation of the Sichuan Basin and its implications

近期,中国石油西南油气田公司风险探井——JT1井在四川盆地中部磨溪地区北斜坡下寒武统沧浪铺组测试获得51.62×104 m3/d的高产气流,实现了继下寒武统龙王庙组气藏之后寒武系又一层系的天然气勘探重大突破。为了加深对于该层系的认识,基于区域地质背景和气藏勘探历程,结合该盆地沧浪铺组的油气地质条件,对其天然气成藏条件进行了综合分析。研究结果表明:①早寒武世沧浪铺期四川盆地及周缘总体处于浅水陆棚沉积体系,沧浪铺早期德阳—安岳裂陷还未填平,受古地貌和物源控制,裂陷东部以清水陆棚碳酸盐岩沉积为主,云化颗粒滩相发育;②受滩相叠加溶蚀作用的影响,沧浪铺组一段发育白云岩孔隙型储层,岩性主要为残余鲕粒云岩、砂屑云岩和粉晶云岩、灰质云岩、云质鲕粒灰岩,储集空间类型主要有粒间溶孔、晶间溶孔、晶间孔,平均孔隙度为4.1%;③地震刻画川中—川北地区沧浪铺组一段发育多个大型滩体,横向上受滩间致密岩性遮挡、纵向上受沧浪铺组二段泥质岩的封盖,在现今单斜背景下具备形成构造—岩性复合圈闭的条件,刻画有利勘探面积逾3200 km2;④沧浪铺组一段滩相储层直接覆盖于下寒武统筇竹寺组优质烃源岩之上,形成下生上储源储组合,蓬莱—射洪—阆中一带靠近德阳—安岳裂陷区寒武系生烃中心,天然气成藏条件优越。结论认为,JT1井沧浪铺组油气勘探首次战略突破,证明了四川盆地寒武系具有较大的油气勘探潜力,对于推进该盆地奥陶系以及寒武系高台组、洗象池组等新领域、新层系的油气勘探工作具有指导意义。

Recently,high-yield gas flow with a tested production rate of 51.62×104 m3/d was obtained from Well Jiaotan 1,a wildcat well of PetroChina Southwest Oil&Gasfield Company in the Lower Cambrian Canglangpu Formation on the north slope of Moxi area,central Sichuan Basin,which means realizing a major natural gas exploration breakthrough in another formation of Cambrian after the gas reservoir of Lower Cambrian Longwangmiao Formation.In order to further understand this formation,this paper comprehensively analyzes its hydrocarbon accumulation conditions based on regional geological background and gas reservoir exploration history,combined with the petroleum geological conditions of Canglangpu Formation in the Sichuan Basin.And the following research results were obtained.First,the Sichuan Basin and its periphery were overall located in the depositional system of shallow shelf in the Canglangpu Age of Early Cambrian.And In the early stage of Canglangpu Age,Deyang–Anyue faulted depression was not leveled out.And under the control of palaeogeomorphology and provenance,clear-water shelf carbonate deposits were dominant and dolomitized grain beach facies was developed in the eastern area of the faulted depression.Second,due to the influence of beach facies superimposed with dissolution,a porous dolomite reservoir is developed in the First Member of Canglangpu Formation.It is lithologically dominated by residual oolitic dolomite,doloarenite and powder crystalline dolomite,limy dolomite and dolomitic oolitic limestone.The main types of reservoir space are intergranular dissolved pores,intercrystalline dissolved pores and intercrystalline pores,with an average porosity of 4.1%.Third,according to the seismic data,multiple large-sized beach bodies are developed in the First Member of Canglangpu Formation in the central-northern Sichuan Basin,and they are laterally under the barrier of inter-beach tight lithology and vertically sealed by argillaceous rocks of the Second Member of Canglangpu Formation.Thus,the conditions for the formation of structural-lithologic traps are satisfied under the background of current anticline and the favorable exploration area is 3200 km2.Fourth,the beach facies reservoir of the First Member of Canglangpu Formation immediately overlies the quality source rocks of Qiongzhusi Formation,so as to form a source rock-reservoir assemblage with source rocks in the lower part and the reservoir in the upper part.The Penglai–Shehong–Langzhong area is close to the Cambrian hydrocarbon generation center of Deyang–Anyue faulted depression,where hydrocarbon accumulation conditions are favorable.In conclusion,the first strategic breakthrough of oil and gas exploration in the Canglangpu Formation in Well Jiaotan 1 proves the greater oil and gas exploration potential in the Cambrian of the Sichuan Basin.The research results are of great significance to promoting the oil and gas exploration in Ordovician,Cambrian Gaotai Formation and Xixiangchi Formation and other emerging fields and strata of the Sichuan Basin.