叠合盆地古老深层碳酸盐岩油气成藏过程和特征——以四川叠合盆地震旦系灯影组为例

四川叠合盆地震旦系(埃迪卡拉系)灯影组是目前中国最古老的油气产层,勘探历史超过50年。其有效烃源岩主要是下寒武统筇竹寺组,储集层主要为灯影组微生物白云岩与受桐湾运动影响形成的风化壳储集层,直接盖层为筇竹寺组泥岩;生储盖组合从层位上来讲主要是上(新)生下(老)储顶盖型,从空间分布来讲主要是旁生侧储顶盖型。其油气成藏过程为"四中心"(生烃中心、生气中心、储气中心和保气中心)耦合,生烃中心生成的油气运移至古构造形成古油藏(生气中心),古油藏内石油深埋裂解形成古气藏(储气中心),受盆地内晚期快速隆升和盆缘造山带影响,灯影组古气藏内的天然气沿灯影组顶不整合面再次发生长距离运移调整成藏或破坏,形成现今天然气藏(保气中心)。灯影组天然气成藏或破坏有5种模式,即高石梯型、威远型、通南巴型、焦石坝型和丁山-林滩场型。四川叠合盆地震旦系灯影组的长期勘探和深入研究揭示出叠合盆地古老深层碳酸盐岩油气成藏特征是:(1)烃源岩生物类型低等化和有机质高演化;(2)储集层成岩强度大、演化时间长,趋于致密化,上覆负荷作用可能导致深层储集层质量变差;(3)油气成藏过程具烃态(固、液、气)转变和多阶段性,油气分布具有突出的差异性和多因素联控;(4)油气形成和保存的关键因素是烃源充足、保存条件佳和构造稳定。

The formation process and characteristics of ancient and deep carbonate petroleum reservoirs in superimposed basins:A case study of Sinian (Ediacaran) Dengying Formation in the Sichuan superimposed basin,China

The Sinian (Ediacaran) Dengying Formation is the oldest gas-bearing carbonate strata in China and it has been explored and studied for more than 50 years.This ancient and deep petroleum system is characterized by high quality reservoir rock of Upper Sinian Dengying Formation microbial dolomite,and by high quality source rock and cap rock of Lower Cambrian Qiongzhusi Foramtion mudstone.The formation processes of petroleum accumulation are the coupling of hydrocarbon generation center,gas generation center,gas accumulation center and gas preservation center.Hydrocarbon in the Dengying Formation is generated from hydrocarbon generation center at first,then migrated into the old pools,and thermally cracked into gas generation center finally.Long distance migration,adjustment and distruction again occur along the unconformity surface of Dengying Formation due to the effect of late stage rapid uplift and orogenic belts around the Sichuan Basin,and eventually form the present gas preservation center.There are 5 models for the pool accumulation and pool distruction of Dengying Formation,the Gaoshiti style,Weiyuan style,Tongnaba style,Jiaoshiba style and Dingshan-Lintanchang style.In general,the typical features of ancient and deep petroleum system in the Ediacaran Dengying Formation across the Sichuan Basin are as follows:(1) Source rock is of high thermal maturity and microbial;(2) Reservoir rock is charaterized by old age,high diagenesis,low-/ultralow porosity and permeability;(3) Mutli-phase changes (i.e.,solid,liquid and gas states) and multistage processes occur due to multifactors;and (4) Key factors to petroleum formation and preservation are abundant source,favorable perservation condition and stable tectonics.