DIAGENESIS EFFECTS OF LOWER TRIASSIC FEIXIANGUAN FORMATION RESERVOIR IN PUGUANG GAS FIELD, NORTHEAST SICHUAN
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摘要: 川东北普光气田下三叠统飞仙关组储层主要为台地边缘鲕滩沉积,岩性以白云岩为主,主要成岩作用有:泥晶化、压实压溶、胶结充填、白云化、新生变形和重结晶、溶蚀、构造破裂。对储层形成有重要贡献的成岩作用有:白云化、溶蚀作用和构造挤压。根据白云石标型特征、有序度及碳氧同位素分析,储层白云岩形成于高盐度流体、快速结晶环境,是准同生期渗透回流白云化的产物。储层发育3期溶蚀作用,其中早期大气淡水溶蚀形成的孔隙与原生粒间孔一起在早成岩期—中成岩早期多为胶结物填塞,现今有效孔隙为埋藏溶孔。埋藏溶蚀有2期,Ⅰ期发生在构造挤压作用之后、大量石油充注之前;Ⅱ期发生在充注石油热演化为沥青之后。构造挤压作用是飞仙关组储层形成的另一重要控制因素,一方面构造挤压作用有利于重结晶;另一方面构造挤压产生裂缝,使晶体破碎,为埋藏溶蚀酸性流体提供通道,并极大地增加了水—岩反应的接触面积,促使埋藏溶蚀广泛发育。Abstract: The Lower Triassic Feixianguan Formation reservoir in the Puguang Gas Field of the Northeast Sichuan mainly consists of platform margin oolitic beach sediments.The main lithology is dolomite.The main diagenesis effects include: micritization,compaction and pressure solution,consolidated fill,dolomitization,nascent deformation and recrystallization,solution and structural disruption.Among which,dolomitization,solution and structural compression work as the key effects for reservoir formation.According to dolomite types,order degree and C,O isotope analyses,dolomite reservoir generates in high salinity fluid and quick crystallization environment.It is the result of dolomitization caused by seepage reflux during the penecontemporaneous stage.Three stages of solution effects have taken place in the reservoir.From the early diagenesis stage to the early middle diagenesis stage,pores generated from fresh water solution and primary intragranular pores are filled by consolidations.The present effective pores are buried ones.The burial solution is divided into two stages.The first stage is after structural compression but before oil filling.The second stage is when the filled oil has transferred to bitumen.Structural compression is another controlling element for reservoir formation in the Feixianguan Formation.On the one hand,structural compression is favorable for recrystallization;on the other hand,it forms fracture and cracks crystals,hence provides pathways for acid fluid.In this way,the contact surface for oil and rock is enlarged,which helps the generation of burial solution.
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Key words:
- diagenesis /
- reservoir /
- Feixianguan Formation /
- Lower Triassic /
- Puguang Gas Field /
- Northeast Sichuan
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