普光与元坝礁滩气田天然气成藏特征对比

摘要

Systematic correlation between the Puguang and Yuanba Gas Fields can guide the natural gas prospecting in adjacent area and reef-bank oil-gas field in other basin. Using the chemical and isotopic composition of natural gases,thin sections, porosity data,and geophysical data,the systematic contrastive research of the origin and resource of nature gas,the scale and property of reservoir,the trap type and process of migration-accumulation,the tectonic deformation and preservation condition between Puguang and Yuanba gas field are summarized. The gas reservoir characters are reflected in four aspects. The difference in carbon isotopic composition of natural gas is related to the thermal evolution and hydrocarbon precursor types of the source rock. The scale of source rock and hydrocarbon potential of Puguang Gas Field is better than Yuanba. The main reservoir of Puguang Gas Field is the oolitic beach dolomite of Feixianguan Formation. In contrast,the reef and the backreef beach dolomite of Changxing Formation is the primary reservoir type of Yuanba. The gas reservoir type of Puguang is structural-lithologic reservoir,however,Yuanba is lithologic gas reservoir,with a relatively weak adjustment and reconstruction in the late stage than Puguang. Because of the superposition of multi-phase tectonic movement,fault-fracture system is relatively developed in both Puguang and Yuanba gas field,but regional giant halite cap rock makes most of the gas reserved. The central position of source rock kitchen and sufficient oil-cracking gas,and unbroken halite cap rock are the key to the formation of the two gas fields.%系统对比普光和元坝气田的天然气成藏特征，可为邻区及其他盆地礁滩油气藏勘探提供参考。利用天然气组份和同位素资料、岩石薄片和物性分析资料及地球物理资料，开展了普光和元坝气田天然气成因与来源、储集层的规模与物性、圈闭类型与运聚过程、构造变形和保存条件的对比研究。认为天然气藏特征差异性主要体现在4个方面：天然气碳同位素组成上的差别与热演化程度和气烃岩母质类型的变化有关，普光气田烃源岩厚度与生烃潜力较元坝气田大；普光气田以飞仙关组鲕粒滩相优质白云岩储层为主，而元坝气田以长兴组生物礁、礁后浅滩相优质白云岩储层为主；普光气田为构造岩性气藏，元坝气田为岩性气藏，天然气晚期调整改造较普光气田弱；多期构造运动的叠加，形成较为发育的断层裂缝系统，但区域性的巨厚膏盐盖层使得绝大部分的天然气得以保存。位于生烃中心且具有充足的原油裂解气源、完整的膏岩盖层是形成两个大气田的关键。