珠江口盆地西江凹陷XJ-A构造古近系成藏主控因素及模式

Main Controlling Factors and Models of Paleogene Hydrocarbon Accumulationin XJ-A Structure of Xijiang Sag,Pearl River Mouth Basin

以珠江口盆地西江凹陷XJ-A构造为研究对象,在构造、地层、地震等资料以及对岩心、薄片和流体包裹体分析的基础上,对其开展油气成藏条件和动态成藏过程研究,厘清成藏主控因素,建立油气成藏模式。结果表明,XJ-A构造古近系烃源岩有机质丰度较高,主要为Ⅱ_(1)~Ⅱ_(2)型干酪根,生油潜力较大;发育辫状河三角洲沉积砂体,多为Ⅱ类及以上级别储层,适合大规模成藏;成藏期通源断裂活动速率降低,油气在超压驱动下主要通过断层、砂体和裂缝输导运移成藏。结合包裹体均一温度测试和埋藏史分析,油气充注可划分为三个期次:第一期(距今15.9~10.8Ma)为低熟原油充注期,第二期(距今10.8~5.4Ma)为成熟原油主力充注期,第三期(距今5.4~0Ma)为成熟原油混合部分天然气的充注期。在烃源岩良好、储集物性优越及超压充注的背景下,XJ-A构造古近系油气成藏主控因素为烃源条件、储集条件和输导条件。油气成藏模式具有“旁生侧储、下生上储、近源成藏、超压强供”的特征。

Taking the XJ-A structure in Xijiang Sag of Pearl River Mouth Basin as the research object,based on structural,stratigraphic,and seismic data and analysis of core,thin sections,and fluid inclusions,the oil and gas accumulation conditions,and dynamic accumulation process is studied to clarify the main controlling fac-tors of oil and gas accumulation and establish the oil and gas accumulation model.The results show that the organic matter of Paleogene source rocks in the XJ-A structure is abundant,forming mainly typeⅡ_(1)-Ⅱ_(2) kerogen with great oil generation potential.Braided river delta sedimentary sand bodies are developed and formed mostly classⅡand above reservoirs suitable for large-scale accumulation.During the accumulation pe-riod,the activity rate of the source faults decreased,and oil and gas were mainly transported and migrated through faults,sand bodies,and fractures under overpressure.Combined with the homogenization temperature test of inclusion and burial history analysis,oil and gas charging can be divided into three phases:the first phase(15.9-10.8Ma from now)is the charging period of low mature crude oil,the second phase(10.8-5.4Ma from now)is the main charging period of mature crude oil,and the third phase(5.4-0Ma from now)is the charg-ing period of mature crude oil mixed with some natural gas.Under the background of good source rocks,su-perior reservoir properties,and charging on overpressure,the main controlling factors of hydrocarbon accumula-tion in the Paleogene of XJ-A structure are hydrocarbon source,reservoir,and transportation conditions.The hydrocarbon accumulation models have the characteristics of"new generation and old reservoir,lower genera-tion and upper reservoir,near source accumulation and overpressure supply".