渤海湾盆地黄河口凹陷渤中29-6油田原油稠化机制及成藏模式

Thickening Mechanism and Reservoir Formation Model of Bozhong 29⁃6 Oilfield in Huanghekou Sag,Bohai Bay Basin

渤中29-6油田位于黄河口凹陷北部陡坡带,具有双洼供烃的有利位置,已发现原油整体表现为稠油特征,生标特征复杂多样,其油气来源及稠油成因机理尚不明确.在前人研究基础之上,基于原油分析化验数据,利用地球化学分析方法,系统梳理了渤中29-6油田稠油来源,阐明了该原油稠化机理,并建立了原油的稠化模式及成藏模式,结果表明:(1)渤中29-6油田表现为双洼混合供烃的特征,其中高硫油主要来源于黄河口东洼,而低硫油主要来源于黄河口中洼;(2)渤中29-6油田整体表现为浅层稠油,其原油物性受二次充注作用、断层活动性、母源条件这3个因素的联合控制,其中断层活动性控制整体原油稠化级别,二次充注作用和母源条件分别可以改善和加剧原油稠化作用,并形成了低熟-弱断弱充注、成熟-强断弱充注、成熟-强断强充注、低熟-强断强充注这4种原油稠化模式;(3)渤中29-6油田具有双洼供烃成藏模式,且因距离洼陷远近而不同,近源形成单洼供烃-断裂垂向输导-强/弱充注-强降解-源上稠油成藏模式,远源形成双洼供烃-砂体或不整合侧向输导-弱充注-强/弱降解稠油成藏模式;(4)渤中29-6油田围区可划分为4个区带:Ⅰ区原油物性最好,Ⅱ区和Ⅳ区稠化最严重,物性最差,Ⅲ区原油物性居中.由于二次充注作用可以明显改善原油物性,中-轻原油勘探和开发应优选Ⅰ区和Ⅲ区.

Bozhong 29-6 oilfield is located in the northern steep slope zone of Huanghekou sag, which has a favorable position for hydrocarbon supply from double depressions. It has been found that the crude oil is characterized by thickened oil as a whole, and the characteristics of biomarkers are complex and diverse, and the source of oil-gas and the genetic mechanism of thickened oil are not clear. Based on previous studies and crude oil analysis, by using geochemical analysis method, the source and thickening mechanism of heavy oil in Bozhong 29-6 oilfield are clarified, and the thickening model and reservoiring model are established. The results show that(1) Bozhong 29-6 oilfield has the characteristics of double-depression mixed hydrocarbon supply. The high sulfuroil mainly derives from the eastern depression of the Huanghekou sag, while the low sulfur-oil mainly derives from the middle depression of the Huanghekou sag;(2) Bozhong 29-6 oilfield group is of shallow heavy oil, and its crude oil properties are controlled by the combination of three factors, namely, secondary filling, fault activity and parent source characteristics. The properties of crude oil are controlled by the combination of three factors which are secondary charge, fault activity and maternal characteristics. Based on three factors, four oil thickening modes are identified, including immature-weak faulting-weak secondary charge, mature-strong faulting-weak secondary charge, mature-strong faulting-strong secondary charge, immaturestrong faulting-strong secondary charge.(3) Bozhong 29-6 oilfield has double depression hydrocarbon supply and accumulation mode, which varies with the distance to the sag. Single depression hydrocarbon supply vertical transportation fault strong filling strong degradation heavy oil reservoir forming mode is formed near source, and double depression hydrocarbon supply sand body or unconformity lateral transportation weak filling strong/weak degradation heavy oil accumulation mode is formed at far source;the hydrocarbon supply from single depression near the source, vertical transportation of fault, strong/weak filling, strong degradation, and heavy oil accumulation mode above the source are formed, and the hydrocarbon supply sand body in double depression or unconformity lateral transportation weak filling strong/weak degradation heavy oil accumulation mode is formed in the far source.(4) The surrounding areas of Bozhong 29-6 oilfield can be divided into four zones: zone I has the best physical properties of crude oil, zone Ⅱ and Ⅳ have the most severe thickening and the worst physical properties, and the crude oil in zone Ⅲ is in the middle. Because the secondary filling can obviously improve the physical properties of crude oil, the exploration and development of medium light crude oil should select area Ⅰ and area Ⅲ.