辽东湾坳陷新近系特稠油成藏模式与成藏过程——以旅大5-2北油田为例

辽东湾坳陷断裂构造带原油稠化作用强烈,形成了复杂的特稠油油藏,其特殊的油藏模式为勘探阶段的油藏评价带来巨大风险。基于测井资料、岩心和薄片观察结果、原油地化分析和包裹体测温等技术,建立了旅大5-2北油田特稠油油藏模式,并对其成藏过程进行研究。结果表明:明化镇组和馆陶组特稠油藏与常规油藏相比具有不统一的油-水界面、弧形的油藏边界、油-水关系倒置以及油顶为分选极差的砂砾岩等特征;在距今约25 Ma东营组沉积末期,来自辽中凹陷和辽西南洼的原油在东营组经历了第一期成藏,由于处于断裂带且埋深较浅,原油遭初步的生物降解作用;自明化镇组沉积期距今5 Ma以来,东营组聚集原油遭受破坏,沿控圈断层作垂向运移至浅层,受早期稠化作用的影响,一方面在很大程度上降低了对保存条件的要求,原油可以在盖层条件较差的储层中聚集成藏,另一方面原油优先选择物性较好的储层进行充注,伴随着聚集后进一步强烈的生物降解作用,形成特殊的油藏模式。

Neogene extra heavy oil accumulation model and process in Liaodong Bay depression: a case study of Lvda 5-2 N oilfield

The thickening of crude oil is intensively enhanced in the fault zone of Liaodong Bay Depression, thus forming complex extra heavy oil reservoir. This special reservoir model brings a great risk to reservoir evaluation in the exploration phase. Based on logging data, core and slice observations, crude-oil geochemical analysis, inclusion temperature measurement and other technologies, the extra heavy oil reservoir model was established for Lvda 5-2 N oilfield, and its accumulation process was also studied. The results indicate that compared with conventional oil reservoirs, the extra heavy oil reservoirs in Minghuazhen Formation and Guantao Formation are characterized by non-uniform oil-water interface, arc-like reservoir boundary, oil-water inversion and glutenite with extremely poor sorting as the oil top. In the end of sedimentary period in Dongying Formation at about 25 Ma, the crude oil from Central Liaoning Depression and Southwest Liaoning Depression experienced the first stage of accumulation in Dongying Formation. Located in the fault zone with shallow buried depth, the crude oil was preliminarily subjected to biodegradation. Since the sedimentary stage of Minghuazhen Formation at about 5 Ma, crude oil accumulated in Dongying Formation has suffered damage and vertically migrated to shallow layer along trap-controlling fault. Due to the influence of early thickening, the requirements for preservation conditions were reduced to a large extent, and crude oil was able to accumulate in the reservoirs with poor cap conditions. On the other hand, the reservoirs with good physical properties were preferentially charged by crude oil. Along with further severe biodegradation after accumulation, a special reservoir model was created.