鄂尔多斯盆地西南部晚三叠世碎屑岩储层成藏差异性及控制因素——以镇北地区延长组长4+5油层组为例

RESERVOIR FORMING DIFFERENCES AND CONTROLLING FACTORS OF LATE TRIASSIC CLASTIC RESERVOIR FORMATION IN SOUTHWESTERN ORDOS BASIN-TAKING YANCHANG CHANG 4+5 OIL FORMATION IN ZHENBEI AREA AS AN EXAMPLE

鄂尔多斯盆地西南部晚三叠世延长组碎屑岩储层油气成藏复杂,勘探开发难度大。文章在大量钻井岩心、薄片鉴定、测试分析及试油成果资料等系统分析基础上,研究了镇北地区延长组长4+5储层及成藏特征,揭示了成藏差异性,建立了成藏模式,分析了主控因素及富集规律。结果表明:盆地西南部发育了辫状河-三角洲沉积体系,西部发育三角洲平原亚相,东部为三角洲前缘亚相,东部储集砂岩结构成熟度和成分成熟度较西部高;储层孔隙度8%~15%,渗透率0.1×10^(-3)μm^(2)~1.0×10^(-3)μm^(2),储层整体为低孔、低渗储层,局部发育高孔高渗区,东部储层物性优于西部;认为优质烃源岩、生烃异常高压、有利沉积相、优质储层分布是油气富集成藏的主要控制因素;盆地西南部长4+5主要发育了岩性油藏和构造-岩性油藏两种油藏类型,东部为岩性油藏,西部发则以构造-岩性油藏为主,东、西部成藏特征差异性明显;东部烃源岩厚度大且生烃增压形成的异常压力值高,可形成连续性好、规模较大的油藏,而西部所形成的油藏规模小。

The clastic rock reservoir of Late Triassic Yanchang Formation in southwestern Ordos Basin is a challenging area for exploration and development due to its complexity.On the basis of systematic analy-sis of drilling core,thin section identification,test analysis and oil test results,this paper focuses on stud-ying the characteristics of Yanchang 4+5 reservoir and its accumulation,in order to reveal its accumula-tion difference,establish the accumulation model,and analyze the main controlling factors and enrichment rules.The results show that the southwest of the basin has the braided river delta depositional system,with the delta plain subfacies in the west and the delta front subfacies in the east,and the reservoir sandstone structural maturity and compositional maturity are higher in the east than in the west of the basin.The porosity of Chang 4+5 reservoir is 8%to 15%and permeability is 0.1×10^(-3)μm^(2)to 1.0×10^(-3)μm^(2).Except local high porosity and high permeability area,the whole reservoir is a low porosity and low perme-ability reservoir.In addition,the physical property of the eastern reservoir is better than that of the western one.It is considered that high quality source rock,abnormal high pressure of hydrocarbon generation,favorable sedimentary facies and high-quality reservoir distribution are the main controlling factors of oil and gas accumulation.In the southwest of the basin,Chang 4+5 mainly develops lithologic reservoirs and tectonic-lithologic reservoirs,with lithologic reservoirs mainly developed in the east and tectonic-lithologic reservoirs in the west.In the eastern part of the reservoir,the thickness of source rocks is large and the abnormal pressure generated by hydrocarbon generation is high,which has a potential to form a continuous and large oil pool.While in the western part,the scale of oil pool is smali.