Shiyou shiyan dizhi (Mar 2022)
Key controlling factors and enrichment mechanisms of tight reservoirs in 6th member of Triassic Yanchang Formation, Chaishangyuan area, southeastern Ordos Basin
Abstract
Chaishangyuan area locates in the Qilicun Oilfield of the southeastern Ordos Basin, the first onshore oil field discovered in China, and its main layer for oil-producing is the 6th member of Triassic Yanchang Formation (Chang 6). At present, the comprehensive study on the key controlling factors of Chang 6 tight oil reservoir in this area is not clear. In this paper, a large number of drilling, logging, core, production test and other data, combined with laboratory experimental observation were carried out to progress the understanding of the factors controlling reservoir formation. In addition, the concepts of the ratio of underlying sand thickness to formation thickness and the ratio of overlying mud thickness to formation thickness were introduced to comprehensively analyze the forming characteristics of Chang 6 reservoir in the study area and the controlling effects of source rocks, reservoirs, structures, caprocks and migration conditions on Chang 6 tight reservoirs. The Chang 6 tight reservoir in the study area is a lithologic reservoir with undeveloped edge and bottom water, which has the characteristics of clustered and quasi-continuous distribution, and its formation and distribution were controlled by four factors: hydrocarbon source, transport condition, reservoir and direct caprock, and the controlling effect of the four factors on the reservoir is weakened in turn. In the eastern area where source rock quality is poor, crude oil was mainly enriched in the lower strata where sand bodies were well developed, while in the western area where source rock quality is relatively better, the enrichment of crude oil was more controlled by caprock and transport conditions. The better the coupling relationship between them, the more conducive to reservoir formation.
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