Shiyou shiyan dizhi (Mar 2024)
Reservoir characteristics and hydrocarbon accumulation significance of metamorphic zones of intrusive rocks and surrounding rocks in second member of Paleocene Funing Formation in Qintong Sag, Subei Basin
Abstract
Volcanic reservoirs play a crucial role in oil and gas exploration. The intrusive rocks in the Qintong Sag of the Subei Basin are widely distributed within active oil and gas deposits, making them a significant area for further exploration and reserve expansion in East China's continental basins. Despite the promising exploration prospects, there is a research gap regarding the impact of volcanics on shale surrounding rock reservoirs and their accumulation potential. It is essential to evaluate whether the shale metamorphic zones could serve as a key exploration target. This study focuses on the metamorphic zones of intrusive rocks and surrounding rocks in the Qintong Sag's second member of the Funing Formation. By integrating core, thin section, whole rock, and well logging data, this work systematically reveals the reservoir characteristics of the mud shale metamorphic zones and defines the contribution of magma intrusion to hydrocarbon accumulation in the metamorphic zones. The results indicate that magma intrusion alters the mud shale of the Funing Formation, resulting in a circular metamorphic zone reservoir with enhanced reservoir properties. This reservoir exhibits two types of spaces, pores and fractures, with development dependent on the thickness and intensity of intrusive rocks. Magma intrusion also leads to a "ripening effect", increasing the Ro of mud shale by 0.4%-0.5% at the same depth. The intrusive rocks of the Funing Formation were formed during the Wubao to Sanduo periods. The intrusion of igneous rocks created a circular metamorphic zone prior to the hydrocarbon charging stage, indicating a favorable accumulation match. Influenced by magma intrusion, spatial distribution of intrusive rocks, and the source-reservoir relationship, the metamorphic zones of intrusive rocks and surrounding rocks in the second member of Funing Formation in the Qintong Sag exhibit characteristics of integrated source-reservoir and near-source enrichment. This presents a new opportunity for significant reservoir enhancement on a large scale.
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