Development and distribution rules of the main Neoproterozoic source and reservoir strata in the Yangtze Block, Southern China

Abstract

In recent years, significant breakthroughs in gas exploration have been made in Neoproterozoic strata in the Yangtze Block, in southern China, as the Anyue super gas field was discovered in the central Sichuan region. The potential of Neoproterozoic exploration in other parts of the Yangtze Block remains a question. Defining the development and distribution rules of Neoproterozoic source and reservoir strata is an important reference for the next step of deep-zone oil and gas explorations in the Yangtze Block. Based on field surveys and sample collections, the analyses of many predecessor field sections and drilling logging data of the Neoproterozoic in the Yangtze Block, source-rock series tests and analyses, as well as analyses of reservoir thin sections, and the distribution rules of the source and reservoir strata were determined by industrial mapping methods. Three sets of source rocks are found in the Neoproterozoic in Yangtze Block, namely, the Datangpo Formation, Doushantuo Formation, and the third member of the Dengying Formation. From top to bottom, the thermal evolutions in the three sets of source rocks show an increasing trend, with the Dengying Formation reaching the stage of over-maturation, while that of Doushantuo and Datangpo formations enter thermal metamorphism stages. The source rocks of the Datangpo Formation are relatively limited in distribution, displaying a northeastward rift style, whereas those of the Doushantuo Formation are distributed widely with two thickness centers. The Neoproterozoic reservoirs in the Yangtze Block developed in the Dengying Formation, with the carbonate reservoir spaces mainly comprising caves, dissolved bores, or pores and cracks. The thickness center of the dolomite reservoirs in Dengying Formation are mainly located in the Middle and Upper Yangtze carbonate platform marginal zones, which are distributed in the eastern Sichuan Basin, and in the Mianyang–Changning rifting platform margin belts in the central Sichuan Basin and the northern Hubei areas. Based on the typical reservoir anatomy, the hydrocarbon accumulation rules of the Neoproterozoic in the Yangtze Block are summarized as “near the rift trough or the passive continental margin hydrocarbon generation centers, adjacent to Karst bioherm-beach reservoir, and stable structural zones afterwards”.