Tectonic-lithofacies paleogeography, large-scale source-reservoir distribution and exploration zones of Cambrian subsalt formation, Tarim Basin, NW China

Abstract

To predict the large-scale source rock and reservoir distribution in Cambrian subsalt formations (Upper Sinian to Mid-Cambrian) in the Tarim Basin, more than 50 2D seismic lines and 3D data volume acquired latest, 22 wells and some outcrops around this area were used to study the tectonic-lithofacies paleogeography, define the distribution of large scale source rocks and reservoirs, and sort out favorable zones. (1) The basin experienced evolution from ramp to deep-water mud-rich ramp, low-gradient slope, weak rimmed to strong rimmed platform, and the differentiation in the platform was controlled by pre-Cambrian palaeo-rifts. (2) The Luonan-Yubei ancient rift controlled the distribution of source rocks in the Lower Cambrian Yuertusi Formation, and this rift together with the northern depression are the main source rock area. (3) There are three sets of large-scale reservoirs, the Upper Sinian Qigebulake Formation, the Lower Cambrian Xiaorbulake Formation and the Wusongger Formation, and shoal-mounds, early dolomitization and multi-levels of unconformities controlled reservoir development. (4) Four favorable zones, the north slope of Tazhong, upper slope of Maigaiti area, Keping-Wensu periphery, and south slope of Tabei, were evaluated. Of them, the north slope of Tazhong is most likely to have exploration breakthrough; the south slope of Tabei is the best area for exploring the Upper Sinian large scale weathering crust dolomite; Maigaiti slope and Keping-Wensu periphery area improved in exploration potentials significantly, and are worth prospecting faster.