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Mao Z.-G.,Petrochina | Mao Z.-G.,China National Petroleum Corporation | Zhu R.-K.,Petrochina | Zhu R.-K.,China National Petroleum Corporation | And 10 more authors.
Petroleum Science

Characterized by complex lithology and strong heterogeneity, volcanic reservoirs in China developed three reservoir space types: primary pores, secondary pores and fractures. The formation of reservoir space went through the cooling and solidification stage (including blast fragmentation, crystallization differentiation and solidification) and the epidiagenesis stage (including metasomatism, filling, weathering and leaching, formation fluid dissolution and tectonism). Primary pores were formed at the solidification stage, which laid the foundation for the development and transformation of effective reservoirs. Secondary pores were formed at the epidiagenesis stage, with key factors as weathering and leaching, formation fluid dissolution and tectonism. In China, Mesozoic–Cenozoic volcanic rocks developed in the Songliao Basin and Bohai Bay Basin in the east and Late Paleozoic volcanic rocks developed in the Junggar Basin, Santanghu Basin and Tarim Basin in the west. There are primary volcanic reservoirs and secondary volcanic reservoirs in these volcanic rocks, which have good accumulation conditions and great exploration potential. © 2015, The Author(s). Source

Dai L.-Q.,University of Science and Technology of China | Zhao Z.-F.,University of Science and Technology of China | Zheng Y.-F.,University of Science and Technology of China | Zhang J.,State Key Laboratory of Continental Dynamics
Geochemistry, Geophysics, Geosystems

Postcollisional mafic igneous rocks commonly exhibit petrological and geochemical heterogeneities, but their origin still remains enigmatic. While source mixing is substantial due to the crust-mantle interaction during continental collision, magma mixing is also significant during postcollisional magmatism. The two processes are illustrated by Early Cretaceous mafic igneous rocks in the Dabie orogen. These mafic rocks show arc-like trace element distribution patterns and enriched Sr-Nd-Pb isotope compositions, indicating their origination from enriched mantle sources. They have variable whole-rock εNd(t) values of -17.6 to -5.2 and zircon εHf(t) values of -29.0 to -7.7, pointing to source heterogeneities. Such whole-rock geochemical features are interpreted by the source mixing through melt-peridotite reaction in the continental subduction channel. Clinopyroxene and plagioclase megacrystals show complex textural and compositional variations, recording three stages of mineral crystallization during magma evolution. Cpx-1 core has low Cr and Ni but high Ba, Rb and K, indicating its crystallization from a mafic melt (Melt 1) derived from partial melting of hydrous peridotite rich in phlogopite. Cpx-1 mantle and Cpx-2 exhibit significantly high Cr, Ni and Al2O3 but low Rb and Ba, suggesting their crystallization from pyroxenite-derived mafic melt (Melt 2). Whole-rock initial 87Sr/86Sr ratios of gabbro lies between those of Pl-1core (crystallized from Melt 1) and Pl-1 mantle and Pl-2 core (crystallized from Melt 2), providing isotopic evidence for magma mixing between Melt 1 and Melt 2. Taken together, a heterogeneously enriched mantle source would be generated by the source mixing due to reaction of the overlying subcontinental lithospheric mantle wedge peridotite with felsic melts derived from partial melting of different rocks of the deeply subducted continental crust during the continental collision. The magma mixing would occur between mafic melts that were derived from partial melting of the heterogeneously metasomatic mantle domains in the postcollisional stage. As a consequence, the source and magma mixing processes in the continental subduction factory are responsible for the significant variations in the whole-rock and mineral geochemistries of postcollisional mafic igneous rocks. © 2015. American Geophysical Union. All Rights Reserved.. Source

Wang B.,State Key Laboratory of Continental Dynamics | Zhang G.,State Key Laboratory of Continental Dynamics | Li S.,Ocean University of China | Yang Z.,Capital Normal University | And 3 more authors.
Gondwana Research

We conducted paleomagnetic investigations on limestone from the Lower Carboniferous Huaitoutala Formation in the Qaidam Basin near Delingha City, Qinghai Province, China. The characteristic remanent magnetization (D = 5.8°, I = − 25.7°, k = 114.3, α95 = 4.8°) passes a fold test and indicates a paleopole position of − 39.2°N, 90.4°E and a paleolatitude of 13.5°N for the Qaidam Block for the early Carboniferous. Based on global tectonic reconstructions and paleontological evidence, we suggest that the Qaidam Block was adjacent to, but independent from, the North China, South China, Alashan–Hexi and Tarim blocks at this time. This result suggests that Pre-Carboniferous sutures reported around the Qaidam Basin represent collisional events within Gondwana, rather than the final sutures that gave rise to the present tectonic configuration. © 2016 International Association for Gondwana Research Source

Wu L.,State Key Laboratory of Continental Dynamics | Wu L.,Northwest University, China | Wu L.,Petrochina | Zhu Y.,State Key Laboratory of Continental Dynamics | And 5 more authors.
Shiyou Kantan Yu Kaifa/Petroleum Exploration and Development

The difficulties of making joint development of coal and natural gas were examined and the technical countermeasures were given through studying the case of the Shenmu gas field of the Ordos Basin, where the mining rights of coal and natural gas overlap completely. Based on the study of the main controlling factors of the distribution of favorable areas in the Upper and Lower Paleozoic formations, technical measures for different areas were determined considering well type, well pattern, efficient drilling and production, and ground gathering technology. The results show: The mining rights overlapping area of coal and natural gas can be developed jointly. The effective reservoirs of the multi-layer tight gas reservoirs can be divided horizontally into the superposition area for multi-boundaries sand body, multi-layers sand body and isolation sand body in the Upper Paleozoic formations, and the superposition area for effective reservoirs in the Upper and Lower Paleozoic formations. A cluster well group which includes nine wells is the optimal well pattern. Different reservoir area should be developed by different well type and patterns. The construction and development period of gas reservoirs will be shortened by the application of cluster well group, optimized technologies of drilling and production, and ground supporting facilities. Practice shows that the three dimensional development of the multi-layer tight gas reservoirs is also realized in the Upper and Lower Paleozoic when the joint development of coal and natural gas is done in the mining rights overlapping areas. © 2015, Science Press. All right reserved. Source

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