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Liu N.,National Engineering Laboratory For Explor And Development Of Low Permeability Oil And Gas Flds | Liu N.,Petrochina | Yao Y.-T.,Southwest Petroleum University | Nan J.-X.,National Engineering Laboratory For Explor And Development Of Low Permeability Oil And Gas Flds | And 3 more authors.
Journal of Chengdu University of Technology (Science and Technology Edition)

The tight sandstone gas resource in Ordos Basin is rich and large gas fields are mostly hosted in the tight sandstone reservoir of the Upper Paleozoic. The petrologic characteristics, pore characteristics, physical properties and diagenetic features of H8 Formation and Taiyuan Formation of Permian in the east of Ordos Basin are researched by means of core observation and analytic techniques in this paper. Then, the paper studies the low yield factors so as to provide the evidence for the effective development of the gas reservoirs. The result shows that the reservoirs of H8 Formation and Taiyuan Formation in the east of Ordos Basin are mainly comprised of lithic sandstone and lithic quartz sandstone. But the difference between the two reservoirs in reservoir characteristics and low yield factor is notable. H8 Formation sandstone is characterized by minor amount of matrix and developing primary intergranular pores which are fully packed by the late diagenetic minerals and its reservoir space is mainly the intercrystal pore. The Taiyuan Formation sandstone has major amount of matrix, poor primary intergranular pores and developing dissolution pores which formed in the late stage of early diagenetic period and the beginning of late diagenetic period. The dissolution of high mica and eruptive rock, feldspar and volcanic ash of Taiyuan sandstone produces abundant reservoir spaces. But silk-net-like illite forming at the high temperature stage during the late diagenetic period packed in pores, plugged up pore throats and affected the percolation ability. This is one of the main reasons to cause the poor reservoir property. The dominant sheet or curl throat, the high effective overburden pressure, the high mica content, the strong stress sensitivity, the low original water saturation and the low reservoir pressure (pressure coefficient: 0.6∼0.8) easily lead to the reservoir's water lock effect in the processes of drilling, fracturing and acidification. This is another main reason of low yield in research area. Source

Han T.-Y.,National Engineering Laboratory For Explor And Development Of Low Permeability Oil And Gas Flds | Han T.-Y.,Petrochina | Li H.,Petrochina | Li W.-H.,Northwest University, China | And 7 more authors.
Northwestern Geology

In our study, we measures the U-Pb age of detrital Zircon in the middle and lower formation of Upper Triassic Yanchang Formation in Yanhe Section of Ordos Basin, the results show that the most outstanding Zircon U-Pb age of the samples are 2 271-2 567 Ma and 1 599-1 937 Ma, and five zircons having a small amount of young magma zircon have a U-Pb ages of 261-285 Ma. The study shows that the time interval of 2 271 Ma and 2 567 Ma with a peak of about 2 500 Ma is an effective evidence for the activity of mantle adding related to basaltic magma in the late Late Archean in North China Craton. While the time interval of 1 599 Ma and 1 973 Ma with a peak of about 1 800 Ma is an effective evidence for tectonic heat event initiated by continent-continent collision of Columbia Supercontinent during the Palaeoproterozoic and the stru6ture movement during the Mesoproterozoic in North China Craton. Magma zircon age distributed between 261Ma and 285Ma of the five zircons is the main evidence for magma intrusion activity during the Early Indo-Chinese. In this paper, we used the detrital zircon age to determine that the Craton provenance of North China from which the clastic sediments of Yanhe Strata Section come from in the interval of about 2500Ma, that is, from the Late Archaean, Palaeoproterozoic deeply metamorphosed diorite, gneiss and granulitite of Yinshan Mountain. Source

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