Lu Z.,Chinese Academy of Geological Sciences |
Zhu Y.,Chinese Academy of Geological Sciences |
Zhang Y.,Chinese Academy of Geological Sciences |
Wen H.,Qinghai No. 105 Coal Geological Exploration Team |
And 2 more authors.
Cold Regions Science and Technology | Year: 2011
Four scientific experimental wells were drilled in the Qilian Mountain permafrost of Qinghai Province, China, in 2008 and 2009. Gas hydrate was obtained from three of four wells and its related anomalous phenomena were observed in all the four wells. Raman spectroscopy was used in the laboratory to evaluate the type of clathrates recovered from these sites, including structures containing large and small cages of hydrocarbon gases. Gas hydrate and associated anomalies occur mainly in fractured mudstone, oily shale, siltstone, and fine-grained sandstone. Secondary occurrences were also present in the pore space of fine to medium grained sandstone in a zone between 133 and 396mbs. This interval was vertically discontinuous and horizontally did not appear to correlate between wells. Gas hydrate occurrences in these wells are not solely related to lithology and are strongly controlled by fissures in the Qilian Mountain permafrost. Gas geochemical characteristics reveal that gas hydrate is primarily composed of CH4, with secondary components of C2H6, C3H8, and CO2. Raman spectra analysis indicates a sII gas hydrate structure. Gas composition and carbon and hydrogen isotope geochemistry show that gases from gas hydrate are mainly thermogenic with a biogenic fraction. In the study area, gas hydrate and its related anomalous phenomena are confined to the gas hydrate stability zone which is constrained by permafrost pressure and temperature conditions. Core observations indicate that individual gas hydrate occurrences are controlled by fissures. It is speculated that, when hydrocarbon gases reach the gas hydrate stability zone, they form into gas hydrate that occurred preferably in fissures beneath the permafrost. © 2011 Elsevier B.V.
Jin C.-S.,Strategic Research Center for Oil and Gas Resources |
Qiao D.-W.,Strategic Research Center for Oil and Gas Resources |
Lu Z.-Q.,Chinese Academy of Geological Sciences |
Zhu Y.-H.,Chinese Academy of Geological Sciences |
And 5 more authors.
Chinese Journal of Geophysics (Acta Geophysica Sinica) | Year: 2011
Based on gas composition and temperature measurements in the course of field drilling, the upper and lower depths of gas hydrate stability zone are calculated by modeling in the Muli permafrost, Qinghai, then the modeling results are compared with the drilling results. The modeling results show that the upper depth of gas hydrate stability zone is 148. 8-122. 7 m and the lower depth of gas hydrate stability zone is 324. 6-354. 8 m, with the thickness of gas hydrate stability zone of 175. 8-232. 2 m: the drilling results indicate that gas hydrate and its related indications occur at the interval of 133-396 m. These two types of results are comparable and thus are basically accordant, suggesting that the modeling can serve as a prediction of the upper and lower depths of gas hydrate stability zone. Gas composition, depth of permafrost, thermal gradients above and below the base of permafrost are sensitive factors affecting the upper and lower depths of gas hydrate stability zone in the Muli permafrost.
Wen H.-J.,Qinghai No. 105 Coal Geological Exploration Team |
Shao L.-Y.,China University of Mining and Technology |
Li Y.-H.,Qinghai No. 105 Coal Geological Exploration Team |
Lu J.,China University of Mining and Technology |
And 3 more authors.
Geological Bulletin of China | Year: 2011
Since gas hydrates were found in the permafrost of the Juhugeng ore district (JHG) in the Muli coalfield of Qinghai Province, the JHG has become one of the hot spot areas in the Tibetan Plateau. This paper has investigated the geological structure, coal-bearing stratigraphy and depositional facies of the Jurassic coal measures in the JHG area. The JHG area is structurally located in the western section of the Qilian depression-folding zone. Controlled by the thrusting faults along the northern margin of the Datongshan and the southern margin of the Tuolaishan, the structures in the JHG area extend from northwest to southeast, and find expression in two synclines, i.e., northern syncline and southern syncline. Coal resources are preferentially preserved in the northern syncline. Coals were formed in the Middle Jurassic Muli Formation and Jiangcang Formation, and the regionally minable coals are preserved in the Upper Member of the Muli Formation. Coal accumulations mainly occur in the swamp environment developed in the abandoned braided river system and in the swamp environment developed by shallowing of the lacustrine and subaqueous delta.
Lu Z.,Oil and Gas Survey |
Zhai G.,Oil and Gas Survey |
Zhu Y.,Oil and Gas Survey |
Zhang Y.,Institute of Exploration Techniques |
And 6 more authors.
International Journal of Offshore and Polar Engineering | Year: 2016
Gas hydrate was successfully sampled again in the DK-9 hole in Qilian Mountain permafrost since it was first discovered in 2008. However, gas hydrate occurrences are heterogeneous both in horizon and in profile, which are restricted just within a limited area. The geological controlling factors that affect gas hydrate occurrences are not yet known in Qilian Mountain permafrost. Since the features of gas hydrate and other related geological information were well recorded in DK-9, on the basis of analyses of geochemical and geological data in this hole, a possible geological pattern is put forward for a gas hydrate reservoir in this area. In this paper, the features of hydrocarbon in headspace gases from cores at various depths are compared with the occurrences of gas hydrate, faults, or fractures in DK-9 in Qilian Mountain permafrost. The results show that gas hydrate and its related anomalies fall into intervals with higher hydrocarbon contents in headspace gases. In the meantime, faults or fracture zones serve as migration paths for gases in the deep and provide accumulation space for gas hydrate in the shallow in Qilian Mountain permafrost. Specifically, the F1 and F2 faults mainly control gas hydrate accumulation in Qilian Mountain permafrost. © by The International Society of Offshore and Polar Engineers.