Origin of subsequent condensate pool in Lunnan low uplift, Northwest China

Abstract

Lunnan (轮南) low uplift, where developed amounts of condensate pools in both Ordovician and Carboniferous reservoirs, locates in the north uplift of Tarim basin, Northwest China. Lunnan area has experienced intensive gas invasion since the Himalayan movement, causing multiple types of accumulation coexisting in the Ordovician reservoir. Geochemical evidence shows that these condensate oils are of low maturity (vitrinite reflectance levels near 1.0%) and the dominant component of the condensate gas is dry gas (the content of CH4 over 94%), which reflects that the condensate pool in Lunnan area is not the product of thermal cracking, but the subsequent accumulation derived from the phase fractionation. Furthermore, our observations on the C₆-C₇ hydrocarbons in Lunnan area are qualitatively similar to the effect of phase fractionation with condensates having higher paraffin and lower aromaticity than residual oils. Thus, two types of the condensates are defined by their phase behavior, which are saturated condensate pool and the nonsaturated one. The saturated condensate pool with an oil ring mainly developed in Ordovician reservoir, with large difference between formation pressure (FMP) and the dew point pressure (DPP). The origin of these condensates is considered as the in-situ segregation triggered by the invasion of excessive dry gas. On the other hand, the nonsaturated condensate pool that almost existed in the Carboniferous reservoir is a hydrocarbon reservoir containing slight difference between FMP and DPP, without oil ring, and evaporative fractionation due to the fault movement controls its generation.

Keywords

Lunnan low uplift / subsequent condensate pool / phase fractionation / gas washing

References

[1] Caňipa-Morales N. K., Galán-Vidal C. A., Guzmán-Vega M. A., . Effect of Evaporation on C7 Light Hydrocarbon Parameters. Org. Geochem., 2003, 34(6): 813-826.

[2] Chang C. T., Lee M. R., Lin L. H., . Application of C₇ Hydrocarbons Technique to Oil and Condensate from Type III Organic Matter in Northwestern Taiwan. International Journal of Coal Geology, 2007, 71: 103-114.

[3] Chen Y. C., Shen Z. M., Li Y. J., . Formation Mechanism and Formation Conditions of Condensate Pools in Lunnan Low-Uplift of Tarim Basin. Journal of Chengdu University of Technology, 2002, 29: 481-486.

[4] Connan J., Cassou A. M.. Properties of Gases and Petroleum Liquids Derived from Terrestrial Kerogen at Various Maturation Levels. Geochimica et Cosmochimica Acta, 1982, 44: 1-24.

[5] Curiale J., Bromley B.. Migration Induced Compositional Changes in Oils and Condensates of a Single Field. Org. Geochem., 1996, 24: 1097-1113.

[6] Danesh A.. PVT and Phase Behaviour of Petroleum Reservoir Fluids. Developments in Petroleum Science, 1998, 47: 107-110.

[7] Dzou L. I. P., Hughes W. B.. Geochemistry of Oils and Condensates, K Field, Offshore Taiwan: A Case Study in Migration Fractionation. Org. Geochem., 1993, 20: 437-462.

[8] Gussow W. C.. Differential Entrapment of Oil and Gas—A Fundamental Principle. Am. Assoc. Petrol. Geol. Bull., 1954, 38: 816-853.

[9] Hao F., Li S. T., Gong Z. S., . Mechanism of Diapirism and Episodic Fluid Injections in the Yinggehai Basin. Science in China (Series D), 2002, 45: 151-159.

[10] Huang R. C., Li J. M., Xie Z. Y., . Formation and Distribution of Condensate Gas Pools in China. Oil & Gas Geology, 1996, 17: 237-242.

[11] Larter S., Mills N.. England W. A., Fleet A. J.. Phase-Controlled Molecular Fractionations in Migrating Petroleum Charges. Petroleum Migration, 1991, London: The Geological Society 137-147.

[12] Li X. D.. Genetical Types and Formation Model of Condensate Gas Pools. Geological Review, 1998, 44: 200-206.

[13] Losh S., Cathles L., Meulbroek P.. Gas Washing of Oil along a Regional Transect Offshore Louisiana. Org. Geochem., 2002, 33: 655-663.

[14] Masterson W. D., Dzou L. I. P., Holba A. G., . Evidence for Biodegradation and Evaporative Fractionation in West Sak, Kuparuk and Prudhoe Bay Field Areas, North Slope, Alaska. Org. Geochem., 2001, 32: 411-441.

[15] Matyasik I., Steczko A., Philp R. P.. Biodegradation and Migrational Fractionation of Oils from the Eastern Carpathians, Poland. Org. Geochem., 2000, 31: 1509-1523.

[16] Meulbroek P., Cathles L., Whelan J.. Phase Fractionation at South Eugene Island Block 330. Org. Geochem., 1998, 29: 223-239.

[17] Meulbroek P.. Equations of State in Exploration. Org. Geochem., 2002, 33: 613-634.

[18] Nissenbaum A., Goldberg M., Aizenshata Z.. Immature Condensate from Southeastern Mediterranean Coastal Plain, Israel. AAPG Bulletin, 1985, 69: 946-949.

[19] Radke M.. Application of Aromatic Compounds as Maturity Indicators in Source Rocks and Crude Oils. Marine Petrol. Geol., 1988, 5: 224-235.

[20] Silverman S. R.. Migration and Segregation of Oil and Gas. Am. Assoc. Petrol. Geol. Mem., 1963, 4: 53-65.

[21] Snowdon L. R., Powell T. G.. Immature Oil and Condensate—Modification of Hydrocarbon Generation Model for Terrestrial Organic Matter. AAPG Bulletin, 1982, 66: 775-788.

[22] Su A. G.., Zhang S. C., Xiang L. B., . Effect of Phase-Controlled and Gas-Wash Fractionation on Variation of Component and Carbon Isotope Composition of Oil and Gas. Geochimica, 2000, 29: 549-555.

[23] Thompson K. F. M.. Fractionated Aromatic Petroleum and Generation of Gas-Condensates. Org. Geochem., 1987, 11: 573-590.

[24] Thompson K. F. M.. Gas-Condensates Migration and Oil Fractionation in Deltaic Systems. Marine Petrol. Geol., 1988, 5: 237-246.

[25] van Graas G. W., Gilje A. E., Isom T. P., . The Effects of Phase Fractionation on the Composition of Oils, Condensates and Gases. Org. Geochem., 2000, 31: 1419-1439.

[26] Wu N., Cai Z. X., Yang H. J., . Quantitative Evaluation and Geochemical Responses of Gas Washing in Lunnan Petroleum Province. Earth Science—Journal of China University of Geosciences, 2009, 34: 486-492.

[27] Zhuze T. P., Ushakova G. S., Yushkevich G. N.. The Influence of High Pressures and Temperatures on the Content and Properties of Condensate in the Gas Phase of Gas-Oil Deposits. Geochemistry, 1962, 8: 797-806.

[28] Zhuze T. P., Yushkevich G. N., Ushakova G. S., . Use of Phase Composition Data in the System Oil-Gas at High Pressures for Ascertaining the Genesis of Some Pools. Petroleum Geology, 1963, 7: 186-191.