Oil Accumulation of Donghe Sandstone Secondary Hydrocarbon Reservoir in the North Tarim Basin,China

Bo, Zhou; Ming, Li; Qiming, Li
Tarim branch institute, Research Institute of Petroleum Exploration&development (Petrochina), Beijing, China.

The Carboniferous Donghe sandstone oil field consist of two hydrocarbon reservoirs(Donghetang and Hadeson) in the north Tarim basin, which is the deepest and largest oil field found in marine sandstone in China. Marine sandstone reservoirs in this field were buried to a depth of about 5,000-6,000m (16,404-19,689ft) and experienced multiphase tectonic movements before oil accumulation. The homogenization temperatures of saline inclusion within secondary silica outgrowth zone in Donghetang and Hadeson sandstone reservoirs are both between 110°C and 120°C,which indicates the oil accumulation occurred during the Neogene period because secondary silica outgrowth ceased after the oil infill. The oil in these two sandstone reservoirs have approximate δ¹³C values between -32.5‰ and -33‰, with present-day thermal maturity between 0.75 and 0.89% equivalent vitrinite reflectance (R0), similar physical properties(density and different components contents) and biomarkers(gonane m/z217).These geochemical data indicates that hydrocarbon most likely generated from Lower Cambrian source rocks, where oil generated during the Hercynian orogeny period, namely, far before the accumulation time. So we conclude the Donghetang and Hadeson sandstone reservoirs are both secondary oil reservoirs. Further study about the tectonic movements showed the Donghetang and Hadeson had different oil accumulation methods. The Donghetang arch formed in the Hercynian orogeny period and preserved to date, then oil remigrated here vertically from the underlying Ordovician carbonate reservoirs via the fractures. While the Hadeson reservoir was a southward sandstone pinchout trap formed during the late Himalayan movement period, then oil remigrated here laterally from the north palaeo-oil pool via the unconformity interface between Carboniferous and Silurian formations.

AAPG Search and Discovery Article #90155©2012 AAPG International Conference & Exhibition, Singapore, 16-19 September 2012