Characteristics and resource prospects of tight oil in Ordos Basin, China

DOI: 10.12040/pr2016010027

 Hua Yang1,2*, Shixiang Li2,3,4 and Xianyang Liu2,3,4

1 PetroChina Changqing Oilfield Company, Xi’an 710018, China

2 National Engineering Laboratory for Exploration & Development of Low-permeability Oil & Gas Fields, Xi’an 710018, China

3 College of Energy Resources, Chengdu University of Technology, Chengdu 610059, China

4 Research Institute of Exploration & Development, PetroChina Changqing Oilfield Company, Xi’an 710018, China Received February 8, 2016; Accepted July 1, 2016


Efficient large-scale development of ultra-low-permeability reservoirs (0.3–1 mD) has been achieved in the Changqing Oilfield, Ordos Basin of China. According to unique features of petroleum exploration and development in this basin, tight oil herein refers to petroleum that occurs in oil-bearing shales and interbedded tight sandstone reservoirs adjacent to source rocks with ambient air permeability <0.3 mD. Tight oil in tight sandstone and shale have generally not yet experienced large-scale long-distance migration. In the Yanchang Formation, tight oil has mainly accumulated in the semi-deep to deep lacustrine facies, typically in oil-bearing shales and tight sandstones of the 7th member oil-bearing formation and tight sandstones of the 6th member oil-bearing formation in the center of the basin. Tight oil resource in the Ordos Basin is characterized by wide spatial distribution, excellent source rocks, extremely tight sandstone reservoirs, complex pore throat structures, poor physical properties, high oil saturation, good crude-oil properties, and low reservoir pressure. A fundamental feature of the continuous oil and gas accumulation in tight oil reservoirs is the widespread development of nano-scale pore-throat systems. In the Yanchang Formation, most of connected pore throats in tight sandstone reservoirs have diameters greater than critical pore throat diameter, allowing oil and gas migration in the tight reservoirs. According to contact relationship between tight reservoirs and source rocks, three types of tight oil reservoirs are identified in the Yanchang Formation, i.e., tight massive sandstone reservoir, sand - shale interbed reservoir, and oilbearing shale reservoir. In the Ordos Basin, tight oil is widely distributed in the 6th and 7th members of the Yanchang Formation, with total resources estimated to be 3×109 t. These include >1×109 t of oil resources in shale in the 7th member of the Yanchang Formation and approximately 0.9×109 t and 1.1×109 t of tight sandstone oil resource in the 6th and 7th members of the Yanchang Formation, respectively. These tight oil resources are the realistic resources addition for the oilfield, which can ensure an annual production of 50×106 t of oil and gas equivalent and maintain long-term stable oil production in the Changqing Oilfield, Ordos Basin, China.

Key words: tight oil; tight sandstone reservoir; shale reservoir;resource potential; Yanchang Formation; Ordos Basin
Received: 2016-12-08
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