Oil-bearing capacity of shale in the first member of Upper Cretaceous Qingshankou Formation, Sanzhao Sag, Central Depression, Songliao Basin

Abstract

The lacustrine dark shale deposits of the Upper Cretaceous Qingshankou Formation in the Central Depression of Songliao Basin contain a considerable amount of shale oil resources, among which the shale oil exploration of the Qingshankou Formation in the Qijia-Gulong Sag has made a major breakthrough. In this paper, methods of sealed thermal release, combined with organic solvent extract and Rock-Eval, has been used for the comprehensive evaluation of shale oil-bearing capacity of the Qingshankou Formation. The TOC of shales from the Qingshankou Formation in the study area range from 1.48% to 6.97% with an average value of 3.40%. The values of Tmax range from 440 ℃ to 453 ℃ with an average of 448 ℃ for the samples after extraction, and the production index ranges from 0.28 to 0.67, indicating a middle stage of oil generation window. The shale oil contents of the studied samples range from 4.00 mg/g to 19.49 mg/g with an average value of 13.74 mg/g. The contents of free oil range from 3.41 mg/g to 13.63 mg/g with an average value of 8.70 mg/g; while the content of adsorbed oil ranges from 0.60 mg/g to 9.43 mg/g with an average value of 5.04 mg/g. Free oil is made up of restricted oil and movable oil in the proportion of 1∶1. The content of restricted oil of the studied samples ranges from 1.81 mg/g to 8.49 mg/g with an average of 4.15 mg/g; while the content of movable oil ranges from 1.36 mg/g to 11.05 mg/g with an average of 4.55 mg/g. The movable oil resource is 12 kg/m3 based on the average content of mobile oil, which reveals good resource potential of movable shale oil in the first member of Qing-shankou Formation of the Sanzhao Sag.

Keywords

• shale oil
• sealed thermal release
• solvent extract
• rock-eval
• qingshankou formation
• central depression
• songliao basin