Evaluation of oil content in shale by sealed thermal desorption: a case study of Jurassic Da'anzhai Member, Sichuan Basin

Abstract

The oil content in shale is still a contentious issue due to the evaporative losses of free hydrocarbon. Considering the objective of the evaluation of oil content in shale and the demand of fast analysis at wellsite, a newly developed sealed rock thermal desorption method is introduced to quantify the content of free hydrocarbon in rock samples which combined the technique of sealed crushing at low temperature and improved the traditional rock pyrolysis (Rock-Eval). Comparison experiments have been conducted on Jurassic Da'anzhai shale from the Sichun Basin. The S0 value ranges from 0.001 to 0.046 mg/g, with S1 value from 0.165 to 4.648 mg/g by routine method of rock pyrolysis. The S0 value by the sealed thermal desorption method, which ranges from 0.026 to 0.984 mg/g, is about 1-2 order of magnitude higher than that of Rock-Eval. By improving the heating program, the sealed thermal desorption method can obtain the hydrocarbon content per unit mass of rock at temperatures of 5, 5-90 and 90-300℃, which not only obtains abundant oil-bearing data, but also shortens detection time. Combined with parameters such as mud gas measurement, shale geochemical parameters, and reservoir fluid properties, the "sweet spots" of shale oil in the Da'anzhai Member of the study well were evaluated, providing a new experimental method for evaluating the oil content of shale oil.

Keywords

• sealed crushing
• thermal release
• free hydrocarbon content
• shale oil
• da'anzhai member
• jurassic
• sichuan basin