Study on hydrocarbon retention and expulsion of kerogen based on centrifugal swelling method

Abstract

Centrifugal swelling experiments using n-hexadecane and 1-methylnaphthalene were carried out to explore the connection between hydrocarbon retention and expulsion in type Ⅰ kerogen. A driving force-hydrocarbon expulsion model was innovatively established through the results of differential centrifugation experiments and low field nuclear magnetic resonance. Additionally, the hydrocarbon expulsion process of kerogen was categorized into three distinct stages based on the driving force, including free, intergranular state and immovable state (adsorption and swelling) hydrocarbon expulsion. A linear correlation also was established between the T₁/T₂ signal and the liquid hydrocarbon content during the swelling process, revealing that low-field NMR technology could effectively detect the retention of alkane compounds in kerogen. The study revealed that when the driving force is greater than 647.4 g N, most of the shale oil retained in the kerogen is in an immobile state, which cannot be exploited. Additionally, the hydrocarbon expulsion model based on the centrifugal experiment presents several advantages, including low equipment requirements, straightforward operation, and a broad range of applications. This model can effectively support various types of laboratories conducting shale oil retention assessment work, especially those in oilfields with relatively simple experimental setups.