The Pore Evolution Of Lacustrine Shales In The Process Of Hydrocarbon Generation

Shale oil,as a kind of ‘unconventional petroleum',has its own characteristics.Shale oil is often stored in mineral matrix pores,organic matter pores and fractures with free state,adsorbed state and a small amount of dissolved state.As the shale oil exploration and development succeeded in North America,shale oil exploration in continental petroliferous basins has been paid much attention increasingly in China.The shale nanopore development and evolution is viewed as one of the key scientific problems in shale oil accumulation mechanism research.This paper takes immature to low-mature organic-rich shales in Cangdong Sag,Huanghua Depression,Bohai Bay Basin as an example to study shale pore variation law during the thermal evolution process of organic matter,so as to provide theoretical basis for shale oil retention and accumulation mechanism study,shale oil ‘sweet area' prediction and shale oil exploration and development practice.Based on the study of geochemical indexes,pore structure parameters and pore development characteristics,this paper draws a conclusion of the shale pore structure variation law on the natural organic matter evolution section.Through the experiments of hydrocarbon-generation thermal simulation,field-emission scanning electron microscope and nitrogen adsorption test,pore development characteristics and pore structure parameters are studied during different hydrocarbon generation stages.Analysis of the experimental results indicates the macropore volumes of nanopores have a tendency of increase at first then decrease,while micropore and mesopore volumes have a tendency of decrease at first then increase as thermal simulation temperature rises.Due to a large generation of organic matter pores and the variation of their morphology and number during the process of hydrocarbon generation,the average pore diameter,total pore volume and specific surface area change regularly.Accordingly,the evolution models of shale pore structure in the process of hydrocarbon generation are built initially.