EXPERIMENTAL SIMULATION OF SEABED HYDROCARBON GAS SEEPAGE:VARIATION OF CONTENT AND MOLECULAR COMPOSITION OF THE HYDROCARBON GAS AND RECONSTRUCTION OF SEEPAGE PROCESS

The experimental simulation for seabed hydrocarbon gases seepage was carried out by the authors. The changes in contents of hydrocarbon gases and their molecular compositions during the seepage were studied through sample collection and analysis at 10 sampling outlets.It is found that the hydrocarbon gas content and molecular composition of each sampling outlets have obvious phase changes with time. There are two stages of seepages in general, the first stage from July 13 to August 5, and the second stage from August 5 to September 25. According to the intensity of seepage, the sampling outlets can be divided into three categories. The first category includes S1, S2, S5, S7 and S8, during which the seepage intensity is not high and thus named as the micro-seepage type in the first and second seepage stages.The second category includes S3, S4 and S9, of which the seepage intensity is low and belonging to micro-seepage type in the first seepage stage, and high in second seepage stage and thus named the type of macro-seepage in this paper. The third category includes S6 and S10 with high seepage intensity and belongs to macro-seepage type. In the process of experimental simulation, hydrocarbon gas seepage is mainly controlled by various interfaces inside the experimental column and sediment grain size.The control factors for hydrocarbon gas seepage at different sampling outlets are different.The simulation results provided the experimental basis to the study of controlling factors and mechanisms of hydrocarbon gas seepage on seabed, such as fault structures, unconformities, lithological boundaries as well as changes in grain size.