Abstract:

Based on principles of natural gas diffusion,mass balance and hydrocarbon concentration sealing,a model was established to assess natural gas diffusion loss from multiple source rocks.The model was applied to the shallow multiple source rocks in the north of the Songliao Basin.There are four shallow gas source rock intervals with a total accumulative gas volume generated of 387.5TCM,in which the 2nd member of the Cretaceous Nenjiang Formation (K₁n²) is the largest in gas volume generated.Peak gas generation occurred at the end of the Nenjiang age.Calculation of the actual gas diffusion loss shows that K₁n² is the highest in diffusion loss,followed by the 2nd and 3rd member of the Cretaceous Qingshankou Formation (K₁qn²⁺³),K₁n¹ and K₁qn¹.The actual cumulative gas diffusion loss with and without hydrocarbon concentration sealing effect considered are 199.42TCM and 105.44TCM,respectively.The ratio of diffusion loss to generation with hydrocarbon concentration sealing effect considered is lower than that without hydrocarbon concentration sealing effect considered.The latter is around 2-3 times as the former.

Key words: multiple source rock, diffusion loss, mass balance, hydrocarbon concentration sealing, Songliao Basin