Conceptual modeling of onshore hydrocarbon seep occurrence in the Dezful Embayment, SW Iran

Petroleum and gas seeps on the ground surface are direct indicators of accumulations of hydrocarbons in the subsurface and could reflect the migration of hydrocarbons in a sedimentary basin. Quantitative analyses of the spatial pattern of hydrocarbon seeps and their spatial associations with geological features could aid in deducing geological controls on their occurrence. In this study the Fry analysis was applied to study the spatial pattern of mapped hydrocarbon seeps, whereas spatial association analyses were implemented to quantify the spatial association of mapped seeps and their alteration products with geological features. The spatial pattern analysis of hydrocarbon seeps showed that oil seeps followed prominent NW–SE and NE–SW trends while gas seeps followed NW–SE and N–S trends suggesting that NNE–SSW and NW–SE fractures are possible migration pathways for hydrocarbons to reach the surface. The results of the spatial association analysis illustrated strong positive spatial associations of oil and gas seeps with the Gachsaran and the Mishan formations, implying upward migration of hydrocarbons through permeable micro-fractures and micro-pores in their strata. A conceptual model has proposed for the occurrence of onshore hydrocarbon seeps in the Dezful Embayment.