Petroleum systems modeling on gas hydrate of the first experimental exploitation region in the Shenhu area, northern South China sea

Two-dimensional gas hydrate petroleum system modeling was conducted to understand gas hydrate accumulation mechanisms and spatial distribution related to geologic and geochemical processes in the first experimental gas hydrate exploitation region in the Shenhu area of the South China Sea. Based on the gas production in core samples, a new biogenic methane generation model was created and incorporated into a kinetic model. With the results of a rock pyrolysis experiment, a thermogenic gas kinetic model for deep formations in the study area was also developed. The entire dynamic evolution process from gas generation to migration and gas hydrate formation and accumulation in the perspective area was simulated with the petroleum system modeling method. The results showed that the gas hydrate stability zone (GHSZ) began to form after 3.88 Ma, and its thickness was greatest when the paleowater depth peaked at 3.66 Ma. The mass of thermogenic gas generation in deep formations is large, and that of biogenic gas in shallow formations is relatively small. Formations that overlap the gas hydrate bearing layers act as cap rocks that prevent the gas from migrating vertically to shallow layers. There was a geological time gap between thermogenic gas generation, migration and GHSZ formation. However, the timing of biogenic gas generation, which is typically of recent generation in the shallow layer, matched well with the formation of the GHSZ. Finally, coupling of the age and space of gas migration and GHSZ formation has allowed gas hydrate accumulation at structural highs in the Shenhu area. The evaluation technique of petroleum system modeling is of great significance for the improvement of gas hydrate exploration in frontier areas in the future, particularly where survey data are limited.