Application of the enlarged wellbore diameter to gas production enhancement from natural gas hydrates by complex structure well in the shenhu sea area

Abstract

The current casing diameters of the production section are about 244 mm in marine natural gas hydrate (NGH) tried tests, which are a small order of magnitude and have the great potential to be enlarged. Expanding the contact areas between the wellbore and the NGH reservoir using complex structure wells has been popularly studied recently. In this study, the enlarged wellbore diameters (casing diameters) of complex structure wells were first proposed to enhance the gas recovery from the NGH reservoir in the Shenhu area of the South China Sea. The gas production characteristics, temperature, and pressure in the NGH reservoir and near the wellbore induced by the depressurization method were analyzed under various wellbore diameters of complex structure wells. Results indicate that using the enlarged wellbore diameter can further expand the contact areas between the wellbore and the NGH reservoir, promoting gas production efficiency, especially in short-term production. The evolutionary trends of temperature and pressure meet the conditions for stable short- and long-term production. Moreover, it was suggested that a relatively significant gas production increase of the enlarged wellbore diameter could be obtained by a slight increase in the wellbore diameter.