Comparisons of different electrical heating assisted depressurization methods for developing the unconfined hydrate deposits in Shenhu area

For the unconfined natural gas hydrate deposits in Shenhu area, in-situ electrical heating methods are proposed to assist depressurization for promoting gas production, such as wellbore and low-frequency electrical heating (WBEH, LFEH). To determine the optimal exploitation method, three LFEH assisted depressurization schemes are designed under dual horizontal wells in this work, whose recovery performances are compared with only depressurization (OD) and WBEH through numerical simulations. Results indicate that LFEH significantly promotes hydrate dissociation and gas production, leading to a halved exploitation time of the two-wells depressurization scheme compared with OD. Besides, the brine flooding scheme recovers more gas and net energy over OD (16.6% and 25.2% higher, respectively) by the enhanced heat convection, validating the potential of LFEH for developing the unconfined hydrate deposits. However, the LEFH huff-puff method does not show obvious superiority over OD due to the reduction of net production time. In addition, more uniform heat distribution of LEFH leads to much lower formation temperature than WBEH, which can avoid wellbore instability by continuous high temperature. Finally, sensitivity analyses show that low-frequency electrical heating should be terminated in advance to avoid unnecessary energy waste and increasing electrical heating power is beneficial to gas and energy recovery.