Economic evaluation of using thermal seawater injection in double-branch horizontal wells for submarine natural gas hydrate exploration

Due to the large submarine natural gas hydrate reserves, it is meaningful to exploit these resources in a cost-effective manner. Given that the existing mining methods all have inherent flaws respectively, a thermal seawater injection method of double-branch horizontal wells is proposed in an attempt to explore the economical, safe and feasible mining methods of natural gas hydrate. The method is based on the research result about “thermal seawater injection method of double-branch horizontal wells” from Kyuro Sasaki, Shinji Ono and others of the Energy School of Kyushu University. It is a new mining method that uses a series of advantageous technologies including seawater source heat pump, shallow-branch horizontal well drilling, and natural gas hydrate decomposition using high-temperature brine. This method fully utilizes the selective drilling and large effectively controlled area of branch horizontal wells to achieve multi-point communication in the reservoir stratum by injecting thermal seawater into double-branch horizontal wells for form “hot water cavities” and perform three-dimensional exploration of natural gas hydrate by injecting from the bottom and mining at the top. This mining method is not only safe and feasible and environmentally friendly, but also economic beneficial. It is a positive, pragmatic and innovative attempt to achieve commercial exploitation of natural gas hydrates in the future.