Numerical simulation on gas production from inclined layered methane hydrate reservoirs in the Nankai Trough: A case study

Abstract

Natural gas hydrate is generally disseminated in tilted sediments. The inclination of hydrate reservoirs significantly affects the fluid migration behaviour and production potential. However, most of the current simulations ideally assume that the hydrate reservoir is horizontally distributed; resulting in the effect of the formation dip on the well deployment and corresponding gas production remains unclear. Here, we implement a real inclined alternating sand–clay hydrate reservoir model based on geological data from the Nankai Trough, Japan, to simulate the production performance of a single horizontal well and dual horizontal wells. Results show that the gas and water productions are enhanced when a single horizontal production well is deployed in the structural low of the reservoir. The gas and water production performance in upper sandy reservoir and the water extraction in the middle muddy reservoir are sensitive to the layout of the production wells, which can cause the daily difference is over 6%. The gas-to-water ratio is independent from the structural deployment positions of the horizontal wells in the same inclined layer. Compared to the single depressurization method, placing a horizontal thermal injection well in the structural high of the upper inclined sandy reservoir and a horizontal production well in the structural low of the same formation improves the gas recovery efficiency nearly twice, which is recommended for production enhancement. Our findings are useful for achieving effective and economic gas recovery from natural inclined layered hydrate reservoirs.

Keywords

• Gas hydrate
• Inclined layered hydrate reservoir
• Horizontal well
• Depressurization combined with thermal stimulation
• Numerical simulation