Experimental investigation of optimization of well spacing for gas recovery from methane hydrate reservoir in sandy sediment by heat stimulation

Abstract

Due to the vast amount of recoverable natural gas predicated (∼3000 TCM) in natural gas hydrate on earth, natural gas hydrate has the potential to become the next generation of unconventional source of fuel. Recently years, laboratory researches are still underway to advance our understanding of the theory and technology for natural gas hydrate exploitation. In this work, experiments of methane hydrate dissociation by heat stimulation with different well-spacing were firstly performed in the Cubic Hydrate Simulator (CHS). The five-spot vertical wells (5-wells) and the dual vertical wells (D-wells) were applied as the multi-well strategies. The well spacing of D-wells is twice as larger as that of the 5-wells. The influences of well spacing on the production behaviors and the heat transfer characteristics during hydrate dissociation are analyzed. The experimental results indicate that a maximum range for hydrate dissociation exists during hydrate dissociation by heat stimulation method, which is in direct proportion to the heat injection rate (Rinj). The optimized well-spacing should equal to the maximum range of hydrate dissociation. For maximizing average gas production rate per well, the larger well spacing and the higher Rinj benefit for gas recovery. On the other hand, for minimizing the heat consumption per unit of gas production (HGP), the moderate Rinj and the shorter well spacing benefit for gas recovery. In order to evaluate the gas recovery by heat stimulation with different well spacing and Rinj, an evaluation factor is firstly proposed, which considers the combined effect of the gas production rate per well, the HGP, and the hydrate dissociation ratio. By calculation, the optimal experimental conditions for hydrate recovery in experiments are the injection rate of 40mL/min with the longer well spacing (D-wells). The study of temperature distribution verifies the maximum range for hydrate dissociation in reservoir by heat stimulation.