Numerical Simulation Analysis of Multi-physics Field Coupling in Deepwater Gas Hydrate Reservoir Drilling
During the drilling process in deepwater gas hydrate reservoirs,the drilling fluid is prone to intrude into the reservoir,leading to temperature and pressure changes in the wellbore,which causes hydrate decomposition and results in instability of the well wall.A multi-field full-coupling model of unsteady heat transfer in the porous media in deepwater natural gas hydrate reservoirs is established with the hydrate dissociation under the action of drilling fluids and the mass and heat transfer in consideration.The simulation results show that when the drilling fluid intrudes,the temperature and pressure of the hydrate reservoir appear to varying degrees of increase.The temperature change rate is 0.618 K per meter along the formation direction,and the pressure change rate is 0.39 MPa per meter.The hydrate saturation gradually decreases in the formation direction,and the average rate of change is 0.06 per meter.Hydrate dissociation leads to a decrease in mechanical strength and an increase in the equivalent plastic strain around the wellbore.The plastic strain around the wellbore reaches 90％after 20 hours,and the instable risk of the wellbore increases.During hydrate reservoir drilling,the temperature of the drilling fluid should be reduced,or wellbore-reservoir transfer shielding of mass and heat should be implemented to achieve safe and efficient drilling.
natural gas hydratesdrilling fluid invasionwellbore-reservoir couplingmulti-physics field couplingwellbore stability
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