Effect of gravel pack permeability on horizontal well productivity loss under secondary methane hydrate formation: Experimental optimization of 3D randomly distributed mixed sand pack

Horizontal well productivity is limited by secondary hydrate formation (temperature drop results from endothermic of hydrate dissociation) during production. Seepage capacity as one of the key indexes for evaluating production efficiency, and efficiency is declined by sand production. Sand control is achieved by using gravel pack technology (selected sands for hindering the sediments particles migration), which extends the production time. However, forecasting the productivity decline trend from quantifying the permeability of the gravel pack after secondary formation remain challenges. To address these issues, a randomly distributed 3D normalized permeability (Kr) model was developed to describe the seepage capacity of gravel pack composed by various particle sizes of mixed glass beads. The theoretical modelling was established by observing micro spatial structure of glass beads with hydrate formation. The new model considered three consolidation modes of hydrate in pores (cementing + bearing, pore filling, and grain coating) and linked them with the productivity ratio equation of a horizontal gas well. To confirm the viability of the model, a series of permeability measurement experiments with various size ratios (α) from 1 to 10 were conducted. Finally, errors comparison and all parameters of the model were analyzed. The results showed that the productivity ratio declined clearly after saturation is >0.79, when α = 4. For long-term production, α = 10 would be better. The new model can help hydrate horizontal wells increase production from laboratory to industrial exploitation.