Study On Sand Control Technology Of Radial Wells In Natural Gas Hydrate Reservoir

Gas hydrates are cage-like solids formed from water and natural gas.It is widely found in tundra at higher latitudes and in seafloor formations.Compared with conventional fossil energy,hydrates are cleaner and have good reserves as a potential alternative energy in the future,and most importantly,they are widely distributed.In view of various advantages,the existence of hydrate has attracted the attention of various countries and oil companies in the world.In 2017 and 2020,China carried out the second test production of natural gas hydrate in the Shenhu waters of the South China Sea,and achieved major breakthroughs.However,there were serious problems of sand production in both test productions.To achieve commercial exploitation of hydrates,it is necessary to meet the sustainability and safety standards of the development process.Whether the problem of sand production is solved well or not is a key factor in whether the standard can be met.In order to explore the effect of mechanical sand control,this thesis proposes an integrated method of drilling and completion of radial wells in gas hydrate reservoir,and independently designs a set of hydrate synthesis and exploitation devices.Through this device,the depressurization experiments of vertical wells and radial wells of hydrate sediments in water-rich environment were exhibited.Three sand control completion meth-ods including 120 mesh sand screen,400 mesh sand screen,120 mesh sand screen combined with gravel packing are adopted.Sand and gas production rates were compared under different well types and sand control completion methods.On the basis of the composite sand control combined with 120 mesh sand control and gravel packing in radial wells,the number of gravel packing meshes was changed,and the sand control effect and productivity before and after changing the mesh number were compared.Results show that the gas production modes of radial wells and vertical wells are almost the same at the same time due to the small experimental scale and high permeability.The sand production of the vertical well with gravel packing combined with a sand-control screen is 50% lower than that of the vertical well with sand control screens only.Radial well with gravel packing combined with sand-control screens produced 87%less sand than screen mesh alone.Regardless of vertical wells or radial wells,the use of composite sand control improves cumulative gas production and recovery compared to using sand screen only.On the basis of the composite sand control,it is found that the mixed gravel packing has obvious productivity advantages compared with single-stage gravel packing by changing the mesh of gravel.Under the current experimental conditions,the composite sand control method combined gravel packing and sand control screen in radial wells can better balance productivity and sand production.In this study,there are still problems such as small experimental scale,sand control failure caused by the intrusion of gravel packing after the secondary formation of hydrate,insufficient development period to judge the effective duration of the gravel packing,the method and the degree of compaction of gravel packing on the effect of sand contol,etc.The problem is for follow-up research.