Study On Natural Gas Hydrate Production Of Sea Area

Natural gas hydrate(NGH)is considered as the new clean resource that could be a good substitute for the traditional petroleum resource.More than 90%of the natural gas hydrate reservoirs in the global sea area are pelitic siltstone types.This type of reservoir is poorly cemented,and shows a semi-flow shape after hydrates decomposition.During gas production,plastic deformation and speed-sensitive reservoir damage are accompanied.To carry out relevant experimental evaluations and productivity rules for this type of hydrate reservoirs is a great significance for the exploitation of this type of hydrate mineral reservoir.A core test system was designed for the characteristics of pelitic siltstone hydrate reservoirs.Based on this,experiments were conducted to resarch the characteristics of pelitic siltstone hydrate reservoirs and provide basic parameters for the evaluation of the productivity of the hydrate mineral reservoir.Combined with experimental test results,taking Japan's first test well as an example,we study the effects of different completion intervals on the productivity of hydrate mineral reservoir.Combined with experimental test results,the ideal model of silt hydrate was established for evaluating the potential of the mineral deposits of silty silt.The main work and understanding are as follows:(1)According to the characteristics of pelitic siltstone hydrate reservoir,a special core holder and small pressure difference stable displacement device were designed.Based on this,experiments were carried out to investigate the influence of fluid flow velocity on the permeability and the measurement of bound water characteristics.The experimentally measured hydrate reservoir core samples'permeability is range from2mD-8mD,the bound water saturation was 63%.The experimental results can not only be used as a benchmark to calibrate the electric curve of the well,it can also provide reference for the selection of relevant parameters for the productivity evaluation of similar pelitic siltstone hydrate mineral reservoir.(2)Based on the geological data of the first test well-AT1P well in the Nankai Trough of Japan,the relevant parameters of the pelitic siltstone hydrate interlayer were taken as experimental test values,a one-year gas production simulation was conducted based on the fitting of on-site test production gas data.A detailed analysis of the evolutionary process of various physical properties during the decompression production process explain the intrinsic causes of the change in production capacity.(3)We evaluate the effect of three different completion intervals on the productivity of hydrate mineral reservoir.The numerical simulation results show that,by using the lower hydrate layer completion method,the rapid reduction of the pressure of the entire hydrate reservoir can be achieved by rapidly produce the water in the underlying aquifer,so as to effectively promote the decomposition of the hydrate achieving the purpose of rapid mining of hydrates.With this completion interval,the maximum gas production is about 47000 m~3/d,and the maximum gas-water ratio is about 37.(4)In the low permeability silt hydrate deposits,the gas production is about180m~3/d,,in the process of reducing pressure production.It is necessary to carry out the research on the production process of fracturing and heating.The production capacity and influence factors of this type of hydrate were evaluated.The results show that the higher the initial permeability of hydrate reservoir,the higher the rate of gas production and water production;The lower the initial temperature of the hydrate reservoir,the lower the capacity of hydrate deposits;The lower the initial saturation of hydrate,the lower the gas content of hydrate decomposition and the higher the water yield of the mineral;The lower the downhole pressure,the higher the capacity of hydrate deposits.