Experimental Study On Sand Production Of Natural Gas Hydrate Reservoir

Natural gas hydrate is considered to be one of the most potential sources of energy in the twenty-first Century,with high density,wide distribution and high resource value.However,with the deepening of research on hydrate resources and the acceleration of test mining process,people gradually realized that sand production was one of the key factors restricting hydrate exploitation.In the development of traditional oil and gas resources,the problem of sand production has been solved well.However,the hydrate reservoir is special,showing weak consolidated or unconsolidated characteristics,especially when the hydrate is decomposed,the cohesive force decreases,the strength decreases,and the porosity increases.The reservoir property is more complex,which greatly increases the risk of sand production.Therefore,it is very important to study the sand production law of hydrate reservoir,to make appropriate sand control measures and to control the amount of sand reasonably.Based on the analysis of the key problems of sand production in a certain block of the South China Sea,and from the analysis of the mechanism and influence factors of hydrate reservoir formation,a proper completion method for sand production was determined.Combined with the particularity of hydrate reservoir exploitation,a set of experimental device for simulating hydrate sand production was designed,which provided sufficient experimental conditions for solving the problem of hydrate control.At the same time,the sand production law of hydrate was studied with the aid of the gas hydrate acoustic monitoring system.Finally,the sand control experiment of hydrate formation was carried out by selecting the screen with different pore sizes.From the analysis of sand production,permeability,sand content and productivity,the design criteria of appropriate sand screening precision were obtained.The research results show that by simulating the size and composition of hydrate formation,we can make artificial rock samples close to hydrate formation by using certain production process and method.If the size of the sieve is too large,then in the case of production pressure less than 1MPa,sand production accounted for 19%of liquid production,indicating serious sand.Judging from the accumulation curve of sand production and the distribution of sand grains,there are some free sand and weak cementation sand in the formation,and then the skeleton of the rock is destroyed,and the amount of sand production is increasing rapidly.As the interior of the formation is not visible,the acoustic monitoring device can be used for auxiliary monitoring.The monitoring result is consistent with the result of sand production,and has a certain reference value.When the size of the sieve is greater than 15 times the median particle size(?>15d₅₀),the sand retaining is invalid.For the smaller sieve mesh(?<4.2D₅₀),the production pressure difference should be controlled within a certain range?<5MPa?,otherwise the sand will clog the channel and greatly reduce the permeability.In the range of moderate sand production?7.8¹3t/10000 m³?,the sieve mesh was determined to be 400 mesh?38?m?and 350 mesh?42?m?.According to the principle of safety priority,the mesh of 400 mesh was selected.According to this screen,the sand content of gas was analyzed.The amount of sand production was within the allowable range of the platform.And through the simulation results of production capacity,the maximum daily gas output can reach 5000m³,which is close to the production of gas in the areas of Mackenzie,Alaska and Shenhu,so as to meet the production requirements.Based on the above analysis,the final design criteria for obtaining high quality screen tubes with very fine sand particles in the hydrate formation is D₅₀=11d₅₀,that is,the screen mesh?=3.8d₅₀.