Experimental Study On Sand Control Of Gravel Packing Medium In Gas Hydrate Exploitation

As a potential energy source in the future,natural gas hydrate has ample reserves and wide distribution.However,reservoir consolidation is weak,and free sand will be produced during the mining process.The problem of sand production caused by gas hydrate mining is the key to the commercial and efficient development of natural gas hydrate.The existing sand control technology mainly includes mechanical and chemical sand control.Gravel pack sand control is the primary sand control technology of mechanical sand control,which has the advantages of good sand control effect,long validity period,and broad applicability.The reservoir structure is damaged in the process of hydrate mining for the shale hydrate reservoir.The fine silt with high muddy content becomes free sand,which intrudes into the gravel sand control layer under the action of gas-liquid flow and causes pore throat blockage.This can lead to reduced permeability,resulting in osmotic damage,affecting the long-term effectiveness of the gravel sand control layer,and resulting in a significant reduction in productivity.Therefore,the in-depth study of the gravel clogging mechanism,permeability damage law,sand production characteristics and the optimization of gravel grading can avoid the blockage of sand control medium caused by reservoir sand invasion,improve the long-term effectiveness of gravel penetration,and better establish the balanced relationship between sand control and permeability.It can provide helpful suggestions for gravel sand control and ensure the long-term safe and effective operation of mining well.In this paper,according to the blocking mechanism and permeability damage of control gravel,through the self-developed sand control test system,the permeability damage law and internal microscopic blockage mechanism of sand control gravel medium under different influencing factors were explored.The sand resistance effect and permeability characteristics of different gradations of gravel were studied,and the optimal gradation of gravel mesh number was optimized from the analysis of permeability,sand production and pore filling degree.Finally,the formation process of mud film was explored according to the vertical stratification of hydrate reservoir properties.The results show that the water content of the mud hydrate reservoir is small,and the permeability damage of the gravel layer is minor.When the water content exceeds 125%,the permeability damage ratio tends to decrease.The change in test pressure and reservoir water content has little influence on the permeability damage,and the test pressure is positively correlated with the permeability damage degree of the control medium.The primary and secondary effects of various factors on the permeability damage of gravel medium are as follows: gravel size > test pressure > reservoir water content.According to the grain size distribution curve and microscopic image analysis of each layer of the medium,the test pressure directly affects the invasion depth of the reservoir sand.The water content of the reservoir mainly affects the permeability damage degree but has little influence on the spatial distribution of the plugging medium of the reservoir sand.For the fine sand outside the migration medium,the particle size of sand production is positively correlated with the reservoir water content and gravel particle size.However,under the condition of more considerable test pressure,the sand particle size is smaller.The optimal gravel size range is 50-70 mesh,the optimal GSR is 24.5,and the fine particle content is about 38%.During the test,the reservoir particles will be rearranged.The water content and porosity of the reservoir are stratified,and the closer to the sand control structure,the smaller the water content and porosity.Fine particles will migrate and deposit to the interface of the reservoir and gravel sand control structure first and quickly form a mud film with a transition of water content from small to large.The mud film thickens with the test,and the sand retaining ability improves gradually.After the formation of the mud structure,it has a particular strength and a stable gas-water seepage channel,which is difficult to be destroyed.