Laboratory Experimental Study On Proppant Tranportation In Complex Fracture Network Of Tight Reservoir

The multi-cluster "volume fracturing" technology of horizontal well is widely used in the development of the present compact oil and gas resources.The transportation and laying of proppant in fracture during fracturing has a direct effect on the effect of fracturing modification.But at present,there are some problems in the study of proppant migration law in volume fracturing fracture of tight reservoir at home and abroad,such as simple model,low agreement between model and actual fracture,etc.Therefore,the existing research results are difficult to truly reflect the proppant transportation in the tight reservoir volume fracturing fracture.In view of the above problems,the purpose of this paper is to set up a complex fracture model and consider different construction parameters of horizontal wells in dense reservoirs with multi-cluster fracturing as the engineering background.The transportation rule of proppant in complex fracturing network of tight reservoir is studied by physical parameters.(1)Fully investigating the fracturing fracture morphology characteristics of tight reservoirs and the development process of physical model of proppant placement experiment at home and abroad,provide the basis for the establishment of the model in this paper.At the same time,the related literatures on proppant transport theory at home and abroad are investigated,and proppant transport and laying are systematically studied.(2)Based on the theory of mechanical design,similarity criteria,optoelectronics and fluid mechanics,and considering the limitations of existing models at home and abroad and the characteristics of fractured fractures in tight reservoirs,a set of large-scale visualized fractured sand laying device is developed and its feasibility is analyzed.The device conforms to the characteristics of fractured fractures in tight reservoirs.(3)Based on the complex fracture model and considering the factors such as displacement,fracturing fluid viscosity,proppant particle size,proppant concentration and fracture angle,the proppant laying law in the complex fracture net of tight reservoir is studied,and the balance time and height of sand dike are adopted.The effect of proppant laying was analyzed by the characterization parameters such as the highest point distance and laying rate of sand embankment.With the increase of pumping displacement and fracturing fluid viscosity,the proppant placement rate in near wellbore decreases and proppant placement rate in deep fracture increases;the smaller the proppant particle size,the higher the proppant placement rate in deep fracture;proppant concentration mainly affects the proppant placement rate in near wellbore;proppant is easier to enter the branch fracture with smaller angle between main fracture;according to the experimental results,the proppant placement rate is optimized.(4)Through the flow measurement systems,the critical flow distribution of proppant when it turns from main fracture to secondary branch fracture and multi-branch fracture is analyzed by including variable displacement,fracturing fluid viscosity,particle size,sand concentration and fracture angle.The process and results of proppant turning to branch fracture are analyzed,and the law of proppant turning to branch fracture is revealed.It is concluded that the critical turning time of proppant to branching cracks at all levels is greatly shortened with increasing displacement;the turning time of proppant is significantly shortened with increasing viscosity,when the viscosity reaches 4mPa.s,the turning distance of proppant reaches the maximum length of cracks in all levels of cracks;increasing proppant concentration or fracture angle is not conducive to the turning of proppant to deep cracks.(5)By changing the particle size combination,proppant proportions of different particle sizes and pumping methods,the research results clarify the proppant separation rule in branching fractures.30/50 mesh and 40/70 mesh large size proppants mainly settle in secondary fractures near the main fracture or near the wellbore end;small size proppants account for a large proportion in deep narrow fractures.In this paper,the construction parameters,physical parameters,fracture network morphology of tight reservoir are considered comprehensively,and the experimental device established is in good agreement with the actual fracturing network of tight reservoir.The research results can provide effective guidance for fracturing scheme design of tight reservoir.