| The characteristics of unconventional reservoir fracturing technology determine that the transport law of sand-carrying fluid and sanding process are more complex in the process of sand-adding,which is more affected by construction parameters.Therefore,it has important guiding significance for optimizing fracturing parameters and improving fracturing effect to explore the transport process of sand-carrying fluid in unconventional reservoir fractures and the influence of construction parameters on it.The ’visual parallel plate fracture simulation system’ was used to conduct the sand paving experiments of 80-120 mesh single particle size proppant under different perforation positions in the main fracture firstly,and the growth mode of sand embankment was analyzed,combined with the evaluation parameters of sand embankment,the influence of perforation position on the transport law of sand-carrying fluid and the morphology of sandbank was quantitatively evaluated,and the optimal perforation position was selected finally.Moreover,the sand paving experiments of 40-80 mesh and 80-120 mesh combined particle size proppants under different perforation positions and different sand-adding sequences were carried out.The effects of perforation position and sand-adding sequences on the transport law of sand-carrying fluid and the morphology of sandbank were evaluated,and the contribution of each particle size proppant to the support effect was analyzed.At the same time,from the perspective of numerical simulation,the influence of displacement,sand ratio,fracturing fluid viscosity and proppant particle size on the morphology of single particle proppant sandbank was explored by CFD software Fluent.The results showed that the growth mode of sandbank was different under different perforation positions,and the height of sandbank at the fracture entrance and the proppant placement rate at fracture front were greatly affected.The perforation position could be divided into three categories,whether it was a single particle size or a combination of particle size proppant,the better fracture filling effect could be formed when the first type perforation(upper perforation)was injected,the height of sandbank at the fracture entrance and proppant placement rate at fracture front were 1.87 times and 1.39 times of the second type perforation,and 21.45 times and 7.41 times of the third type perforation.Simultaneously,the morphology and paving effect of the combined sand-adding process were also greatly affected by the injection sequences.The large particle size to small particle size injection could produced a certain thickness of mixed sand layer and was beneficial to the transport of small particle size proppant to the deep fracture.When adopted small particle size to large particle size injection,the change of sandbank height was more uniform,and the paving effect of main fracture was improved by about 4%.The large particle size proppant contributed more to the supporting effect of the main fracture,and proppant placement rate at fracture front and total fracture were 2.50 times and 4.59 times of the small particle size proppant.Small particle proppant transport state was more sensitive to parameter changes,and was easy to be transported to the depth of the fracture,which could significantly improve the overall supporting effect.The mathematical model had good accuracy and feasibility in simulating the transport of sandcarrying fluid.The modeling results showed that the growth mode of sandbank in main fracture was not affected by construction parameters.The large displacement and high viscosity injection shortened the time of sandbank reaching equilibrium height in the main fracture,improved the transport ability of proppant,but reduced the overall supporting effect.High sand ratio and large particle size injection could achieve ideal filling effect in a short time,but the transport ability of proppant was poor. |
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