充填密实程度对砾石层挡砂效果及稳定性影响实验

针对砾石充填类防砂工艺，为了探究砾石层充填密实程度对挡砂效果和稳定性的影响规律和程度，利用挡砂介质综合性能测试实验装置，使用石英砂和人造陶粒2种材料，模拟100%、98%、96%和95%共4种充填密实程度进行砾石层挡砂径向流驱替实验，通过渗透率、过砂率和冲蚀形态变化评价砾石层挡砂效果及其稳定性。实验结果表明，射孔孔眼入流会造成砾石层冲蚀孔洞，随着充填密实程度降低，冲蚀孔洞区域越大，地层砂侵入砾石层深度越深；当充填密实程度低于95%时，会形成相对较大的冲蚀孔洞从而失去稳定性，砾石层被地层砂完全穿透从而失去挡砂作用；随着充填密实程度的降低，松散的颗粒在流体冲击作用下重新排列组合，形成的孔洞使得地层砂侵入砾石层的深度也越大，过砂率越高，挡砂效果越差。对于套管射孔井管内砾石充填防砂，应尽可能提高密实程度使其不低于95%，且机械筛管缝宽或挡砂精度按照能够直接阻挡地层砂的原则进行设计。

Experimental study on the influence of filling density on the sand blocking effect and stability of gravel

To explore the influential laws and degrees of gravel packing solidity on its sand blocking effect and stability when the sand control technologies of gravel packing is carried out, the experimental device for testing the comprehensive performance of sand retention media was applied to radial flow displacement experiment of sand blocking gravel. In the experiment, quartz sand and artificial ceramsite were adopted and four packing solidities were simulated, i.e., 100%, 98%, 96% and 95%. And the sand blocking effect and stability of gravel were evaluated based on permeability, sand passing ratio and erosion morphology change. The following experimental results were obtained. First, perforation inflow can lead to erosion vugs in the gravel, and with the reduction of packing solidity, the area of erosion vug and the invasion depth of formation sand into the gravel are increased. Second, when the packing solidity is lower than 95%, larger vugs are formed and the gravel gets instable. And consequently, the formation sand flows through the gravel completely and the gravel is invalid to sand blocking. Third, as the packing solidity decreases, the unconsolidated particles are rearranged under the effect of fluid impact, and the generated vugs increase the invasion depth of formation sand into the gravel and the sand passing ratio. As a result, the sand blocking effect gets worse. And fourth, to realize the sand control of inside casing gravel packing in casing perforating wells, the packing solidity shall be higher than 95% as much as possible, and the slot width or sand blocking accuracy of mechanical screen shall be designed according to the principle of blocking the formation sand directly.