Research On Influence Of Fine Migration In Shaly Loose Sandstone Reservoir On Fracture Conductivity During Production

The decline of fracture conductivity in oil and gas field production is a common problem.For loose sandstone reservoir,the decrease of fracture conductivity is due to the narrowing of fracture caused by the embedment of proppant,and the decrease of fracture permeability caused by the invasion of fines in loose sandstone reservoir.The study of the scientific law of the decline of conductivity has important guiding significance for the efficient development of loose sandstone reservoir in oilfields.By studying the mechanism of particle migration in shaly loose sandstone reservoir,a particle migration model is established based on the principle of mass conservation and particle retention equation.Based on elastic-plastic mechanics and considering Hertzian contact theory,a proppant embedding model was established.Based on these two influencing factors,a theoretical model of fine migration considering proppant embedment was established.In the model,the concept of filtration coefficient is used to express the ratio of the volume of particles in a unit length porous medium to the volume of fines.According to the similarity principle,the shaly unconsolidated sandstone cores are fabricated.A set of experimental equipment considering the influence of proppant embedment and fine migration was designed.The influence of proppant embedment,closing pressure,fluid velocity on fracture conductivity and the change of inlet pressure were studied by the experimental device.The errors of theoretical calculation and measured parameters are compared and analyzed.The results show that the experimental errors are less than 11%.The effects of proppant parameters,formation rock parameters and filtration coefficient on the conductivity of particles in fracture are studied by theoretical model.The results show that the fracture conductivity decreases with the increase of closure pressure,fluid particle concentration,fluid velocity and elastic modulus of formation.With the decrease of filtration coefficient of formation core,the particles entering proppant mainly stay at the front of fracture.In order to slow down the decline of formation conductivity,proppant with larger size and higher elastic modulus should be selected.In order to study the influencing factors of filtration coefficient in particle transport model,a method based on network model is proposed in this paper.The method solves the filtration coefficient by constructing a network,defining particle motion and fluid flow.The simulation results show that the filter coefficient increases with the increase of particle size,the increase of porous media throat size and the decrease of fluid velocity.