Research Of Sand Production Mechanism And Prediction Method Of Medium-consolidated Sandstone Reservoir

Sand production from oil and gas wells has long plagued the development of sandstone reservoirs.For unconsolidated sandstone or weakly consolidated sandstones with low consolidation strength,the mechanism and law of sand production have been fully studied.However,for medium-consolidated sandstones with a certain cementing strength,scholars have not sufficiently studied mechanism and characteristics of sand production.The prediction of critical conditionsn and volume for medium-consolidated sandstone reservoirs is important for designing of well completion and sand control strategy.Accurate prediction of sanding can prevent or solve the sand production problems for medium-consolidated sandstone reservoirs,and increase the oil and gas production.Therefore,in order to understand the sand production mechanism and predict the sand production of medium consolidated sandstone,this paper investated the mechanical and physical characteristics of medium consolidated sandstone,the deformation and failure characteristics of medium consolidated sandstone,and the sand production characteristics by means of indoor rock mechanics experiments and sand production simulation experiments.On the basis of experiment and theoretical analysis,the finite element model was established to further clarify the critical condition of sand production of medium consolidated sandstone,and accurately predict the sand production,so as to provide supports for well completion and design of sand control.It is found that under the confining pressure condition,the moderately consolidated sandstone shows the process of elastic deformation,yielding,shear failure(peak failure),softening stress-strain characteristics and residual strength.The simulation experiment of sand production shows that under the action of stress,the rock around the hole has shear failure,serious failure could form a "V" shaped failure area around the hole.Without changing the stress state of the sample,the hole will tend to be stable,and the stress state and rock strength determine the sand production.Based on the results of unloading experiments under different stress conditions,it is considered that shear failure is the necessary condition for sand production in moderately consolidated sandstone.The falling blocks and discrete sands produced by the shear failure zone provide material resources for sand production,and,the volume of sanding is determined by the volume of rocks in the conjugate shear zones.In addition,it is observed that most of the discrete particles are sand aggregates,and the particle size distribution is more concentrated,and the average particle size is larger than the original sands.Based on the experimental results,a finite element model for sand production prediction of medium consolidated sandstone is established.A conjugate shear failure zone is formed around the borehole by the model considering the softening characteristics of the rock.The volume of the rock surrounded by the shear failure zone is taken as the parameter to calculate the sand production,and the influence of rock strength,production pressure difference and in-situ stress on sand production is analyzed.The results show that under the action of in-situ stress and pore pressure,too large production pressure difference will produce large-scale shear failure area around the borehole and resulting in serious sand production.