Research On Proppant Flowback And Control In Fracturing Gas Well Production

In China,the percentage of low-permeability oil and gas reservoirs is large,and fracturing measures have become the preferred method to increase production in low-permeability oil and gas reservoirs.In terms of fractured gas wells,due to the large production of gas wells and high flow rates during the actual production of gas wells,proppants in the propped fractures will be returned to the gas wells,which will cause great harm to gas field production.At present,based on this problem,researches about the reflow mechanism,the related reflow model,proppant backflow prevention and control technology have been carried out.Their understanding of the reflow mechanism mostly relies on the empirical formula derivation,and less for the reflow lab simulation experiment.In terms of prevention and control technology,fiber sand control and chemical film sand control technologies have been developed.However,this technology has many defects such as large damage to the permeability of the filling layer and influencing the normal production of gas wells,so it is difficult to be widely used.In order to solve the above problems,on the one hand,based on the proppant flowback mechanism in the production process of gas wells,I carried out the proppant reflow simulating lab test,created the proppant flowback prediction model,programmed.the proppant flowback prediction software,and analysed the sensitivity factors.On the other hand,a new modified proppant has been developed,which has the characteristics of low cost,greatly improving the proppant reflow strength,and overcomes the problems of the traditional modified proppant damaging to the permeability of the filling layer.The main contents and results of this paper are as follows:(1)A proppant reflow simulating lab test was conducted,and an API standard diversion channel conforming to the API international standard size was independently developed.Innovated on the basis of the traditional API diversion trench and added a screw rod structure to make the disassembly more convenient.The method of the mutation of the permeability in the filling layer to characterize the instability of the proppant in the filling layer was proposed.Through the scientific experimental program,the influence of closing pressure and seam width on proppant reflow was obtained.(2)Based on the theory of force balance of proppant during reflow,a reversal mechanics model was established to determine the relevant critical conditions for proppant reflux.The proppant reflux model was combined with the gas flow model to obtain the proppant reflux mathematical model.The gas critical flow velocity and critical flow rate of the proppant reflow were finally obtained by the transformation and solution of the mathematical relationship.Compared with the experimental data,the reliability of the model was determined.(3)Through proppant reflow prediction model,software for predicting the back flow of proppant in gas well production was programmed.Through the use of software,30 reflow gas wells in Su SouthEast Gas Field were calculated.Among them,28 wells satisfied the actual conditions,with the accuracy rate of 93.3%,which supposed the accuracy of software calculation was high.The software was used to analyze the effects of the fracture length,fracture width,particle diameter,fonnation temperature,water saturation,and the producing differential pressure on the degree of proppant backflow and a corresponding improvement method was proposed.(4)Laboratory evaluation of the new modified proppant was developed.The new proppant can spontaneously accumulate in water and extend the settling time of the proppant.Under the same conditions of four closed pressures,the proppant flowback critical gas volume was increased from 2.6L/min,2.8L/min,3.0L/min,3.1L/min to 3.5L/min,3.8L/min,4.1 L/min and 4.3L/min,resulting in a substantial increase of the proppant reflow intensity.Using the new modified proppant,the permeability of the filling layer is about 800×10-3 μm2 when the reflow occurs,and the resin coated proppant is about 450×10-3 μm2.The new modified proppant has little damage to the permeability of the filling layer.The comprehensive effect is better and it is more beneficial to the actual product of gas wells.