Productivity Evaluation And Numerical Simulation Of Horizontal Wells In Daniudi Low Permeability Gas Field

Da-niu-di Gas Field in the Ordos Basin is a typical field of low permeability,big resistance,complex pore structure and poor connectivity.Horizontal well has some advantages,such as big drainage area,high single-well output and high production.So it plays as an effective way of increasing the output and enhancing the ultimate gas recovery ratio.Due to stress sentivity,threshold pressure gradient,the deliverability equation basing on normal horizontal wells does not fit.Basing on previous literatures,the present study uses experiment,theory and numerical simulation to study seepage mechanics and evaluation of horizontal wells as well as fractured horizontal wells in Da-niu-di low permeability gas reservoir and analyze parameters of threshold pressure gradient and stress sensitivity on output and development indicators,combining with petrology,geology,seepage flow mechanics and numerical simulation.The author attempts to study the following questions:(1)Conduct with the section authentication experiment,the mercury injection experiment,and the scanning electron microscope experiment in the samples from the Da-Niu-Di low permeability gas reservoir.(2)Carrying out the low speed seepage experiment on Da-niu-di samples,find reasons of forming threshold preliminarily and evaluate the value of threshold pressure of Da-Niu-Di gas reservoir.,with the results of capillary pressure experiment and numeric simulation.(3)According to the stress sensitivity experiment,the theory of effective stress and three kinds of rock stress sensitivity evaluation methods,evaluate the stress sensitivity of Da-Niu-Di low permeability gas reservoir.(4)According to Joshi theory,apply stress sensitivity,threshold pressure gradient and non-Darcy seepage into conformal transformation and equivalent filtrational resistance principle and develop the stable deliverability equation which fits the low permeability gas reservoirs.Analyze the effect of threshold pressure gradient and stress sensitivity on horizontal wells' outputs.(5)According the stable pressure drop formula of any point in radiate stratum,using the pressure drop superposition principle and the theory of rotation of axes,combining the seepage in fractures and horizontal wells,considering stress sensitivity,threshold pressure gradient and non-Darcy seepage,develop the stable fractured horizontal well's deliverability equation.Obtain output of fractured horizontal wells by the semi-analytical method.(6)Use the deliverability equation of fractured horizontal well to evaluate the output of fractured horizontal wells of Da-niu-di Gas Field.And analyze the effect of threshold pressure gradient,stress sensitivity and non-Darcy flow effect on fractured horizontal wells'outputs.(7)Seek the optimization design strategy of fractured horizontal wells from the influence factors of output,such as the fracture flow conductivity,fracture number,fracture length.(8)Use PEBI to construct model of fractured horizontal wells and the existing numerical simulator to simulate fractured horizontal wells,which have the threshold pressure gradient(considering the capillary force)and do not have the threshold pressure gradient(regardless of the capillary force).Study whether the capillary force can affect development indicators or not by comparing the simulative results.A complete theory on the microscopic pore structure,threshold pressure gradient,stress sensitivity,evaluation and simulation of horizontal wells and fractured horizontal wells of low permeability gas reservoir was obtained by this studying.The understanding of production law of the horizontal wells and fractured horizontal wells in the low permeability gas field has been improved.And this work also gets a theoretical foundation for the evaluation of the horizontal wells and fractured horizontal wells in Da-niu-di Gas field.